TY - CONF TI - Skewed height distributions of kinetically roughened films AU - Kleban, P. AU - Krim, J. AU - Ruffing, C. C2 - 1997/// C3 - Materials Research Society Symposium - Proceedings DA - 1997/// VL - 440 SP - 311-315 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-0031378188&partnerID=MN8TOARS ER - TY - JOUR TI - Dominance of phonon friction for a xenon film on a silver (111) surface AU - Tomassone, M.S. AU - Sokoloff, J.B. AU - Widom, A. AU - Krim, J. T2 - Physical Review Letters AB - Molecular dynamic simulations for a Xe film sliding on an Ag(111) substrate are performed from the submonolayer through the bilayer regime, which, when compared to both friction and surface resistivity measurements, demonstrate that the friction in this system is dominated by phonon excitations. Slip times are found both by direct calculation of the decay of the center-of-mass velocity, as well as from the decay of the velocity correlation function. Agreement of the slip times from the two methods supports the occurrence of a friction force linear in velocity over a wide velocity range. DA - 1997/// PY - 1997/// DO - 10.1103/PhysRevLett.79.4798 VL - 79 IS - 24 SP - 4798-4801 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-6144266282&partnerID=MN8TOARS ER - TY - JOUR TI - Quartz crystal microbalance studies of disorder-induced lubrication AU - Mak, Chihong AU - Krim, Jacqueline T2 - Faraday Discussions AB - We report here a quartz crystal microbalance (QCM) study of the friction associated with sliding of solid and liquid krypton films on ordered and disordered gold substrates, where lower friction is observed for the disordered substrates. The gold substrates on which the measurements were performed were prepared by depositing gold films onto polished quartz substrates held at 80 and 300 K, the 80 K samples being the more disordered of the two. The fact that lower friction levels were observed for more disordered systems may, potentially, be explained by the inhibition of phonon excitations in these systems. DA - 1997/// PY - 1997/// DO - 10.1039/a703481d VL - 107 SP - 389-397 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-0039771951&partnerID=MN8TOARS ER - TY - CONF TI - Measurement and modeling of surface micromachined, electrostatically actuated microswitches AU - Majumder, Sumit AU - McGruer, N.E. AU - Zavracky, Paul M. AU - Adams, George G. AU - Morrison, Richard H. AU - Krim, Jacqueline C2 - 1997/// C3 - International Conference on Solid-State Sensors and Actuators, Proceedings DA - 1997/// VL - 2 SP - 1145-1148 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-0030675959&partnerID=MN8TOARS ER - TY - JOUR TI - Friction at the atomic scale AU - Krim, Jacqueline T2 - Lubrication Engineering DA - 1997/// PY - 1997/// DO - 10.1038/scientificamerican1096-74 VL - 53 IS - 1 SP - 8-13 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-0030733371&partnerID=MN8TOARS ER - TY - CONF TI - Polarized epithermal neutron studies of magnetic domains AU - Alfimenkov, V. P. AU - Chernikov, A. N. AU - Lason, L. AU - Mareev, Yu. D. AU - Novitsky, V. V. AU - Pikelner, L. B. AU - Skoy, V. R. AU - Tsulaya, M. I. AU - Gould, C. R. AU - Haase, D. G. AU - Roberson, N. R. T2 - The fourteenth international conference on the application of accelerators in research and industry A2 - Duggan, J.L. A2 - Morgan, I.L. AB - The average size and shape of magnetic domains in a material can be determined from the precession of polarized neutrons traversing the material. Epithermal neutrons (0.5 eV, AIP AB - The National Research Council has recently released a 262-page document that attempts to define what it means to be scientifically literate and how teachers and schools can approach that goal. This paper presents the progress that has been made by the Standards committees and highlights areas where they still fall short despite numerous objections and suggestions from within the physics community. An overview of the standards themselves, how they were developed, and how they will probably be implemented in the light of experience with standards in other areas will also be discussed. DA - 1997/// PY - 1997/// DO - 10.1063/1.53114 SP - 289–298 ER - TY - PAT TI - Method For Deflecting The Arc Of An Electrodeless Hid Lamp AU - P, Lapatovich Walter AU - J, Butler Scott AU - R, Bochinski Jason AU - H, Goss Harold C2 - 1997/3/12/ DA - 1997/3/12/ PY - 1997/3/12/ UR - https://www.lens.org/099-108-197-104-029 ER - TY - PAT TI - Electrodeless High Intensity Discharge Lamp Having A Boron Sulfide Fill AU - P, Lapatovich Walter AU - J, Butler Scott AU - R, Bochinski Jason C2 - 1997/8/6/ DA - 1997/8/6/ PY - 1997/8/6/ UR - https://www.lens.org/108-721-940-381-795 ER - TY - PAT TI - Electrodeless High Intensity Discharge Lamp Having A Phosphorus Fill AU - P, Lapatovich Walter AU - J, Butler Scott AU - R, Bochinski Jason C2 - 1997/8/6/ DA - 1997/8/6/ PY - 1997/8/6/ UR - https://www.lens.org/036-076-949-733-073 ER - TY - PAT TI - Electrodeless High Intensity Discharge Lamp Having A Phosphorus Fill AU - P, Lapatovich Walter AU - J, Butler Scott AU - R, Bochinski Jason C2 - 1997/11/12/ DA - 1997/11/12/ PY - 1997/11/12/ UR - https://www.lens.org/077-398-386-713-165 ER - TY - PAT TI - Electrodeless High Intensity Discharge Lamp Having A Boron Sulfide Fill AU - P, Lapatovich Walter AU - J, Butler Scott AU - R, Bochinski Jason C2 - 1997/11/12/ DA - 1997/11/12/ PY - 1997/11/12/ UR - https://www.lens.org/137-533-462-093-900 ER - TY - JOUR TI - Optical imaging of carrier dynamics in silicon with subwavelength resolution AU - La Rosa, A.H. AU - Yakobson, B.I. AU - Hallen, H.D. T2 - Applied Physics Letters AB - Characteristic rate variations of carrier processes are imaged using near-field scanning optical microscopy. We couple both a visible pump and an infrared probe light through a subwavelength aperture to investigate the interband recombination and intraband diffusion of excess carriers in oxidized silicon. Typical values of the locally measured life time constants agree well with those obtained by conventional space-averaged techniques. Moreover, the images locate defects, reveal variations, and can map the regions in which a recombination process is active. DA - 1997/// PY - 1997/// DO - 10.1063/1.118661 VL - 70 IS - 13 SP - 1656 - 1658 UR - http://dx.doi.org/10.1063/1.118661 ER - TY - CONF TI - Prediction of fast fading parameters by resolving the interference pattern AU - Eyceoz, T. AU - Duel-Hallen, A. AU - Hallen, H. AB - We investigated a new deterministic approach to the estimation and prediction of the fading channel by exploiting the physical nature of the flat fading signal. Since the direct signal and the reflected signals form an interference pattern, the received signal is given by a sum of several scattered components. These are distinguished by their Doppler shifts at the mobile. The slowly varying parameters associated with these components are determined and tracked, and the composite fading signal is predicted. This approach will potentially result in the ability to anticipate and avoid "deep fades" which severely limit the performance of wireless communications systems and will aid in the development of low power mobile radio systems. C2 - 1997/// C3 - Conference Record of the Thirty-First Asilomar Conference on Signals, Systems and Computers (Cat. No.97CB36136) DA - 1997/// DO - 10.1109/ACSSC.1997.680049 VL - 1 SP - 167-171 UR - http://dx.doi.org/10.1109/ACSSC.1997.680049 ER - TY - JOUR TI - Near-field optical spectroscopy: enhancing the light budget AU - Paesler, M.A. AU - Hallen, H.D. AU - Yakobson, B.I. AU - Jahncke, C.J. AU - Boykin, P.O. AU - Meixner, A. T2 - Microscopy and Microanalysis DA - 1997/// PY - 1997/// VL - 3 SP - 815 ER - TY - CHAP TI - Lens AU - Hallen, H.D. AU - Paesler, M. A. T2 - The Macmillan Encyclopedia of Physics A2 - Rigden, John S. PY - 1997/// PB - Macmillan ER - TY - JOUR TI - Driving the driven atom: Spectral signatures AU - Yu, C. C. AU - Bochinski, J. R. AU - Kordich, T. M. V. AU - Mossberg, T. W. AU - Ficek, Z. T2 - Physical Review A AB - We have measured the emission spectrum of two-level-like Ba atoms driven by a continuous-wave bichromatic field containing a strong resonant component and a weaker component detuned from atomic resonance by the strong-field Rabi frequency. With the specified detuning, the weak field resonantly drives a transition of the atom--strong-field dressed states. Observed spectra show that each peak of the normal (single-driving-field) resonance fluorescence triplet is split into three subpeaks separated by one-half the weak-field Rabi frequency. Also seen is another triplet of peaks displaced from the atomic resonance by twice the strong-field Rabi frequency. Splitting of the normal triplet peaks can be explained through weak-field dressing of the strong-field dressed states. The origin of the additional triplet is less transparent. Comparison with theory is made. DA - 1997/// PY - 1997/// DO - 10.1103/physreva.56.r4381 VL - 56 IS - 6 SP - R4381-R4384 ER - TY - JOUR TI - Intrinsically Irreversible Multiphoton Laser Gain Mechanisms AU - Sellin, P. B. AU - Yu, C. C. AU - Bochinski, J. R. AU - Mossberg, T. W. T2 - Physical Review Letters AB - Single-photon stimulated radiative interactions are universally symmetric relative to emission and absorption. We point out that certain multiphoton stimulated processes, whose completion is dependent on the spontaneous emission of at least one photon, do not behave analogously. The broken symmetry found in such cases invalidates simple correlations between population inversion and laser gain. DA - 1997/2// PY - 1997/2// DO - 10.1103/physrevlett.78.1432 VL - 78 IS - 8 SP - 1432-1435 ER - TY - JOUR TI - Fluorescence efficiencies of thin scintillating films in the extreme ultraviolet spectral region AU - McKinsey, D.N. AU - Brome, C.R. AU - Butterworth, J.S. AU - Golub, R. AU - Habicht, K. AU - Huffman, P.R. AU - Lamoreaux, S.K. AU - Mattoni, C.E.H. AU - Doyle, J.M. T2 - Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms DA - 1997/// PY - 1997/// VL - 132 IS - 3 SP - 351-358 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-0031268266&partnerID=MN8TOARS ER - TY - CONF TI - Update on IMPEC: An integrated first-year Engineering curriculum at N.C. State University AU - Beichner, R. J. C2 - 1997/// C3 - Conference Proceedings DA - 1997/// PB - Washington, DC: ASEE ER - TY - DATA TI - Interactive journey through physics CD-ROM AU - Schwarz, C. AU - Beichner, R. DA - 1997/// PY - 1997/// PB - Englewood Cliffs, NJ: Prentice-Hall ER - TY - JOUR TI - Visualizing potential surfaces with a spreadsheet AU - Beichner, Robert T2 - Physics Teacher AB - First Page DA - 1997/// PY - 1997/// DO - 10.1119/1.2344604 VL - 35 IS - 2 SP - 95–97 ER - TY - JOUR TI - Energy of isolated systems at retarded times as the null limit of quasilocal energy AU - Brown, JD AU - Lau, , SR AU - York, JW T2 - PHYSICAL REVIEW D AB - We define the energy of a perfectly isolated system at a given retarded time as the suitable null limit of the quasilocal energy $E$. The result coincides with the Bondi-Sachs mass. Our $E$ is the lapse-unity shift-zero boundary value of the gravitational Hamiltonian appropriate for the partial system $\Sigma$ contained within a finite topologically spherical boundary $B = \partial \Sigma$. Moreover, we show that with an arbitrary lapse and zero shift the same null limit of the Hamiltonian defines a physically meaningful element in the space dual to supertranslations. This result is specialized to yield an expression for the full Bondi-Sachs four-momentum in terms of Hamiltonian values. DA - 1997/2/15/ PY - 1997/2/15/ DO - 10.1103/physrevd.55.1977 VL - 55 IS - 4 SP - 1977-1984 SN - 2470-0029 UR - http://inspirehep.net/record/423731 ER - TY - JOUR TI - Photoluminescence characteristics of GaN/InGaN/GaN quantum wells AU - Shmagin, IK AU - Muth, JF AU - Kolbas, RM AU - Krishnankutty, S AU - Keller, S AU - Abare, AC AU - Coldren, LA AU - Mishra, UK AU - DenBaars, SP T2 - JOURNAL OF ELECTRONIC MATERIALS DA - 1997/3// PY - 1997/3// DO - 10.1007/s11664-997-0172-y VL - 26 IS - 3 SP - 325-329 SN - 0361-5235 KW - GaN/InGaN KW - photoluminescence (PL) KW - quantum wells (QWs) ER - TY - JOUR TI - Observation of lasing from photopumped InGaN/GaN heterostructures in an edge emitting configuration AU - Shmagin, IK AU - Muth, JF AU - Kolbas, RM AU - Krishnankutty, S AU - Keller, S AU - Mishra, UK AU - DenBaars, SP T2 - JOURNAL OF APPLIED PHYSICS AB - Optically pumped lasing from InGaN/GaN single heterojunctions (SH) was observed in an edge emitting configuration at 77 K. The heterojunctions were grown by atmospheric pressure metalorganic chemical vapor deposition on c-plane sapphire substrates. The frequency tripled output of a mode-locked titanium:sapphire laser with a pulse width of 250 fs, operating at 280 nm, was used as the photoexcitation source. The nonlinear dependence of output emission intensity on input power density, the observations of a strongly polarized output emission, and distinct Fabry–Perot modes are discussed. DA - 1997/2/15/ PY - 1997/2/15/ DO - 10.1063/1.364058 VL - 81 IS - 4 SP - 2021-2023 SN - 0021-8979 ER - TY - JOUR TI - X-ray microscopy and NEXAFS spectroscopy of macrophase-separated random block copolymer/homopolymer blends AU - Smith, AP AU - Laurer, JH AU - Ade, HW AU - Smith, SD AU - Ashraf, A AU - Spontak, RJ T2 - MACROMOLECULES AB - ADVERTISEMENT RETURN TO ISSUEPREVCommunication to the...Communication to the EditorNEXTX-ray Microscopy and NEXAFS Spectroscopy of Macrophase-Separated Random Block Copolymer/Homopolymer BlendsArchie P. Smith, Jonathan H. Laurer, Harald W. Ade, Steven D. Smith, Arman Ashraf, and Richard J. SpontakView Author Information Departments of Materials Science & Engineering and Physics, North Carolina State University, Raleigh, North Carolina 27695, and Corporate Research Division, The Procter & Gamble Company, Cincinnati, Ohio 45239 Cite this: Macromolecules 1997, 30, 3, 663–666Publication Date (Web):February 10, 1997Publication History Received20 August 1996Revised13 November 1996Published online10 February 1997Published inissue 1 February 1997https://doi.org/10.1021/ma9612687Copyright © 1997 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views143Altmetric-Citations9LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. 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Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit Read OnlinePDF (158 KB) Get e-AlertsSUBJECTS:Colloids,Copolymers,Energy,Transmission electron microscopy,X-rays Get e-Alerts DA - 1997/2/10/ PY - 1997/2/10/ DO - 10.1021/ma9612687 VL - 30 IS - 3 SP - 663-666 SN - 0024-9297 ER - TY - JOUR TI - Variation of GaN valence bands with biaxial stress and quantification of residual stress AU - Edwards, NV AU - Yoo, SD AU - Bremser, MD AU - Weeks, TW AU - Nam, OH AU - Davis, RF AU - Liu, H AU - Stall, RA AU - Horton, MN AU - Perkins, NR AU - Kuech, TF AU - Aspnes, DE T2 - APPLIED PHYSICS LETTERS AB - Low-temperature reflectance data on epitaxial GaN thin-film samples covering the widest range of tensile and compressive stress (−3.8–3.5 kbar) thus far explicitly show the nonlinear behavior of the B–A and C–A splittings versus the energy of the A exciton. Lineshape ambiguities that hindered previous interpretations have been resolved with reciprocal-space analysis, allowing us to obtain band parameters such as ΔSO=17.0±1meV with increased confidence. DA - 1997/4/14/ PY - 1997/4/14/ DO - 10.1063/1.119089 VL - 70 IS - 15 SP - 2001-2003 SN - 0003-6951 ER - TY - CONF TI - Multilevel approaches toward monitoring and control of semiconductor epitaxy AU - Aspnes, D. E. AU - Dietz, N. AU - Rossow, U. AU - Bachmann, K. J. C2 - 1997/// C3 - Control of semiconductor surfaces and interfaces: Symposium held December 2-5, 1996, Boston, Massachusetts, U.S.A. (Materials Research Society Symposium proceedings, no. 448) CN - QC611.6.S9 C68 1997 DA - 1997/// DO - 10.1557/proc-448-451 SP - 451–462 PB - Pittsburgh, PA: Materials Research Society ER - TY - JOUR TI - Molecular theory of a charged particle in a polarizable nonpolar liquid AU - Lado, F T2 - JOURNAL OF CHEMICAL PHYSICS AB - A generalization of liquid state theory that treats internal degrees of freedom on the same mathematical footing as orientational degrees of freedom is used to calculate the Maxwell field of a charged particle in a fluid of polarizable nonpolar molecules. The polarizable fluid is modeled by Lennard-Jones molecules with classical Drude oscillators. The electric field E(r) of the charged impurity is given in terms of a screening function that yields the correct dielectric constant at large r and can be computed using standard procedures for the pair correlation function of classical liquid state theory. Sample numerical results using the hypernetted-chain approximation are compared with simulation. DA - 1997/3/15/ PY - 1997/3/15/ DO - 10.1063/1.473507 VL - 106 IS - 11 SP - 4707-4713 SN - 0021-9606 ER - TY - CONF TI - Low pH chemical etch route for smooth H-terminated Si(100) and study of subsequent chemical stability AU - Hinds, B. J. AU - Aspenes, D. E. AU - Lucovsky, G. C2 - 1997/// C3 - Environmental, safety, and health issues in IC production: Symposium held December 4-5, 1996, Boston, Massachusetts, U.S.A. (Materials Research Society Symposium proceedings, no. 447) CN - TK7836 .E58 1997 DA - 1997/// SP - 191-196 PB - Pittsburgh, PA: Materials Research Society ER - TY - CONF TI - Variation of GaN valence bands with biaxial stress: quantification of residual stress and impact on fundamental band parameters AU - Edwards, N. V. AU - Yoo, S. D. AU - Bremser, M. D. AU - Horton, M. N. AU - Perkins, N. R. AU - Weeks, T. W. AU - Liu, H. AU - Stall, R. A. AU - Kuech, T. F. AU - Davis, R. F. AU - Aspnes, D. E. C2 - 1997/// C3 - III-V nitrides: symposium held December 2-6, 1996, Boston, Massachusetts, U.S.A. (Materials Research Society symposia proceedings ; v. 449) CN - QC176.9.M84 A14 1997 DA - 1997/// DO - 10.1557/proc-449-781 SP - 781–786 PB - Pittsburgh, Pa.: Materials Research Society ER - TY - CONF TI - In-plane optical anisotropies of Al(x)Ga(1-x)N films in their regions of transparency AU - Rossow, U. AU - Edwards, N. V. AU - Bremser, M. D.. AU - Kern, R. S. AU - Liu, H. AU - Davis, R. F. AU - Aspnes, D. E. C2 - 1997/// C3 - III-V nitrides: symposium held December 2-6, 1996, Boston, Massachusetts, U.S.A. (Materials Research Society symposia proceedings ; v. 449) CN - QC176.9.M84 A14 1997 DA - 1997/// DO - 10.1557/proc-449-835 SP - 835–840 PB - Pittsburgh, Pa.: Materials Research Society ER - TY - CONF TI - Extended x-ray absorption fine structure study of mercury speciation in a flood plain soil AU - Wang, Z. AU - Hesterberg, D. AU - Zhou, W. AU - Sayers, D. E. AU - Robarge, W. P. C2 - 1997/// C3 - Contaminated soils: 3rd International Conference on the Biogeochemistry of Trace Elements, Paris (France), May 15-19, 1995 DA - 1997/// M1 - 1997 PB - Paris: INRA Editions ER - TY - JOUR TI - The role of hydrogen atoms in metastable defect formation at Si-SiO2 interfaces and in hydrogenated amorphous Si (a-Si:H) AU - Lucovsky, G. AU - Yang, H. AU - Jing, Z. AU - Whitten, J. L. T2 - Physica Status Solidi. A, Applications and Materials Science DA - 1997/// PY - 1997/// VL - 159 IS - 1997 SP - 5-10 ER - TY - CHAP TI - Translational regulation of bioiron AU - Theil, E. C. T2 - Metal ions in gene regulation A2 - S. Silver, A2 - Walden, W. CN - QP532 .M473 1998 PY - 1997/// DO - 10.1007/978-1-4615-5993-1_6 SP - 131-156 PB - New York: Chapman & Hall ER - TY - JOUR TI - Plane shear waves in a fully saturated granular medium with velocity and stress controlled boundary conditions AU - Gordon, MS AU - Shearer, M AU - Schaeffer, D T2 - INTERNATIONAL JOURNAL OF NON-LINEAR MECHANICS AB - A one-dimensional system describing small shearing disturbances in a semi-infinite, fully saturated granular medium is studied. The system is fully non-linear as a result of the incrementally non-linear constitutive law for the material. In particular, there are two different wave speeds corresponding to loading or unloading of the material. Global solutions are constructed with boundary data consisting of a single pulse in either velocity or stress. In the case of velocity controlled boundary conditions, the solution is a traveling pulse of increasing kinetic energy which eventually unloads the material, regardless of whether the initial pulse loads or unloads. The solution with stress controlled boundary conditions has these features only if the initial stress pulse unloads the material. If the initial stress pulse is loading then the solution is a slowly traveling pulse of decreasing kinetic energy which is also loading. DA - 1997/5// PY - 1997/5// DO - 10.1016/S0020-7462(96)00080-7 VL - 32 