TY - JOUR TI - ULTRAFAST RECOMBINATION AND TRAPPING IN AMORPHOUS-SILICON AU - ESSER, A AU - SEIBERT, K AU - KURZ, H AU - PARSONS, GN AU - WANG, C AU - DAVIDSON, BN AU - LUCOVSKY, G AU - NEMANICH, RJ T2 - Journal of Non-Crystalline Solids AB - Abstract We have studied time-resolved reflectivity changes induced by femtosecond laser pulses in a-Si and a-Si:H thin-films. By varying pump-power, we have identified a non-radiative recombination process which controls the free-carrier density, N, on a picosecond time scale for N>5 ×1018cm−3 in a-Si:H and >5×1019 cm−3 in a-Si. At lower carrier densities, transients are controlled by trapping of free-carriers. DA - 1989/// PY - 1989/// DO - 10.1016/0022-3093(89)90654-6 VL - 114 SP - 573-575 UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:A1989CK49800062&KeyUID=WOS:A1989CK49800062 ER - TY - JOUR TI - REDUCTION OF DEFECTS BY HIGH-TEMPERATURE ANNEALING (150-DEGREES-C-240-DEGREES-C) IN HYDROGENATED AMORPHOUS-SILICON FILMS DEPOSITED AT ROOM-TEMPERATURE AU - PARSONS, GN AU - WANG, C AU - WILLIAMS, MJ AU - LUCOVSKY, G T2 - Journal of Non-Crystalline Solids AB - We have deposited undoped a-Si:H films with hydrogen content from 0% to 19% with the substrate temperature near room temperature (Ts=40°C). We find an “intrinsic” defect density of 1018cm−3 in the as-deposited films with [H]=12%. Annealing the films at temperatures >150°C reduces the defect density and increased the photoresponse to levels the same as those in films deposited at Ts > 200°C. DA - 1989/// PY - 1989/// DO - 10.1016/0022-3093(89)90105-1 VL - 114 SP - 178-180 UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:A1989CK49700056&KeyUID=WOS:A1989CK49700056 ER - TY - JOUR TI - RAMAN-SCATTERING FROM MICROCRYSTALLINE SI FILMS - CONSIDERATIONS OF COMPOSITE STRUCTURES WITH DIFFERENT OPTICAL-ABSORPTION PROPERTIES AU - NEMANICH, RJ AU - BUEHLER, EC AU - LEGRICE, YM AU - SHRODER, RE AU - PARSONS, GN AU - WANG, C AU - LUCOVSKY, G AU - BOYCE, JB T2 - Journal of Non-Crystalline Solids AB - Raman scattering measurements are used to characterize the amorphous and crystalline components of microcrystalline Si films. A model is described which addresses the properties of Raman scattering from composites of materials of different optical absorption. The analysis shows that the observed spectra is dependent on both the percentage of the components and on the domain size of the more highly absorbing domains. Samples of microcrystalline silicon prepared by excimer laser exposure of hydrogenated a-Si and by magnetron sputtering were measured, and the results were analyzed in terms of the model. The experimental results reflect the length scales of the domains and vibrational excitations. DA - 1989/// PY - 1989/// DO - 10.1016/0022-3093(89)90729-1 VL - 114 SP - 813-815 UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:A1989CK49800139&KeyUID=WOS:A1989CK49800139 ER - TY - JOUR TI - PRECURSORS FOR THE DEPOSITION OF AMORPHOUS-SILICON HYDROGEN ALLOYS BY REMOTE PLASMA ENHANCED CHEMICAL VAPOR-DEPOSITION AU - PARSONS, GN AU - TSU, DV AU - WANG, C AU - LUCOVSKY, G T2 - Journal of Vacuum Science & Technology a-Vacuum Surfaces and Films AB - We have grown thin films of intrinsic and doped a-Si:H alloys by remote plasma enhanced chemical vapor deposition (remote PECVD) and studied their optical, electrical, and infrared vibrational properties. The electronic properties of remote PECVD films deposited at Ts =240 °C are similar to glow discharge (GD) films produced at the same Ts . Remote PECVD a-Si:H films deposited at Ts =100 °C show predominantly monohydride bonding in the infrared absorbance spectrum, and have electrical properties that are markedly improved over GD films deposited at this same relatively low Ts. We have studied the deposition process by mass spectrometry and optical emission spectroscopy and find that the concentration of silane fragments (SiHx, x=0–3) and higher silanes (e.g., disilane, Si2H6) in the gas phase is below our detection limit of 1%. Bias experiments and a comparison of the a-Si:H deposition rate with the known concentration of silane in the gas phase suggest that in remote PECVD, electrons from the He plasma produce vibrationally excited silane molecules (as opposed to silane fragments) in the gas phase or on the deposition surface which then act as the precursors for the a-Si:H thin-film deposition reactions. DA - 1989/// PY - 1989/// DO - 10.1116/1.576240 VL - 7 IS - 3 SP - 1124-1129 UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:A1989U715300104&KeyUID=WOS:A1989U715300104 ER - TY - JOUR TI - OPTICAL-EMISSION AND MASS SPECTROSCOPIC STUDIES OF THE GAS-PHASE DURING THE DEPOSITION OF SIO2 AND A-SI-H BY REMOTE PLASMA-ENHANCED CHEMICAL VAPOR-DEPOSITION AU - TSU, DV AU - PARSONS, GN AU - LUCOVSKY, G AU - WATKINS, MW T2 - Journal of Vacuum Science & Technology a-Vacuum Surfaces and Films AB - This paper will present mass spectrometric and optical emission spectroscopic studies of the deposition process of amorphous hydrogenated silicon (a-Si:H) and silicon dioxide (SiO2) by remote plasma-enhanced chemical vapor deposition (remote PECVD). We have established that the silane reactant, which is not directly exposed to a rf plasma in either of the deposition processes, is not fragmented or chemically combined in the gas phase. Specifically there is no evidence for the formation of disilane, Si2H6, or siloxanes or silanols in the gas phase, as in the direct PECVD process. In the case of the a-Si:H depositions, the silane is excited in the gas phase and the excited species, SiH*4 , is the deposition precursor. In the case of the SiO2 depositions, the active species promoting deposition is an O2 metastable neutral molecule. The by-products of the respective reactions are H2 and H2O. DA - 1989/// PY - 1989/// DO - 10.1116/1.576239 VL - 7 IS - 3 SP - 1115-1123 UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:A1989U715300103&KeyUID=WOS:A1989U715300103 ER - TY - JOUR TI - LOW-TEMPERATURE DEPOSITION OF HYDROGENATED AMORPHOUS-SILICON (A-SI-H) - CONTROL OF POLYHYDRIDE INCORPORATION AND ITS EFFECTS ON THIN-FILM PROPERTIES AU - LUCOVSKY, G AU - PARSONS, GN AU - WANG, C AU - DAVIDSON, BN AU - TSU, DV T2 - Solar Cells AB - It is shown how remote plasma-enhanced chemical vapor deposition (remote PECVD) and reactive magnetron sputtering (RMS) can be adopted to limit the relative fraction of polyhydride bonding groups for low substrate temperature depositions (Ts < 200 °C) of a-Si:H. These process modifications provide new options for the processing of device structures by combinations of low-temperature deposition and post-deposition, short-term thermal annealing. It is shown for several different deposition processes, including conventional glow-discharge deposition (GD), RMS, and remote PECVD, that the distribution of bonded hydrogen between monohydride and polyhydride bonding groups is determined by the total amount of bonded hydrogen [H] in the film and is not intrinsically related to Ts, or any other deposition parameter. A statistical model is presented, which provides a basis for translating process-dependent representations of data for the relative monohydride and polyhydride fractions to a universally obeyed scaling relationship in which the independent variable is [H]. Finally, selected properties of low-Ts films formed by RMS and remote PECVD are briefly discussed. DA - 1989/// PY - 1989/// DO - 10.1016/0379-6787(89)90022-7 VL - 27 IS - 1-4 SP - 121-136 UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:A1989CM44500012&KeyUID=WOS:A1989CM44500012 ER - TY - JOUR TI - INCORPORATION OF POLYHYDRIDE BONDING GROUPS INTO THIN-FILMS OF HYDROGENATED AMORPHOUS-SILICON (A-SI-H) AU - LUCOVSKY, G AU - DAVIDSON, BN AU - PARSONS, GN AU - WANG, C T2 - Journal of Non-Crystalline Solids AB - We show for several different deposition methods, including conventional glow-discharge (GD), reactive magnetron sputtering (RMS), and remote plasma-enhanced chemical-vapor deposition (remote PECVD), that the distribution of hydrogen between monohydride and polyhydride groups is a function of the total amount of bonded hydrogen in the film, and is not uniquely determined by the substrate temperature, or any other single deposition process variable. We demonstrate that RMS and remote PECVD offer advantages over the GD process in control of polyhydride formation in a-Si:H films. DA - 1989/// PY - 1989/// DO - 10.1016/0022-3093(89)90097-5 VL - 114 SP - 154-156 UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:A1989CK49700048&KeyUID=WOS:A1989CK49700048 ER - TY - JOUR TI - EFFECTS OF GAS ADDITIVES ON THE PROPERTIES OF A-SI-H FILMS AU - WANG, C AU - PARSONS, GN AU - LUCOVSKY, G T2 - Journal of Non-Crystalline Solids AB - We show that the addition of small amounts of water vapor, or O2 into the processing ambient leads to significant improvements in the properties of a-Si:H films deposited by reactive magnetron sputtering at substrate temperatures <150°C. The relative fraction of polyhydride bonding, and defect densities are both reduced; the films show increased stability against light-soaking induced defects; while levels of oxygen in the films remain below ∼5×1018/cm3. DA - 1989/// PY - 1989/// DO - 10.1016/0022-3093(89)90110-5 VL - 114 SP - 193-195 UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:A1989CK49700061&KeyUID=WOS:A1989CK49700061 ER - TY - JOUR TI - DEPENDENCE OF A-SI-H/SI3N4 INTERFACE PROPERTIES ON THE DEPOSITION SEQUENCE IN AMORPHOUS-SILICON THIN-FILM TRANSISTOR PRODUCED BY REMOTE PECVD PROCESS AU - KIM, SS AU - PARSONS, GN AU - FOUNTAIN, GG AU - LUCOVSKY, G T2 - Journal of Non-Crystalline Solids AB - Two different layer deposition sequences using Remote PECVD have been investigated by in-situ Auger Electron Spectroscopy and photoconductivity. The carrier lifetime at the interface depends on the specific dielectric and on the film deposition sequence. A field effect mobility of 0.74 cm2/Vs is measured for the inverted staggered a-Si TFT formed at 238°C using a Si3N4bottom gate dielectric. DA - 