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1. Al Composition Dependence of Band Offsets for SiO ₂ on α-(Al _x Ga _1−x ) ₂ O ₃

   https://doi.org/10.1149/2162-8777/ac39a8  

   Xia, Xinyi; Fares, Chaker; Ren, Fan; Hassa, Anna; von Wenckstern, Holger; Grundmann, Marius; Pearton, S. J. (November 2021, ECS Journal of Solid State Science and Technology)

   Valence band offsets for SiO 2 deposited by Atomic Layer Deposition on α -(Al x Ga 1-x ) 2 O 3 alloys with x = 0.26–0.74 were measured by X-ray Photoelectron Spectroscopy. The samples were grown with a continuous composition spread to enable investigations of the band alignment as a function of the alloy composition. From measurement of the core levels in the alloys, the bandgaps were determined to range from 5.8 eV (x = 0.26) to 7 eV (x = 0.74). These are consistent with previous measurements by transmission spectroscopy. The valence band offsets of SiO 2 with these alloys of different composition were, respectively, were −1.2 eV for x = 0.26, −0.2 eV for x = 0.42, 0.2 eV for x = 0.58 and 0.4 eV for x = 0.74. All of these band offsets are too low for most device applications. Given the bandgap of the SiO 2 was 8.7 eV, this led to conduction band offsets of 4.1 eV (x = 0.26) to 1.3 eV (x = 0.74). The band alignments were of the desired nested configuration for x > 0.5, but at lower Al contents the conduction band offsets were negative, with a staggered band alignment. This shows the challenge of finding appropriate dielectrics for this ultra-wide bandgap semiconductor system. 

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2. Distinct Nucleation and Growth Kinetics of Amorphous SrTiO ₃ on (001) SrTiO ₃ and SiO ₂ /Si: A Step toward New Architectures

   https://doi.org/10.1021/acsami.7b12978  

   Chen, Yajin; Yusuf, M. Humed; Guan, Yingxin; Jacobson, RB; Lagally, Max G.; Babcock, Susan E.; Kuech, Thomas F.; Evans, Paul G. (November 2017, ACS Applied Materials & Interfaces)
3. Stability of the Y ₂ O ₃ –SiO ₂ system in high‐temperature, high‐velocity water vapor

   https://doi.org/10.1111/jace.16915  

   Parker, Cory G; Opila, Elizabeth J (April 2020, Journal of the American Ceramic Society)

   Abstract High‐temperature, high‐velocity water vapor (steam‐jet) exposures were conducted on Y₂O₃, Y₂SiO₅, Y₂Si₂O₇, and SiO₂for 60 hours at 1400°C. Volatility of Y₂O₃was not observed. Phase‐pure Y₂SiO₅exhibited SiO₂loss forming Y₂O₃and porosity. A mixed porous and dense Y₂SiO₅layer formed on the surface of Y₂Si₂O₇due to SiO₂depletion. The mechanisms and kinetics of the reaction between SiO₂and H₂O(g) to form Si(OH)₄(g) from Y₂SiO₅, Y₂Si₂O₇, and SiO₂are discussed. 

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4. Annealing Effects on the Band Alignment of ALD SiO ₂ on (In _x Ga _1−x ) ₂ O ₃ for x = 0.25–0.74

   https://doi.org/10.1149/2162-8777/ab8364  

   Fares, Chaker; Xian, Minghan; Smith, David J.; McCartney, M. R.; Kneiß, Max; von Wenckstern, Holger; Grundmann, Marius; Tadjer, Marko; Ren, Fan; Pearton, S. J. (April 2020, ECS Journal of Solid State Science and Technology)

   The band alignment of Atomic Layer Deposited SiO₂on (In_xGa_1−x)₂O₃at varying indium concentrations is reported before and after annealing at 450 °C and 600 °C to simulate potential processing steps during device fabrication and to determine the thermal stability of MOS structures in high-temperature applications. At all indium concentrations studied, the valence band offsets (VBO) showed a nearly constant decrease as a result of 450 °C annealing. The decrease in VBO was −0.35 eV for (In_0.25Ga_0.75)₂O₃, −0.45 eV for (In_0.42Ga_0.58)₂O₃, −0.40 eV for (In_0.60Ga_0.40)₂O₃, and −0.35 eV (In_0.74Ga_0.26)₂O₃for 450 °C annealing. After annealing at 600 °C, the band alignment remained stable, with <0.1 eV changes for all structures examined, compared to the offsets after the 450 °C anneal. The band offset shifts after annealing are likely due to changes in bonding at the heterointerface. Even after annealing up to 600 °C, the band alignment remains type I (nested gap) for all indium compositions of (In_xGa_1−x)₂O₃studied. 

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5. The effect of strong metal–support interaction (SMSI) on Pt–Ti/SiO ₂ and Pt–Nb/SiO ₂ catalysts for propane dehydrogenation

   https://doi.org/10.1039/d0cy00897d  

   Zhu Chen, Johnny; Gao, Junxian; Probus, Paige R.; Liu, Wei; Wu, Xianli; Wegener, Evan C.; Kropf, A. Jeremy; Zemlyanov, Dmitry; Zhang, Guanghui; Yang, Xin; et al (September 2020, Catalysis Science & Technology)

   null (Ed.)

   In this study, we show how strong metal–support interaction (SMSI) oxides in Pt–Nb/SiO 2 and Pt–Ti/SiO 2 affect the electronic, geometric and catalytic properties for propane dehydrogenation. Transmission electron microscopy (TEM), CO chemisorption, and decrease in the catalytic rates per gram Pt confirm that the Pt nanoparticles were partially covered by the SMSI oxides. X-ray absorption near edge structure (XANES), in situ X-ray photoelectron spectroscopy (XPS), and resonant inelastic X-ray scattering (RIXS) showed little change in the energy of Pt valence orbitals upon interaction with SMSI oxides. The catalytic activity per mol of Pt for ethylene hydrogenation and propane dehydrogenation was lower due to fewer exposed Pt sites, while turnover rates were similar. The SMSI oxides, however, significantly increase the propylene selectivity for the latter reaction compared to Pt/SiO 2 . In the SMSI catalysts, the higher olefin selectivity is suggested to be due to the smaller exposed Pt ensemble sites, which result in suppression of the alkane hydrogenolysis reaction; while the exposed atoms remain active for dehydrogenation. 

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