IS - 3 SP - 489-503 SN - 0020-7462 KW - plane shear waves KW - saturated granular material KW - hypoplastic flow rule KW - scale-invariant problem KW - characteristic wave KW - shock wave KW - rarefaction wave KW - wave curve KW - state space KW - kinetic energy ER - TY - JOUR TI - Correlation of morphology and electrical properties of nanoscale TiSi2 epitaxial islands on Si (001) AU - Yang, W AU - Jedema, FJ AU - Ade, H AU - Nemanich, RJ T2 - THIN SOLID FILMS AB - The morphology and electrical properties of nanoscale epitaxial islands of TiSi2 are explored. The TiSi2 islands are prepared by ultra-high vacuum (UHV) deposition of ultra-thin Ti (0.3–2 nm) on both smooth and roughened Si (001) substrates. The roughened substrates are prepared by etching with atomic H produced in a plasma. The island formation is initiated by annealing to 800–1000°C. The morphologies of the substrate before and after island formation are examined by atomic force microscopy (AFM). In particular, the influence of surface-roughness on both the formation of islands and the size distribution of islands is investigated. Islands with a lateral dimension of ~35 nm and a vertical dimension of ~2.5 nm on a roughened substrate (RMS=12 nm) were observed, with a uniform distribution of 120 nm spacing between the islands. It was found that for similar processing conditions the size distribution of islands formed on a rough surface was smaller than islands formed on smooth surfaces. The results are discussed in terms of surface energy, diffusion and the strain field around the islands. The island structures can affect the electrical characteristics of the interface and the Schottky barrier was obtained from diodes formed with a Pt layer deposited over the islanded interface. The Schottky barrier was lowest for interfaces with the smaller TiSi2 islands. DA - 1997/10/31/ PY - 1997/10/31/ DO - 10.1016/S0040-6090(97)00431-8 VL - 308 IS - 1997 Oct. 31 SP - 627-633 SN - 1879-2731 KW - TiS2 epitaxial islands KW - size distribution KW - Si (001) substrates KW - Schottky barrier ER - TY - JOUR TI - A VLA study of the expansion of Tycho's supernova remnant AU - Reynoso, EM AU - Moffett, DA AU - Goss, WM AU - Dubner, GM AU - Dickel, , JR AU - Reynolds, SP AU - Giacani, EB T2 - ASTROPHYSICAL JOURNAL AB - We have measured the expansion of Tycho's supernova remnant (SNR) over a 10 yr interval by comparing new VLA observations at 1375 MHz made in 1994 and 1995 with previous observations made in 1983 and 1984 using the same array configurations, bandwidths, calibrators, and integration times. To compute the expansion of the outer rim, we estimate the expansion rate for radial sectors of 4°. The overall mean expansion obtained is 305 but varies between 1'' and 5'' around the shell. The weighted average fractional expansion rate is 0.1126% yr-1, corresponding to a power-law index (expansion parameter) ν ≡ d ln R/d ln t = 0.471, with an error of ~6%. We also compute the expansion of interior features, and find a comparable global expansion parameter. The value of ν obtained is in excess of the pure Sedov value of 0.4, indicating that Tycho's SNR is still in transition from an earlier phase to the Sedov adiabatic phase of evolution, and supporting expansion into a medium without a strong radial density gradient, as expected for a Type Ia supernova. In addition, the significant local variations that we observe suggest that a unique average expansion rate is an oversimplified description for Tycho. Both radio flux and polarization were found to remain almost constant during the intervening 10 years. DA - 1997/12/20/ PY - 1997/12/20/ DO - 10.1086/304997 VL - 491 IS - 2 SP - 816-828 SN - 0004-637X KW - ISM, individual (Tycho, 3C 10) KW - ISM, kinematics and dynamics KW - supernova remnants ER - TY - CONF TI - Physical conditions in NGC 6543 AU - Lame, N. J. AU - Harrington, J. P. AU - Borkowski, K. A2 - H. J. Habing, A2 - Lamers, H. J. G. L. M. AB - We observed NGC 6543 (the Cat's Eye Nebula) with the HST WFPC2 camera in ten narrow-band filters covering a range of emission lines. These images are used to further look at the physical conditions in NGC 6543. We discuss the [O III] electron temperature, ionization state throughout the nebula, and the results of photoionization models of individual structures. C2 - 1997/// C3 - Proceedings of the 180th Symposium of the International Astronomical Union, held in Groningen, The Netherlands, August 26-30, 1996 CN - QB855.5 .I58 1996 DA - 1997/// DO - 10.1017/s0074180900130712 VL - 180 SP - 252-253 PB - Boston, Mass.: Kluwer Academic Publishers, 1997 ER - TY - CONF TI - Modeling hydrogen-deficient planetary nebulae AU - Harrington, J. P. AU - Borkowski, K. J. AU - Tsvetanov, Z. I. A2 - H. J. Habing, A2 - Lamers, H. J. G. L. M. C2 - 1997/// C3 - Planetary nebulae: Proceedings of the 180th Symposium of the International Astronomical Union, held in Groningen, The Netherlands, August 26-30, 1996 CN - QB855.5 .I58 1996 DA - 1997/// DO - 10.1007/978-94-011-5244-0_91 VL - 180 SP - 235 PB - Boston, Mass.: Kluwer Academic Publishers, 1997 ER - TY - PAT TI - Integrated heterostructures of Group III-V nitride semiconductor materials including epitaxial ohmic contact, non-nitride buffer layer and methods of fabricating same AU - Schetzina, J. F. C2 - 1997/// DA - 1997/// PY - 1997/// ER - TY - CONF TI - Effect of ambient wind velocity on planetary nebula morphology AU - Dwarkadas, V. V. AU - Chevalier, R. A. AU - Blondin, John A2 - H. J. Habing, A2 - Lamers, H. J. G. L. M. C2 - 1997/// C3 - Planetary nebulae: Proceedings of the 180th Symposium of the International Astronomical Union, held in Groningen, The Netherlands, August 26-30, 1996 CN - QB855.5 .I58 1996 DA - 1997/// DO - 10.1007/978-94-011-5244-0_81 VL - 180 SP - 224 PB - Boston, Mass.: Kluwer Academic Publishers, 1997 ER - TY - JOUR TI - Relations among the light-cone quark models with the invariant meson mass scheme and the model prediction of the eta-eta' mixing angle AU - Choi, HM AU - Ji, CR T2 - PHYSICAL REVIEW D AB - We analyze the relations among the light-cone quark models which are based on the invariant meson mass scheme. We find that the difference from the Jacobi factor in model wave functions is substantially reduced in the numerical predictions for the physical observables once the best fit parameters are chosen. The difference in the choice of radial wave function [e.g., harmonic oscillator (HO) wave function versus power-law wave function] is, however, still appreciable even though the best fit parameters are used. We also observe an excellent agreement between the HO model predictions and the experimental data on the radiative decays of pseudoscalar $(P)$ and vector $(V)$ mesons and $P\ensuremath{\rightarrow}\ensuremath{\gamma}\ensuremath{\gamma}$ processes, if we use the constraint obtained by the axial anomaly plus partial conservation of axial-vector current relations and choose the $\ensuremath{\eta}\ensuremath{-}{\ensuremath{\eta}}^{\ensuremath{'}}$ mixing angle ${\ensuremath{\theta}}_{\mathrm{SU}(3)}$ $\ensuremath{\approx}\ensuremath{-}19\ifmmode^\circ\else\textdegree\fi{}.$ DA - 1997/11/1/ PY - 1997/11/1/ DO - 10.1103/physrevd.56.6010 VL - 56 IS - 9 SP - 6010-6013 SN - 0556-2821 ER - TY - JOUR TI - Quantitative interpretation of K-edge NEXAFS data for various nickel hydroxides and the charged nickel electrode AU - Qian, X. AU - Sambe, H. AU - Ramaker, D. E. AU - Pandya, K. I. AU - O'Grady, W. E. T2 - Journal of Physical Chemistry. B, Condensed Matter, Materials, Surfaces, Interfaces & Biophysical DA - 1997/// PY - 1997/// VL - 101 IS - 46 SP - 9441-9446 ER - TY - JOUR TI - High strain rate fracture and C-chain unraveling in carbon nanotubes AU - Yakobson, BI AU - Campbell, MP AU - Brabec, CJ AU - Bernholc, J T2 - COMPUTATIONAL MATERIALS SCIENCE AB - Nanotube behavior at high rate tensile strain (~ 1 MHz) is studied by molecular dynamics using a realistic many-body interatomic potential. The simulatins performed for single- and double-walled nanotubes of different helicities, and at different temperatures, show that nanotubes have an extremely large breaking strain. It decreases somewhat with increasing temperature and smaller strain rate, while the influence of helicity is very weak. At later stages of fracture, the nanotube fragments are connected by a set of unraveling monoatomic chains. The chains ‘compete’ with each other for carbon atoms popping out of the original tube segments. The interaction between chains eventually leads to a single chain, which grows up to hundreds of atoms in length before its breakage. DA - 1997/9// PY - 1997/9// DO - 10.1016/S0927-0256(97)00047-5 VL - 8 IS - 4 SP - 341-348 SN - 0927-0256 ER - TY - JOUR TI - XAFS characterization of copper contamination in the unsaturated and saturated zones of a soil profile AU - Sayers, DE AU - Hesterberg, D AU - Zhou, W AU - Robarge, WP AU - Plummer, GM T2 - JOURNAL DE PHYSIQUE IV AB - The fate of heavy-metal contaminants in the environment, and the design and success of remediation strategies at hazardous waste sites depend on the chemical speciation of the contaminants. The objective of this study was to determine the molecular-scale chemical form (species) of heavy metals in different zones of a contaminated soil having a shallow ground water table. Copper in the unsaturated surface horizon and the water-saturated and partially-saturated subsurface horizons of a disturbed soil from the lower eastern coastal plain of North Carolina was characterized using XAFS spectroscopy. Extended x-ray absorption fine structure (EXAFS) and x-ray absorption near edge structure (XANES) data showed that the dominant form of Cu(II) bonding ranged from Cu-S in the deeper soil zones to Cu-O in the shallowest zone. The results suggest that the surface and subsurface horizons will respond differently to remediation treatments. DA - 1997/4// PY - 1997/4// DO - 10.1051/jp4:1997252 VL - 7 IS - C2 SP - 831-832 SN - 1155-4339 ER - TY - JOUR TI - XAFS Characterization of Copper in Model Aqueous Systems of Humic Acid and Illite AU - Hesterberg, D. AU - Sayers, D. E. AU - Zhou, W. AU - Robarge, W. P. AU - Plummer, G. M. T2 - Le Journal de Physique IV AB - Adsorption of heavy metals at mineral surfaces and complexation with reactive organic-matter functional groups are important processes regulating the solubility and fate of soil contaminants. To determine the nature of Cu(II) bonding in complex clay-organic systems, XAFS analyses were conducted on aqueous suspensions containing Cu(II) in various forms: (i) complexed with soil humic acid (HA) at various HA:Cu ratios, (ii) bound to illite, or (iii) bound in a mixture of illite and HA. Spectral features for Cu bound to HA did not depend significantly on the HA:Cu ratio, and average first-shell Cu-O bond lengths were consistently shorter than for the Cu-illite systems. In the mixed clay-organic suspension, Cu bonding was more characteristic to that of Cu bound with HA. DA - 1997/4// PY - 1997/4// DO - 10.1051/jp4:1997253 VL - 7 IS - C2 SP - C2-833-C2-834 J2 - J. Phys. IV France OP - SN - 1155-4339 UR - http://dx.doi.org/10.1051/jp4:1997253 DB - Crossref ER - TY - JOUR TI - X-ray absorption spectroscopy of lead and zinc speciation in a contaminated groundwater aquifer AU - Hesterberg, D AU - Sayers, DE AU - Zhou, WQ AU - Plummer, GM AU - Robarge, WP T2 - ENVIRONMENTAL SCIENCE & TECHNOLOGY AB - The formation of insoluble metal sulfides in the environment may reduce the mobility and bioavailability of heavy metal contaminants and potentially eliminate the need for ex situ remediation of certain hazardous waste sites. To assist in assessing remediation strategies for the Bypass 601 Superfund site, groundwater aquifer samples were analyzed using synchrotron X-ray absorption spectroscopy (XAS) to determine whether lead and zinc sulfides were dominant mineral phases. Moist aquifer solids contained between 150 and 1800 mg of Pb/kg and between 100 and 250 mg of Zn/kg. Lead sulfide was not dominant in any of the samples analyzed, including one sample collected from a well in a flood plain that contained 70% of zinc bonded to sulfur, probably as ZnS. This portion of the aquifer had apparently been under reducing conditions. In all other samples, first-shell bonding of Pb and Zn was predominantly to oxygen. Data indicated that PbO, PbCO3, PbSO4, and ZnO were not dominant metal species. The XAS analyses showed that with one exception, metal sulfides were not prevalent. DA - 1997/10// PY - 1997/10// DO - 10.1021/es970077w VL - 31 IS - 10 SP - 2840-2846 SN - 1520-5851 ER - TY - JOUR TI - Theory of interfaces and surfaces in wide-gap nitrides AU - Nardelli, MB AU - Rapcewicz, K AU - Bernholc, J T2 - JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B AB - A selection of the results of a theoretical investigation of the properties of interfaces and surfaces of the wide-gap III–V nitride semiconductors is reviewed. The electronic properties of wurtzite heteroepitaxial interfaces of AlN and GaN, incorporating the effects of strain, are discussed. In particular, we find that this interface is of type I and have calculated the valence-band offset to be −0.57 eV. The surface energies and atomic geometries of the 2×2 reconstructions of the (0001) face of GaN are also presented. In conditions which are rich in a given species, an adatom reconstruction of that species is found to be the most energetically favorable: for gallium-rich conditions, the reconstruction with a gallium adatom on a T3 site is the most stable, while for nitrogen-rich conditions the reconstruction with a nitrogen adatom on the H3 site is energetically the most favorable. DA - 1997/// PY - 1997/// DO - 10.1116/1.589429 VL - 15 IS - 4 SP - 1144-1147 ER - TY - JOUR TI - The physics of hollow lithium atom AU - Chung, K. T. T2 - Chinese Journal of Physics [Taiwan] DA - 1997/// PY - 1997/// VL - 35 IS - 4 SP - 453-461 ER - TY - JOUR TI - The influence of conserved tyrosine 30 and tissue-dependent differences in sequence on ferritin function: use of blue and purple Fe(III) species as reporters of ferroxidation AU - Fetter, J. AU - Cohen, J. AU - Danger, D. P. AU - Sanders, Loehr J. AU - Theil, E. C. T2 - Journal of Biological Inorganic Chemistry AB - Ferritins uniquely direct the vectorial transfer of hydrated Fe(II)/Fe(III) ions to a condensed ferric phase in the central cavity of the soluble protein. Secondary, tertiary and quaternary structure are conserved in ferritin, but only five amino acid residues are conserved among all known ferritins. The sensitivity of ferroxidation rates to small differences in primary sequence between ferritin subunits that are cell-specifically expressed or to the conservative replacement of the conserved tyrosine 30 residue was demonstrated by examining recombinant (frog) H-type (red blood cell predominant) and M-type subunit (liver predominant) proteins which are both fast ferritins; the proteins form two differently colored Fe(III)-protein complexes absorbing at 550 nm or 650 nm, respectively. The complexes are convenient reporters of Fe(III)-protein interaction because they are transient in contrast to the Fe(III)-oxy complexes measured in the past at 310–420 nm, which are stable because of contributions from the mineral itself. The A650-nm species formed 18-fold faster in the M-subunit protein than did the 550-nm species in H-subunit ferritin, even though all the ferroxidase residues are the same; the Vmax was fivefold faster but the Hill coefficents were identical (1.6), suggesting similar mechanisms. In H-subunit ferritin, substitution of phenylalanine for conserved tyrosine 30 (located in the core of the subunit four-helix bundle) slowed ferroxidation tenfold, whereas changing surface tyrosine 25 or tyrosine 28 had no effect. The Fe(III)-tyrosinate was fortunately not changed by the mutation, based on the resonance Raman spectrum, and remained a suitable reporter for Fe(III)-protein interactions. Thus, the A550/650 nm can also report on post-oxidation events such as transport through the protein. The impact of Y30F on rates of formation of Fe(III)-protein complexes in ferritin, combined with Mössbauer spectroscopic studies that showed the parallel formation of multiple Fe(III) postoxidation species (three dinuclear oxy and one trinuclear oxy species) (A. S. Periera et al., Biochemistry 36 : 7917–7927, 1997) and the loss of several of the multimeric Fe(III) post-oxidation species in a Y30F alteration of human recombinant H-ferritin (E. R. Bauminger et al., Biochem J. 296 : 709–719, 1993), indicate that at least one of the pathways for Fe oxidation/transfer in ferritin is through the center of the four-helix bundle and is influenced by structural features dependent on tyrosine 30. DA - 1997/// PY - 1997/// DO - 10.1007/s007750050180 VL - 2 IS - 5 SP - 652-661 ER - TY - JOUR TI - The H-2((p)over-right-arrow,gamma)He-3 and H-1((d)over-right-arrow,gamma)He-3 reactions below 80 keV AU - Schmid, GJ AU - Rice, BJ AU - Chasteler, RM AU - Godwin, MA AU - Kiang, GC AU - Kiang, LL AU - Laymon, CM AU - Prior, RM AU - Tilley, DR AU - Weller, HR T2 - PHYSICAL REVIEW C AB - The details of a recent experimental study of the ${}^{2}\mathrm{H}(p\ensuremath{\rightarrow},\ensuremath{\gamma}{)}^{3}$He and the ${}^{1}\mathrm{H}(d\ensuremath{\rightarrow},\ensuremath{\gamma}{)}^{3}$He reactions for beam energies below 80 keV are discussed. In this study, both polarized and unpolarized incident beams were used to measure the cross section $\ensuremath{\sigma}(\ensuremath{\theta},E)$, the astrophysical $S$ factor $S(\ensuremath{\theta},E)$, the vector analyzing power ${A}_{y}(\ensuremath{\theta},E)$, and the tensor analyzing power ${T}_{20}(\ensuremath{\theta})$. In addition, the $\ensuremath{\gamma}$-ray linear polarization ${P}_{\ensuremath{\gamma}}(\ensuremath{\theta})$ was measured for an unpolarized incident beam. The experimental details of these measurements are discussed and the data are analyzed to obtain the amplitudes and phases of the contributing transition-matrix elements. The results of our measurements are compared with recent ab initio three-body theoretical calculations. This comparison reveals the large sensitivity of the polarization observables, especially the vector analyzing power ${(A}_{y})$, to the presence of meson-exchange current effects and indicates the need for further study. The tensor analyzing power data $[{T}_{20}(\ensuremath{\theta})$] are used to extract a value of the asymptotic $D$- to $S$-state ratio, $\ensuremath{\eta}$, for ${}^{3}$He. DA - 1997/11// PY - 1997/11// DO - 10.1103/physrevc.56.2565 VL - 56 IS - 5 SP - 2565-2581 SN - 1089-490X ER - TY - JOUR TI - Surface and interface effects on ellipsometric spectra of crystalline Si AU - Bell, KA AU - Mantese, L AU - Rossow, U AU - Aspnes, DE T2 - JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B AB - We present the first systematic investigation of the differences among reference-quality ellipsometrically measured pseudodielectric function 〈ε〉 spectra of crystalline Si, which are nominally used to approximate the bulk dielectric function of this material. In addition to the expected influence of residual overlayers, we identify surface-local-field and energy-derivative effects, the latter representing shifts between bulk and measured critical point energies, as well as changes in excited-carrier lifetimes due to the surface. Model calculations indicate that these four effects account for nearly all differences among spectra studied, although a second-energy-derivative component appears at the E1 transition in some cases. The isotropic contribution to the surface-local-field effect is observed for the first time. DA - 1997/// PY - 1997/// DO - 10.1116/1.589440 VL - 15 IS - 4 SP - 1205-1211 ER - TY - JOUR TI - Sublimation growth and characterization of bulk aluminum nitride single crystals AU - Balkas, CM AU - Sitar, Z AU - Zheleva, T AU - Bergman, L AU - Nemanich, R AU - Davis, RF T2 - JOURNAL OF CRYSTAL GROWTH AB - Single crystalline platelets of aluminum nitride (AlN) ⩽ 1 mm thick have been grown within the temperature range of 1950–2250°C on 10 × 10 mm2 α(6H)-silicon carbide (SiC) substrates via sublimation-recondensation in a resistively heated graphite furnace. The source material was sintered AlN. A maximum growth rate of 500 μm/h was achieved at 2150°C and a source-to-seed separation of 4 mm. Growth rates below 2000°C were approximately one order of magnitude lower. Crystals grown at high temperatures ranged in color from blue to green due to the incorporation of Si and C from the SiC substrates; those grown at lower temperatures were colorless and transparent. Secondary-ion mass spectroscopy (SIMS) results showed almost a two order of magnitude decrease in the concentrations of these two impurities