@article{kumar_liu_li_iyer_reynolds_2020, title={Doping Dependent Magnetic Behavior in MBE Grown GaAs1-xSbx Nanowires}, volume={10}, ISSN={["2045-2322"]}, DOI={10.1038/s41598-020-65805-4}, abstractNote={AbstractIntrinsic and Te-doped GaAsSb nanowires with diameters ~100–120 nm were grown on a p-type Si(111) substrate by molecular beam epitaxy (MBE). Detailed magnetic, current/voltage and low-energy electron energy loss spectroscopy measurements were performed to investigate the effect of Te-doping. While intrinsic nanowires are diamagnetic over the temperature range 5–300 K, the Te-doped nanowires exhibit ferromagnetic behavior with the easy axis of magnetism perpendicular to the longitudinal axis of the nanowire. The temperature dependence of coercivity was analyzed and shown to be in agreement with a thermal activation model from 50–350 K but reveal more complex behavior in the low temperature regime. The EELS data show that Te doping introduced a high density of states (DOS) in the nanowire above the Fermi level in close proximity to the conduction band. The plausible origin of ferromagnetism in these Te-doped GaAsSb nanowires is discussed on the basis of d0 ferromagnetism, spin ordering of the Te dopants and the surface-state-induced magnetic ordering.}, number={1}, journal={SCIENTIFIC REPORTS}, author={Kumar, Raj and Liu, Yang and Li, Jia and Iyer, Shanthi and Reynolds, Lewis}, year={2020}, month={Jun} }
 @article{akouala_kumar_punugupati_reynolds_reynolds_mily_maria_narayan_hunte_2019, title={Planar Hall effect and anisotropic magnetoresistance in semiconducting and conducting oxide thin films}, volume={125}, ISSN={0947-8396 1432-0630}, url={http://dx.doi.org/10.1007/S00339-019-2592-Y}, DOI={10.1007/s00339-019-2592-y}, number={5}, journal={Applied Physics A}, publisher={Springer Science and Business Media LLC}, author={Akouala, Christer R. and Kumar, Raj and Punugupati, Sandhyarani and Reynolds, C. Lewis and Reynolds, Judith G. and Mily, Edward J. and Maria, Jon-Paul and Narayan, Jagdish and Hunte, Frank}, year={2019}, month={Apr} }
 @article{li_zhang_qiao_yu_peterson_zafar_kumar_curtarolo_hunte_shannon_et al._2016, title={All The Catalytic Active Sites of MoS2 for Hydrogen Evolution}, volume={138}, ISSN={0002-7863 1520-5126}, url={http://dx.doi.org/10.1021/jacs.6b05940}, DOI={10.1021/jacs.6b05940}, abstractNote={MoS2 presents a promising low-cost catalyst for the hydrogen evolution reaction (HER), but the understanding about its active sites has remained limited. Here we present an unambiguous study of the catalytic activities of all possible reaction sites of MoS2, including edge sites, sulfur vacancies, and grain boundaries. We demonstrate that, in addition to the well-known catalytically active edge sites, sulfur vacancies provide another major active site for the HER, while the catalytic activity of grain boundaries is much weaker. The intrinsic turnover frequencies (Tafel slopes) of the edge sites, sulfur vacancies, and grain boundaries are estimated to be 7.5 s-1 (65-75 mV/dec), 3.2 s-1 (65-85 mV/dec), and 0.1 s-1 (120-160 mV/dec), respectively. We also demonstrate that the catalytic activity of sulfur vacancies strongly depends on the density of the vacancies and the local crystalline structure in proximity to the vacancies. Unlike edge sites, whose catalytic activity linearly depends on the length, sulfur vacancies show optimal catalytic activities when the vacancy density is in the range of 7-10%, and the number of sulfur vacancies in high crystalline quality MoS2 is higher than that in low crystalline quality MoS2, which may be related with the proximity of different local crystalline structures to the vacancies.}, number={51}, journal={Journal of the American Chemical Society}, publisher={American Chemical Society (ACS)}, author={Li, Guoqing and Zhang, Du and Qiao, Qiao and Yu, Yifei and Peterson, David and Zafar, Abdullah and Kumar, Raj and Curtarolo, Stefano and Hunte, Frank and Shannon, Steve and et al.}, year={2016}, month={Dec}, pages={16632–16638} }
