@article{moog_singamaneni_prater_biegalski_tsui_2018, title={Magneto-optical properties of BaTiO3/La0.76Sr0.24MnO3/BaTiO3 heterostructures}, volume={8}, ISSN={["2158-3226"]}, DOI={10.1063/1.5006458}, abstractNote={The magnetic properties of epitaxial BaTiO3/La0.76Sr0.24MnO3/BaTiO3 (BTO/LSMO/BTO) heterostructures have been studied using magneto-optic Kerr effect (MOKE) technique. Both longitudinal and polar MOKE were probed as a function of magnetic field and temperature (in the range between 80 and 320 K) for epitaxial films of BTO/LSMO/BTO and LSMO grown on TiO2-terminated SrTiO3 (001) substrates by pulsed laser deposition technique. The LSMO film without the BTO layers exhibits nearly square field-dependent MOKE hysteresis loops with low saturation fields below a bulk-like Curie temperature (TC) of ∼ 350K. In contrast, the film with the BTO layers exhibits a significantly suppressed TC of 155 K, accompanied by significantly enhanced coercive fields and perpendicular magnetic anisotropy.}, number={5}, journal={AIP ADVANCES}, author={Moog, M. and Singamaneni, S. R. and Prater, J. T. and Biegalski, M. D. and Tsui, F.}, year={2018}, month={May} }
 @article{singamaneni_prater_glavic_lauter_narayan_2018, title={Polarized neutron reflectivity studies on epitaxial BiFeO3/La0.7Sr0.3MnO3 heterostructure integrated with Si (100)}, volume={8}, ISSN={2158-3226}, url={http://dx.doi.org/10.1063/1.5006473}, DOI={10.1063/1.5006473}, abstractNote={This work reports polarized neutron reflectivity (PNR) measurements performed using the Magnetism Reflectometer at Oak Ridge National Laboratory on epitaxial BiFeO3(BFO)/La0.7Sr0.3MnO3(LSMO)/SrTiO3(STO)/MgO/TiN heterostructure deposited on Si (100) substrates. By measuring the angular dependence of neutrons reflected from the sample, PNR can provide insights on interface magnetic spin structure, chemical composition and magnetic depth profiles with a nanometer resolution. Our first analysis of nuclear scattering length density (NSLD) and magnetic scattering length density (MSLD) depth profiles measured at 4 K have successfully reproduced most of the expected features of this heterostructure, such as the NSLD for the Si, TiN, MgO, STO, LSMO layers and remanent magnetization (2.28μB/Mn) of bulk LSMO. However, the SLD of the BFO is decreased by about 30% from the expected value. When 5 V was applied across the BFO/LSMO interface, we found that the magnetic moment of the LSMO layer could be varied by about 15-20% at 6 K. Several mechanisms such as redistribution of oxygen vacancies, interface strain, charge screening and valence state change at the interface could be at play. Work is in progress to gain an improved in-depth understanding of these effects using MOKE and STEM-Z interface specific measurements.}, number={5}, journal={AIP Advances}, publisher={AIP Publishing}, author={Singamaneni, S. R. and Prater, J. T. and Glavic, A. and Lauter, V. and Narayan, J.}, year={2018}, month={May}, pages={055821} }
 @article{singamaneni_prater_glavic_lauter_narayan_2018, title={Polarized neutron reflectivity studies on epitaxial BiFeO3/La0.7Sr0.3MnO3 heterostructure integrated with Si (100)}, volume={8}, number={5}, journal={AIP Advances}, author={Singamaneni, S. R. and Prater, J. T. and Glavic, A. and Lauter, V. and Narayan, J.}, year={2018} }
 @article{singamaneni_prater_narayan_2017, title={Exchange bias in Ba0.4Sr0.6TiO3/La0.7Sr0.3MnO3 heterostructures}, volume={7}, number={5}, journal={AIP Advances}, author={Singamaneni, S. R. and Prater, J. T. and Narayan, J.}, year={2017} }