in the transparent crystals. Plan view transmission electron microscopy (TEM) of these crystals showed no line or planar defects. Raman spectroscopy and X-ray diffraction (XRD) studies indicated a strain free material. DA - 1997/8// PY - 1997/8// DO - 10.1016/S0022-0248(97)00160-7 VL - 179 IS - 3-4 SP - 363-370 SN - 0022-0248 ER - TY - JOUR TI - Spins, parity, excitation energies, and octupole structure of an excited superdeformed band in Hg-194 and implications for identical bands AU - Hackman, G AU - Khoo, TL AU - Carpenter, MP AU - Lauritsen, T AU - LopezMartens, A AU - Calderin, IJ AU - Janssens, RVF AU - Ackermann, D AU - Ahmad, I AU - Agarwala, S AU - Blumenthal, DJ AU - Fischer, SM AU - Nisius, D AU - Reiter, P AU - Young, J AU - Amro, H AU - Moore, EF AU - Hannachi, F AU - Korichi, A AU - Lee, IY AU - Macchiavelli, AO AU - Dossing, T AU - Nakatsukasa, T T2 - PHYSICAL REVIEW LETTERS AB - An excited superdeformed band in ${}^{194}\mathrm{Hg}$, observed to decay directly to both normal-deformed and superdeformed yrast states, is proposed to be a ${K}^{\ensuremath{\pi}}{\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}2}^{\ensuremath{-}}$ octupole vibrational band, based on its excitation energies, spins, and likely parity. The transition energies are identical to those of the yrast superdeformed band in ${}^{192}\mathrm{Hg}$, but originate from levels with different spins and parities. The evolution of transition energies with spin suggests that cancellations between pairing and particle alignment are partly responsible for the identical transition energies. DA - 1997/11/24/ PY - 1997/11/24/ DO - 10.1103/PhysRevLett.79.4100 VL - 79 IS - 21 SP - 4100-4103 SN - 0031-9007 ER - TY - JOUR TI - Spectroscopic ellipsometric study of Zn(1-x)Mn(x)Te films grown on GaAs AU - Choi, S. G. AU - Kim, Y. D. AU - Klein, M. V. AU - Yoo, S. D. AU - Aspnes, David E. AU - Xin, S. H. AU - Furdyna, J. K. T2 - Journal of the Korean Physical Society DA - 1997/// PY - 1997/// VL - 31 IS - 1 SP - 202-205 ER - TY - JOUR TI - Reconfigurable optical properties in InGaN/GaN quantum wells AU - Shmagin, IK AU - Muth, JF AU - Kolbas, RM AU - Mack, MP AU - Abare, AC AU - Keller, S AU - Coldren, LA AU - Mishra, UK AU - DenBaars, SP T2 - APPLIED PHYSICS LETTERS AB - Reconfigurable optical properties were studied in InGaN/GaN multiple quantum well (MQW) structures. It was observed that a short time exposure to a high intensity ultraviolet light results in long term, but reversible changes of the optical properties of InGaN/GaN MQW samples. The photoinduced changes can be observed using an optical microscope under low intensity ultraviolet light and are visible as a high contrast pattern. The retention time at room temperature for 12 and 20 MQW samples was longer than five days and four weeks, respectively. The effect was studied at room and cryogenic temperatures. DA - 1997/9/15/ PY - 1997/9/15/ DO - 10.1063/1.119935 VL - 71 IS - 11 SP - 1455-1457 SN - 0003-6951 ER - TY - JOUR TI - Raman analysis of the configurational disorder in AlxGa1-xN films AU - Bergman, L AU - Bremser, MD AU - Perry, WG AU - Davis, RF AU - Dutta, M AU - Nemanich, RJ T2 - APPLIED PHYSICS LETTERS AB - Raman analysis of the E2 mode of AlxGa1−xN in the composition range 0⩽x⩽1 is presented. The line shape was observed to exhibit a significant asymmetry and broadening toward the high energy range. The spatial correlation model is discussed, and is shown to account for the line shape. The model calculations also indicate the lack of a long-range order in the chemical vapor deposition alloys. These results were confirmed by x-ray scattering: the relative intensity of the superlattice line was found to be negligible. The line broadening of the E2 mode was found to exhibit a maximum at a composition x≅0.5 indicative of a random disordered alloy system. DA - 1997/10/13/ PY - 1997/10/13/ DO - 10.1063/1.119367 VL - 71 IS - 15 SP - 2157-2159 SN - 0003-6951 ER - TY - JOUR TI - Radiative proton capture to discrete states in N-31 at 98 and 176 MeV AU - Bright, TB AU - Hoistad, B AU - Johansson, R AU - Traneus, E AU - Cotanch, , SR T2 - NUCLEAR PHYSICS A AB - Abstract A high resolution magnetic pair spectrometer for medium energy photons has been used for studies of the exclusive (p,γ) reaction on 12 C at 98 and 176 MeV. We present angular distributions of the differential cross section for transitions to the ground state and the first three excited states of 13 N. The distributions from these four states are compared with predictions from a microscopic continuum shell model calculation using a realistic finite-ranged effective interaction with tensor components. In general, reasonable agreement is obtained for reactions to states described by p shell single particle wave functions, but poor agreement is obtained for transitions described by sd shell single particle wave functions. Nevertheless we find, however, that the dominant reaction mechanism is a direct capture process. We also compare the (p,γ) data with existing data on the exclusive (p,π) reaction at 185 MeV revealing notable differences between the two reactions. DA - 1997/8/11/ PY - 1997/8/11/ DO - 10.1016/S0375-9474(97)00185-1 VL - 621 IS - 3 SP - 754-766 SN - 0375-9474 KW - C-12(p, gamma), E = 98, 176 MeV KW - high resolution magnetic pair spectrometer KW - microscopic continuum shell model KW - high resolution magnetic pair spectrometer ER - TY - JOUR TI - Preliminary analysis of amphibian red cell M ferritin in a novel tetragonal unit cell AU - Ha, Y AU - Theil, EC AU - Allewell, NM T2 - ACTA CRYSTALLOGRAPHICA SECTION D-STRUCTURAL BIOLOGY AB - The ferritins are a multigene family of proteins that concentrate and store iron in all prokaryotic and eukaryotic cells. 24 monomeric subunits which fold as four-helix bundles assemble to form a protein shell with 432 cubic symmetry and an external diameter of approximately 130 A. The iron is stored inside the protein shell as a mineralized core approximately 80 A in diameter. Recombinant amphibian red cell M ferritin crystallizes in approximately 2 M (NH(4))(2)SO(4) at pH 4.6 in a space group that has not been reported previously. Electron microscopy, precession photography, Patterson and Fourier maps of the native protein and a UO(2)(2+) derivative, and simulations were used to determine that the unit-cell dimensions are a = b = 169.6, c = 481.2 A, alpha = beta = gamma = 90 degrees and the space group is P4(1)2(1)2 or P4(3)2(1)2. A preliminary model of the structure was obtained by molecular replacement, with amphibian red cell L ferritin as the model. In contrast to previously determined ferritin crystal structures which have intermolecular contacts at the twofold and threefold molecular axes, M ferritin crystals have a novel intermolecular interaction mediated by interdigitation of the DE loops of two molecules at the fourfold molecular axes. DA - 1997/9/1/ PY - 1997/9/1/ DO - 10.1107/S0907444997003983 VL - 53 SP - 513-523 SN - 2059-7983 ER - TY - JOUR TI - Li-7((p)over-right-arrow,gamma)Be-8 reaction at E-p=80-0 keV AU - Godwin, MA AU - Laymon, CM AU - Prior, RM AU - Tilley, DR AU - Weller, HR T2 - PHYSICAL REVIEW C AB - The ${}^{7}\mathrm{Li}(p\ensuremath{\rightarrow},\ensuremath{\gamma}{)}^{8}\mathrm{Be}$ reaction has been studied in the laboratory energy range ${E}_{p}=80$--0 keV. The vector analyzing powers ${A}_{y}(\ensuremath{\theta})$ and the angular distributions of the cross section $d\ensuremath{\sigma}/d\ensuremath{\Omega}(\ensuremath{\theta})$ for capture to the ground, first-, and third-excited states are reported. Additionally, the absolute cross section ${\ensuremath{\sigma}}_{T}(E)$ and (equivalently) the astrophysical $S$ factor $S(E)$ have been measured for capture to the third-excited state. Calculations have been performed for all three transitions using the direct capture model to which the known nearby $M$1 resonances were added. While they predict the angular distribution observed for the cross section and analyzing power in the case of both the first and third-excited states of ${}^{8}$Be, they do not reproduce those for the ground state. These calculations predict negligible $M$1 strength below 80 keV for capture to the third-excited state ${(2}^{+}$, $T=0+1$, 16.6 MeV), and we therefore conclude that the extrapolation of the astrophysical $S$ factor for the ${}^{7}\mathrm{Be}(p,\ensuremath{\gamma}{)}^{8}\mathrm{B}$ reaction, which has been performed previously by assuming pure $E$1 capture, is valid with regard to the neglect of any significant $p$-wave capture strength. DA - 1997/9// PY - 1997/9// DO - 10.1103/physrevc.56.1605 VL - 56 IS - 3 SP - 1605-1612 SN - 1089-490X ER - TY - JOUR TI - Evidence of near-surface localization of excited electronic states in crystalline Si AU - Mantese, L AU - Bell, KA AU - Rossow, U AU - Aspnes, DE T2 - JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B AB - Surface- and interface-related spectra, obtained either directly by techniques such as reflectance-difference (-anisotropy) spectroscopy or indirectly by subtracting pseudodielectric function spectra obtained ellipsometrically on surfaces with different chemical termination, exhibit features related to energy derivatives of the bulk dielectric function. We argue that these spectra provide direct evidence that the excitations involved are localized both in space and time. These data unequivocally indicate that critical point energies obtained from above-band-gap ellipsometric or reflectrometric optical spectra are not necessarily equal to bulk values, and that surface chemical and structural termination is at least one contributing factor. Present surface-optical calculations do not include these effects, which may explain, in part, remaining discrepancies between theory and experiment. DA - 1997/// PY - 1997/// DO - 10.1116/1.589438 VL - 15 IS - 4 SP - 1196-1200 SN - 2166-2746 ER - TY - JOUR TI - Electrical and structural properties of zirconium germanosilicide formed by a bilayer solid state reaction of Zr with strained Si1-xGex alloys AU - Wang, Z AU - Aldrich, DB AU - Nemanich, RJ AU - Sayers, DE T2 - JOURNAL OF APPLIED PHYSICS AB - The effects of alloy composition on the electrical and structural properties of zirconium germanosilicide (Zr–Si–Ge) films formed during the Zr/Si1−xGex solid state reaction were investigated. Thin films of Zr(Si1−yGey) and C49 Zr(Si1−yGey)2 were formed from the solid phase reaction of Zr and Si1−xGex bilayer structures. The thicknesses of the Zr and Si1−xGex layers were 100 and 500 Å, respectively. It was observed that Zr reacts uniformly with the Si1−xGex alloy and that C49 Zr(Si1−yGey)2 with y=x is the final phase of the Zr/Si1−xGex solid phase reaction for all compositions examined. The sheet resistance of the Zr(Si1−yGey)2 thin films was higher than the sheet resistance of similarly prepared ZrSi2 films. The stability of Zr(Si1−yGey)2 in contact with Si1−xGex was investigated and compared to the stability of Ti(Si1−yGey)2 in contact with Si1−xGex. The Ti(Si1−yGey)2/Si1−xGex structure is unstable when annealed for 10 min at 700 °C, with Ge segregating from Ti(Si1−yGey)2 and forming Ge-rich Si1−zGez precipitates at grain boundaries. In contrast, no Ge segregation was detected in the Zr(Si1−yGey)2/Si1−xGex structures. We attribute the stability of the Zr-based structure to a smaller thermodynamic driving force for germanium segregation and stronger atomic bonding in C49 Zr(Si1−yGey)2. Classical thermodynamics were used to calculate Zr(Si1−yGey)2–Si1−xGex tie lines in the Zr–Si–Ge ternary phase diagram. The calculations were compared with previously calculated Ti(Si1−yGey)2–Si1−xGex tie lines. DA - 1997/9/1/ PY - 1997/9/1/ DO - 10.1063/1.366043 VL - 82 IS - 5 SP - 2342-2348 SN - 0021-8979 ER - TY - JOUR TI - Determination of the gamma-ray background in a pulsed epithermal neutron beam AU - Yen, YF AU - Bowman, JD AU - Lowie, LY AU - Masuda, Y AU - Mitchell, GE AU - Penttila, SI T2 - NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT AB - The γ-ray background in the pulsed neutron beam at the Los Alamos Neutron Scattering Center was measured with an array of 10B-loaded liquid scintillators. With the method employed the γ-ray contribution in the neutron beam can be determined without knowledge of the energy spectrum of the γ-rays. The ratio of γ-ray to neutron intensities in the beam was determined during the time interval following the beam burst that corresponds to neutron energies from En = 1 to 340 eV. The γ-ray content in the beam ranges from 2% at 1 eV to 10% at 340 eV. DA - 1997/10/1/ PY - 1997/10/1/ DO - 10.1016/s0168-9002(97)00709-2 VL - 397 IS - 2-3 SP - 365-370 SN - 0168-9002 ER - TY - JOUR TI - Comparison of electron affinity and Schottky barrier height of zirconium and copper-diamond interfaces AU - Baumann, PK AU - Nemanich, RJ T2 - JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B AB - In this study, the evolution from diamond surfaces to metal–diamond interfaces has been examined. The electron affinity and the Schottky barrier height of a few Å thick films of Zr and Cu deposited in ultrahigh vacuum (UHV) onto IIb substrates were correlated. Prior to metal deposition, the diamond surfaces have been cleaned by different anneals and plasma treatments in UHV, and the surfaces were characterized by Auger electron spectroscopy and atomic force microscopy. The initial surfaces were terminated with oxygen, or free of chemisorbed species. Ultraviolet photoemission spectroscopy was employed to determine whether the samples exhibited a positive electron affinity or a negative electron affinity (NEA) before and after metal deposition. For Zr, the Schottky barrier height was found to change very little with the presence or absence of chemisorbed species at the interface. A NEA was observed for Zr on diamond independent of the surface termination. However, for Cu, the surface cleaning prior to metal deposition had a more significant effect. The Schottky barrier height changed strongly depending on the chemical species at the interface. A NEA was only detected for Cu on clean diamond surfaces. The differences between Zr on the one hand and Cu on the other are correlated with differences in interface chemistry and structure. DA - 1997/// PY - 1997/// DO - 10.1116/1.589444 VL - 15 IS - 4 SP - 1236-1240 ER - TY - JOUR TI - Characterization of carbon supported Pt/Ru alloy particles using EXAFS spectroscopy AU - Pandya, KI AU - Anderson, EB AU - Sayers, DE AU - OGrady, WE T2 - JOURNAL DE PHYSIQUE IV AB - mu alloys are used for electmoxidation of methanol in direct methanol he1 cells. Theii catalytic activity shun& depends upon the stmckm and +tim of the We have investigated the stmhre of PtlRu alloy particles #anhighsurface~csrtmhthreedifferent compositions, namely Pt:Ru,8.5:1.5.1:1 and 1.5:8.5. The samples were prepared by impregnating the carbon with salt solutions ofthe two metals fdlowed by redwAon to the alloy. The total metal hdiag was I0 wt%. The Pt L, andRuKEXAFS -ts were e'. Data Processing: The EXAFS function ~(k) was separated from the experimentally measured absorption specbum using the standard procedures. The R L, and Ru Kedge radial shwture functions (RSFs) for the alloy samples are shown in the figures 3 and 4, respectively. The RSFs are sigdkdy different from each other indicating that the structure strongly depends upon the composition. The effect of the DA - 1997/4// PY - 1997/4// DO - 10.1051/jp4:1997299 VL - 7 IS - C2 SP - 955-956 SN - 1155-4339 ER - TY - JOUR TI - An integrated growth and analysis system for in-situ XAS studies of metal-semiconductor interactions AU - Wang, Z AU - Goeller, PT AU - Boyanov, BI AU - Sayers, DE AU - Nemanich, RJ T2 - JOURNAL DE PHYSIQUE IV AB - A UHV system for in-situ studies of metal-semiconductor interactions has been designed and assembled at North Carolina State University and recently installed and tested at the NSLS. The UHV system consists of interconnected deposition and analysis chambers, each of which is capable of maintaining a base pressure of approximately 1 x 10 -10 Torr. Up to three materials can be co-deposited on 25 mm wafers by electron-beam evaporation. Substrate temperature can be controlled in the range 30-900 °C during deposition, and the growth process may be monitored with RHEED. The deposited materials and their reaction products can be studied in-Situ with a variety of technique: XAFS, AES, XPS, UPS and ARXPS/UPS. We describe the capabilities of the system and present our first EXAFS results on the stabilization of Co + 2 Si films co-deposited on Si 0.8 Ge 0.2 alloys. Preliminary results indicate that Co + 2Si forms a stable film on Si 0.8 Ge 0.2 with a CoSi 2 -like reaction path. As is the case with CO/Si 0.8 Ge 0.2 , silicide formation is complete at 700 °C. However, the Co+2Si/Si 0.8 Ge 0.2 system does not undergo a Cosi → CoSi 2 transition when annealed at 500-700 °C, and exhibits only weak CoSi features in this temperature range. DA - 1997/4// PY - 1997/4// DO - 10.1051/jp4/1997096 VL - 7 IS - C2 SP - 561-564 SN - 1155-4339 ER - TY - JOUR TI - Above bandgap dielectric function of epitaxial ZnSe layers AU - Kim, Y. D. AU - Ko, Y. D. AU - Choi, S. G. AU - Yoo, S. D. AU - Aspnes, D. E. AU - Jonker, B. T. T2 - Journal of the Korean Physical Society DA - 1997/// PY - 1997/// VL - 31 IS - 4 SP - L553-555 ER - TY - JOUR TI - Tidal mass transfer in elliptical-orbit binary stars AU - Layton, J. T. AU - Blondin, John AU - Owen, M. P. AU - Stevens, I. R. T2 - New Astronomy AB - High mass X-ray binary star systems with elliptical orbits, like GX 301-2, often exhibit a peak in X-ray luminosity associated with periastron passage. We use a two dimensional hydrodynamics code to examine the possibility that these X-ray flares result from tidal stripping of gas from the primary star, and subsequent accretion of this gas onto the compact companion. We find that if the primary star is rotating near corotation with the orbiting compact companion at periastron, tidally stripped gas can accrete, causing X-ray flares. Such a tidally induced flare will occur substantially after periastron, at a phase of ∼ 0.2 for the parameters used in our model. This flare is characterized by a brief disk accretion phase with a large angular momentum accretion rate. However, in our particular model this disk accretion phase was followed by an equally brief phase of accretion with the opposite sign of angular momentum, resulting in no long-term spin up of the X-ray pulsar. DA - 1997/// PY - 1997/// DO - 10.1016/s1384-1076(97)00047-x VL - 3 IS - 2 SP - 111–119 ER - TY - JOUR TI - The decay-out of superdeformed bands in the A=190 region: What have we learned? AU - Lauritsen, T. AU - Hackman, G. AU - Khoo, T. L. AU - Carpenter, M. P. AU - Janssens, R. V. F. AU - Lopez-Martens, A. AU - Ackermann, D. AU - Ahmad, I. AU - Amro, H. AU - Blumenthal, D. J. AU - Fischer, S. M. AU - Nisius, D. T. AU - Hannachi, F. AU - Korichi, A. AU - Moore, E. F. T2 - Acta Physica Hungarica. New Series, Heavy Ion Physics DA - 1997/// PY - 1997/// VL - 6 IS - 1-4 SP - 229-240 ER - TY - JOUR TI - Surface preparation of ZnSe substrates for MBE growth of II-VI light emitters AU - Hughes, WC AU - Boney, C AU - Johnson, MAL AU - Cook, JW AU - Schetzina, JF T2 - JOURNAL OF CRYSTAL GROWTH AB - Abstract This paper describes substrate surface preparation techniques used in the development II–VI light emitting diode and laser diode structures on high-quality, bulk ZnSe substrates supplied by Eagle-Picher Industries. The use of ZnSe substrates eliminates many of the problems associated with lattice mismatch in heteroepitaxy of II–VI light emitters on GaAs substrates. However, defects still form during nucleation of an epitaxial layer on ZnSe substrates because of surface roughness, contamination, and defects. We have employed a variety of wet chemical etches, vacuum anneals, plasma treatments, and characterization techniques such as RHEED, Auger electron spectroscopy, and SEM studies to improve the ZnSe substrate surface prior to MBE film growth. A combination of hydrogen plasma exposure and annealing was found to be the most effective way to remove contaminants from ZnSe substrates but less than optimum homoepitaxial quality showed that the surface preparation is more complex than simply cleaning the polished surface. Since polishing can leave residual damage in the form of near-surface defects, the top layer of these substrates was removed by reactive ion etching with BCl 3 . Parameters were chosen such that this etch was homogeneous and smoothed the ZnSe surface. Etch pit density measurements revealed that the polish-induced damage to ZnSe extended up to about 5 μm deep. A dramatic improvement in the characteristics of blue/green light emitting devices was observed for devices grown on ZnSe