@article{devkota_parakh_ramaswamy_kuchoor_penn_reynolds_iyer_2022, title={A Study on the Effects of Gallium Droplet Consumption and Post Growth Annealing on Te-Doped GaAs Nanowire Properties Grown by Self-Catalyzed Molecular Beam Epitaxy}, volume={12}, ISSN={["2073-4344"]}, DOI={10.3390/catal12050451}, abstractNote={In this work, the effects of arsenic (As) flux used during gallium (Ga) seed droplet consumption and the post-growth annealing on the optical, electrical, and microstructural properties of self-catalyzed molecular beam epitaxially grown tellurium (Te)-doped GaAs nanowires (NWs) have been investigated using a variety of characterization techniques. NWs using the same amount of As flux for growth of the seed droplet consumption demonstrated reduced density of stacking faults at the NW tip, with four-fold enhancement in the 4K photoluminescence (PL) intensity and increased single nanowire photocurrent over their higher As flux droplet consumption counterparts. Post-growth annealed NWs exhibited an additional low-energy PL peak at 1.31 eV that significantly reduced the overall PL intensity. The origin of this lower energy peak is assigned to a photocarrier transition from the conduction band to the annealing assisted Te-induced complex acceptor state (TeAsVGa−). In addition, post-growth annealing demonstrated a detrimental impact on the electrical properties of the Te-doped GaAs NWs, as revealed by suppressed single nanowire (SNW) and ensemble NW photocurrent, with a consequent enhanced low-frequency noise level compared to as-grown doped NWs. This work demonstrates that each parameter in the growth space must be carefully examined to successfully grow self-catalyzed Te-doped NWs of high quality and is not a simple extension of the growth of corresponding intrinsic NWs.}, number={5}, journal={CATALYSTS}, author={Devkota, Shisir and Parakh, Mehul and Ramaswamy, Priyanka and Kuchoor, Hirandeep and Penn, Aubrey and Reynolds, Lewis and Iyer, Shanthi}, year={2022}, month={May} }
 @article{zhang_penn_wysocki_zhang_loosdrecht_kornblum_lebeau_lindfors-vrejoiu_kumah_2022, title={Thickness and temperature dependence of the atomic-scale structure of SrRuO3 thin films}, volume={10}, ISSN={["2166-532X"]}, url={https://doi.org/10.1063/5.0087791}, DOI={10.1063/5.0087791}, abstractNote={The temperature-dependent layer-resolved structure of 3 to 44 unit cell thick SrRuO3 (SRO) films grown on Nb-doped SrTiO3 substrates is investigated using a combination of high-resolution synchrotron x-ray diffraction and high-resolution electron microscopy to understand the role that structural distortions play in suppressing ferromagnetism in ultra-thin SRO films. The oxygen octahedral tilts and rotations and Sr displacements characteristic of the bulk orthorhombic phase are found to be strongly dependent on temperature, the film thickness, and the distance away from the film–substrate interface. For thicknesses, t, above the critical thickness for ferromagnetism (t > 3 uc), the orthorhombic distortions decrease with increasing temperature above TC. Below TC, the structure of the films remains constant due to the magneto-structural coupling observed in bulk SRO. The orthorhombic distortions are found to be suppressed in the 2–3 interfacial layers due to structural coupling with the SrTiO3 substrate and correlate with the critical thickness for ferromagnetism in uncapped SRO films.}, number={5}, journal={APL MATERIALS}, author={Zhang, Xuanyi and Penn, Aubrey N. and Wysocki, Lena and Zhang, Zhan and Loosdrecht, Paul H. M. and Kornblum, Lior and LeBeau, James M. and Lindfors-Vrejoiu, Ionela and Kumah, Divine P.}, year={2022}, month={May} }
 @article{chrysler_gabel_lee_penn_matthews_kepaptsoglou_ramasse_paudel_sah_grassi_et al._2021, title={Tuning band alignment at a semiconductor-crystalline oxide heterojunction via electrostatic modulation of the interfacial dipole}, volume={5}, ISSN={["2475-9953"]}, DOI={10.1103/PhysRevMaterials.5.104603}, abstractNote={We demonstrate that the interfacial dipole associated with bonding across the SrTiO3/Si heterojunction can be tuned through space charge, thereby enabling the band alignment to be altered via doping. Oxygen impurities in Si act as donors that create space charge by transferring electrons across the interface into SrTiO3. The space charge induces an electric field that modifies the interfacial dipole, thereby tuning the band alignment from type-II to type-III. The transferred charge, resulting in built-in electric fields, and change in band alignment are manifested in electrical transport and hard x-ray photoelectron spectroscopy measurements. Ab initio models reveal the interplay between polarization and band offsets. We find that band offsets can be tuned by modulating the density of space charge across the interface. Functionalizing the interface dipole to enable electrostatic altering of band alignment opens new pathways to realize novel behavior in semiconducting heterojunctions.}, number={10}, journal={PHYSICAL REVIEW MATERIALS}, author={Chrysler, M. and Gabel, J. and Lee, T-L and Penn, A. N. and Matthews, B. E. and Kepaptsoglou, D. M. and Ramasse, Q. M. and Paudel, J. R. and Sah, R. K. and Grassi, J. D. and et al.}, year={2021}, month={Oct} }