1989/// PY - 1989/// DO - 10.1016/0022-3093(89)90363-3 VL - 115 IS - 1-3 SP - 69-71 UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:A1989CK50000019&KeyUID=WOS:A1989CK50000019 ER - TY - JOUR TI - DEFECTS IN A-SI-H FILMS PRODUCED BY REMOTE PLASMA ENHANCED CHEMICAL VAPOR-DEPOSITION AU - PARSONS, GN AU - TSU, DV AU - LUCOVSKY, G T2 - Journal of Non-Crystalline Solids AB - Abstract We have grown films of hydrogenated amorphous silicon, a-Si:H, by RPECVD with substrate temperatures, T s , between 38 and 400°C and have studied the hydrogen incorporation by infrared ( ir ) analysis, the optical absorbance (including sub-bandgap absorbance), the defect state density in annealed and light soaked states, and other photoelectronic properties. The RPECVD films differ from conventional glow discharge (GD) and sputtered films, most notably in the T s dependence of the hydrogen bonding environments (SiH, SiH 2 , etc.) and the photoconductivity. RPECVD films produced with T s = 235°C are similar to ‘device grade’ GD films. We have compared defect density with photoconductivity and inferred a value for the capture cross section. We have determined the effect of light soaking on the defect density (Staebler-Wronski effect) as a function of T s and have related these results to hydrogen bonding environments, hydrogen concentration and photoelectronic properties. DA - 1989/// PY - 1989/// DO - 10.1016/0022-3093(89)90475-4 VL - 107 IS - 2-3 SP - 295-300 UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:A1989T362800023&KeyUID=WOS:A1989T362800023 ER - TY - CONF TI - The development of high temperatures in titanium alloys during fast fracture AU - Jagannadham, K. AU - Kunze, H.-D. AU - Meyer, L.W. AU - Wilsdorf, H.G.F. T2 - 8th International Conference On The Strength Of Metals and Alloys AB - A titanium alloy, Ti-10V-2Fe-3Al, was fractured in tensile loading at strain rates between 70 sec-1 and 103 sec-1. Fracture surfaces were investigated by scanning electron microscopy showing in all specimens areas characterized by a deterioration of the normal dimple structure. A computer model was developed that is capable of showing a large temperature increase at the fast moving crack tip. An additional temperature rise due to the rupture of micro-ligaments can bring the localized temperature under certain conditions above the melting point of the alloy at the moment of final separation. C2 - 1989/// C3 - Strength of Metals and Alloys (ICSMA 8) CY - Tampere, Finland DA - 1989/// PY - 1988/8// DO - 10.1016/B978-0-08-034804-9.50173-X VL - 3 SP - 1095–1100 PB - Department of Material Science & Engineering, North Carolina State University ER - TY - CONF TI - Microstructure and in-situ processing of epitaxial high-Tc films AU - Narayan, J. AU - Singh, R.K. AU - Singh, A.K. AU - Krishnaswamy, J. AU - Jagannadham, K. AU - Lee, C.B. AU - Prasad, R.K. AU - Parikh, N.R. T2 - 1989 Symposium on High Temperature Superconducting Oxides--Processing & Related Properties T3 - Proceedings of the 1989 Symposium C2 - 1989/// C3 - High temperature superconducting compounds : processing & related properties : proceedings of the 1989 Symposium on High Temperature Superconducting Oxides--Processing & Related Properties, which was sponsored by the Superconducting Materials Committee and held in Las Vegas, NV, February 27 and 28, 1989, at the 118th Annual Meeting of the Minerals, Metals & Materials Society CY - Las Vegas, NV DA - 1989/// PY - 1989/2/27/ SP - 337–358 PB - The Metallurgical Society Inc ER - TY - JOUR TI - Chemical model for intrinsic detonation velocities AU - Brenner, Donald W. AU - White, C. T. AU - Elert, Mark L. AU - Walker, Franklin E. T2 - International Journal of Quantum Chemistry AB - Straightforward considerations suggest that chemical reactions including fragmentation processes at or near the front of a chemically sustained shock wave can be important in regulating the shock velocity. This picture is supported by results of recent computer simulations of a model A-B energetic material. DA - 1989/6/19/ PY - 1989/6/19/ DO - 10.1002/qua.560360836 VL - 36 IS - S23 SP - 333–337 SN - 0020-7608 1097-461X UR - http://dx.doi.org/10.1002/qua.560360836 ER - TY - JOUR TI - Modelling of microstructural features in Y-Ba-Cu-O superconductors AU - Jagannadham, K. AU - Narayan, J. T2 - Philosophical Magazine A: Physics of Condensed Matter, Structure, Defects and Mechanical Properties AB - Abstract We have investigated characteristics of four important microstructural features, namely, grain boundaries (small-and large-angle), twins, stacking faults and cracks in high-Tc YBa2Cu3O7-x superconducting oxides using transmission electron microscopy techniques. A detailed analysis of these microstructural features is carried out to understand their effect on the superconducting properties, mechanical properties and their environmental sensitivity. An atomic model of the small-angle and large-angle grain boundaries in these superconducting oxides is provided using a geometric description. Some important