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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

Graduate Institute of Applied Physics and Department of Physics, National Taiwan University, Taipei 10617, Taiwan
Department of Electrophysics, National Chiayi University, Chiayi 60004, Taiwan
Department of Physics, National Tsing Hua University, Hsinchu 30013, Taiwan
National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan
Authors to whom correspondence should be addressed.
Nanomaterials 2019, 9(4), 554;
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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