Browsing by Author "Santosh, KC"
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Item Electrode-Electrolyte Interface for Solid State Li-Ion Batteries: Point Defects and Mechanical StrainSantosh, KC; Longo, Roberto C.; Xiong, Ka; Cho, Kyeongjae; 0000-0003-2698-7774 (Cho, K)In this work, we present an ab-initio investigation of point defects in solid electrolyte γ-Li₃PO₄ and in negative electrode-electrolyte interface (Li/γ-Li₃PO₄). Our results on Li defects on γ-Li₃PO₄ exhibit that Li interstitial defects dominate over vacancy defects, and that Li vacancy-interstitial pair defect formation energy in-the-interface is comparable to the sum of-Li vacancy defect in the electrode and Li ion interstitial defects in the electrolyte region. Our study reveals that the high Li ion defect formation energy is the determining factor for the low ionic conductivity across Li metal/electrolyte interface. Moreover, in a realistic interface, the mechanical strain at the interface increases with the concentration of the impurities produced as a result of the cycling of the battery or due to surface impurities, also affecting the electrostatic potential and charge distribution. Thus, the study of the Li metal/electrolyte interface provides information on the defect formation and mechanical stability and, hence, it helps to understand the realistic modeling of the interface-as a way to-improve the ionic conductivity and stability of future solid state Li-ion batteries.Item In Situ Study of E-Beam Al And Hf Metal Deposition on Native Oxide InP (100)Dong, Hong; Santosh, KC; Azcatl, Angelica; Cabrera, Wilfredo; Qin, Xiaoye; Brennan, Barry; Zhernokletov, Dmitry; Cho, Kyeongjie; Wallace, Robert M.The interfacial chemistry of thin Al (∼3 nm) and Hf (∼2 nm) metal films deposited by electron beam (e-beam) evaporation on native oxide InP (100) samples at room temperature and after annealing has been studied by in situ angle resolved X-ray photoelectron spectroscopy and low energy ion scattering spectroscopy. The In-oxides are completely scavenged forming In-In/In-(Al/Hf) bonding after Al and Hf metal deposition. The P-oxide concentration is significantly decreased, and the P-oxide chemical states have been changed to more P-rich oxides upon metal deposition. Indium diffusion through these metals before and after annealing at 250 °C has also been characterized. First principles calculation shows that In has lower surface formation energy compared with Al and Hf metals, which is consistent with the observed indium diffusion behavior.Item In Situ Study of the Role of Substrate Temperature during Atomic Layer Deposition of HfO2 on InP(2013-10-16) Dong, Hong; Santosh, KC; Qin, Xiaoye; Brennan, Barry; McDonnell, Steven; Zhernokletov, Dmitry; Hinkle, Christopher L.; Kim, Jiyoung; Cho, Kyeongjie; Wallace, Robert M.; 70133685 (Kim, J)The dependence of the "self cleaning" effect of the substrate oxides on substrate temperature during atomic layer deposition (ALD) of HfO₂ on various chemically treated and native oxide InP (100) substrates is investigated using in situ X-ray photoelectron spectroscopy. The removal of In-oxide is found to be more efficient at higher ALD temperatures. The P oxidation states on native oxide and acid etched samples are seen to change, with the total P-oxide concentration remaining constant, after 10 cycles of ALD HfO₂ at different temperatures. An (NH₄)₂ S treatment is seen to effectively remove native oxides and passivate the InP surfaces independent of substrate temperature studied (200°C, 250°C and 300°C) before and after the ALD process. Density functional theory modeling provides insight into the mechanism of the changes in the P-oxide chemical states.