differences between the grain-boundary structure of the superconducting oxides and that of metals have been identified. The environmental sensitivity of the superconducting oxide is explained in terms of the atomic structure of dislocations associated with the grain-boundary configurations. The strain energy associated with the twinned regions and oriented domains is determined using discrete dislocation analysis. It is found that oriented domains should be more difficult to form than twins in these superconducting oxides. The nucleation of cracks along stacking faults is analysed to understand the brittle behaviour of these materials. The energy associated with the crack configurations is determined from the discrete dislocation analysis. The formation of moisture-induced stacking faults, followed by further nucleation of cracks along the faulted regions, is found to be an important mechanism for degradation of the mechanical and superconducting properties of this material. DA - 1989/// PY - 1989/// DO - 10.1080/01418618908209828 VL - 59 IS - 5 SP - 917-937 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-0024666627&partnerID=MN8TOARS ER - TY - JOUR TI - Modeling the temperature rise at the tip of a fast crack AU - Jagannadham, Kasi AU - Wilsdorf, Heinz G.F. T2 - Zeitschrift fuer Metallkunde/Materials Research and Advanced Techniques DA - 1989/// PY - 1989/// VL - 80 IS - 10 SP - 698-709 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-0024749727&partnerID=MN8TOARS ER - TY - JOUR TI - Misfit dislocations in superconducting thin films on SrTiO3{010} AU - Narayan, J. AU - Sharan, S. AU - Singh, R.K. AU - Jagannadham, K. T2 - Materials Science and Engineering B AB - We have studied the nature of strain-induced dislocations during epitaxial growth of YBa2Cu3-O7−δ films on SrTiO3{010} substrate. From the contrast analysis under different diffraction vectors, it was determined that the dislocations of a[110] and [011] Burgers vectors are formed in (110) and (011) planes respectively. At the points of intersection, they react (a[110]+a[011]→a[101]) to form a[101] segments in (010) planes. We have analyzed the formation of dislocations near the free surface above a critical thickness to minimize the total energy of the system. The dislocations glide into the film and the substrate. The importance of these results in the fabrication of thin film superconducting devices is emphasized. DA - 1989/// PY - 1989/// DO - 10.1016/0921-5107(89)90009-3 VL - 2 IS - 4 SP - 333-337 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-0024641446&partnerID=MN8TOARS ER - TY - JOUR TI - Low energy cleavage fracture associated with the hydrogen embrittlement of refractory metal alloys AU - Jagannadham, K. AU - Armstrong, R.W. AU - Hirth, J.P. T2 - Materials Science and Engineering A AB - Three dislocation models are investigated for explaining the hydrogen embrittlement of refractory (b.c.c.) metal alloy single crystals and large-grain polycrystals on the basis of cleavage initiation. The models considered are: (1) stress-induced dislocation pile-ups and dislocation reactions; (2) hydrogen-enhanced decohesion of slip plane pile-ups and planar dislocation arrays; and (3) slip and hydrogen interactions with lineage subgrain boundaries. Emphasis is given in each case to the crystallographic features of low strain cleavage initiations in the presence of hydrogen as observed in three refractory alloy systems. Electron microscope observations, including the occurrence of deformation twinning, are presented for the hydrogen-charged materials as a function of strain. Cumulative (low energy) stress fields are described for the dislocation pile-ups and the lineage boundaries. The enhancement of hydrogen concentration in the presence of the stress fields of these dislocation configurations is determined. The slip-twinning relationship and cleavage associated with hydride microprecipitates are considered. DA - 1989/// PY - 1989/// DO - 10.1016/0921-5093(89)90322-5 VL - 113 IS - C SP - 339-366 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-0024701756&partnerID=MN8TOARS ER - TY - JOUR TI - Dislocation cell size in a spatially varying stress field of a crack tip region AU - Jagannadham, K. AU - Pollock, T.C. AU - Wilsdorf, H.G.F. T2 - Materials Science and Engineering A AB - The spatially varying crack tip stress field is used to determine the dislocation density in the plastic zone. The rearrangement of dislocations is formulated using the minimization of the total energy of the configuration to form the cell structure in the presence of the spatially varying crack tip stress field. The equilibrium dislocation cell size is obtained for the lowest total energy of the configuration which consists of the self-energy and interaction energy terms associated with the dislocations within the cell walls and the work done by the crack tip stress field on the rearrangement of dislocations. A crack along (001) with two equally inclined {111} slip planes giving rise to a cell