 @article{punugupati_kumar_nori_hunte_narayan_2016, title={Structural, magnetic and magnetotransport properties of bi-epitaxial La0.7Sr0.3MnO3 (110) thin films integrated on Si (001)}, volume={106}, ISSN={["1873-2453"]}, DOI={10.1016/j.actamat.2015.12.054}, abstractNote={We report the growth of bi-epitaxial La0.7Sr0.3MnO3 (110) thin films on Si (001) substrate with cubic yttria stabilized zirconia (c-YSZ)/SrTiO3 (STO) buffer layers by pulsed laser deposition. The La0.7Sr0.3MnO3 and STO thin films were grown with a single [110] out-of-plane orientation and with two in-plane domain variants, which is confirmed by XRD and detailed TEM studies. The growth of STO on c-YSZ can be explained by the paradigm of domain matching epitaxy. The epitaxial relationship between STO and c-YSZ can be written as [110] (001) c-YSZ ‖ [1¯11¯] (110) STO (or) [110] (001) c-YSZ ‖ [1¯12¯] (110) STO. The La0.7Sr0.3MnO3 thin films are ferromagnetic with Curie temperature 324 K and showed metal to insulator transition at 285 K. The La0.7Sr0.3MnO3 thin films showed hysteresis loops in magnetoresistance when magnetic field is applied along both in-plane (110) and out-of-plane [110] directions. The highest magnetoresistance obtained in this study is −32% at 50 K and 50 kOe for in-plane configuration, whereas the room-temperature magnetoresistance is −4% at 10 kOe and −17% at 50 kOe. The hysteresis in the magnetoresistance and the controlled domain boundaries in bi-epitaxial La0.7Sr0.3MnO3 films integrated on Si can offer significant advantages over the polycrystalline counterparts.}, journal={ACTA MATERIALIA}, author={Punugupati, Sandhyarani and Kumar, Raj and Nori, Sudhakar and Hunte, Frank and Narayan, Jagdish}, year={2016}, month={Mar}, pages={40–47} }
 @article{kumar_brom_redwing_hunte_2015, title={Magnetotransport phenomena in Bi2Se3 thin film topological insulators grown by hybrid physical chemical vapor deposition}, volume={117}, ISSN={["1089-7550"]}, DOI={10.1063/1.4907802}, abstractNote={Intrinsic defects in Bi2Se3 topological insulators tend to produce a high carrier concentration and current leakage through the bulk material. Bi2Se3 thin films were grown by hybrid physical chemical vapor deposition on (0001) Al2O3 substrates with high Se vapor pressure to reduce the occurrence of Se vacancies as the main type of defect. Consequently, the carrier concentration was reduced to ∼5.75 × 1018 cm−3 comparable to reported carrier concentration in Bi2Se3 thin films. Magnetotransport measurements were performed on the films and the data were analyzed for weak anti-localization using the Hikami-Larkin-Nagaoka model. The estimated α and lϕ values showed good agreement with the symplectic case of 2-D transport of topological surface states in the quantum diffusion regime. The temperature and angular dependence of magnetoresistance indicate a large contribution of the 2-D surface carriers to overall transport properties of Bi2Se3 thin film.}, number={6}, journal={JOURNAL OF APPLIED PHYSICS}, author={Kumar, Raj and Brom, Joseph E. and Redwing, Joan M. and Hunte, Frank}, year={2015}, month={Feb} }