substrates from which this damaged layer had been removed. This surface preparation procedure has led to the brightest and longest lasting II–VI green LEDs made in the world today. DA - 1997/5// PY - 1997/5// DO - 10.1016/S0022-0248(96)01022-6 VL - 175 SP - 546-551 SN - 0022-0248 ER - TY - JOUR TI - Strain effects on the interface properties of nitride semiconductors AU - Nardelli, MB AU - Rapcewicz, K AU - Bernholc, J T2 - PHYSICAL REVIEW B AB - An ab initio study of nitride-based heteroepitaxial interfaces that uses norm-conserving pseudopotentials and explicitly treats the strain due to lattice mismatch is presented. Strain effects on the band offsets range from 20% to 40%. The AlN/GaN/InN interfaces (with AlN in-plane lattice constant) are all of type I, while the ${\mathrm{Al}}_{0.5}$${\mathrm{Ga}}_{0.5}$N/AlN zinc-blende (001) interface is of type II. Further, the bulk polarizations in wurtzite AlN and GaN are -1.2 and -0.45 \ensuremath{\mu}C/${\mathrm{cm}}^{2}$, respectively, and the interface contribution to the polarization in the GaN/AlN wurtzite multiquantum-well is small. DA - 1997/3/15/ PY - 1997/3/15/ DO - 10.1103/physrevb.55.r7323 VL - 55 IS - 12 SP - R7323-R7326 SN - 2469-9969 ER - TY - JOUR TI - Spectroscopic ellipsometry study of GaAs/AlAs superlattices and Al(0.5)Ga(0.5)As alloy AU - Choi, S. G. AU - Kim, Y. D. AU - Yoo, S. D. AU - Aspnes, David E. AU - Rhee, S. J. AU - Woo, J. C. AU - Woo, D. H. AU - Kim, S. H. AU - Kang, K. N. T2 - Journal of the Korean Physical Society DA - 1997/// PY - 1997/// VL - 30 IS - suppl. SP - 108-112 ER - TY - JOUR TI - Spectral analysis of above-, below-, and near-bandedge phenomena in GaN thin films AU - Edwards, NV AU - Yoo, SD AU - Bremser, MD AU - Zheleva, T AU - Horton, MN AU - Perkins, NR AU - Weeks, TW AU - Liu, H AU - Stall, RA AU - Kuech, TF AU - Davis, RF AU - Aspnes, DE T2 - MATERIALS SCIENCE AND ENGINEERING B-SOLID STATE MATERIALS FOR ADVANCED TECHNOLOGY AB - We report spectroscopic ellipsometry (SE) and low-temperature reflectance data on epitaxial GaN thin film samples covering the widest range of tensile and compressive stress (−3.8–3.5 kbar) thus far. SE allows us to assess the preparation of smooth and abrupt GaN surfaces by chemical treatments in real time, and, coupled with the reflectance data, the E dn/dE contribution to dispersion, which is important for laser action. The reflectance data explicitly show the nonlinear behavior of the B–A and C–A splittings versus the energy of the A exciton. Lineshape ambiguities that hindered previous interpretations have been resolved with reciprocal space analysis, allowing us to obtain band parameters such as ΔSO=17.0±1 meV and ΔCF=9.8±1 meV with increased confidence. DA - 1997/12/18/ PY - 1997/12/18/ DO - 10.1016/s0921-5107(97)00151-7 VL - 50 IS - 1-3 SP - 134-141 SN - 0921-5107 KW - GaN thin films KW - spectroscopic ellipsometry KW - bandedge phenomena ER - TY - JOUR TI - Real-time monitoring of surface processes by p-polarized reflectance AU - Dietz, N AU - Sukidi, N AU - Harris, C AU - Bachmann, KJ T2 - JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A-VACUUM SURFACES AND FILMS AB - Understanding surface chemistry under steady-state epitaxial growth involving organo-metallic chemical precursor molecules is essential for optimizing growth processes. Surface-sensitive optical real-time sensor techniques are very well suited for this task as their applications are not limited to a high vacuum environment. In this article we report the combined application of the optical sensor techniques p-polarized reflectance (PR) and laser light scattering for the real-time monitoring of low temperature growth of epitaxial GaP/GaxIn1−xP heterostructures on Si(001) and GaAs(001) substrates by pulsed chemical beam epitaxy. The high surface sensitivity of PR allows to follow growth processes with submonolayer resolution during the sequential precursor exposure of the surface that causes periodic alterations in composition and thickness of a surface reaction layer (SRL), the effect of which is monitored by PR as a periodic fine structure. This fine structure is superimposed on interference oscillations, resulting from back reflection at the substrate-layer interface with increasing layer thickness. In a linear approximation of the complex four-layer stack reflectance amplitude RR4 in the phase factor Φ1, the optical response to the SRL is formulated as an additive term in the three-layer model that describes the underlying film growth process. Analytical expressions for the first derivative of the PR signal are presented and discussed with respect to the time scale of observation that allows the separation of film growth induced changes from SRL effects. The amplitude modulation and the turning points in the fine structure are assessed and compared to experimental results, showing that an average complex dielectric function of an ultrathin SRL can be quantified, independent of surface coverage. DA - 1997/// PY - 1997/// DO - 10.1116/1.580712 VL - 15 IS - 3 SP - 807-815 SN - 0734-2101 ER - TY - JOUR TI - QCD and hadronic physics AU - Swanson, E. S. T2 - Nuclear Physics. B DA - 1997/// PY - 1997/// IS - suppl. SP - 166-170 ER - TY - JOUR TI - Prone breast tumor imaging using vertical axis-of-rotation (VAOR) SPECT: An initial study AU - Wang, HL AU - Scarfone, C AU - Greer, KL AU - Coleman, RE AU - Jaszczak, RJ T2 - IEEE TRANSACTIONS ON NUCLEAR SCIENCE AB - The authors propose the use of a single photon emission computed tomography (SPECT) system equipped with multiple cameras which revolve around a vertical axis-of-rotation (VAOR) for prone-dependent (i.e., patient in prone position) breast tumor imaging. This geometry for nuclear medicine breast imaging reduces the amount of attenuating material between the breast tissue and the gamma camera and, in addition, it offers a minimal radius-of-rotation compared to breast imaging using conventional (i.e., 360/spl deg/, horizontal axis-of-rotation) SPECT. The decrease in attenuation and radius-of-rotation results in an increase in detected counts and increased collimator resolution. Because VAOR SPECT systems are currently not commercially available, the authors conducted their experiments on a conventional SPECT system using an isolated breast phantom to investigate the proposed VAOR method. The authors' experimental setup simulated a VAOR SPECT study with a prone-dependent breast in the camera's field-of-view. The results of the experiment indicate that VAOR breast SPECT with Trionix low-energy super-high resolution (LESR) parallel-hole collimation is capable of detecting a breast lesion with an outer diameter of 10 mm and a lesion-to-background concentration ratio of 6-to-1. The results also demonstrate that VAOR breast SPECT provides improved lesion parallel-hole planar imaging (i.e., scintimammography) and breast imaging using horizontal axis-of-rotation SPECT. DA - 1997/6// PY - 1997/6// DO - 10.1109/23.597000 VL - 44 IS - 3 SP - 1271-1276 SN - 0018-9499 ER - TY - JOUR TI - Photoluminescence from mechanically milled Si and SiO2 powders AU - Shen, TD AU - Shmagin, I AU - Koch, CC AU - Kolbas, RM AU - Fahmy, Y AU - Bergman, L AU - Nemanich, RJ AU - McClure, MT AU - Sitar, Z AU - Quan, MX T2 - PHYSICAL REVIEW B AB - The photoluminescence (PL) in as-received and milled Si and ${\mathrm{SiO}}_{2}$ powder is reported. The Si and ${\mathrm{SiO}}_{2}$ powder is characterized by chemical analysis, Raman scattering, x-ray photoelectron spectra, infrared absorption, x-ray diffraction, and differential thermal analysis. The results indicate that the Si powder has amorphous Si oxide and suboxide surface layers. The milling of Si powder results in the formation of nanocrystalline/amorphous Si components. An amorphous ${\mathrm{SiO}}_{2}$ component is formed by milling crystalline ${\mathrm{SiO}}_{2}$ . The PL spectra for as-received Si, milled Si, and ${\mathrm{SiO}}_{2}$ powder exhibit similar peak shapes, peak maxima, and full width at half maximum values. For both the as-received and the milled Si powder, experimental results appear to exclude mechanisms for PL related to an amorphous Si component or Si-H or Si-OH bonds, or the quantum confinement effect. Similarly, for milled ${\mathrm{SiO}}_{2}$ powder mechanisms for PL do not appear related to Si-H or Si-OH bonds. Instead the greatly increased intensity of PL for milled ${\mathrm{SiO}}_{2}$ can be related to both the increased volume fraction of the amorphous ${\mathrm{SiO}}_{2}$ component and the increased density of defects introduced in the amorphous ${\mathrm{SiO}}_{2}$ upon milling. It is suggested that the PL for as-received Si, milling-induced nanocrystalline/amorphous Si, and milled ${\mathrm{SiO}}_{2}$ results from defects, such as the nonbridging oxygen hole center, in the amorphous Si suboxide and/or ${\mathrm{SiO}}_{2}$ components existing in these powder samples. The PL measurement for milled ${\mathrm{SiO}}_{2}$ is dependent on air pressure whereas that for as-received ${\mathrm{SiO}}_{2}$ is not, suggesting that new emitting centers are formed by milling. DA - 1997/3/15/ PY - 1997/3/15/ DO - 10.1103/physrevb.55.7615 VL - 55 IS - 12 SP - 7615-7623 SN - 0163-1829 ER - TY - JOUR TI - Photoelectron spectroscopy measurements and theoretical calculations of the lowest doubly hollow lithium state AU - Diehl, S AU - Cubaynes, D AU - Chung, KT AU - Wuilleumier, FJ AU - Kennedy, ET AU - Bizau, JM AU - Journel, L AU - Blancard, C AU - VoKy, L AU - Faucher, P AU - Hibbert, A AU - Berrah, N AU - Morgan, TJ AU - Bozek, J AU - Schlachter, AS T2 - PHYSICAL REVIEW A AB - We have measured, using electron spectroscopy, the lowest-energy doubly hollow lithium triply excited ${(3l3l}^{\ensuremath{'}}{3l}^{\ensuremath{''}})$ ${}^{2}P$ state. Energies, widths, and partial cross sections have been measured and calculated using the saddle-point technique and the $R$-matrix approximation. Our results show good agreement between experimental and theoretical data for the energy and the width of the doubly hollow state. DA - 1997/8// PY - 1997/8// DO - 10.1103/PhysRevA.56.R1071 VL - 56 IS - 2 SP - R1071-R1074 SN - 1094-1622 ER - TY - JOUR TI - Optical metastability in bulk GaN single crystals AU - Shmagin, IK AU - Muth, JF AU - Lee, JH AU - Kolbas, RM AU - Balkas, CM AU - Sitar, Z AU - Davis, RF T2 - APPLIED PHYSICS LETTERS AB - Bulk GaN single crystals were grown from cold pressed GaN powder by sublimation in flowing ammonia. Optical transmission measurements indicated that the absorption coefficient for the transparent samples is 50 cm−1 in the wavelength region from 650 to 400 nm. Optical metastability in bulk GaN crystals was studied through time dependent photoluminescence both at room and liquid–nitrogen temperatures. The observation included decreasing output intensity of the ultraviolet emission attributed to the band edge and increasing output intensity of a new emission band centered at 378 nm at room temperature. At liquid–nitrogen temperature, the photoinduced emission band consisted of at least one LO-phonon replica of the zero-phonon line centered at 378 nm. The ratio of output intensities of the photoinduced band to the band edge increased by a factor of 10 during 27 min of exposure time. The photoinduced effect is attributed to the metastable nature of traps in bulk GaN. DA - 1997/7/28/ PY - 1997/7/28/ DO - 10.1063/1.119577 VL - 71 IS - 4 SP - 455-457 SN - 0003-6951 ER - TY - JOUR TI - Optical data storage in InGaN/GaN heterostructures AU - Shmagin, IK AU - Muth, JF AU - Kolbas, RM AU - Dupuis, RD AU - Grudowski, PA AU - Eiting, CJ AU - Park, J AU - Shelton, BS AU - Lambert, DJH T2 - APPLIED PHYSICS LETTERS AB - Optical storage data was realized using an InGaN/GaN single heterostructure. It was observed that exposure to a high power density ultraviolet light temporarily changes the optical properties of the InGaN epitaxial layer. The photo-induced changes can be observed under an optical microscope with low intensity ultraviolet excitation. This effect was used to create high contrast optical patterns on the sample at room temperature and 77 K. The photo-induced changes completely disappear in about four hours at room temperature. After the recorded pattern is erased, the information can be rewritten without a change in efficiency or retention time. DA - 1997/9/8/ PY - 1997/9/8/ DO - 10.1063/1.119900 VL - 71 IS - 10 SP - 1382-1384 SN - 0003-6951 ER - TY - JOUR TI - Numerical simulation of the platinum L (III) edge white line relative to nanometer scale clusters AU - Bazin, D. AU - Sayers, D. E. AU - Rehr, J. J. AU - Mottet, C. T2 - Journal of Physical Chemistry. B, Condensed Matter, Materials, Surfaces, Interfaces & Biophysical DA - 1997/// PY - 1997/// VL - 101 IS - 27 SP - 5332-5336 ER - TY - JOUR TI - Neutron resonance spectroscopy of Ag-107 and Ag-109 AU - Lowie, LY AU - Bowman, JD AU - Crawford, BE AU - Delheij, PPJ AU - Haseyama, T AU - Knudson, JN AU - Masaike, A AU - Matsuda, Y AU - Mitchell, GE AU - Penttila, SI AU - Postma, H AU - Roberson, NR AU - Seestrom, SJ AU - Sharapov, EI AU - Stephenson, SL AU - Yen, YF AU - Yuan, VW T2 - PHYSICAL REVIEW C AB - Parity violation has been observed in a number of previously unreported neutron resonances in silver. Analysis of these parity violation data requires improved neutron resonance spectroscopy. The neutron total cross section for natural silver was measured for ${E}_{n}=10$--800 eV with the time-of-flight method at the Los Alamos Neutron Scattering Center. The neutron capture reaction was studied with both a natural silver target and a highly enriched sample (98.29%) of ${}^{107}$Ag. A total of 38 previously unreported resonances were observed. The combination of the two measurements allowed assignment of the newly observed resonances to ${}^{107}$Ag or to ${}^{109}$Ag. Resonance parameters were determined for almost all of the neutron resonances observed. DA - 1997/7// PY - 1997/7// DO - 10.1103/physrevc.56.90 VL - 56 IS - 1 SP - 90-97 SN - 1089-490X ER - TY - JOUR TI - Low-temperature (<450 degrees C), plasma-assisted deposition of poly-Si thin films on SiO2 and glass through interface engineering AU - Wolfe, DM AU - Wang, F AU - Lucovsky, G T2 - JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A-VACUUM SURFACES AND FILMS AB - A low-temperature, two-stage process that employs interface engineering is investigated for deposition of poly-Si thin films on SiO2 and glass. In this two-stage process, film growth is separated into two regimes: (i) interface formation and (ii) bulk film growth. Interface formation (stage 1) was optimized for remote plasma enhanced chemical-vapor deposition (PECVD) of ultra thin (&lt;100 Å) μc-Si films on the oxide. This layer acts as a seed template, providing ordered growth sites for the next stage of film growth. Bulk Si film deposition (stage 2) was then initiated on the seed template using remote PECVD process conditions shown to produce low-temperature (&lt;450 °C), epitaxial-Si films on crystalline silicon substrates, so as to drive a transition to larger grain growth off of the seed crystals. Results showed that the seed layer had a dramatic impact on bulk film crystallinity. Films deposited without a μc-Si seed layer were amorphous, whereas films deposited using a seed layer, in conjunction with the appropriate second stage conditions, were highly oriented (220) poly-Si. DA - 1997/// PY - 1997/// DO - 10.1116/1.580426 VL - 15 IS - 3 SP - 1035-1040 SN - 0734-2101 ER - TY - JOUR TI - Lifetime measurements and decay of superdeformed bands in Hg isotopes T2 - Zeitschrift fur Physik. A, Hadrons and Nuclei DA - 1997/// PY - 1997/// VL - 358 IS - 2 SP - 219-223 ER - TY - JOUR TI - Jejunal glucose uptake and oxygen consumption in turkey poults selected for rapid growth AU - Fan, YK AU - Croom, J AU - Christensen, VL AU - Black, BL AU - Bird, AR AU - Daniel, LR AU - McBride, BW AU - Eisen, EJ T2 - POULTRY SCIENCE AB - Two lines of turkey poults, one selected for rapid growth at 16 wk of age (F line) and the other a randombred control line (RBC2) were used to investigate the effect of selection for rapid growth on jejunal O2 consumption and glucose transport as well as whole-body O2 consumption. All trials used unsexed poults and were designed as a randomized complete block with day and line as independent variables. In Trial 1, 120 turkey poults, fed a standard starter ration (25.5% CP), were used to examine the effect of selection on feed intake, body weight gain, and efficiency from hatching (Day 0) to 13 d of age. At Day 14, 36 of 60 birds from each line were killed to measure intestinal length and weight and jejunal O2 consumption after 18 h of feed deprivation. Compared with the RBC2 line, the F line had relatively shorter but heavier small intestinal segments when adjusted by 18 h feed-deprived body weight (FBW; P < 0.001). The F line consumed more O2 over the entire jejunum adjusted to FBW than RBC2 line (43.8 vs 34.6 nmol O2/min.g FBW; P < 0.001). Jejunal ouabain- and cycloheximide-sensitive O2 consumption were greater (P < 0.05) in the F line. In Trial 2, 16 14-d-old poults from each line were used to measure in vitro jejunal glucose transport rate. There was no difference in glucose transport of the jejunum (nanomoles per minute per gram of FBW) between the lines. In Trial 3, 20 poults from each line were used to measure whole-body O2 consumption at 7 to 10 d of age. The F and RBC2 lines had similar whole-body O2 consumption rate per gram of FBW. These data suggest that selection of turkeys for rapid growth at 16 wk of age did not increase efficiency of jejunal glucose uptake in 14-d-old turkey poults. DA - 1997/12// PY - 1997/12// DO - 10.1093/ps/76.12.1738 VL - 76 IS - 12 SP - 1738-1745 SN - 0032-5791 KW - turkey KW - small intestine KW - glucose active transport KW - respiration KW - genetic selection ER - TY - JOUR TI - Inner-shell excitation spectroscopy of polymer and monomer isomers of dimethyl phthalate AU - Urquhart, SG AU - Hitchcock, AP AU - Smith, AP AU - Ade, H AU - Rightor, EG T2 - JOURNAL OF PHYSICAL CHEMISTRY B AB - The C 1s X-ray absorption spectra (XAS) of poly(diallyl phthalate), poly(diallyl isophthalate), and poly(ethylene terephthalate) (PET) have been recorded using transmission detection. The phthalate segments of these polymers are isomers with different patterns of substitution (ortho, meta, para) of the methyl carboxylate groups on the phenyl ring. The C 1s and O 1s electron energy loss spectra (EELS) of the corresponding isomeric monomers, dimethyl phthalate, dimethyl isophthalate, and dimethyl terephthalate, have also been recorded in the gas phase using inelastic electron scattering under conditions dominated by electric dipole transitions. Good agreement is found in overall shape and in the energies of the spectral features of the same isomer in monomeric (EELS) versus polymeric (XAS) form. Ab initio calculations are used to provide a detailed interpretation of the spectra, in particular the origin of the isomeric variations. The analytical potential for using inner shell excitation spectroscopy to identify isomeric character and to map spatial distributions of polymer isomeric substitution is assessed. DA - 1997/3/27/ PY - 1997/3/27/ DO - 10.1021/jp963419d VL - 101 IS - 13 SP - 2267-2276 SN - 1520-6106 ER - TY - JOUR TI - Injection and acceleration of thermal protons at quasi-parallel shocks: a hybrid simulation parameter survey AU - Giacalone, J. AU - Burgess, D. AU - Schwartz, S. J. AU - Ellison, D. C. AU - Bennett, L. T2 - Journal of Geophysical Research. Space Physics AB - Collisionless shocks that propagate along the mean magnetic field are known to accelerate some fraction of the incident charged particles directly from the thermal pool to energies that are considerably higher than the energy at which the plasma rams into the shock. Using hybrid simulations, we address two issues: (1) the dependence of the injection/acceleration of thermal protons to energies much higher than the plasma ram energy on various shock parameters such as Mach number, plasma beta, etc., and (2) the effect of the high‐energy particles, accelerated directly from the thermal population by the shock, on the macroscopic properties of the shock, most notably, on the density compression. We find that for supercritical Mach numbers the acceleration of the thermal plasma is efficient enough that the back pressure due to the energetic particles can significantly increase the density compression across the shock, above the value expected from the simple Rankine‐Hugoniot prediction. Additionally, at low Alfvén Mach number, where the acceleration of the thermal plasma is inefficient, the density compression is smaller than the simple Rankine‐Hugoniot prediction owing to the nonresonant fire hose instability. The