structure is analyzed. The results obtained using the crack tip stress field to generate a plastic zone without general yield illustrate that the cell size increases with increasing radial distance from the crack tip and increasing difference in the angular orientation from planes of maximum shear stress. It is further found that dislocation cell walls should align themselves on surfaces with constant shear stress. Experimental observations in beryllium foils, several microns thick and deformed in situ in the tensile stage of a high voltage microscope, are presented to show the validity of low energy configurations determined analytically. DA - 1989/// PY - 1989/// DO - 10.1016/0921-5093(89)90324-9 VL - 113 IS - C SP - 373-383 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-0024702294&partnerID=MN8TOARS ER - TY - JOUR TI - A two-parameter representation of dynamic dislocation distributions AU - Jagannadham, K. AU - Conrad, H. T2 - Materials Science and Engineering A AB - A two-parameter representation of the dislocation segment length distribution is offered to represent the plastically deformed state of a material. This distribution function represents the radii to which dislocations are bowed during plastic deformation. It is based on the premise that both a minimum and a maximum value of radius exist. Various quantities associated with the plastically deformed state, namely the fraction of mobile dislocations, the stress dependence of strain rate and of the dislocation velocity are derived from the two-parameter distribution function. The distribution function is also applied to the plastic deformation behavior of polycrystalline copper in tension, in torsion and in tension plus torsion. The results illustrate that the two-parameter distribution explains different characteristic features of plastic deformation and also distinguishes the different forms of plastic deformation of solids. DA - 1989/// PY - 1989/// DO - 10.1016/0921-5093(89)90307-9 VL - 113 IS - C SP - 197-206 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-0024698924&partnerID=MN8TOARS ER - TY - JOUR TI - Mechanisms of Improvement of Fracture Strength in Laser‐Surface‐Modified Ceramics AU - Jagannadham, K. AU - Narayan, J. T2 - Journal of the American Ceramic Society AB - Three mechanisms of improvement in fracture strength of laser‐surface‐modied ceramic materials are proposed to explain the experimental observations of more than 50% increase in fracture strength. First, the improvement in fracture strength by about 50% is considered to arise from either a complete or partial closure of crack surfaces at the interface of the laser‐modified overlayer. The second mechanism of improvement in fracture strength is derived from the physical displacement of the crack tip away from the free surface when a laser‐modified layer is introduced. Thus, the critical crack size, defmed as a crack that propagates with decreasing energy, is increased almost 100%. The Wid mechanism is based upon the compressive stresses introduced in the laser‐modified region. The fast cooling rates attained after laser irradiation are responsible for development of regions of compressive internal stresses. These sources of improvement in fracture strength are analyzed and the results of the calculations compared with experimental results. Through the present understanding of the mechanisms of improvement in fracture strength, it has become possible to calculate a critical thickness of the laser‐modifed layer. It is concluded that the possible improvement of fracture strength is achieved when the thickness of the laser‐modified overlayer is equal to or greater than this critical value. DA - 1989/// PY - 1989/// DO - 10.1111/j.1151-2916.1989.tb09706.x VL - 72 IS - 7 SP - 1185-1191 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-0346453318&partnerID=MN8TOARS ER - TY - JOUR TI - Fracture behavior of laser-modified ceramic materials AU - Jagannadham, K. AU - Narayan, J. T2 - Materials Letters AB - The healing of surface cracks in laser surface modified ceramic materials is analyzed. A partial or complete welding of the crack surfaces as a result of laser surface modification of silicon carbide with nickel overlayer is shown to be effective in improving the fracture toughness. The presence of the coherent second phase of nickel changes the nature of applied stress on the crack surfaces and welds the crack tip. Dislocation modelling of the partially closed crack surfaces is presented along with the development of constitutive energy equations associated with the crack in the two-phase medium. Crack configurations under either an applied tensile stress or an antiplane strain condition are analyzed and the results compared. These results show that the critical size of the crack at the interface in the laser surface modified materials is always larger than that of the surface crack. This leads to an improvement of fracture toughness, consistent with experimental observations. DA - 1989/// PY - 1989/// DO - 