 @article{foley_singamaneni_prater_narayan_2016, title={Control of Magnetic Coercivity in epitaxial Ni/VO2/YSZ/Si(001) heterostructures by manipulation of Ni thin film growth modes}, volume={1}, ISSN={["2059-8521"]}, DOI={10.1557/adv.2016.397}, abstractNote={The control of ferromagnetic properties by external stimuli is of great interest in the electronics community. One method of producing such a control is through proximity of a ferromagnetic film with a material that has a semiconductor-to-metal transition (SMT). In order for these magnetic heterostructures to be beneficial, they must consist of high-quality, crystalline films. Epitaxial films increase the reproducibility of both devices and properties. We have investigated the trend in magnetic coercivity in epitaxial nickel films on VO_2. We show that not only does the interaction between the Ni and VO_2 change the normal coercivity trend found in Ni M-H curves with no proximity to VO_2, but that the crystalline growth mode of the Ni film also impacts the magnetic coercivity as a function of temperature.}, number={50}, journal={MRS ADVANCES}, author={Foley, Gabrielle M. and Singamaneni, Srinivasa Rao and Prater, John and Narayan, Jay}, year={2016}, pages={3409–3414} }
 @article{singamaneni_punugupati_prater_narayan_2016, title={Diamagnetism to ferromagnetism in Sr-substituted epitaxial BaTiO3 thin films}, volume={108}, number={14}, journal={Applied Physics Letters}, author={Singamaneni, S. R. and Punugupati, S. and Prater, J. T. and Narayan, J.}, year={2016} }
 @article{singamaneni_prater_narayan_2016, title={Enhanced Coercivity in BiFeO3/SrRuO3 heterostructures}, volume={1}, ISSN={["2059-8521"]}, DOI={10.1557/adv.2016.220}, abstractNote={Transition metal oxide thin film heterostructures have garnered increasing research interest in the last decade due to their multifunctional properties, such as ferromagnetism and ferroelectricity, which may be utilized in next generation device applications. Many previous works reported on the deposition of such structures on oxide substrates such as SrTiO_3, which are not compatible with CMOS applications where Si(100) is the mainstay substrate material . BiFeO_3 (BFO) is a room temperature insulating ferroelectric and antiferromagnet, a well-known multiferroic material. SrRuO_3 (SRO) is a ferromagnetic metal with the Curie temperature (T_C) of 165K. Unexpected properties emerge when these two dissimilar materials are conjoined. However, there has been no report on exploring the magnetic properties of BFO when it is in contact with SRO, and particularly when they are integrated with Si(100) substrates, which is the subject of present study. BFO/SRO thin films have been epitaxially grown on Si (100) substrates by introducing MgO/TiN epitaxial buffer layers using pulsed laser deposition. BFO thin films show room temperature ferroelectricity as observed from piezo force microscopy (PFM) measurements. The magnetic data collected from BFO thin films show typical antiferromagnetic features as expected. The T_C of SRO in all the samples studied was found be ~ 170K, close to the reported value of 165K. Interestingly, we have noticed that the coercive field of SRO layer increased from 4 kOe to 15 kOe (nearly fourfold) by reducing its thickness from 180 to 23nm, while keeping the thickness of BFO layer constant at 100nm. Pinning of Ru ions by ferroelectric domain walls in BFO, strong interfacial exchange coupling and SRO layer thickness could cause the observed enhancement in coercivity. Our near future work will address the precise underlying mechanisms in greater detail.}, number={9}, journal={MRS ADVANCES}, author={Singamaneni, Srinivasa Rao and Prater, J. T. and Narayan, J.}, year={2016}, pages={597–602} }
 @article{moatti_bayati_singamaneni_narayan_2016, title={Epitaxial integration of TiO2 with Si(100) through a novel approach of oxidation of TiN/Si(100) epitaxial heterostructure}, volume={1}, ISSN={["2059-8521"]}, DOI={10.1557/adv.2016.463}, abstractNote={In this study, we provide a novel approach to the epitaxial integration of TiO_2 with Si(100) and investigate the defect mediated ferromagnetism in TiO_2 structure. Epitaxial TiO_2 thin films were grown on a TiN/Si(100) epitaxial heterostructure through oxidation of TiN where a single crystalline rutile-TiO_2 (r-TiO_2) with a [110] out-of-plane orientation was obtained. The epitaxial relationship is determined to be TiO_2(1 $\overline 1 $ 0)||TiN(100) and TiO_2(110)||TiN(110). We rationalized this epitaxy using the domain matching epitaxy paradigm. First TiN is grown epitaxially on Si(100). Subsequently, TiN/Si(100) samples are oxidized to create r-TiO_2/TiN/Si(100) epitaxial heterostructures. The details of