acceleration efficiency increases with Mach number except at very high Alfvén Mach numbers, where it begins to decrease for Mach numbers greater than ∼ 10. This is due to the presence of a fixed, free‐escape boundary that limits the size of the foreshock region measured in units of the mean‐free paths of the accelerated particles. Additionally, we find that regardless of the upstream plasma parameters, the acceleration efficiency increases with both the density compression ratio across the shock and the distance to the free‐escape boundary measured in units of the mean‐free path of the energetic particles. Both of these are consistent with analytic theory and numerical models that use a phenomenological scattering law. DA - 1997/// PY - 1997/// DO - 10.1029/97JA01529 VL - 102 IS - A9 SP - 19789-19804 ER - TY - JOUR TI - Hydrogen chemisorption on silica-supported Pt clusters: In situ X-ray absorption spectroscopy AU - Reifsnyder, SN AU - Otten, MM AU - Sayers, DE AU - Lamb, HH T2 - JOURNAL OF PHYSICAL CHEMISTRY B AB - Hydrogen chemisorption on small silica-supported Pt clusters was investigated using in situ extended X-ray absorption fine structure (EXAFS) spectroscopy and X-ray absorption near-edge structure (XANES) spectroscopy. The clusters were found to exhibit a bulklike Pt first nearest neighbor (NN) distance (2.76 Å) and low disorder while covered by chemisorbed hydrogen. In contrast, bare Pt clusters produced by heating in vacuo at 300 °C are characterized by a contracted Pt NN distance (2.66 Å) and greater disorder. These effects are reversed by re-exposure of the bare Pt clusters to H2 at 25 °C. The metal−support interface is characterized by a short Pt−O distance, irrespective of the presence of chemisorbed hydrogen. An apparent L3 edge shift of 0.8 eV relative to bulk Pt is observed for the hydrogen-covered clusters. This shift is attributed to a decrease in the Pt L3 edge resonance (white line) intensity, as no corresponding shift is observed at the L2 edge. A hydrogen-related L2,3 XANES feature at 9 eV appears with nearly equal intensity at each edge. This peak is assigned to electronic transitions from Pt 2p levels to H 1s−Pt 5d antibonding states with mixed d3/2−d5/2 character. From the L2,3 XANES analysis, we find that the number of unoccupied d states in hydrogen-covered Pt clusters is 23% less than in bulk Pt. In contrast, the L2,3 XANES spectra of bare silica-supported Pt clusters are closely similar to those of bulk Pt; quantitative analysis reveals only a slight (4%) decrease in the number of unoccupied d states. DA - 1997/6/19/ PY - 1997/6/19/ DO - 10.1021/jp970244e VL - 101 IS - 25 SP - 4972-4977 SN - 1089-5647 ER - TY - JOUR TI - Hydrogen atom participation in metastable defect formation at Si-SiO2 interfaces AU - Lucovsky, G AU - Yang, H AU - Jing, Z AU - Whitten, JL T2 - APPLIED SURFACE SCIENCE AB - This paper discusses mechanisms for defect metastability with H atom participation at SiSiO2 interfaces as in field effect transistors. Reaction pathways are associated with differences in defect bonding properties between positively charged (i) Si atoms and (ii) O and N atoms. Defect reaction equations, supported by quantum chemistry calculations, are presented. The metastable defects emphasized here are created by hole trapping followed by H atom attachment. DA - 1997/6// PY - 1997/6// DO - 10.1016/S0169-4332(97)80077-3 VL - 117 SP - 192-197 SN - 0169-4332 KW - Si-SiO2 interfaces KW - metastable defects KW - defect reactions KW - interface traps KW - fixed oxide charge ER - TY - JOUR TI - High-resolution imagery of Bd +30 degrees 3639 and its dusty halo AU - Harrington, J. P. AU - Lame, N. J. AU - White, S. M. AU - Borkowski, K. J. T2 - Nanostructured Materials DA - 1997/// PY - 1997/// VL - 113 IS - 6 SP - 2147 ER - TY - JOUR TI - Growth of GaN, InGaN, and AlGaN films and quantum well structures by molecular beam epitaxy AU - Johnson, MAL AU - Hughes, WC AU - Rowland, WH AU - Cook, JW AU - Schetzina, JF AU - Leonard, M AU - Kong, HS AU - Edmond, JA AU - Zavada, J T2 - JOURNAL OF CRYSTAL GROWTH AB - GaN, AlGaN and InGaN films have been grown by molecular beam epitaxy (MBE) using RF plasma sources for the generation of active nitrogen. These films have been deposited homoepitaxially onto GaNSiC substrates and heteroepitaxially onto LiGaO2 substrates. LiGaO2 is an ordered and closely-lattice-matched orthorhombic variant of the wurtzite crystal structure of GaN. A low-temperature AlN buffer layer is necessary in order to nucleate GaN on LiGaO2. Thick GaN and AlGaN layers may then be grown once deposition is initiated. InGaN has been grown by MBE at mole fractions of up to 20% as a quantum well between GaN cladding layers. The indium containing structures were deposited onto GaNSiC substrates to focus the development effort on the InGaN growth process rather than on heteroepitaxial nucleation. A modulated beam technique, with alternating short periods of (In, Ga)N and (Ga)N, was used to grow high-quality InGaN. The modulated beam limits the nucleation of metal droplets on the growth surface, which form due to thermodynamic limitations. A narrow PL dominated by band edge luminescence at 421 nm results from this growth technique. Growth of GaN at high temperatures is also reported. DA - 1997/5// PY - 1997/5// DO - 10.1016/S0022-0248(96)01019-6 VL - 175 SP - 72-78 SN - 1873-5002 ER - TY - JOUR TI - Fluorine atom induced decreases to the contribution of infrared vibrations to the static dielectric constant of Si-O-F alloy films AU - Lucovsky, G AU - Yang, H T2 - JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A-VACUUM SURFACES AND FILMS AB - Si–O–F alloy films deposited by chemical vapor deposition have static dielectric constants, εs, significantly reduced with respect to those of similarly prepared SiO2, ∼3.2 to 3.4 as compared to 4.0 to 4.2. Infrared absorption spectra provide a basis modeling the molecular structure of these alloys, as well as helping to identify microscopic mechanisms responsible for static dielectric constant reductions. Contributions of electronic and vibrational transitions to εs are discussed in terms of an empirical chemical bonding model. Ab initio calculations are then used to identify inductive effects of Si–F bonds on the properties of Si–O–Si groups that are back-bonded to the Si atom of that Si–F group. The ab initio calculations provide a theoretical framework for understanding why relatively low concentrations of F atoms; ∼10–12 at. %, produce significant decreases in εs, ∼22%, as reported for the Si–O–F alloys. DA - 1997/// PY - 1997/// DO - 10.1116/1.580717 VL - 15 IS - 3 SP - 836-843 SN - 0734-2101 ER - TY - JOUR TI - Elimination of sub-oxide transition regions at Si-SiO2 interfaces by rapid thermal annealing at 900 degrees C AU - Lucovsky, G AU - Banerjee, A AU - Niimi, H AU - Koh, K AU - Hinds, B AU - Meyer, C AU - Lupke, G AU - Kurz, H T2 - APPLIED SURFACE SCIENCE AB - In many spectroscopic studies, particularly by X-ray photoelectron spectroscopy, XPS, it has been generally assumed that the existence of sub-oxide transition regions at SiSiO2 interfaces were not strongly dependent on synthesis chemistries and processing conditions. This paper presents experimental evidence for a kinetically-limited phase transition at SiSiO2 interfaces at approximately 900°C that can minimize and to a large degree eliminate significant interfacial sub-oxide transition regions. The paper emphasizes a connection between (i) differences in photoluminescence from SiOx bulk films before and after 900°C annealing and (ii) differences in electrical performance of SiSiO2 interfaces and optical second harmonic generation from SiSiO2 interfaces, also before and after 900°C annealing DA - 1997/6// PY - 1997/6// DO - 10.1016/S0169-4332(97)80079-7 VL - 117 SP - 202-206 SN - 1873-5584 KW - Si-SiO2 interfaces KW - sub-oxide transition regions KW - plasma processing KW - rapid thermal annealing ER - TY - JOUR TI - Collimation of astrophysical jets: The proto-planetary nebula He 3-1475 AU - Borkowski, KJ AU - Blondin, JM AU - Harrington, JP T2 - ASTROPHYSICAL JOURNAL AB - The proto-planetary nebula He 3-1475 was imaged in the [N II] λ6584 line with the Wide Field Planetary Camera 2 on board the Hubble Space Telescope. This image has revealed what appear to be large-scale flows being collimated into narrow bipolar jets. This is a unique object: we may be observing the actual collimation process of an astrophysical jet. Analytical models and hydrodynamical simulations suggest that the jet in He 3-1475 may be produced by purely hydrodynamical means, through focusing of a weakly collimated bipolar outflow into jets by oblique radiative shocks. DA - 1997/6/10/ PY - 1997/6/10/ DO - 10.1086/310679 VL - 482 IS - 1 SP - L97-& SN - 0004-637X KW - hydrodynamics KW - ISM, jets and outflows KW - planetary nebulae, individual (He 3-1475) KW - shock waves ER - TY - JOUR TI - A shear force feedback control system for near-field scanning optical microscopes without lock-in detection AU - Hsu, JWP AU - McDaniel, AA AU - Hallen, HD T2 - REVIEW OF SCIENTIFIC INSTRUMENTS AB - An improvement to the currently used ac impedance detection method for tip-sample distance control in near-field scanning optical microscopes is described and demonstrated. The output signal of the electronic bridge is increased by a factor of 5000 so that a root-mean-square chip can be used in place of sensitive lock-in detection. It is shown that the signal-to-noise ratio of this new method is high enough to detect 0.07 nm changes in topography. In addition, this modification makes the electronics for the shear force feedback compact and inexpensive. DA - 1997/8// PY - 1997/8// DO - 10.1063/1.1148247 VL - 68 IS - 8 SP - 3093-3095 SN - 0034-6748 UR - http://dx.doi.org/10.1063/1.1148247 ER - TY - JOUR TI - UV, blue and green light emitting diodes based on GaN-InGaN multiple quantum wells over sapphire and (111) spinel substrates AU - Khan, MA AU - Chen, Q AU - Yang, J AU - Sun, CJ AU - Lim, B AU - Temkin, H AU - Schetzina, J AU - Shur, MS T2 - MATERIALS SCIENCE AND ENGINEERING B-SOLID STATE MATERIALS FOR ADVANCED TECHNOLOGY AB - Recently Nakamura et al. have reported on high brightness visible LEDs based on AlGaN-InGaN multiple quantum wells (MQWs) using atmospheric pressure metal-organic chemical vapor deposition (MOCVD) and AlGaN barrier layers around an InxGa1 − xN-InyGa1 − yN multiple quantum well region. We now report the fabrication of high brightness vertical cavity UV, blue and green light emitting diodes using low pressure MOCVD with GaN-InxGa1 − xN multiple quantum wells surrounded by GaN barrier layers. Our device structures over sapphire and cubic (111) spinel substrates consisted of a 10 period GaN-InGaN MQW (25 Å well-50 Å barrier) surrounded by n- and p-GaN layers. Structures with both Mg-doped and undoped quantum wells (active regions) were deposited. Mesa type LED structures were then fabricated using Ti-Al and Ni-Au for the n-and p-ohmic contacts. Light emission was observed in a vertical cavity geometry from the sapphire or the spinel substrate side. For 250 mm diameter mesa devices the series resistances ranged from 10 to 25 Ω. These are some of the lowest reported values. Spectral emission linewidths (FWHM) of 12, 25 and 40 nm were obtained respectively for the UV, blue, and green MQW LEDs. These linewidths are similar to those of Nakamura et al. We also report on optically pumped MQW InGaN-GaN lasers with different quantum well thicknesses. In these devices, we observed the quantum shift related to the subband energy dependence on the well thickness and estimated the effective conduction band discontinuity at the GaN-InGaN heterointerface from these data. DA - 1997/1// PY - 1997/1// DO - 10.1016/s0921-5107(96)01903-4 VL - 43 IS - 1-3 SP - 265-268 SN - 0921-5107 KW - light emitting diode KW - GaN-InGaN laser KW - multiple quantum wells KW - metal-organic chemical vapor deposition ER - TY - JOUR TI - Test of parity-conserving time-reversal invariance using polarized neutrons and nuclear spin aligned holmium AU - Huffman, PR AU - Roberson, NR AU - Wilburn, WS AU - Gould, CR AU - Haase, DG AU - Keith, CD AU - Raichle, BW AU - Seely, ML AU - Walston, , JR T2 - PHYSICAL REVIEW C AB - A test of parity-conserving, time-reversal noninvariance (PC TRNI) has been performed in 5.9 MeV polarized neutron transmission through nuclear spin aligned holmium. The experiment searches for the $T$-violating fivefold correlation via a double modulation technique---flipping the neutron spin while rotating the alignment axis of the holmium. Relative cross sections for spin-up and spin-down neutrons are found to be equal to within $1.2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$ (80% confidence). This is a two orders of magnitude improvement compared to traditional detailed balance studies of time reversal, and represents the most precise test of PC TRNI in a dynamical process, to our knowledge. DA - 1997/5// PY - 1997/5// DO - 10.1103/physrevc.55.2684 VL - 55 IS - 5 SP - 2684-2696 SN - 2469-9993 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-0031502630&partnerID=MN8TOARS ER - TY - JOUR TI - Spectroscopy of the Si-29(p,gamma) reaction for E(p)=1.00-1.75 MeV AU - Vavrina, GA AU - Bilpuch, EG AU - Bybee, CR AU - Mitchell, GE AU - Moore, EF AU - Shriner, JD AU - Shriner, JF AU - Wallace, PM AU - Westerfeldt, CR T2 - PHYSICAL REVIEW C AB - The ${}^{29}$Si$(p,\ensuremath{\gamma})$ reaction has been studied in the range ${E}_{p}=1.00$--1.75 MeV. Three previously unknown states in ${}^{30}$P were identified, and one state previously assigned to ${}^{30}$P was identified as a state in ${}^{14}$N. Gamma-ray strengths were determined for the three new levels, and branching ratios were measured for 17 resonances. Revised ${J}^{\ensuremath{\pi}};T$ assignments were made for nine of these states. DA - 1997/3// PY - 1997/3// DO - 10.1103/physrevc.55.1119 VL - 55 IS - 3 SP - 1119-1125 SN - 1089-490X ER - TY - JOUR TI - Spectroscopic ellipsometric characterization of undoped ZnTe films grown on GaAs AU - Kim, YD AU - Choi, SG AU - Klein, MV AU - Yoo, SD AU - Aspnes, DE AU - Xin, SH AU - Furdyna, JK T2 - APPLIED PHYSICS LETTERS AB - We report highly accurate dielectric function data for ZnTe. These data were made possible by the high quality of the heteroepitaxial material and the development of a chemical etching procedure for producing abrupt surfaces on ZnTe; they provided the first observation of the E0+Δ0 structure in ZnTe by spectroscopic ellipsometry and evidence for several contributions to the E2 structure. Accurate critical point energies were obtained by Fourier analysis. DA - 1997/2/3/ PY - 1997/2/3/ DO - 10.1063/1.118289 VL - 70 IS - 5 SP - 610-612 SN - 0003-6951 ER - TY - JOUR TI - Spectromicroscopy of poly(ethylene terephthalate): Comparison of spectra and radiation damage rates in x-ray absorption and electron energy loss AU - Rightor, EG AU - Hitchcock, AP AU - Ade, H AU - Leapman, RD AU - Urquhart, SG AU - Smith, AP AU - Mitchell, G AU - Fischer, D AU - Shin, HJ AU - Warwick, T T2 - JOURNAL OF PHYSICAL CHEMISTRY B AB - The C 1s and O 1s X-ray absorption spectra of poly(ethylene terephthalate) (PET) have been recorded using transmission, fluorescence, and electron yield detection. The corresponding electron energy loss spectra (EELS) have been recorded in a scanning transmission electron microscope. These results are compared to the C 1s and O 1s spectra of gas phase 1,4-dimethyl terephthalate (the monomer of PET) recorded using EELS. The comparison of monomer and polymer materials in different phases and with different techniques has aided the understanding of the relative strengths and limitations of each technique as well as assisting the spectral interpretation. Good agreement is found in the overall shape and the energies of the spectral features. Relatively minor differences in intensities can be understood in terms of the properties of the individual spectroscopic techniques. The critical dose for radiation damage by 100 keV electrons incident on PET at 100 K is found to be (1.45 ± 0.15) × 103 eV nm-3. In contrast, the critical dose for radiation damage by 302 eV X-rays incident on PET at 300 K is (1.2 ± 0.6) × 104 eV nm-3. A figure of merit involving the product of critical energy dose and spectral efficiency (as expressed by the appropriate G value) is developed. This indicates that, for near-edge studies involving a 20 eV spectral width, there is ∼500-fold advantage of X-ray absorption studies on room temperature PET relative to electron energy loss studies of cooled PET. DA - 1997/3/13/ PY - 1997/3/13/ DO - 10.1021/jp9622748 VL - 101 IS - 11 SP - 1950-1960 SN - 1520-5207 ER - TY - JOUR TI - Schouten-Nijenhuis brackets AU - Norris, LK T2 - JOURNAL OF MATHEMATICAL PHYSICS AB - The Poisson and graded Poisson Schouten–Nijenhuis algebras of symmetric and antisymmetric contravariant tensor fields, respectively, on an n-dimensional manifold M are shown to be n-symplectic. This is accomplished by showing that both brackets may be defined in a unified way using the n-symplectic structure on the bundle of linear frames LM of M. New results in n-symplectic geometry are presented and then used to give globally defined representations of the Hamiltonian operators defined by the Schouten–Nijenhuis brackets. DA - 1997/5// PY - 1997/5// DO - 10.1063/1.531981 VL - 38 IS - 5 SP - 2694-2709 SN - 0022-2488 ER - TY - JOUR TI - Pulsed operation lasing in a cleaved-facet InGaN/GaN MQW SCH laser grown on 6H-SiC AU - Bulman, GE AU - Doverspike, K AU - Sheppard, ST AU - Weeks, TW AU - Kong, HS AU - Dieringer, HM AU - Edmond, JA AU - Brown, JD AU - Swindell, JT AU - Schetzina, JF T2 - ELECTRONICS LETTERS AB - Room temperature pulsed-operation lasing has been achieved for the first time in an InGaN laser grown on a 6H-SiC substrate. The laser structure is an 8-well InGaN/GaN MQW having Al0.06Ga0.94N waveguide and Al0.13Ga0.87N cladding layers. The index-guided laser having uncoated cleaved facets emits at 402 nm with a threshold current Ith of 1.2 A (42V), corresponding to a current density of 48 kA/cm2. A narrow line width of 0.8 Å is observed at 1.09 Ith. Far field measurements indicate that the devices operate in the TEM01 mode with FWHP of 5.7 and 19° for the in-plane and perpendicular directions, respectively. DA - 1997/8/28/ PY - 1997/8/28/ DO - 10.1049/el:19971025 VL - 33 IS - 18 SP - 1556-1557 SN - 0013-5194 KW - semiconductor junction lasers KW - silicon carbide KW - semiconductor quantum wells ER - TY - JOUR TI - P-2(0) resonances of the lithium atom in the inelastic scattering region AU - Wu, LJ AU - Chung, KT T2 - JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS AB - Recently, Kiernan and co-workers observed many new resonances in the inelastic scattering region in a high-resolution synchrotron radiation experiment. They also reported the energy (64.569(10) eV) and width (0.1 eV) for the lowest resonance, . In this work, we carried out multichannel saddle-point complex-rotation calculations for the 15 resonances between the and thresholds. Relativistic corrections are included. Our results for the , 3s energy and width are 64.568 and 0.117 eV, thus confirming the identification of the experiment unambiguously. However, we found that the structure observed near 65.2 eV is also caused by a resonance at 65.152 eV with a width of 89.7 meV. Our results agree with experiment except for the state. We found the position of this state to be below the threshold. DA - 1997/3/14/ PY - 1997/3/14/ DO - 10.1088/0953-4075/30/5/012 VL - 30 IS - 5 SP - 1173-1178 SN - 1361-6455 ER - TY - JOUR TI - Near-surface electrons and acoustic phonons: Energy and momentum relaxation AU - Sirenko, YM AU - Kim, KW AU - Stroscio, MA T2 - PHYSICAL REVIEW B AB - We study energy and momentum relaxation of a two-dimensional (2D) electron channel located at a finite distance $\mathcal{l}$ from a free crystal surface. The interaction with a complete set of bulklike, totally reflected, and Rayleigh acoustic phonon modes is taken into account. In most cases of interest the relaxation rates have the same temperature dependence as for 2D or bulk electrons interacting with bulk phonons. Numerical calculations demonstrate that the presence of a surface results in approximately a 10% modification of scattering rates in the high-temperature region. In the opposite limit (Bloch-Gr\"uneisen regime), the contribution of the surface phonons may dominate over that of bulklike modes. Oscillations of the relaxation rates as a function of the distance $\mathcal{l}$ between the electron channel and the surface are also predicted. DA - 1997/12/15/ PY - 1997/12/15/ DO - 10.1103/physrevb.56.15770 VL - 56 IS - 24 SP - 15770-15781 SN - 0163-1829 ER - TY - JOUR