10.1016/0167-577X(89)90014-1 VL - 7 IS - 9-10 SP - 303-315 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-0024305382&partnerID=MN8TOARS ER - TY - JOUR TI - Critical thickness during three-dimensional epitaxial growth-A self-consistent approach AU - Jagannadham, K. AU - Narayan, J. T2 - Materials Science and Engineering A AB - Abstract A self-consistent model is developed to describe the formation of misfit dislocation loops in hemispherical epilayers of finite size grown on thick substrates. The lattice mismatch between the substrate and the epilayer is described by virtual interfacial dislocation loops situated in the interface. The free surface boundary conditions are satisfied by the surface dislocation loops situated on the surface of the hemispherical island. A misfit dislocation loop is nucleated and the changes in the energy of the configuration are used to determine if a lowering in the total energy of the configuration can occur. The model consisting of the primatic dislocation loops in the epilayer is replaced by a simpler dislocation model consisting of glide dislocation loops so that the stress fields and interaction energy terms between dislocations in a two-phase medium could be evaluated. The energy associated with the coherent epilayer and that with the misfit dislocation are evaluated by the minimization of the total energy of the configuration with respect to the Burgers vectors of the surface dislocation loops. The position of the misfit dislocation loop from the interface is changed for a given size of the hemispherical island and the energy terms are determined. The formation of a misfit dislocation loop is considered favorable when the energy of the configuration in the presence of the misfit dislocation is lower than that of the coherent epilayer. The numerical analysis is carried out for hemispherical islands of GaAs grown on (100) Si with a misfit dislocation of Burgers' vector 3.84 A. It has been found energetically favorable to nucleate a misfit dislocation loop at a distance of 3 A from the interface when the radius of the hemispherical island is equal to or greater than 40 A. In addition, a misfit dislocation loop could be nucleated at a larger distance from the interface when the size of the epilayer is larger. The results are interpreted in terms of the favorable position for nucleation of the misfit dislocation and its glide motion towards the interface. DA - 1989/// PY - 1989/// DO - 10.1016/0921-5093(89)90294-3 VL - 113 IS - C SP - 65-73 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-0024701108&partnerID=MN8TOARS ER - TY - JOUR TI - A STATISTICAL-THEORY OF COMPOSITE-MATERIALS STRENGTH AU - ZHU, YT AU - ZHOU, BL AU - HE, GH AU - al., T2 - JOURNAL OF COMPOSITE MATERIALS DA - 1989/// PY - 1989/// VL - 23 IS - 3 SP - 280-287 ER - TY - JOUR TI - Thin‐film deposition by a new laser ablation and plasma hybrid technique AU - Krishnaswamy, J. AU - Narayan, J. AU - Vedam, K. AU - McHargue, C.J. AU - Rengan, A. T2 - Applied Physics Letters DA - 1989/12/6/ PY - 1989/12/6/ VL - 54 IS - 24 SP - 2455-2457 ER - TY - JOUR TI - In situ processing of epitaxial Y‐Ba‐Cu‐O high Tc superconducting films on (100) SrTiO3and (100) YS‐ZrO2 substrates at 500–650 °C AU - Singh, R.K. AU - Narayan, J. AU - Singh, A.K. AU - Krishnaswamy, J. T2 - Applied Physics Letters DA - 1989/5/29/ PY - 1989/5/29/ VL - 54 IS - 22 SP - 2271–2273 ER - TY - JOUR TI - A novel method for simulating laser-solid interactions in semiconductors and layered structures AU - Singh, Rajiv K. AU - Narayan, Jagdish T2 - Materials Science and Engineering: B DA - 1989/1/8/ PY - 1989/1/8/ VL - 3 IS - 3 SP - 217–230 ER - TY - JOUR TI - Reduction of defects by high temperature (180 degrees c-240 degrees c) annealing in room temperature deposited hydrogenated amorphous silicon AU - Parsons, G.N. AU - Wang, C. AU - Lucovsky, G. T2 - Journal of Non-crystalline Solids DA - 1989/// PY - 1989/// SP - 114 ER - TY - JOUR TI - Precursors for the deposition of amorphous silicon hydrogen alloys by remote plasma enhanced CVD AU - Parsons, G.N. AU - Tsu, D.V. AU - Wang, C. AU - Lucovsky, G. T2 - Journal of Vacuum Science & Technology DA - 1989/// PY - 1989/// VL - A IS - 7 SP - 1124-1129 ER - TY - JOUR TI - Mass and optical emission spectroscopic studies of the gas phase during the deposition of SiO2 and a-Si:H by remote plasma enhanced chemical vapor deposition AU - Tsu, D.V. AU - Parsons, G.N. AU - Lucovsky, G. AU - Watkins, M.W. T2 - Journal of Vacuum Science & Technology DA - 1989/// PY - 1989/// VL - A IS - 7 SP - 1115-1123 ER - TY - JOUR TI - Dependence of the chemical, electrical and photoelectronic properties of a-Si:H/Si3N4 interfaces on the deposition sequence AU - Kim, S.S. AU - Parsons, G.N. AU - Lucovsky, G. T2 - Journal of Non-Cyrstalline Solids DA - 1989/// PY - 1989/// VL - 114 ER - TY - JOUR TI - Defects in a-Si:H films produced by remote plasma enhanced CVD AU - Parsons, G.N. AU - Tsu, T.V. AU - Lucovsky, G. T2 - Journal of Non-crystalline Solids DA - 1989/// PY - 1989/// VL - 107 SP - 295-300 ER - TY - JOUR TI - SYNTHESIS AND REACTIVITY OF ANIONIC TETRAOSMIUM CLUSTERS ON HIGHLY DEHYDROXYLATED MGO AU - LAMB, HH AU - HASSELBRING, LC AU - DYBOWSKI, C AU - GATES, BC T2 - JOURNAL OF MOLECULAR CATALYSIS AB - The deprotonation of H4Os4(CO)12 on MgO gave the supported clusters [H3Os4(CO)12]− and [H2Os4(CO)12]2. The surface-bound anions were extracted from the support by cation metathesis and characterized in solution by infrared and 1H NMR spectroscopies. The anions on highly dehydroxylated MgO were examined by infrared, 13C MAS NMR and UV-vis spectroscopies. The 13C chemical shifts are consistent with a mixture of [H3Os4(CO)12]− and [H2Os4(CO)12]2− surface species. The v(CO) infrared spectrum of [H3Os4(CO)12]−/MgO suggests a simpler structure than the mixture of C2 and C3v isomers observed in solution. We speculate that the relatively nonpolar environment of the MgO surface strongly favors a nonpolar C3v isomer of [H3Os4(CO)12]− in which the negative charge is delocalized over a face of the Os4 tetrahedron. When water was co-adsorbed on the surface, the v(CO) infrared spectrum of [H3Os4(CO)12]− on MgO was brought into close agreement with that of its soluble analog. After treatment of the supported anions in CO + H2 at 200 °C and 1 atm, [H3Os4(CO)12]− and [H2Os4(CO)12]2− (trace) were the only osmium carbonyl species detected by infrared spectroscopy and extraction of surface-bound anions. DA - 1989/11/15/ PY - 1989/11/15/ DO - 10.1016/0304-5102(89)80170-1 VL - 56 IS - 1-3 SP - 36-49 SN - 0304-5102 ER - TY - JOUR TI - SURFACE-MEDIATED ORGANOMETALLIC SYNTHESIS - PREPARATION OF [OS5C(CO)14]2- AND [OS10C(CO)24]2- ON THE BASIC MAGNESIUM-OXIDE SURFACE AU - LAMB, HH AU - FUNG, AS AU - TOOLEY, PA AU - PUGA, J AU - KRAUSE, TR AU - KELLEY, MJ AU - GATES, BC T2 - JOURNAL OF THE AMERICAN CHEMICAL SOCIETY AB - ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTSurface-mediated organometallic synthesis: preparation of osmium carbonyl clusters [Os5C(CO)14]2- and [Os10C(CO)24]2- on the basic magnesium oxide surfaceH. Henry Lamb, Anthony S. Fung, Patricia A. Tooley, Jose Puga, Theodore R. Krause, Michael J. Kelley, and Bruce C. GatesCite this: J. Am. Chem. Soc. 1989, 111, 22, 8367–8373Publication Date (Print):October 1, 1989Publication History Published online1 May 2002Published inissue 1 October 1989https://doi.org/10.1021/ja00204a007RIGHTS & PERMISSIONSArticle Views177Altmetric-Citations51LEARN 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. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (941 KB) Get e-Alerts Get e-Alerts DA - 1989/10/25/ PY - 1989/10/25/ DO - 10.1021/ja00204a007 VL - 111 IS - 22 SP - 8367-8373 SN - 0002-7863 ER - TY - JOUR TI - SUPPORTED METALS AND SUPPORTED ORGANOMETALLICS AU - GATES, BC AU - LAMB, HH T2 - JOURNAL OF MOLECULAR CATALYSIS AB - Organometallic chemistry and heterogeneous catalysis are developing into common territory, illustrated by catalysts incorporating structures ranging from mononuclear metal complexes to metal aggregates (crystallites) on metal oxide supports. Reactions of precursors such as metal carbonyls and metal allyls with metal oxide surfaces have been understood on the basis of solution organometallic chemistry combined with functional group chemistry of the supports. The supported species are transformed by processes including reductive carbonylation (whereby metal complexes and salts are converted into metal clusters) and oxidative fragmentation (whereby metal clusters and aggregates are converted into mononuclear metal complexes). Extended X-ray absorption fine structure (EXAFS) spectroscopy has been used in conjunction with other techniques to characterize bonds between mononuclear metal complexes and metal oxide surfaces and also to provide structural information about metal-support interfaces in highly dispersed supported metal aggregates. EXAFS results are also helping to define the limitations of standard methods for estimating surface areas of highly dispersed metals by measurements of chemisorption of H2 and CO. Some supported ‘molecular’ organometallics are structurally and catalytically novel, indicating possibilities for design of surface catalytic sites. Ensembles consisting of three Re complexes on MgO are active for the structure-sensitive cyclopropane hydrogenolysis, whereas a catalyst consisting of the same complexes (evidently isolated on the support surface) is inactive. ‘Molecular’ osmium carbonyl clusters stabilized on the basic MgO surface and in basic zeolites catalyze CO hydrogenation, and 10-atom aggregates of osmium, formed by removal of CO ligands from a ‘molecular’ precursor, are active for n-butane hydrogenolysis. These structurally well-defined catalysts offer good opportunities for understanding metal-support interactions and structure sensitivity in metal catalysis. DA - 1989/6/22/ PY - 1989/6/22/ DO - 10.1016/0304-5102(89)80078-1 VL - 52 IS - 1 SP - 1-18 SN - 0304-5102 ER - TY - PAT TI - Metal-insulator-semiconductor capacitor formed on silicon