the mechanism behind the oxidation of single crystalline TiN to TiO_2 was investigated using atomic scale high resolution electron microscopy techniques. Defects introduced to the heterostructure during oxidation caused ferromagnetism in TiO_2 thin film which is reversible and can be tuned by controlling oxygen partial pressure. The source of magnetization is correlated with the presence of oxygen vacancy leading to introduction of two localized states; hybrid and polaron among neighboring Ti atoms, and titanium vacancy providing four holes to form molecular oxygen. We present structure property correlations and its impact on the next generation solid state devices.}, number={37}, journal={MRS ADVANCES}, author={Moatti, A. and Bayati, R. and Singamaneni, S. and Narayan, J.}, year={2016}, pages={2629–2634} }
 @article{singamaneni_prater_wu_narayan_2016, title={Ferromagnetic oxide heterostructures on silicon}, volume={6}, ISSN={["2159-6867"]}, DOI={10.1557/mrc.2016.22}, abstractNote={Heterostructures consisting of two ferromagnetic oxides La_0.7Ca_0.3MnO_3 (LCMO) and SrRuO_3 (SRO) were epitaxially grown by pulsed laser deposition onto a silicon (Si) substrate buffered by SrTiO_3 (STO)/MgO/TiN. The x-ray scans and electron-diffraction patterns reveal the epitaxial nature of all five layers. From transmission electron microscopy, the thicknesses of the LCMO and SRO layers were estimated to be -100 and -200 nm, respectively. The magnetic properties of individual SRO and LCMO layers are in good agreement with the previous studies reported for those individual layers deposited on lattice-matched substrates, such as STO. The LCMO/SRO heterostructures showed enhanced switching field (from 6008 to 7600 Oe), which may originate from the bulk part of the heterostructure. The ability to grow these multifunctional structures on Si provides a route for wafer scale integration with Si, in contrast to oxide substrates that are not suitable for CMOS integration for microelectronics and spintronics applications.}, number={3}, journal={MRS COMMUNICATIONS}, author={Singamaneni, Srinivasa Rao and Prater, J. T. and Wu, Fan and Narayan, J.}, year={2016}, month={Sep}, pages={234–240} }
 @article{singamaneni_prater_lee_misra_narayan_2016, title={Memristive behavior in BaTiO3/La0.7Sr0.3MnO3 heterostructures integrated with semiconductors}, volume={1}, ISSN={["2059-8521"]}, DOI={10.1557/adv.2016.70}, abstractNote={Ferroelectric materials such as BaTiO_3 have been studied for emerging non-volatile memory applications. However, most of the previous work has been focused on this material when it was deposited on insulting oxide substrates such as SrTiO_3. Unfortunately, this substrate is not suitable for CMOS-based microelectronics applications. This motivated us to carry out the present work. We have studied the resistive switching behavior in BaTiO_3/La_0.7Sr_0.3MnO_3 (BTO/LSMO) heterostructures integrated with semiconducting substrates Si (100) using MgO/TiN buffer layers by pulsed laser deposition. Current-Voltage (I-V) measurements were conducted on BTO (500nm)/LSMO (25nm) devices at 200K. We have observed a broad hysteresis in forward and reverse voltage sweeps which is an important property for memory applications. Secondly, the R_ON/R_OFF ratio is estimated at ~ 150, consistent with the reported numbers (30-100) in the literature. Thirdly, the device is stable at least up to 50 cycles. However, we found that hysteretic behavior was suppressed upon oxygen annealing of the device at 1 atmospheric pressure, 200^o C for 1hr, inferring the important role of oxygen vacancies in the resistive switching behavior of BTO/LSMO device. Future work will focus on investigating the correlation between ferroelectricity and resistive switching in these devices using local probe technique piezo force microscopy (PFM) technique.}, number={4}, journal={MRS ADVANCES}, author={Singamaneni, Srinivasa Rao and Prater, John and Lee, Bongmook and Misra, Veena and Narayan, Jay}, year={2016}, pages={275–280} }