 @article{lee_kumar_hunte_narayan_schwartz_2015, title={Microstructure and transport properties of epitaxial topological insulator Bi2Se3 thin films grown on MgO (100), Cr2O3 (0001), and Al2O3 (0001) templates}, volume={118}, number={12}, journal={Journal of Applied Physics}, author={Lee, Y. F. and Kumar, R. and Hunte, F. and Narayan, J. and Schwartz, J.}, year={2015} }
 @article{wang_hewitt_kumar_boltersdorf_guan_hunte_maggard_brom_redwing_dougherty_2014, title={Molecular Doping Control at a Topological Insulator Surface: F-4-TCNQ on Bi2Se3}, volume={118}, ISSN={["1932-7447"]}, DOI={10.1021/jp412690h}, abstractNote={Recent electrical measurements have accessed transport in the topological surface state band of thin exfoliated samples of Bi2Se3 by removing the bulk n-type doping by contact with thin films of the molecular acceptor F4-TCNQ. Here we report on the film growth and interfacial electronic characterization of F4-TCNQ grown on Bi2Se3. Atomic force microscopy shows wetting layer formation followed by 3D island growth. X-ray photoelectron spectroscopy is consistent with this picture and also shows that charge transferred to the molecular layer is localized on nitrogen atoms. Ultraviolet photoelectron spectroscopy shows a work function increase and an upward shift of the valence band edge that suggest significant reduction in carrier density at the Bi2Se3 surface.}, number={27}, journal={JOURNAL OF PHYSICAL CHEMISTRY C}, author={Wang, J. and Hewitt, A. S. and Kumar, R. and Boltersdorf, J. and Guan, T. and Hunte, F. and Maggard, P. A. and Brom, J. E. and Redwing, J. M. and Dougherty, D. B.}, year={2014}, month={Jul}, pages={14860–14865} }
 @article{lee_wu_kumar_hunte_schwartz_narayan_2013, title={Epitaxial integration of dilute magnetic semiconductor Sr3SnO with Si (001)}, volume={103}, number={11}, journal={Applied Physics Letters}, author={Lee, Y. F. and Wu, F. and Kumar, R. and Hunte, F. and Schwartz, J. and Narayan, J.}, year={2013} }
 @article{kajbafvala_nachtrab_kumar_hunte_wong_schwartz_2013, title={High strength oxide dispersion strengthened silver aluminum alloys optimized for Bi2Sr2CaCu2O8+x round wire}, volume={26}, ISSN={["1361-6668"]}, DOI={10.1088/0953-2048/26/12/125012}, abstractNote={High strength dispersion strengthened (DS) Ag/Al alloys with various Al content are studied as candidates for sheathing Bi2Sr2CaCu2O8+x (Bi2212) wire. The Ag/Al alloys are fabricated by powder metallurgy and internally oxidized in pure oxygen. The time and temperature of the internal oxidation heat treatment is varied to maximize the strength after undergoing the Bi2212 partial melt process (PMP). Vickers micro-hardness number (HVN), room temperature tensile behavior, optical and scanning electron microscopy, ion channeling contrast imaging using a focused ion beam and electrical resistivity measurements are used to characterize the alloys. An Ag/0.2wt%Mg (Ag/Mg) alloy is used for comparison. Results show that internal oxidation at 650–700  ° C for 4 h produces the highest HVN for the DS Ag/Al alloy; when oxidized at 675 ° C for 4 h the HVN, yield strength and tensile strength of the DS Ag/Al are 50% higher than the corresponding values of Ag/Mg. Microstructural observations show that Al2O3 precipitates play the main role in strengthening the DS Ag/Al alloy. The alloy retains its fine grain structure and strength after PMP heat treatment.}, number={12}, journal={SUPERCONDUCTOR SCIENCE & TECHNOLOGY}, author={Kajbafvala, Amir and Nachtrab, William and Kumar, Raj and Hunte, Frank and Wong, Terence and Schwartz, Justin}, year={2013}, month={Dec} }