TI - Microdisk laser structures formed in III-V nitride epilayers AU - Zavada, JM AU - Abernathy, CR AU - Pearton, SJ AU - Mackenzie, JD AU - Mileham, , JR AU - Wilson, RG AU - Schwartz, RN AU - HaggerottCrawford, M AU - Shul, RJ AU - Kilcoyne, SP AU - Zhang, D AU - Kolbas, RM T2 - SOLID-STATE ELECTRONICS AB - Several kinds of nitride-based micro-resonators have been fabricated. Firstly, a microdisk laser structure comprising three InGaNGaN quantum wells on a thick AlN buffer has been grown by metal-organic molecular beam epitaxy and fabricated using a combination of non-selective Cl2/CH4/H2/Ar dry etching and selective KOH-based wet etching of the AlN. These structures are of potential use in short wavelength photonic or optoelectronic circuits. In a second structure Er was implanted into a GaN layer to produce strong emission at 1.54 μm. Similar results have been obtained in Er-implanted AlN, and AlN doped during epitaxial growth. DA - 1997/2// PY - 1997/2// DO - 10.1016/S0038-1101(96)00244-4 VL - 41 IS - 2 SP - 353-357 SN - 0038-1101 ER - TY - JOUR TI - MBE growth and properties of GaN on GaN/SiC substrates AU - Johnson, MAL AU - Fujita, S AU - Rowland, WH AU - Bowers, KA AU - Hughes, WC AU - He, YW AU - ElMasry, NA AU - Cook, JW AU - Schetzina, JF AU - Ren, J AU - Edmond, JA T2 - SOLID-STATE ELECTRONICS AB - Abstract Growth of III–V nitrides by molecular beam epitaxy (MBE) is being studied at NCSU using an r.f. nitrogen plasma source. GaN SiC substrates consisting of ∼ 3 μm thick GaN buffer layers grown on 6HSiC wafers by MOVPE at Cree Research Inc. are being used as substrates in the MBE film growth experiments. The MBE-grown GaN films exhibit excellent structural and optical properties—comparable to the best GaN films grown by MOVPE—as determined from photoluminescence, X-ray diffraction, and vertical-cross-section TEM micrographs. Mg and Si have been used as dopants for p -type and n -type layers, respectively. Al x Ga 1 − x N films ( x ∼ 0.06-0.08) and Al x Ga 1 − x N GaN multi-quantum-well structures have been grown which display good optical properties. Light-emitting diodes based on double-heterostructures of Al x Ga 1 − x N GaN which emit violet light at ∼400 nm have also been demonstrated. Growth of GaN on LiGaO 2 substrates is also reported for comparison. DA - 1997/2// PY - 1997/2// DO - 10.1016/S0038-1101(96)00169-4 VL - 41 IS - 2 SP - 213-218 SN - 0038-1101 ER - TY - JOUR TI - Local dipole field contributions to bond-stretching silicon-hydrogen vibrational modes on flat and vicinal Si(111) surfaces AU - Yang, HY AU - Lucovsky, G T2 - SURFACE REVIEW AND LETTERS AB - Bond-stretching frequencies for bonded-H (and D) on flat and vicinal Si(111) surfaces have been calculated using a model that includes (i) short range valence forces and (ii) dynamic effects due to dipole–dipole interactions. Dipole–dipole interactions have been calculated exactly for flat surfaces, and for vicinal surfaces off-cut in the [Formula: see text] and [Formula: see text] directions terminated respectively by monohydride, Si–H, and dihydride, Si–H 2 , bonding at the step edges. Using short range force constants and effective charges obtained from isolated Si–H and Si–H 2 stretching modes in hydrogenated amorphous Si, a-Si:H, as input parameters, the calculated coupled mode frequencies are in excellent agreement with experiment, i.e. using 5 empirical parameters, 16 frequencies in the range of 1500–2150 cm -1 are fit to better than 0.14%, or ±2–3 cm -1 . DA - 1997/10// PY - 1997/10// DO - 10.1142/S0218625X97000985 VL - 4 IS - 5 SP - 891-896 SN - 0218-625X ER - TY - JOUR TI - Kinetics of metal-catalyzed growth of single-walled carbon nanotubes AU - Maiti, A AU - Brabec, CJ AU - Bernholc, J T2 - PHYSICAL REVIEW B AB - Molecular-dynamics and total-energy calculations using a realistic three-body potential for carbon reveal the basic atomic processes by which single-shelled nanotubes can grow out of metal-carbide particles by the root growth mechanism. We find that nanometer-sized protrusions on the metal-particle surface lead to the nucleation of very narrow tubes. Wide bumps lead to a strained graphene sheet and no nanotube growth. The results also explain the absence of multishelled tubes in metal-catalyzed growth. DA - 1997/3/1/ PY - 1997/3/1/ DO - 10.1103/physrevb.55.r6097 VL - 55 IS - 10 SP - R6097-R6100 SN - 2469-9969 ER - TY - JOUR TI - Higher quarkonia AU - Barnes, T. AU - Close, F. E. AU - Page P. R., AU - Swanson, E. S. T2 - Physical Review. D, Particles and Fields DA - 1997/// PY - 1997/// VL - 55 IS - 7 SP - 4157-4188 ER - TY - JOUR TI - Growth, doping and characterization of AlxGa1-xN thin film alloys on 6H-SiC(0001) substrates AU - Bremser, MD AU - Perry, WG AU - Zheleva, T AU - Edwards, NV AU - Nam, OH AU - Parikh, N AU - Aspnes, DE AU - Davis, RF T2 - DIAMOND AND RELATED MATERIALS AB - Thin films of AlxGa1 − xN (0.05≤x≤0.96) having smooth surfaces were deposited directly on both vicinal and on-axis 6H-SiC(0001) substrates. Cross-sectional transmission electron microscopy of Al0.13Ga0.87N revealed stacking faults near the SiC/nitride alloy interface and numerous threading dislocations. Energy dispersive analysis, Auger electron spectroscopy (AES) and Rutherford backscattering were used to determine the compositions. These were paired with their respective cathodoluminescence (CL) near band-edge emission energies. A negative bowing parameter was determined. The CL emission energies were similar to the bandgap energies obtained by spectroscopic ellipsometry. Field emission AES of the initial growth of Al0.2Ga0.8N revealed an Al-rich layer near the interface. N-type (Si) doping was achieved for AlxGa1 − xN for 0.12≤x≤0.42. DA - 1997/3// PY - 1997/3// DO - 10.1016/S0925-9635(96)00626-7 VL - 6 IS - 2-4 SP - 196-201 SN - 0925-9635 KW - GaN KW - alloy KW - AlGaN epitaxy KW - SiC substrates ER - TY - JOUR TI - Growth of GaN and Al0.2Ga0.8N on patterened substrates via organometallic vapor phase epitaxy AU - Nam, OH AU - Bremser, MD AU - Ward, BL AU - Nemanich, RJ AU - Davis, RF T2 - JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS & EXPRESS LETTERS AB - The selective growth of GaN and Al 0.2 Ga 0.8 N has been achieved on stripe and circular patterned GaN/AlN/6H-SiC(0001) multilayer substrates. Growth morphologies on the stripe patterns were a function of the widths of the stripes and the flow rate of triethylgallium. No ridge growth was observed along the top edges of the truncated stripe patterns. Smooth (0001) top facets formed on stripes ≥5 µ m wide. Uniform hexagonal pyramid arrays of undoped GaN and Si-doped GaN were successfully grown on 5 µ m circular patterns. Field emission measurements of a Si-doped GaN hexagonal pyramid array exhibited a turn-on field of 25 V/µ m for an emission current of 10.8 nA at an anode-to-sample distance of 27 µ m. DA - 1997/5/1/ PY - 1997/5/1/ DO - 10.1143/JJAP.36.L532 VL - 36 IS - 5A SP - L532-L535 SN - 0021-4922 KW - GaN KW - AlGaN KW - 6H-SiC KW - selective growth KW - organometallic vapor phase epitaxy KW - hexagonal pyramid array KW - field emission KW - lateral diffusion ER - TY - JOUR TI - Going beyond the peaking approximation in the PQCD analysis of exclusive heavy meson pair production AU - Ji, CR AU - Pang, A T2 - PHYSICAL REVIEW D AB - In the PQCD analyses of the exclusive production of higher generation hadrons, the quark distribution amplitude of the heavy quark system has often been approximated by a \ensuremath{\delta} function from the nonrelativistic consideration. Going beyond the peaking approximation, the factorization of the covariant hard scattering amplitude from the nonperturbative quark distribution amplitude is no longer valid. We therefore use the light-cone time-ordered perturbation theory which is the step prior to the usual factorization formula and calculate the form factor of a pseudoscalar meson composed of a heavy quark and antiquark. However, we find that the numerical results for the cross section of exclusive heavy meson pair production in ${e}^{+}{e}^{\ensuremath{-}}$ annihilation are not much different from those of the peaking approximation. DA - 1997/2/1/ PY - 1997/2/1/ DO - 10.1103/physrevd.55.1253 VL - 55 IS - 3 SP - 1253-1256 SN - 0556-2821 ER - TY - JOUR TI - From current to constituent quarks: a renormalization-group-improved Hamiltonian-based description of hadrons AU - Szczepaniak, A. P. AU - Swanson, E. S. T2 - Physical Review. D, Particles and Fields DA - 1997/// PY - 1997/// VL - 55 IS - 3 SP - 1578-1591 ER - TY - JOUR TI - Excited states in Hg-176,Hg-178 and shape coexistence in very neutron-deficient Hg isotopes AU - Carpenter, MP AU - Janssens, RVF AU - Amro, H AU - Blumenthal, DJ AU - Brown, LT AU - Seweryniak, D AU - Woods, PJ AU - Ackermann, D AU - Ahmad, I AU - Davids, C AU - Fischer, SM AU - Hackman, G AU - Hamilton, JH AU - Khoo, TL AU - Lauritsen, T AU - Lister, CJ AU - Nisius, D AU - Ramayya, AV AU - Reviol, W AU - Schwartz, J AU - Simpson, J AU - Wauters, J T2 - PHYSICAL REVIEW LETTERS AB - Excited states have been observed for the first time in the neutron-deficient ${}^{176,178}\mathrm{Hg}$ nuclei using the recoil-decay tagging (RDT) technique in which prompt $\ensuremath{\gamma}$ rays are associated with a particular isotope through a correlation with the characteristic ground state $\ensuremath{\alpha}$ decay. Below $N\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}102$, the excitation energy of a rotational band built on a prolate shape $({\ensuremath{\beta}}_{2}\ensuremath{\sim}0.25)$ increases with decreasing mass to the point where there is no longer any evidence for its presence at low spin in ${}^{176}\mathrm{Hg}$. The data are in qualitative agreement with recent mean field calculations. DA - 1997/5/12/ PY - 1997/5/12/ DO - 10.1103/PhysRevLett.78.3650 VL - 78 IS - 19 SP - 3650-3653 SN - 0031-9007 ER - TY - JOUR TI - Energy and orientation dependence of neutron depolarization in a large single crystal of ferromagnetic holmium AU - Alfimenkov, VP AU - Chernikov, AN AU - Lason, L AU - Mareev, YD AU - Novitsky, , VV AU - Pikelner, LB AU - Skoy, VR AU - Tsulaya, MI AU - Gould, CR AU - Haase, DG AU - Roberson, NR T2 - JOURNAL OF APPLIED PHYSICS AB - We report measurements of the depolarization of epithermal neutrons (1.7–59 eV) in magnetic domains of a 2.0-cm-diam cylindrical single crystal of ferromagnetic holmium. The neutrons were polarized by a dynamically polarized proton target and polarization analyzed using a statically polarized rare-earth spin filter. Based on the dependence of the depolarization on neutron energy and crystal orientation, we determined the domains to be laminar, or needlelike, with the long axis slightly deflected from the c crystalline axis and having an average width of 59 μm. DA - 1997/2/1/ PY - 1997/2/1/ DO - 10.1063/1.364179 VL - 81 IS - 3 SP - 1358-1361 SN - 0021-8979 ER - TY - JOUR TI - Direct determination of the doublet and quartet M1 cross sections in p-d radiative capture at near-thermal energies AU - Rice, BJ AU - Wulf, EA AU - Canon, RS AU - Kelley, JH AU - Prior, RM AU - Spraker, M AU - Tilley, DR AU - Weller, HR T2 - PHYSICAL REVIEW C AB - Data obtained from studies of the $p(d\ensuremath{\rightarrow},\ensuremath{\gamma}{)}^{3}\mathrm{He}$ and the $d(p\ensuremath{\rightarrow},\ensuremath{\gamma}{)}^{3}\mathrm{He}$ reactions have been used to extract the transition amplitudes corresponding to $S=1/2$ (doublet) and $S=3/2$ (quartet) $M1$ radiative capture. Protons (deuterons) of 40 keV (80 keV) were stopped in ${\mathrm{D}}_{2}\mathrm{O}$ $({\mathrm{H}}_{2}\mathrm{O})$ ice targets. Angular distributions of $\ensuremath{\sigma}$, ${A}_{y},$ ${T}_{20},$ ${P}_{\ensuremath{\gamma}}$, and ${\mathrm{iT}}_{11}$ were fit simultaneously in terms of the four possible $E1$ $p$-wave capture amplitudes and the two $(S=1/2$ and $3/2)$ possible $M1$ $s$-wave capture amplitudes. The results obtained at ${E}_{\mathrm{cm}}=23.3$ keV indicate that the $S=1/2$ $M1$ capture cross section is 13.77 $\ifmmode\pm\else\textpm\fi{}$ 0.66 nb, while the $S=3/2$ $M1$ capture cross section is 6.74 $\ifmmode\pm\else\textpm\fi{}$ 0.44 nb. These results agree with the predictions of a recent three-body theoretical calculation which includes two-body currents [e.g., meson-exchange currents (MEC's)]. They also agree with the previous experimental determination of the doublet and quartet fusion rates obtained using the Wolfenstein-Gerstein effect to vary the relative population of $S=1/2$ and $3/2$ nuclear spins in the $\ensuremath{\mu}$-$p$-$d$ molecule prior to fusion. DA - 1997/12// PY - 1997/12// DO - 10.1103/physrevc.56.r2917 VL - 56 IS - 6 SP - R2917-R2919 SN - 1089-490X ER - TY - JOUR TI - Differential lifetime measurements and identical superdeformed bands in (192,194)Hg T2 - Physical Review. C, Nuclear Physics DA - 1997/// PY - 1997/// VL - 55 IS - 5 SP - R2150-2154 ER - TY - JOUR TI - Comparison between X ray absorption spectroscopy, anomalous wide angle X ray scattering, anomalous small angle X ray scattering, and diffraction anom AU - Bazin, D. C. AU - Sayers, D. A. AU - Rehr, J. J. T2 - Journal of Physical Chemistry. B, Condensed Matter, Materials, Surfaces, Interfaces & Biophysical DA - 1997/// PY - 1997/// VL - 101 IS - 51 SP - 11040-11050 ER - TY - JOUR TI - Characterization of metal-diamond interfaces: Electron affinity and Schottky barrier height AU - Baumann, PK AU - Bozeman, SP AU - Ward, BL AU - Nemanich, RJ T2 - DIAMOND AND RELATED MATERIALS AB - In this study, the electron affinity and Schottky barrier height of thin Cu and Zr films on diamond (100) substrates were correlated by means of UV photoemission spectroscopy (UPS) measurements. Prior to metal deposition the diamond crystals were cleaned by a 1150°C or 500°C anneal in UHV, and the surfaces were characterized by AES and AFM. This resulted in surfaces terminated with oxygen or free of chemisorbed species. By means of UPS it was found that whether a metal did induce a negative electron affinity (NEA) on a diamond surface was dependent on the surface preparation before metal deposition and on the metal work function. In particular, the Schottky barrier height for clean surfaces was lower than for surfaces terminated by oxygen. Metal-diamond interfaces exhibiting a NEA had a lower Schottky barrier height than those exhibiting a positive electron affinity. These effects were attributed to different interfacial layers. Field emission measurements were performed before and after metal deposition. For all cases a reduction in the threshold electric field was observed upon metal overgrowth. DA - 1997/3// PY - 1997/3// DO - 10.1016/S0925-9635(96)00601-2 VL - 6 IS - 2-4 SP - 398-402 SN - 0925-9635 KW - metal-diamond interfaces KW - electron affinity KW - Schottky barrier height ER - TY - JOUR TI - Absorption coefficient, energy gap, exciton binding energy, and recombination lifetime of GaN obtained from transmission measurements AU - Muth, JF AU - Lee, JH AU - Shmagin, IK AU - Kolbas, RM AU - Casey, HC AU - Keller, BP AU - Mishra, UK AU - DenBaars, SP T2 - APPLIED PHYSICS LETTERS AB - The absorption coefficient for a 0.4-μm-thick GaN layer grown on a polished sapphire substrate was determined from transmission measurements at room temperature. A strong, well defined exciton peak for the A and B excitons was obtained. The A, B, and C excitonic features are clearly defined at 77 K. At room temperature, an energy gap Eg=3.452±0.001 eV and an exciton binding energy ExA,B=20.4±0.5 meV for the A and B excitons and ExC=23.5±0.5 meV for the C exciton were determined by analysis of the absorption coefficient. From this measured absorption coefficient, together with the detailed balance approach of van Roosbroek and Shockley, the radiative constant B=1.1×10−8 cm3/s was obtained. DA - 1997/11/3/ PY - 1997/11/3/ DO - 10.1063/1.120191 VL - 71 IS - 18 SP - 2572-2574 SN - 0003-6951 ER - TY - JOUR TI - A versatile stable scanning proximal probe microscope AU - Jahncke, CL AU - Hallen, HD T2 - REVIEW OF SCIENTIFIC INSTRUMENTS AB - We present a novel scanning proximal probe microscope design utilizing a piezoelectric driven coarse positioning mechanism in x, y, and z, while maintaining relatively small lateral dimensions. The instrument is suitable for insertion into a Dewar. The primary purpose of this work is to develop a stable yet versatile instrument in order to meet the signal averaging limitations imposed by low signal level measurements. We have implemented a near field scanning optical microscope with this system, whose key features include simultaneous detection of reflected and transmitted signals, unique “center of mass” tip oscillator for shear force feedback, and overall microscope stability. DA - 1997/4// PY - 1997/4// DO - 10.1063/1.1147988 VL - 68 IS - 4 SP - 1759-1763 SN - 0034-6748 UR - http://dx.doi.org/10.1063/1.1147988 ER - TY - JOUR TI - Thin films of aluminum nitride and aluminum gallium nitride for cold cathode applications AU - Sowers, A. T. AU - Christman, J. A. AU - Bremser, M. D. AU - Ward, B. L. AU - Davis, R. F. AU - Nemanich, R. J. T2 - Applied Physics Letters AB - Cold cathode structures have been fabricated using AlN and graded AlGaN structures (deposited on n-type 6H-SiC) as the thin film emitting layer. The cathodes consist of an aluminum grid layer separated from the nitride layer by a SiO2 layer and etched to form arrays of either 1, 3, or 5 μm holes through which the emitting nitride surface is exposed. After fabrication, a hydrogen plasma exposure was employed to activate the cathodes. Cathode devices with 5 μm holes displayed emission for up to 30 min before failing. Maximum emission currents ranged from 10–100 nA and required grid voltages ranging from 20–110 V. The grid currents were typically 1 to 104 times the collector currents. DA - 1997/// PY - 1997/// DO - 10.1063/1.120052 VL - 71 IS - 16 SP - 2289-2291 ER - TY - JOUR TI - Real-time optical analysis and control of semiconductor epitaxy: Progress and opportunity AU - Aspnes, DE T2 - SOLID STATE COMMUNICATIONS AB - Various optical techniques have been developed in the last few years for real-time analysis of surfaces and near-surface regions during semiconductor epitaxy. These techniques are providing new insights into microscopic mechanisms of crystal growth and new opportunities for several levels of closed-loop feedback control of epitaxy, including control at the product (sample) level. The latter is made possible by new data-reduction algorithms that return the dielectric response of the most recently deposited material even if nothing is known about the underlying sample structure. Examples are provided, and opportunities and challenges discussed. DA - 1997/1// PY - 1997/1// DO - 10.1016/S0038-1098(96)00447-4 VL - 101 IS - 2 SP - 85-92 SN - 0038-1098 ER - TY - JOUR TI - Real space multigrid methods for large scale electronic structure problems AU - Bernholc, Jerzy AU - Briggs, E. L. AU - Sullivan, D. J. AU - Brabec, C. J. AU - Nardelli, M. B. AU - Rapcewicz, K. AU - Roland, C. AU - Wensell, M. T2 - International Journal of Quantum Chemistry AB - We describe the development and applications of a new electronic structure method that uses a real-space grid as a basis. Multigrid techniques provide preconditioning and convergence acceleration at all length scales and therefore lead to particularly efficient algorithms. The salient points of our implementation include: (i) new compact discretization schemes in real space for systems with cubic, orthorhombic, and hexagonal symmetry and (ii) new multilevel algorithms for the iterative solution of Kohn–Sham and Poisson equations. The accuracy of the discretizations was tested by direct comparison with plane-wave calculations, when possible, and the results were in excellent agreement in all cases. These techniques are very suitable for use on massively parallel computers and in O(N) methods. Tests on the Cray-T3D have shown nearly linear scaling of the execution time up to the maximum number of processors (512). The above methodology was tested on a large number of systems, such as the C60 molecule, diamond, Si and GaN supercells, and quantum molecular dynamics simulations for Si. Large-scale applications include a simulation of surface melting of Si and investigations of electronic and structural properties of surfaces, interfaces, and biomolecules. © 1997 John Wiley & Sons, Inc. Int J Quant Chem 65: 531–543, 1997 DA - 1997/// PY - 1997/// DO - 10.1002/(SICI)1097-461X(1997)65:5<531::AID-QUA18>3.0.CO;2-5 VL - 65 IS - 5 SP - 531–543 ER - TY - JOUR TI - Polarization field effects on the electron-hole recombination dynamics in In0.2Ga0.8N/In1-xGaxN multiple quantum wells AU - Nardelli, M. B. AU - Rapcewicz, K. AU - Bernholc, Jerzy T2 - Applied Physics Letters AB - The effect of the polarization