 @article{nellutla_nori_singamaneni_prater_narayan_smirnov_2016, title={Multi-frequency ferromagnetic resonance investigation of nickel nanocubes encapsulated in diamagnetic magnesium oxide matrix}, volume={120}, number={22}, journal={Journal of Applied Physics}, author={Nellutla, S. and Nori, S. and Singamaneni, S. R. and Prater, J. T. and Narayan, J. and Smirnov, A. I.}, year={2016} }
 @article{moatti_bayati_singamaneni_narayan_2016, title={Thin film bi-epitaxy and transition characteristics of TiO2/TiN buffered VO2 on Si(100) substrates}, volume={1}, ISSN={["2059-8521"]}, DOI={10.1557/adv.2016.544}, abstractNote={Bi-epitaxial VO_2 thin films with [011] out-of-plane orientation were integrated with Si(100) substrates through TiO_2/TiN buffer layers. At the first step, TiN is grown epitaxially on Si(100), where a cube-on-cube epitaxy is achieved. Then, TiN was oxidized in-situ ending up having epitaxial r-TiO_2. Finally, VO_2 was deposited on top of TiO_2. The alignment across the interfaces was stablished as VO_2(011)║TiO_2(110)║TiN(100)║Si(100) and VO_2(110) /VO_2(010)║TiO_2(011)║TiN(112)║Si(112). The inter-planar spacing of VO_2(010) and TiO_2(011) equal to 2.26 and 2.50 Å, respectively. This results in a 9.78% tensile misfit strain in VO_2(010) lattice which relaxes through 9/10 alteration domains with a frequency factor of 0.5, according to the domain matching epitaxy paradigm. Also, the inter-planar spacing of VO_2(011) and TiO_2(011) equals to 3.19 and 2.50 Å, respectively. This results in a 27.6% compressive misfit strain in VO_2(011) lattice which relaxes through 3/4 alteration domains with a frequency factor of 0.57. We studied semiconductor to metal transition characteristics of VO_2/TiO_2/TiN/Si heterostructures and established a correlation between intrinsic defects and magnetic properties.}, number={37}, journal={MRS ADVANCES}, author={Moatti, Adele and Bayati, Reza and Singamaneni, Srinivasa Rao and Narayan, Jagdish}, year={2016}, pages={2635–2640} }
 @article{singamaneni_fan_prater_narayan_2015, title={Complete vertical M-H loop shift in La0.7Sr0.3MnO3/SrRuO3 thin film heterostructures}, volume={117}, number={17}, journal={Journal of Applied Physics}, author={Singamaneni, S. R. and Fan, W. and Prater, J. T. and Narayan, J.}, year={2015} }
 @article{nair_yadav_adiga_rao_tol_elizabeth_2015, title={Ferrimagnetism and magnetic phase separation in Nd1-xYxMnO3 studied by magnetization and high frequency electron paramagnetic resonance}, volume={456}, ISSN={["1873-2135"]}, DOI={10.1016/j.physb.2014.08.044}, abstractNote={Ferrimagnetism and metamagnetic features tunable by composition are observed in the magnetic response of Nd1−xYxMnO3, for x=0.1–0.5. For all values of x in the series, the compound crystallizes in orthorhombic Pbnm space group similar to NdMnO3. Magnetization studies reveal a phase transition of the Mn-sublattice below TNMn≈80K for all compositions, which, decreases up on diluting the Nd-site with Yttrium. For x=0.35, ferrimagnetism is observed. At 5 K, metamagnetic transition is observed for all compositions x<0.4. The evolution of magnetic ground states and appearance of ferrimagnetism in Nd1−xYxMnO3 can be accounted for by invoking the scenario of magnetic phase separation. The high frequency electron paramagnetic resonance measurements on x=0.4 sample, which is close to the critical composition for phase separation, revealed complex temperature dependent lineshapes clearly supporting the assumption of magnetic phase separation.}, journal={PHYSICA B-CONDENSED MATTER}, author={Nair, Harikrishnan S. and Yadav, Ruchika and Adiga, Shilpa and Rao, S. S. and Tol, Johan and Elizabeth, Suja}, year={2015}, month={Jan}, pages={108–114} }
 @article{singamaneni_prater_nori_kumar_lee_misra_narayan_2015, title={Ferroelectric and magnetic properties of multiferroic BiFeO3-La0.7Sr0.3MnO3 heterostructures integrated with Si (100)}, volume={117}, number={17}, journal={Journal of Applied Physics}, author={Singamaneni, S. R. and Prater, J. T. and Nori, S. and Kumar, D. and Lee, B. and Misra, V. and Narayan, J.}, year={2015} }
