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Open AccessArticle

Microscopic Views of Atomic and Molecular Oxygen Bonding with epi Ge(001)-2 × 1 Studied by High-Resolution Synchrotron Radiation Photoemission

1
Graduate Institute of Applied Physics and Department of Physics, National Taiwan University, Taipei 10617, Taiwan
2
Department of Electrophysics, National Chiayi University, Chiayi 60004, Taiwan
3
Department of Physics, National Tsing Hua University, Hsinchu 30013, Taiwan
4
National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan
*
Authors to whom correspondence should be addressed.
Nanomaterials 2019, 9(4), 554; https://doi.org/10.3390/nano9040554
Received: 21 February 2019 / Revised: 28 March 2019 / Accepted: 30 March 2019 / Published: 4 April 2019
In this paper, we investigate the embryonic stage of oxidation of an epi Ge(001)-2 × 1 by atomic oxygen and molecular O2 via synchrotron radiation photoemission. The topmost buckled surface with the up- and down-dimer atoms, and the first subsurface layer behaves distinctly from the bulk by exhibiting surface core-level shifts in the Ge 3d core-level spectrum. The O2 molecules become dissociated upon reaching the epi Ge(001)-2 × 1 surface. One of the O atoms removes the up-dimer atom and the other bonds with the underneath Ge atom in the subsurface layer. Atomic oxygen preferentially adsorbed on the epi Ge(001)-2 ×1 in between the up-dimer atoms and the underneath subsurface atoms, without affecting the down-dimer atoms. The electronic environment of the O-affiliated Ge up-dimer atoms becomes similar to that of the down-dimer atoms. They both exhibit an enrichment in charge, where the subsurface of the Ge layer is maintained in a charge-deficient state. The dipole moment that was originally generated in the buckled reconstruction no longer exists, thereby resulting in a decrease in the ionization potential. The down-dimer Ge atoms and the back-bonded subsurface atoms remain inert to atomic O and molecular O2, which might account for the low reliability in the Ge-related metal-oxide-semiconductor (MOS) devices. View Full-Text
Keywords: Ge(001)-2 × 1; oxidation; synchrotron radiation photoemission Ge(001)-2 × 1; oxidation; synchrotron radiation photoemission
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MDPI and ACS Style

Cheng, Y.-T.; Wan, H.-W.; Cheng, C.-P.; Kwo, J.; Hong, M.; Pi, T.-W. Microscopic Views of Atomic and Molecular Oxygen Bonding with epi Ge(001)-2 × 1 Studied by High-Resolution Synchrotron Radiation Photoemission. Nanomaterials 2019, 9, 554.

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