field in wurtzite In0.2Ga0.8N/In1−xGaxN (x&gt;0.8) multiple quantum wells is studied from first principles. The pyroelectric and piezoelectric fields naturally present in the system due to its wurtzite structure are strong enough to reduce the interband recombination rate in an ideal quantum well. We suggest that composition fluctuations, observed in the active region of actual devices, provide the necessary confinement for an improved recombination rate and lasing. DA - 1997/// PY - 1997/// DO - 10.1063/1.120269 VL - 71 IS - 21 SP - 3135–3137 ER - TY - JOUR TI - Molecular layer epitaxy by real-time optical process monitoring AU - Bachmann, K. J. AU - Hopfner, C. AU - Sukidi, N. AU - Miller, A. E. AU - Harris, C. J. AU - Aspnes, D. E. AU - Dietz, N. A. AU - Tran, Hien AU - Beeler, S. C. AU - Ito, K. AU - Banks, H. T. T2 - Applied Surface Science AB - In this paper we consider modern methods of optical process monitoring and control in the context of atomic layer epitaxy. One specific method, p-polarized reflectance spectroscopy (PRS), is chosen to assess details of layer-by-layer growth. We show that PRS monitoring under conditions of steady-state growth by pulsed chemical beam epitaxy (PCBE) can achieve the deposition of molecular layers of GaP on silicon (100) deposited with a precision of 5%, which can be improved by reducing the growth rate and increasing the period of time averaging of the reflectance data. Since in the nucleation period prior to formation of a contiguous heteroepitaxial film inhomogeneous surface chemistry and roughening complicates the modeling of the overgrowth process, advances in both experimental methods and theory are required for extending the control to non-steady-state growth conditions. Results of simultaneous single-wavelength PR monitoring and laser light scattering measurements in conjunction with atomic force microscopy studies of short period heteroepitaxial overgrowth processes are presented. The extension of PRS to the monitoring of organometallic chemical vapor deposition at higher pressures is also discussed. DA - 1997/// PY - 1997/// DO - 10.1016/S0169-4332(96)00975-0 VL - 112 IS - 1997 Mar. SP - 38–47 ER - TY - JOUR TI - Local atomic bonding in fluorinated silicon oxides: Bond-ionicity-controlled contributions of infrared-active vibrations to the static dielectric constant AU - Lucovsky, G AU - Yang, H T2 - JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS AB - There is considerable interest in insulating films with static dielectric constants lower than that of SiO 2 . One alloy system that has attracted much recent attention is F-doped SiO 2 or Si–O–F. This paper i) reviews the published experimental results for the infrared optical properties of Si–O–F alloys, ii) discusses the bonding arrangements of F atoms in the SiO 2 network structure, iii) develops a procedure for characterizing the composition of these materials in a pseudo-binary alloy notation, iv) explains the reductions in the dielectric constant induced by F atoms in terms of bond-ionicity-controlled contributions from electronic and vibrational dipole transitions, and v) addresses briefly the chemical stability of the films. DA - 1997/3// PY - 1997/3// DO - 10.1143/JJAP.36.1368 VL - 36 IS - 3B SP - 1368-1373 SN - 0021-4922 KW - low-dielectric constant materials KW - Si-O-F alloys KW - infrared active vibrations KW - Si-O bond-stretching vibrations KW - Si-F bond-stretching vibrations KW - infrared effective charges KW - chemical stability ER - TY - JOUR TI - Halozeotypes: a new generation of zeolite-type materials AU - Martin, JD AU - Greenwood, KB T2 - ANGEWANDTE CHEMIE-INTERNATIONAL EDITION IN ENGLISH AB - The first non-oxide, direct analogues of aluminosilicate zeolites are materials with the anionic partial structure [CunZnm–nCl2m]n−. Varying the templating alkylammonium counterion results in different framework structures: [HNMe3][CuZn5Cl12] adopts the known sodalite structure, whereas [H2NEt2][CuZn5Cl12] exhibits a novel three-dimensional channel structure with eleven- and eight-ring channels (the latter is depicted on the right). Controlled addition of methanol or water results in formation of colloidal particles that are implicated as intermediates in the construction of open frameworks. DA - 1997/10/17/ PY - 1997/10/17/ DO - 10.1002/anie.199720721 VL - 36 IS - 19 SP - 2072-2075 SN - 0570-0833 KW - copper KW - microporosity KW - solid-state structures KW - zeolite analogues KW - zinc ER - TY - JOUR TI - Galactic cosmic rays from supernova remnants .2. Shock acceleration of gas and dust AU - Ellison, DC AU - Drury, LOC AU - Meyer, JP T2 - ASTROPHYSICAL JOURNAL AB - We present a quantitative model of Galactic cosmic-ray (GCR) origin and acceleration, wherein a mixture of interstellar and/or circumstellar gas and dust is accelerated by a supernova remnant blast wave. The gas and dust are accelerated simultaneously, but differences in how each component is treated by the shock leave a distinctive signature, which we believe exists in the cosmic-ray composition data. A reexamination of the detailed GCR elemental composition, presented in a companion paper, has led us to abandon the long-held assumption that GCR abundances are somehow determined by first ionization potential. Instead, volatility and mass (presumably mass-to-charge ratio) seem to better organize the data: among the volatile elements, the abundance enhancements relative to solar increase with mass (except for the slightly high H/He ratio); the more refractory elements seem systematically overabundant relative to the more volatile ones in a quasi-mass-independent fashion. If this is the case, material locked in grains in the interstellar medium must be accelerated to cosmic-ray energies more efficiently than interstellar gas-phase ions. Here we present results from a nonlinear shock model that includes (1) the direct acceleration of interstellar gas-phase ions, (2) a simplified model for the direct acceleration of weakly charged grains to ~100 keV amu-1 energies, simultaneously with the acceleration of the gas ions, (3) the energy losses of grains colliding with the ambient gas, (4) the sputtering of grains, and (5) the simultaneous acceleration of the sputtered ions to GeV and TeV energies. We show that the model produces GCR source abundance enhancements of the volatile, gas-phase elements that are an increasing function of mass, as well as a net, mass-independent enhancement of the refractory, grain elements over protons, consistent with cosmic-ray observations. We also investigate the implications of the slightly high H/He ratio. The GCR22Ne excess may also be accounted for in terms of the acceleration of 22Ne-enriched presupernova Wolf-Rayet star wind material surrounding the most massive supernovae. We also show that cosmic-ray source spectra, at least below ~1014 eV, are well matched by the model. DA - 1997/9/20/ PY - 1997/9/20/ DO - 10.1086/304580 VL - 487 IS - 1 SP - 197-217 SN - 1538-4357 KW - acceleration of particles KW - cosmic rays KW - shock waves KW - supernova remnants ER - TY - JOUR TI - Galactic cosmic rays from supernova remnants .1. A cosmic-ray composition controlled by volatility and mass-to-charge ratio AU - Meyer, JP AU - Drury, LOC AU - Ellison, DC T2 - ASTROPHYSICAL JOURNAL AB - We show that the Galactic cosmic-ray source (GCRS) composition is best described in terms of (1) a general enhancement of the refractory elements relative to the volatile ones, and (2) among the volatile elements, an enhancement of the heavier elements relative to the lighter ones. This mass dependence most likely reflects a mass-to-charge (A/Q) dependence of the acceleration efficiency; among the refractory elements, there is no such enhancement of heavier species, or only a much weaker one. We regard as coincidental the similarity between the GCRS composition and that of the solar corona, which is biased according to first ionization potential. In a companion paper, this GCRS composition is interpreted in terms of an acceleration by supernova shock waves of interstellar and/or circumstellar (e.g.,22Ne-rich Wolf-Rayet wind) gas-phase and, especially, dust material. DA - 1997/9/20/ PY - 1997/9/20/ DO - 10.1086/304599 VL - 487 IS - 1 SP - 182-196 SN - 1538-4357 KW - cosmic rays KW - ISM, abundances KW - stars, abundances KW - supernova remnants ER - TY - JOUR TI - Ellipsometric studies of Cd1-xMgxTe (0<=x<=0.5) alloys AU - Choi, S. G. AU - Kim, Y. D. AU - Yoo, Sang AU - Duk, Aspnes AU - Miotkowski, David E. AU - I. AU - Ramdas, A. K. T2 - APPLIED PHYSICS LETTERS AB - The determination of the above band gap optical properties of zincblende Cd1−xMgxTe (0⩽x⩽0.5) ternary alloys are reported on. Using the parabolic-band critical point model, room-temperature critical point energies of the E0, E0+Δ0, E1, E1+Δ1, E2, and E0′ interband transitions from numerically calculated second energy derivatives of ellipsometric spectra were obtained. The presence of two distinct structures in the E2 feature for x&gt;0 was also observed. DA - 1997/7/14/ PY - 1997/7/14/ DO - 10.1063/1.119511 VL - 71 IS - 2 SP - 249-251 SN - 1077-3118 ER - TY - JOUR TI - Effects of an oxygen-enriched environment on the survival of turkey embryos between twenty-five and twenty-eight days of age AU - Christensen, VL AU - Donaldson, WE AU - Nestor, KE T2 - POULTRY SCIENCE AB - The hypothesis was tested that increased partial pressure of oxygen during the plateau (25 to 26 d of incubation for turkeys) and paranatal (27 to 28 d of incubation) stages of incubation may increase survival rates of turkeys from selected genetic lines. Partial pressure of oxygen inside the incubator cabinet was increased to 171 + 3 mm Hg of the barometric pressure during the plateau stage in oxygen consumption and compared to ambient oxygen (152 + 3 mm Hg). Turkey embryos from genetic lines selected for egg production (E) or growth (F) were compared to their respective randombred controls. These genetic lines have previously been shown to differ in egg weight, eggshell conductance, length of incubation period, embryonic gluconeogenesis, and survival rates during late incubation. Blood, liver, heart, and pipping muscle samples were obtained prior to pipping, at internal pipping and external pipping, and at hatching. The blood was analyzed for glucose concentration and the remaining tissues were assayed for glycogen concentrations. Survival rates were determined on approximately 2,200 eggs in each of three independent trials of the experiment. Interactions of oxygen treatment and genetic line were observed for embryonic survival, heart growth, and hepatic glycogen content. The data suggest that the response to increased oxygen tension in selected genetic lines has been diminished. It was concluded that embryos have been altered metabolically by genetic selection and the concomitant increase in mortality of selected lines during the plateau and paranatal stages is not simply the result of shell quality and hypoxia. DA - 1997/11// PY - 1997/11// DO - 10.1093/ps/76.11.1556 VL - 76 IS - 11 SP - 1556-1562 SN - 0032-5791 KW - turkey embryo KW - incubation KW - oxygen KW - metabolism KW - livability ER - TY - JOUR TI - Diffraction enhanced X-ray imaging AU - Chapman, D. AU - Thomlinson, W. AU - Johnston, R. E. AU - Washburn, D. AU - Pisano, E. AU - Gmur, N. AU - Zhong, Z. AU - Menk, R. AU - Arfelli, F. AU - Sayers, D. E. T2 - Physics in Medicine & Biology DA - 1997/// PY - 1997/// VL - 42 IS - 11 SP - 2015-2025 ER - TY - JOUR TI - X-ray spectromicroscopy of polymers and tribological surfaces at beamline X1A at the NSLS AU - Ade, H AU - Smith, AP AU - Zhang, H AU - Zhuang, GR AU - Kirz, J AU - Rightor, E AU - Hitchcock, A T2 - JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA AB - We provide a general overview of microspectroscopy and spectromicroscopy for materials characterization at beamline X1A at the national synchrotron light source (NSLS). Two instruments, the scanning transmission X-ray microscope (STXM) and scanning photoemission microscope (SPEM), are available. The STXM has been able to provide a spatial resolution of better than 50 nm for several years and near edge X-ray absorption fine structure (NEXAFS) spectroscopy is performed in transmission from thin samples at an energy resolution of typically 0.3 eV at the carbon K-edge. Numerous applications in polymer science and biology have been performed to date. We restrict our review to polymer science applications and present new results of several polymer systems. The SPEM has a spatial resolution of about 250 nm in routine operation and was recently upgraded with a hemispherical sector analyzer to improve the data throughput. We present the latest SPEM results, which were generated from a tribological sample. DA - 1997/3// PY - 1997/3// DO - 10.1016/S0368-2048(97)00013-3 VL - 84 IS - 1-3 SP - 53-71 SN - 1873-2526 KW - polymers KW - tribology KW - X-ray microscopy KW - NEXAFS KW - XPS KW - spectroscopy ER - TY - JOUR TI - Ultra-thin gate dielectrics prepared by low-temperature remote plasma-assisted oxidation AU - Niimi, H AU - Koh, K AU - Lucovsky, G T2 - NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS AB - Abstract This paper discusses the formation of ultra-thin nitrided gate oxides by a low temperature plasma assisted oxidation process using remotely excited N2O as the source gas for both oxygen and nitrogen atoms. Three aspects of this process are addressed: (i) the differences in oxide growth rates for O2 or N2O plasma oxidation processes; (ii) the reaction pathways for the incorporation of nitrogen at the SiSiO2 interface for the N2O plasma process; and (iii) possible nitrogen atom depletion during processing steps that follow the plasma assisted oxidation/nitridation process. DA - 1997/5// PY - 1997/5// DO - 10.1016/S0168-583X(96)00958-5 VL - 127 SP - 364-368 SN - 0168-583X ER - TY - JOUR TI - Transfer matrix method for interface optical-phonon modes in multiple-interface heterostructure systems AU - Yu, SG AU - Kim, KW AU - Stroscio, MA AU - Iafrate, GJ AU - Sun, JP AU - Haddad, GI T2 - JOURNAL OF APPLIED PHYSICS AB - Interactions of carriers with interface optical phonons dominate over other carrier–phonon scatterings in narrow quantum-well structures. Herein, a transfer matrix method is used to establish a formalism for determining the dispersion relations, electrostatic potentials, and Fröhlich interaction Hamiltonians of the interface optical phonons for multiple-interface heterostructure systems within the framework of the macroscopic dielectric continuum model. This method facilitates systematic calculations for complex structures where the conventional method is very difficult to implement. Several specific cases are treated to illustrate the advantages of the general formalism. DA - 1997/10/1/ PY - 1997/10/1/ DO - 10.1063/1.365649 VL - 82 IS - 7 SP - 3363-3367 SN - 0021-8979 ER - TY - JOUR TI - The characterization of strain, impurity content, and crush strength of synthetic diamond crystals AU - McCormick, TL AU - Jackson, WE AU - Nemanich, RJ T2 - JOURNAL OF MATERIALS RESEARCH DA - 1997/1// PY - 1997/1// DO - 10.1557/JMR.1997.0033 VL - 12 IS - 1 SP - 253-263 SN - 0884-2914 ER - TY - JOUR TI - Sustainable solution for dietary iron deficiency through plant biotechnology and breeding to increase seed ferritin control AU - Theil, E. C. AU - Burton, J. W. AU - Beard, J. L. T2 - European Journal of Clinical Nutrition DA - 1997/// PY - 1997/// VL - 51 IS - Suppl. 4 SP - S28-31 ER - TY - JOUR TI - Soft x-ray spectromicroscopy development for materials science at the advanced light source AU - Warwick, T AU - Ade, H AU - Hitchcock, AP AU - Padmore, H AU - Rightor, EG AU - Tonner, BP T2 - JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA AB - Several third generation synchrotron radiation facilities are now operational, and the high brightness of these photon sources offers new opportunities for X-ray microscopy. Well developed synchrotron radiation spectroscopy techniques are being applied in new instruments capable of imaging the surface of a material with a spatial resolution smaller than 1 μm. There are two aspects to this. One is to further the field of surface science by exploring the effects of spatial variations across a surface on a scale not previously accessible to X-ray measurements. The other is to open up new analytical techniques in materials science using X-rays on a spatial scale comparable with that of the processes or devices to be studied. The development of the spectromicroscopy program at the Advanced Light Source will employ a variety of instruments, some of which are already operational. Their development and use will be discussed, and recent results will be presented to illustrate their capabilities. DA - 1997/3// PY - 1997/3// DO - 10.1016/S0368-2048(97)00026-1 VL - 84 IS - 1-3 SP - 85-98 SN - 0368-2048 KW - soft x-ray spectromicroscopy KW - synchrotron radiation ER - TY - JOUR TI - Rapid and parallel formation of Fe3+ multimers, including a trimer, during H-type subunit ferritin mineralization AU - Pereira, AS AU - Tavares, P AU - Lloyd, SG AU - Danger, D AU - Edmondson, DE AU - Theil, EC AU - Huynh, BH T2 - BIOCHEMISTRY AB - Conversion of Fe ions in solution to the solid phase in ferritin concentrates iron required for cell function. The rate of the Fe phase transition in ferritin is tissue specific and reflects the differential expression of two classes of ferritin subunits (H and L). Early stages of mineralization were probed by rapid freeze-quench Mossbauer, at strong fields (up to 8 T), and EPR spectroscopy in an H-type subunit, recombinant frog ferritin; small numbers of Fe (36 moles/mol of protein) were used to increase Fe3+ in mineral precursor forms. At 25 ms, four Fe3+-oxy species (three Fe dimers and one Fe trimer) were identified. These Fe3+-oxy species were found to form at similar rates and decay subsequently to a distinctive superparamagentic species designated the "young core." The rate of oxidation of Fe2+ (1026 s(-1)) corresponded well to the formation constant for the Fe3+-tyrosinate complex (920 s(-1)) observed previously [Waldo, G. S., & Theil, E. C. (1993) Biochemistry 32, 13261] and, coupled with EPR data, indicates that several or possibly all of the Fe3+-oxy species involve tyrosine. The results, combined with previous Mossbauer studies of Y30F human H-type ferritin which showed decreases in several Fe3+ intermediates and stabilization of Fe2+ [Bauminger, E. R., et al. (1993) Biochem. J. 296, 709], emphasize the involvement of tyrosyl residues in the mineralization of H-type ferritins. The subsequent decay of these multiple Fe3+-oxy species to the superparamagnetic mineral suggests that Fe3+ species in different environments may be translocated as intact units from the protein shell into the ferritin cavity where the conversion to a solid mineral occurs. DA - 1997/6/24/ PY - 1997/6/24/ DO - 10.1021/bi970348f VL - 36 IS - 25 SP - 7917-7927 SN - 0006-2960 ER - TY - JOUR TI - Orthogonal polynomial approach to fluids with internal degrees of freedom: the case of nonpolar, polarizable molecules AU - Lado, F. T2 - Physical Review. E, Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics DA - 1997/// PY - 1997/// VL - 55 IS - 1 (part A) SP - 426-443 ER - TY - JOUR TI - Minimization of sub-oxide transition regions at Si-SiO2 interfaces by 900 degrees C rapid thermal annealing AU - Lucovsky, G AU - Banerjee, A AU - Hinds, B AU - Claflin, B AU - Koh, K AU - Yang, H T2 - MICROELECTRONIC ENGINEERING AB - Abstract Combining previously reported optical second harmonic generation (SHG) data with i) newly-reported X-ray photoelectron spectroscopy (XPS) data and ii) the Auger electron spectroscopy (AES) results presented in this paper demonstrates that interfacial sub-oxide bonding (SiOx, x DA - 1997/6// PY - 1997/6// DO - 10.1016/s0167-9317(97)00049-x VL - 36 IS - 1-4 SP - 207-210 SN - 0167-9317 ER - TY - JOUR TI - Local heteroepitaxy of diamond on silicon (100): a study of the interface structure AU - Maillard-Schaller, E. AU - Kuttel, O. M. AU - Groning, P. AU - Groning, O. AU - Agostino, R. G. AU - Aebi, P. AU - Schlapbach, L. AU - Wurzinger, P. AU - Pongratz, P. T2 - Physical Review. B, Condensed Matter and Materials Physics DA - 1997/// PY - 1997/// VL - 55 IS - 23 SP - 15895-15904 ER - TY - JOUR TI - Growth of bulk InGaN films and quantum wells by atmospheric pressure metalorganic chemical vapour deposition AU - Keller, S AU - Keller, BP AU - Kapolnek, D AU - Mishra, UK AU - DenBaars, SP AU - Shmagin, IK AU - Kolbas, RM AU - Krishnankutty, S T2 - JOURNAL OF CRYSTAL GROWTH AB - InGaN bulk layers and single quantum wells were grown on 1.4 to 2.4 μm thick GaN on sapphire films by atmospheric pressure metalorganic chemical vapour deposition (AP-MOCVD). The morphology