 @article{singamaneni_tol_ye_tour_2015, title={Intrinsic and extrinsic defects in a family of coal-derived graphene quantum dots}, volume={107}, DOI={10.1063/1.4936204}, abstractNote={In this letter, we report on the high frequency (239.2 and 336 GHz) electron spin resonance (ESR) studies performed on graphene quantum dots (GQDs), prepared through a wet chemistry route from three types of coal: (a) bituminous, (b) anthracite, and (c) coke; and from non-coal derived GQDs. The microwave frequency-, power-, and temperature-dependent ESR spectra coupled with computer-aided simulations reveal four distinct magnetic defect centers. In bituminous- and anthracite-derived GQDs, we have identified two of them as intrinsic carbon-centered magnetic defect centers (a broad signal of peak to peak width = 697 (10−4 T), g = 2.0023; and a narrow signal of peak to peak width = 60 (10−4 T), g = 2.003). The third defect center is Mn2+ (6S5/2, 3d5) (signal width = 61 (10−4 T), g = 2.0023, Aiso = 93(10−4 T)), and the fourth defect is identified as Cu2+ (2D5/2, 3d9) (g⊥ = 2.048 and g‖ = 2.279), previously undetected. Coke-derived and non-coal derived GQDs show Mn2+ and two-carbon related signals, and no Cu2+ signal. The extrinsic impurities most likely originate from the starting coal. Furthermore, Raman, photoluminescence, and ESR measurements detected no noticeable changes in the properties of the bituminous GQDs after one year. This study highlights the importance of employing high frequency ESR spectroscopy in identifying the (magnetic) defects, which are roadblocks for spin relaxation times of graphene-based materials. These defects would not have been possible to probe by other spin transport measurements.}, number={21}, journal={Applied Physics Letters}, author={Singamaneni, S. R. and Tol, J. and Ye, R. Q. and Tour, J. M.}, year={2015} }
 @misc{singamaneni_prater_narayan_2015, title={Magnetic exchange coupling in bilayers of two epitaxial ferromagnetic oxides}, volume={19}, ISSN={["1879-0348"]}, DOI={10.1016/j.cossms.2015.03.002}, abstractNote={Despite a decade of research effort on La0.7Sr0.3MnO3/SrRuO3 (LSMO/SRO) bilayers (BLs), a full knowledge on the magnetic properties and integration of these BLs on silicon substrate is not yet in sight. In this paper, we report on the magnetic exchange coupling observed from the above two ferromagnetic oxide thin film BLs, prepared through a novel approach, called ‘domain matching epitaxy’. LSMO (100 nm)/SRO (45 nm) and LSMO (31 nm)/SRO (45 nm) bilayers have been epitaxially integrated with Si (1 0 0). Notably, in the former sample, positive exchange bias is observed – an indication of antiferromagnetic exchange coupling and is found to be absent in the latter. Furthermore, in the former sample, the cross-over from antiferromagnetic to ferromagnetic interface exchange coupling is noticed by varying the cooling field. We have verified that this coupling is of magnetic origin, not due to electrostatic interaction by inserting a thin (∼10 nm) SrTiO3 layer between LSMO and SRO. We believe that in addition to the formation of interface domain walls, the strong interplay among Zeeman, anisotropic and exchange energies could play a dominant role. Our results would have important implications for devices comprising of magnetic exchange coupled systems.}, number={5}, journal={CURRENT OPINION IN SOLID STATE & MATERIALS SCIENCE}, author={Singamaneni, Srinivasa Rao and Prater, John T. and Narayan, Jagdish}, year={2015}, month={Oct}, pages={301–304} }
 @misc{singamaneni_narayan_prater_2015, title={Multifunctional heterostructures integrated on Si (100)}, volume={4}, number={1}, journal={Emerging Materials Research}, author={Singamaneni, S. R. and Narayan, J. and Prater, J. T.}, year={2015}, pages={50–70} }
 @article{rao_lee_prater_smirnov_narayan_2014, title={Laser annealing induced ferromagnetism in SrTiO3 single crystal}, volume={105}, number={4}, journal={Applied Physics Letters}, author={Rao, S. S. and Lee, Y. F. and Prater, J. T. and Smirnov, A. I. and Narayan, J.}, year={2014} }