 @article{devkota_parakh_johnson_ramaswamy_lowe_penn_reynolds_iyer_2020, title={A study of n-doping in self-catalyzed GaAsSb nanowires using GaTe dopant source and ensemble nanowire near-infrared photodetector}, volume={31}, ISSN={["1361-6528"]}, DOI={10.1088/1361-6528/abb506}, abstractNote={Abstract}, number={50}, journal={NANOTECHNOLOGY}, author={Devkota, Shisir and Parakh, Mehul and Johnson, Sean and Ramaswamy, Priyanka and Lowe, Michael and Penn, Aubrey and Reynolds, Lew and Iyer, Shanthi}, year={2020}, month={Dec} }
 @article{pokharel_ramaswamy_devkota_parakh_dawkins_penn_cabral_reynolds_iyer_2020, title={Epitaxial High-Yield Intrinsic and Te-Doped Dilute Nitride GaAsSbN Nanowire Heterostructure and Ensemble Photodetector Application}, volume={2}, ISSN={["2637-6113"]}, DOI={10.1021/acsaelm.0c00450}, abstractNote={Band gap engineering of GaAsSbN nanowires (NWs) grown by Ga-assisted molecular beam epitaxy and demonstration of a Te-doped axial GaAsSbN NW-based Schottky barrier photodetector on p-Si (111) in th...}, number={9}, journal={ACS APPLIED ELECTRONIC MATERIALS}, author={Pokharel, Rabin and Ramaswamy, Priyanka and Devkota, Shisir and Parakh, Mehul and Dawkins, Kendall and Penn, Aubrey and Cabral, Matthew and Reynolds, Lewis and Iyer, Shanthi}, year={2020}, month={Sep}, pages={2730–2738} }
 @article{chen_hauwiller_kumar_penn_lebeau_2020, title={Expanding the Dimensions of a Small, Two-Dimensional Diffraction Detector}, volume={26}, ISSN={["1435-8115"]}, DOI={10.1017/S1431927620024277}, abstractNote={Abstract}, number={5}, journal={MICROSCOPY AND MICROANALYSIS}, author={Chen, Xi and Hauwiller, Matthew R. and Kumar, Abinash and Penn, Aubrey N. and LeBeau, James M.}, year={2020}, month={Oct}, pages={938–943} }
 @article{nalamati_devkota_li_lavelle_huet_snyder_penn_garcia_reynolds_iyer_2020, title={Hybrid GaAsSb/GaAs Heterostructure Core-Shell Nanowire/Graphene and Photodetector Applications}, volume={2}, ISBN={2637-6113}, DOI={10.1021/acsaelm.0c00433}, abstractNote={We report the growth of vertical, high-quality GaAs0.9Sb0.1 nanowires (NWs) with improved density on oxygen (O2) plasma-treated monolayer graphene/SiO2/p-Si(111) by self-catalyzed molecular beam ep...}, number={10}, journal={ACS APPLIED ELECTRONIC MATERIALS}, author={Nalamati, Surya and Devkota, Shisir and Li, Jia and Lavelle, Robert and Huet, Benjamin and Snyder, David and Penn, Aubrey and Garcia, Roberto and Reynolds, Lewis, Jr. and Iyer, Shanthi}, year={2020}, pages={3109–3120} }
 @article{koohfar_georgescu_penn_lebeau_arenholz_kumah_2019, title={Confinement of magnetism in atomically thin La0.7Sr0.3CrO3/La0.7Sr0.3MnO3 heterostructures}, volume={4}, ISSN={2397-4648}, url={http://dx.doi.org/10.1038/s41535-019-0164-1}, DOI={10.1038/s41535-019-0164-1}, abstractNote={Abstract}, number={1}, journal={npj Quantum Materials}, publisher={Springer Science and Business Media LLC}, author={Koohfar, Sanaz and Georgescu, Alexandru B. and Penn, Aubrey N. and LeBeau, James M. and Arenholz, Elke and Kumah, Divine P.}, year={2019}, month={May} }
 @article{trappen_grutter_huang_penn_mottaghi_yousefi_haertter_kumari_lebeau_kirby_et al._2019, title={Effect of oxygen stoichiometry on the magnetization profiles and negative magnetization in LSMO thin films}, volume={126}, ISSN={["1089-7550"]}, DOI={10.1063/1.5111858}, abstractNote={The depth-dependent magnetization in thin film oxygen stoichiometric and oxygen-deficient La0.7Sr0.3MnO3 is investigated by using polarized neutron reflectivity and DC bulk magnetometry. The polarized neutron reflectivity results reveal that the stoichiometric sample shows enhanced interfacial magnetization relative to the rest of the film. The oxygen-deficient sample exhibits a reduced average magnetization from the optimized recipe. Both films show regions of suppressed magnetization at the surface regardless of the growth pressure. The oxygen stoichiometric film does not show an interfacial dead layer, whereas the oxygen-deficient film exhibits a dead layer whose thickness changes with temperature. At a low applied field, we observe striking differences in the depth dependence of the magnetic ordering, with the oxygen-deficient film exhibiting exchange spring behavior, while the stoichiometric film shows a constant magnetization direction across the film. These results suggest that the incorporation of oxygen vacancies during growth leads to an accumulation of vacancies at the interface, which is enhanced at higher temperature due to increased oxygen mobility, creating a region of reduced magnetism that couples to the rest of the film. These results offer insight into the complex behavior and role of oxygen vacancies in the magnetism of these systems. Additionally, the study reveals further details of the negative magnetization in La0.7Sr0.3MnO3 reported in previous studies, which are discussed here.}, number={10}, journal={JOURNAL OF APPLIED PHYSICS}, author={Trappen, Robbyn and Grutter, Alexander J. and Huang, Chih-Yeh and Penn, Aubrey and Mottaghi, Navid and Yousefi, Saeed and Haertter, Allison and Kumari, Shalini and LeBeau, James and Kirby, Brian J. and et al.}, year={2019}, month={Sep} }