carbide AU - Palmour, J. W. C2 - 1989/// DA - 1989/// PY - 1989/// ER - TY - PAT TI - Dry etching of silicon carbide AU - Palmour, J. W. C2 - 1989/// DA - 1989/// PY - 1989/// ER - TY - PAT TI - Sublimation of silicon carbide to produce large, device quality single crystals of silicon carbide AU - Davis, R. F. AU - Carter, C. H. AU - Hunter, C. E. C2 - 1989/// DA - 1989/// PY - 1989/// ER - TY - JOUR TI - EFFECTS OF THE NEAREST NEIGHBORS AND THE ALLOY MATRIX ON SIH STRETCHING VIBRATIONS IN THE AMORPHOUS SIOR-H (0-LESS-THAN-R-LESS-THAN-2) ALLOY SYSTEM AU - TSU, DV AU - LUCOVSKY, G AU - DAVIDSON, BN T2 - PHYSICAL REVIEW B AB - Hydrogenated silicon suboxides, ${\mathrm{SiO}}_{\mathrm{r}}$:H, for alloy range (0<r<2) have been deposited by remote plasma-enhanced chemical vapor deposition (remote PECVD) under conditions in which hydrogen is incorporated predominantly in monohydride or SiH bonding configurations. We have investigated both the SiH bond-stretching and bond-bending absorption bands by infrared (ir) absorption spectroscopy as a function of r, the alloy composition. In this paper, we have focused on the bond-stretching absorption bands, and have modeled the shape of the bond-stretching band as a function of the alloy composition. There are four distinct local environments for the SiH group in the sub- oxides; these can be written as HSi-${\mathrm{Si}}_{3\mathrm{\ensuremath{-}}\mathrm{n}}$${\mathrm{O}}_{\mathrm{n}}$, for n=0--3. A sum of Gaussian functions, one for each environment, is used to synthesize the absorption in the SiH stretching band. The peak positions of these Gaussians are calculated by an induction model which includes both local and matrix (or alloy) effects; the amplitude weightings are determined from a random statistical model for the local bonding environments of the Si-O groups in the ${\mathrm{SiO}}_{\mathrm{r}}$ alloy. We find that the frequency shifts caused by changes in the matrix, and associated with different values of r, are comparable to the shifts associated with the different local environments. The combination of these effects serves to diminish the discreteness of subband features in the absorption spectrum. DA - 1989/7/15/ PY - 1989/7/15/ DO - 10.1103/physrevb.40.1795 VL - 40 IS - 3 SP - 1795-1805 SN - 0163-1829 ER - TY - JOUR TI - GROWTH OF CUBIC PHASE GALLIUM NITRIDE BY MODIFIED MOLECULAR-BEAM EPITAXY AU - PAISLEY, MJ AU - SITAR, Z AU - POSTHILL, JB AU - DAVIS, RF T2 - JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A-VACUUM SURFACES AND FILMS AB - Gallium nitride is a compound semiconductor with a wide direct band gap (3.45 eV) and a large saturated electron drift velocity. Nearly all single-crystal thin films grown to date have been wurtzite (hexagonal) structure. Cubic GaN has the potential for higher saturated electron drift velocity and somewhat lower band gap. These properties could increase its applicability for high-frequency devices (such as impact ionization avalanche transit time diodes) as well as short-wavelength light emitting diodes and semiconductor lasers. This paper reports the growth of cubic phase single-crystal thin-film GaN using a modified molecular-beam epitaxy technique. A standard effusion cell was used for gallium, but to activate nitrogen gas prior to deposition, a microwave glow discharge was used. Auger electron spectroscopy showed a nominally stoichiometric GaN film. Transmission electron microscopy with selected area diffraction indicated the crystal structure to be zinc blende. DA - 1989/// PY - 1989/// DO - 10.1116/1.575869 VL - 7 IS - 3 SP - 701-705 SN - 0734-2101 ER - TY - JOUR TI - MATERIALS SYNTHESIS BY MECHANICAL ALLOYING AU - KOCH, CC T2 - ANNUAL REVIEW OF MATERIALS SCIENCE AB - This article reviews published data on the mechanical properties of additively manufactured metallic materials. The additive manufacturing techniques utilized to generate samples covered in this review include powder bed fusion (e.g., EBM, SLM, DMLS) and ...Read More DA - 1989/// PY - 1989/// DO - 10.1146/annurev.ms.19.080189.001005 VL - 19 SP - 121-143 SN - 0084-6600 ER - TY - JOUR TI - A THEORY OF MINIMUM PLASTIC SPIN IN CRYSTAL MECHANICS AU - FUH, S AU - HAVNER, KS T2 - PROCEEDINGS OF THE ROYAL SOCIETY OF LONDON SERIES A-MATHEMATICAL AND PHYSICAL SCIENCES AB - A theory of minimum plastic spin (i. e. minimum relative rate-of-rotation of gross crystalline material and underlying atomic lattice) is proposed for the finite deformation of crystals, consistent with loading conditions and constraints. Three families of multiple-slip configurations of f. c. c. crystals are comprehensively investigated: (i) pure plane strain compression with a [100] axis of free extension; (ii) (110) loading in channel die compression; and (iii) all multiple-slip orientations in uniaxial tension. It is established that, in each case, minimum plastic spin uniquely predicts the experimentally observed behaviour. DA - 1989/3/8/ PY - 1989/3/8/ DO - 10.1098/rspa.1989.0025 VL - 422 IS - 1862 SP - 193-239 SN - 0080-4630 ER -