 @article{singamaneni_stesmans_tol_kosynkin_tour_2014, title={Magnetic defects in chemically converted graphene nanoribbons: electron spin resonance investigation}, volume={4}, ISSN={["2158-3226"]}, DOI={10.1063/1.4870942}, abstractNote={Electronic spin transport properties of graphene nanoribbons (GNRs) are influenced by the presence of adatoms, adsorbates and edge functionalization. To improve the understanding of the factors that influence the spin properties of GNRs, local (element) spin-sensitive techniques such as electron spin resonance (ESR) spectroscopy are important for spintronics applications. Here, we present results of multi-frequency continuous wave (CW), pulse and hyperfine sublevel correlation (HYSCORE) ESR spectroscopy measurements performed on oxidatively unzipped graphene nanoribbons (GNRs), which were subsequently chemically converted (CCGNRs) with hydrazine. ESR spectra at 336 GHz reveal an isotropic ESR signal from the CCGNRs, of which the temperature dependence of its line width indicates the presence of localized unpaired electronic states. Upon functionalization of CCGNRs with 4-nitrobenzene diazonium tetrafluoroborate, the ESR signal is found to be 2 times narrower than that of pristine ribbons. NH3 adsorption/desorption on CCGNRs is shown to narrow the signal, while retaining the signal intensity and g value. The electron spin-spin relaxation process at 10 K is found to be characterized by slow (163 ns) and fast (39 ns) components. HYSCORE ESR data demonstrate the explicit presence of protons and 13C atoms. With the provided identification of intrinsic point magnetic defects such as proton and 13C has been reported, which are roadblocks to spin travel in graphene-based materials, this work could help in advancing the present fundamental understanding on the edge-spin (or magnetic)-based transport properties of CCGNRs.}, number={4}, journal={AIP ADVANCES}, author={Singamaneni, Srinivasa Rao and Stesmans, Andre and Tol, Johan and Kosynkin, D. V. and Tour, James M.}, year={2014}, month={Apr} }
 @article{singamaneni_fan_prater_narayan_2014, title={Magnetic properties of BaTiO3/La0.7Sr0.3MnO3 thin films integrated on Si(100)}, volume={116}, number={22}, journal={Journal of Applied Physics}, author={Singamaneni, S. R. and Fan, W. and Prater, J. T. and Narayan, J.}, year={2014} }
 @article{rao_prater_wu_shelton_maria_narayan_2013, title={Interface Magnetism in Epitaxial BiFeO3-La0.7Sr0.3MnO3 Heterostructures Integrated on Si(100)}, volume={13}, ISSN={["1530-6992"]}, DOI={10.1021/nl4023435}, abstractNote={We report on the heteroepitaxial growth of ferroelectric (FE)-antiferromagnetic (AFM) BiFeO3 (BFO) on ferromagnetic La0.7Sr0.3MnO3 (LSMO), integrated on Si(100) using pulsed laser deposition via the domain matching epitaxy paradigm. The BFO/LSMO films were epitaxially grown on Si(100) by introducing epitaxial layers of SrTiO3/MgO/TiN. X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, X-ray photo absorption spectroscopy, and atomic force microscopy were employed to fully characterize the samples. Furthermore, we have investigated the magnetic behavior of this five layer heterostructure, in which a d(5) system (Fe(3+)) manifested in FE-AFM BFO is epitaxially conjoined at the interface to a multivalent transition metal ion such as Mn(3+)/Mn(4+) in LSMO. The temperature- and magnetic field-dependent magnetization measurements reveal an unexpected enhancement in magnetic moment and improved magnetic hysteresis squareness originating from the BFO/LSMO interface. We observe a stronger temperature dependence of HEB when the polarity of field cooling is negative as compared to positive field cooling. We believe such an enhancement in magnetic moment and magnetic coupling is likely directly related to an electronic orbital reconstruction at the interface and complex interplay between orbital and spin degrees of freedom, similar to what has previously been reported in the literature. Future work will involve the linearly polarized X-ray absorption measurements to prove this hypothesis. This work represents a starting step toward the realization of magneto-electronic devices integrated with Si(100).}, number={12}, journal={NANO LETTERS}, author={Rao, S. S. and Prater, J. T. and Wu, Fan and Shelton, C. T. and Maria, J. -P. and Narayan, J.}, year={2013}, month={Dec}, pages={5814–5821} }