of the epitaxial layers was strongly affected by the VIII ratio in the gas phase. The incorporation efficiency of indium was observed to increase with higher growth rates and decreasing temperature, but was independent of the VIII ratio in the investigated parameter range. In0.16Ga0.84N single quantum wells showed intense quantum well related luminescence at room temperature, with a full width at half maximum of 7.9 nm at a thickness of 50 Å. Single quantum wells embedded in InGaN of graded composition showed superior properties compared to quantum wells with In0.04Ga0.94N barriers of constant composition. DA - 1997/1// PY - 1997/1// DO - 10.1016/S0022-0248(96)00553-2 VL - 170 IS - 1-4 SP - 349-352 SN - 0022-0248 ER - TY - JOUR TI - Distribution of shell model reduced transition probabilities in Na-22 AU - Adams, AA AU - Mitchell, GE AU - Ormand, WE AU - Shriner, JF T2 - PHYSICS LETTERS B AB - The distribution of reduced transition probabilities in 22Na has been studied using the shell model. B(M1) and B(E2) values have been calculated for transitions among the first 25 states with each spin from J = 0 to J = 8, positive parity, and isospins T = 0 or T = 1. No dependence on spin, isospin, electromagnetic character, or excitation energy was found. The results were consistent with a χ2(ν) distribution with ν = 1, suggesting that 22Na is chaotic in the energy range studied. DA - 1997/1/23/ PY - 1997/1/23/ DO - 10.1016/S0370-2693(96)01510-9 VL - 392 IS - 1-2 SP - 1-6 SN - 0370-2693 ER - TY - JOUR TI - Differential lifetime measurements and configuration-dependent quadrupole moments for superdeformed bands in nuclei near Dy-152 AU - Nisius, D AU - Janssens, RVF AU - Moore, EF AU - Fallon, P AU - Crowell, B AU - Lauritsen, T AU - Hackman, G AU - Ahmad, I AU - Amro, H AU - Asztalos, S AU - Carpenter, MP AU - Chowdhury, P AU - Clark, RM AU - Daly, PJ AU - Deleplanque, MA AU - Diamond, RM AU - Fischer, SM AU - Grabowski, ZW AU - Khoo, TL AU - Lee, IY AU - Macchiavelli, AO AU - Mayer, RH AU - Stephens, FS AU - Afanasjev, AV AU - Ragnarsson, I T2 - PHYSICS LETTERS B AB - High-precision lifetime measurements have been performed in superdeformed (SD) bands of 151,152Dy and 151Tb with the Doppler-shift attenuation method. Differences found in the quadrupole moments Q0 of the yrast SD bands are understood in terms of shape polarization effects by the high-N intruder orbitals. Q0 moments are also presented for three excited SD bands in 151Dy. Recent calculations can account for most of the observations. DA - 1997/1/23/ PY - 1997/1/23/ DO - 10.1016/S0370-2693(96)01517-1 VL - 392 IS - 1-2 SP - 18-23 SN - 0370-2693 ER - TY - JOUR TI - Dependence of the C49-C54 TiSi2 phase transition temperature on film thickness and Si substrate orientation AU - Jeon, H AU - Yoon, G AU - Nemanich, RJ T2 - THIN SOLID FILMS AB - The C49 to C54 phase transition and the surface and interface morphologies were examined for titanium silicides formed on atomically clean Si substrates. The properties were explored as a function of the Ti film thickness, deposition temperature and Si substrate orientation. Ti films of thicknesses between 5 nm and 40 nm were deposited at elevated temperatures from 500 °C to 900 °C in increments of 100 °C onto Si(100) and Si(111) wafers. The titanium silicides are analyzed with X-ray diffraction, Raman, scanning and transmission electron microscopy for phase identification and measurement of the surface and interface morphologies. The C49 to C54 TiSi2 phase transition is observed to occur between 600 °C and 700 °C for the thickest films on (100) wafers, but the transition temperature is observed to increase as the film thickness is decreased or for films formed on Si(111) substrates. For a 20 nm Ti film deposited onto Si(100), the transition temperature occurs between 600 °C and 700 °C. However, for the same thickness of Ti on Si(111), the transition temperature is found between 700 °C and 800 °C. This retardation of the phase transition is discussed in terms of surface and volume free-energy considerations. DA - 1997/5/15/ PY - 1997/5/15/ DO - 10.1016/S0040-6090(96)09042-6 VL - 299 IS - 1-2 SP - 178-182 SN - 0040-6090 KW - phase transition KW - titanium silicide KW - silicon ER - TY - JOUR TI - An accurate theoretical description of fluids composed of fully anisotropic molecules: Application to C-2v symmetry AU - Alvarez, M AU - Lado, F AU - Lomba, E AU - Lombardero, M AU - Martin, C T2 - JOURNAL OF CHEMICAL PHYSICS AB - We use two molecular integral equation approximations to compute the thermodynamic properties and microscopic structure of two liquids composed of planar molecules with C2v symmetry, namely SO2 and H2S. These approximations couple the exact molecular Ornstein–Zernike equation with the hypernetted chain (HNC) and reference-hypernetted chain (RHNC) closures. The theoretical results obtained for various thermodynamic states agree remarkably well with molecular dynamics calculations. In particular, the atom-atom distribution functions are very well reproduced. We find that the RHNC approximation with a hard-sphere fluid reference system offers notable improvement over HNC in the pressure calculation. We include also a self-consistent mean field calculation to incorporate the effect of polarizability on the dielectric constant of liquid SO2. Final results for this quantity are in excellent agreement with experimental values. In contrast, the model used for the electrostatic interactions in H2S leads to anomalously high permanent dipole moments, compared to experiment, and consequently to dielectric constants that are completely off the experimental data. DA - 1997/9/22/ PY - 1997/9/22/ DO - 10.1063/1.474825 VL - 107 IS - 12 SP - 4642-4647 SN - 0021-9606 ER - TY - JOUR TI - Structure and stability of cobalt-silicon-germanium thin films AU - Goeller, PT AU - Boyanov, BI AU - Sayers, DE AU - Nemanich, RJ T2 - NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS AB - The phase formation and stability of CoSi2 on strained epitaxial Si0.80Ge0.20Si (0 0 1) thin films has been investigated. Silicide films prepared via direct deposition of cobalt (CoSiGe), and via co-deposition of silicon and cobalt (Co+2SiSiGe), were compared. EXAFS, XRD, and sheet-resistance measurements indicated that co-deposited Co+2Si films annealed at 400–700°C exhibit the expected low-resistivity CoSi2 structure but were susceptible to roughening, pinhole formation, and agglomeration. In contrast, the CoSiGe structure formed CoSi2 only after annealing at 700°C and silicide formation was accompanied by Ge segregation in the contact region. In situ RHEED experiments indicated that growth of CoSi2 co-deposited on SiGe at 400–500°C results in immediate island formation. Template methods, which are often used to enhance the quality of co-deposited Co+2SiSi structures, did not lead to two-dimensional growth in the Co+2SiSiGe system. In situ EXAFS measurements of 2 Å Co films deposited on SiGe substrates and annealed at 450°C suggested that the failure to achieve two-dimensional growth may be due to preferential bonding of Co to Si atoms at the interface, which prevents the formation of a continuous CoSi2 template. DA - 1997/12// PY - 1997/12// DO - 10.1016/S0168-583X(97)00458-8 VL - 133 IS - 1-4 SP - 84-89 SN - 0168-583X KW - cobalt silicide KW - silicon-germanium alloys KW - metal-semiconductor contacts KW - molecular beam epitaxy ER - TY - JOUR TI - Nanotubes AU - Bernholc, J AU - Roland, C AU - Yakobson, BI T2 - CURRENT OPINION IN SOLID STATE & MATERIALS SCIENCE AB - The field of nanotubes is undergoing an explosive growth, fueled by brakethroughs in synthesis and the promise of unique applications. Highly unusual properties and devices have been predicted and/or observed, including extremely high strength and flexibility, nanoscale electronic devices consisting entirely of carbon, and strong capillary effects leading to the production of exceptionally thin wires, cold cathode field emission and other effects. DA - 1997/12// PY - 1997/12// DO - 10.1016/s1359-0286(97)80014-9 VL - 2 IS - 6 SP - 706-715 SN - 1879-0348 ER - TY - JOUR TI - Evolution of cold shock bounded slabs AU - Blondin, John AU - Marks, B. S. T2 - New Astronomy AB - The stability and evolution of cold, shock-bounded slabs is studied using numerical hydrodynamic simulations. We confirm the analysis of Vishniac (1994) [ApJ, 428, 186], who showed that such slabs are unstable if they are perturbed by a displacement larger than their width. The growth rate of this nonlinear thin shell instability (NTSI) is found to increase with decreasing wavelength, in qualitative agreement with Vishniac's analysis. The NTSI saturates when the bending angle becomes large and the growth in the width of the slab pinches off the perturbation. After saturation, the slab remains greatly extended with an average density much less than the original slab density, supported primarily by supersonic turbulence within the slab. Linear perturbations are also found to be unstable in that they can lead to turbulent flow within the slab, although this response to linear perturbations is distinct from, and much less violent than the NTSI. Richard McCray DA - 1997/// PY - 1997/// DO - 10.1016/s1384-1076(96)00019-x VL - 1 IS - 3 SP - 235–244 ER - TY - JOUR TI - Doping properties of C, Si, and Ge impurities in GaN and AlN AU - Boguslawski, P AU - Bernholc, J T2 - PHYSICAL REVIEW B AB - Doping properties of substitutional C, Si, and Ge impurities in wurtzite GaN and AlN were studied by quantum molecular dynamics. We considered incorporation of impurities on both cation and anion sublattices. When substituting for cations, Si and Ge are shallow donors in GaN, while Ge becomes a deep donor in AlN. Both impurities are deep acceptors on the N site. Substitutional C${}_{\mathrm{cation}}$ is a shallow donor in GaN, but a deep one in AlN; C${}_{\mathrm{N}}$ is a relatively shallow acceptor in both materials. Two effects that potentially quench doping efficiency were investigated. The first one is the transition of a donor from a substitutional position to a $\mathrm{DX}$-like configuration. In crystals with a wurtzite symmetry, there are two possible variants of a $\mathrm{DX}$-like state, and they have substantially different properties. In GaN, ${\mathrm{DX}}^{\ensuremath{-}}$ states of both Si and Ge are unstable, or metastable, and thus they do not affect doping efficiency. In contrast, they are stable in AlN, and therefore neither Si nor Ge is a dopant in this material. Estimates obtained for Al${}_{x}$Ga${}_{1\ensuremath{-}x}$N alloys show that the crossover composition for $\mathrm{DX}$ stability is much lower for Ge $(x\ensuremath{\simeq}0.3)$ than for Si $(x\ensuremath{\simeq}0.6)$. The second effect quenching the doping efficiency is self-compensation, i.e., simultaneous incorporation of impurity atoms on both cation and anion sublattice. This effect may be enhanced by the formation of nearest-neighbor donor-acceptor pairs. The calculated binding energies of such pairs are large, about 1 eV, influencing self-compensation in some cases. Finally, the computed formation energies are used to identify growth conditions under which all these impurities may be efficient dopants in wide-band-gap nitrides. DA - 1997/10/15/ PY - 1997/10/15/ DO - 10.1103/physrevb.56.9496 VL - 56 IS - 15 SP - 9496-9505 SN - 0163-1829 ER - TY - JOUR TI - Decays of hybrid mesons AU - Swanson, E. S. AU - Szczepaniak, A. P. T2 - Physical Review. D, Particles and Fields DA - 1997/// PY - 1997/// VL - 56 IS - 9 SP - 5692-5695 ER - TY - JOUR TI - Black holes with short hair AU - Brown, J. D. AU - Husain, V. T2 - International Journal of Modern Physics. D, Gravitation, Astrophysics, Cosmology AB - We present spherically symmetric black hole solutions for Einstein gravity coupled to anisotropic matter. We show that these black holes have arbitrarily short hair, and argue for stability by showing that they can arise from dynamical collapse. We also show that a recent "no short hair" theorem does not apply to these solutions. DA - 1997/// PY - 1997/// DO - 10.1142/s0218271897000340 VL - 6 IS - 5 SP - 563–573 UR - http://inspirehep.net/record/445594 ER - TY - JOUR TI - Spectromicroscopy: preface AU - Ade, H. T2 - Journal of Electron Spectroscopy and Related Phenomena DA - 1997/// PY - 1997/// VL - 84 IS - 1-3 SP - R9 ER - TY - JOUR TI - Preferential Co-SI bonding at the Co/SiGe(100) interface AU - Boyanov, B. I. AU - Goeller, P. T. AU - Sayers, D. E. AU - Nemanich, R. J. T2 - Applied Physics Letters AB - The initial stages of the reaction of Co with Si0.79Ge0.21(100) were studied in situ with extended x-ray absorption fine structure spectroscopy and reflection high energy electron diffraction. The Si:Ge ratio in the first coordination shell of Co in sub-monolayer Co films was found to increase with film thickness and annealing temperature, indicating preferential formation of Co–Si bonds. The impact of the observed preference for Co–Si bonding on the morphology of epitaxial CoSi2/Si1−xGex heterostructures is discussed. DA - 1997/// PY - 1997/// DO - 10.1063/1.119436 VL - 71 IS - 21 SP - 3060-3062 ER - TY - JOUR TI - Plasma-assisted formation of low defect density SiC-SiO2 interfaces AU - Golz, A. AU - Lucovsky, G. AU - Koh, K. AU - Wolfe, D. AU - Niimi, H. AU - Kurz, H. T2 - Journal of Vacuum Science & Technology. B, Microelectronics and Nanometer Structures DA - 1997/// PY - 1997/// VL - 15 IS - 4 SP - 1097-1104 ER - TY - JOUR TI - Photoionization of lithium in the inelastic scattering region AU - Chung, KT T2 - PHYSICAL REVIEW LETTERS AB - The photoionization of lithium to energies between the ${\mathrm{Li}}^{+}$ $1s2s{}^{3}S$ and $1s2p{}^{1}P$ thresholds is studied with accurate ground and target state wave functions. Saddle-point full-core plus correlation wave functions are used for the closed channel. The result agrees with recent photoion measurements. Thirty nine resonances are found in the observed spectra and the predicted sharp peaks agree with experiment to meV levels. The predicted line profile agrees closely with experiment. Several earlier identifications are reassigned. Strong mixing of different resonance series is also found in a few instances. DA - 1997/2/24/ PY - 1997/2/24/ DO - 10.1103/PhysRevLett.78.1416 VL - 78 IS - 8 SP - 1416-1419 SN - 0031-9007 ER - TY - JOUR TI - Photoionization of lithium below the Li+ 1s2s S-3 threshold AU - Chung, KT T2 - PHYSICAL REVIEW A AB - A saddle-point complex-rotation method is used to calculate the resonance energy, width, and photoionization cross section (PICS) of lithium below the ${\mathrm{Li}}^{+}$ $1s2s$${}^{3}S$ threshold. Fourteen ${}^{2}{P}^{o}$ resonances are studied. These results are compared with the most precise experimental data in the literature. Most of the Auger widths of these resonances are extremely narrow, which makes a direct theory-experiment PICS comparison difficult. However, if we convolute the predicted cross section with a Gaussian profile using the experimental resolution for full width at half maximum, the resulting profile agrees closely with the high-resolution photoion measurement. DA - 1997/11// PY - 1997/11// DO - 10.1103/PhysRevA.56.R3330 VL - 56 IS - 5 SP - R3330-R3333 SN - 1094-1622 ER - TY - JOUR TI - On the DIRAC structure of confinement AU - Szczepaniak, A. P. AU - Swanson, E. S. T2 - Physical Review. D, Particles and Fields DA - 1997/// PY - 1997/// VL - 55 IS - 7 SP - 3987-3993 ER - TY - JOUR TI - Light-cone quark model predictions for radiative meson decays AU - Choi, HM AU - Ji, CR T2 - NUCLEAR PHYSICS A AB - We investigate the radiative decay of pseudoscalar (π, K, η, η′), vector (ϱ, K∗, ω, ƒ) and axial-vector (A1) mesons using a simple relativistic constituent quark model. For both simplicity and relativity, we take advantage of the distinguished features in the light-cone quantization method: (1) the Fock state expansion of meson wave functions are not contaminated by the vacuum fluctuation, (2) the problem of assigning quantum numbers JPC to mesons is circumvented by the Melosh transformation. Except the well-known constituent quark masses of (u, d, s) quarks and the spin-averaged meson masses, the only parameter in the model is the Gaussian parameter β which determines the broadness (or sharpness) of the radial wave function. Our overall predictions of pseudoscalar, vector and axial-vector meson radiative decay processes are in remarkably good agreement with the experimental data. DA - 1997/6/2/ PY - 1997/6/2/ DO - 10.1016/S0375-9474(97)00052-3 VL - 618 IS - 3 SP - 291-316 SN - 0375-9474 KW - radiative meson decays KW - light-cone quark model KW - transition form factors KW - eta-eta' mixing ER - TY - JOUR TI - In-rich 4X2 reconstruction in novel planar growth of InAs on GaAs(001) AU - Xue, Q. K. AU - Hasegawa, Y. AU - Ogino, T. AU - Kiyama, H. AU - Sakurai, T. T2 - Journal of Vacuum Science & Technology. B, Microelectronics and Nanometer Structures DA - 1997/// PY - 1997/// VL - 15 IS - 4 SP - 1270-1273 ER - TY - JOUR TI - Fullerene nanotubes: C (1,000,000) and beyond AU - Yakobson, B. I. AU - Smalley, R. E. T2 - American Scientist DA - 1997/// PY - 1997/// VL - 85 IS - 4 SP - 324-337 ER - TY - JOUR TI - Electron-optical-phonon scattering in wurtzite crystals AU - Lee, BC AU - Kim, KW AU - Dutta, M AU - Stroscio, MA T2 - PHYSICAL REVIEW B AB - We present Fr\"ohlich-like electron--optical-phonon interaction Hamiltonian for wurtzite crystals in the long-wavelength limit based on the macroscopic dielectric continuum model and the uniaxial model. In general, the optical-phonon branches support mixed longitudinal and transverse modes due to the anisotropy. We calculate electron scattering rate due to the optical phonons in the bulk wurtzite GaN and demonstrate that the scattering rate due to transverselike phonon processes can be strongly enhanced over a range of angles with respect to the $c$ axis. For the case of longitudinal-like modes, the anisotropy is small and the result is almost the same as that obtained with the cubic Fr\"ohlich Hamiltonian. DA - 1997/7/15/ PY - 1997/7/15/ DO - 10.1103/physrevb.56.997 VL - 56 IS - 3 SP - 997-1000 SN - 1098-0121 ER - TY - JOUR TI - Duality invariance of black hole creation rates AU - Brown, JD T2 - PHYSICAL REVIEW D AB - Pair creation of electrically charged black holes and its dual process, pair creation of magnetically charged black holes, are considered. It is shown that the creation rates are equal provided the boundary conditions for the two processes are dual to one another. This conclusion follows from a careful analysis of boundary terms and boundary conditions for the Maxwell action. DA - 1997/7/15/ PY - 1997/7/15/ DO - 10.1103/physrevd.56.1001 VL - 56 IS - 2 SP - 1001-1004 SN - 0556-2821 UR - http://inspirehep.net/record/440617 ER - TY - JOUR TI - Control of Si(100) sublimation with dopants AU - Roland, CM AU - Wensell, MG AU - Hong, Y AU - Tsong, IST T2 - PHYSICAL REVIEW LETTERS AB - The sublimation of the Si(100)-( $2\ifmmode\times\else\texttimes\fi{}1$) surface under a tensile strain, induced by dopant segregation, was investigated with low-energy electron microscopy. At a given temperature, samples containing relatively large concentrations of dopants exhibit a step-flow behavior during sublimation. By contrast, the formation and proliferation of terrace vacancies, followed by a disintegration of the surface steps, dominates the sublimation of the lightly doped samples. Molecular dynamics simulations indicate that this striking difference in behavior is due to a strain-induced increase in the formation energy of dimer vacancies on the surface. DA - 1997/3/31/ PY - 1997/3/31/ DO - 10.1103/PhysRevLett.78.2608 VL - 78 IS - 13 SP - 2608-2611 SN - 1079-7114 ER - TY - JOUR TI - A coupling-of-modes approach to the analysis of STW devices AU - Strashilov, VL AU - Djordjev, KD AU - Boyanov, BI AU - Avramov, ID T2 - IEEE TRANSACTIONS ON ULTRASONICS FERROELECTRICS AND FREQUENCY CONTROL AB - The dispersion characteristics of surface transverse waves (STW) on 36/spl deg/ rotated Y-cut quartz have been analyzed numerically. A closed form dispersion relation has been derived and introduced in the equations of the coupling-of-modes (COM) theory to account for the variation of energy trapping with frequency. The transmission and reflection coefficients at the finger edges have been determined from the stopband characteristics. Through the introduction of an electromechanical coupling which varies linearly with the electrode mass loading, quantitative agreement with experimental results on two different types of two-port STW resonators has been achieved, and characteristic features have been explained. DA - 1997/5// PY - 1997/5// DO - 10.1109/58.658322 VL - 44 IS - 3 SP - 652-657 SN - 0885-3010 ER -