Oxidation of a Tb2O3(111) Thin Film on Pt(111) by Gas-Phase Oxygen Atoms

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• 作者：William Cartas ; Rahul Rai ; Ajinkya Sathe ; Andreas Schaefer ; Jason F. Weaver
• 刊名：Journal of Physical Chemistry C
• 出版年：2014
• 出版时间：September 11, 2014
• 年：2014
• 卷：118
• 期：36
• 页码：20916-20926
• 全文大小：524K
• ISSN：1932-7455

文摘

We used X-ray photoelectron spectroscopy and temperature-programmed desorption (TPD) to investigate the oxidation of Tb₂O₃(111) films on Pt(111) by gaseous oxygen atoms. We find that plasma-generated O atom beams are highly effective at completely oxidizing the Tb₂O₃ films to TbO₂ at 300 K, for film thicknesses up to at least seven layers. Heating to 鈭?000 K in ultrahigh vacuum restores the films to the Tb₂O₃ stoichiometry and produces two distinct O₂ TPD features centered at 鈭?85 and 660 K, which we attribute to the release of lattice oxygen from the surface vs bulk trilayers, respectively. We also find that the adsorption of plasma-activated oxygen at 90 K produces a weakly bound state of oxygen on the TbO_x films which desorbs between 鈭?00 and 270 K during TPD. This oxygen state is consistent with a form of chemisorbed oxygen, possibly an atomic and/or molecular species that bonds on-top of Tb atoms at the surface. TPD experiments of the oxidation of Tb₂¹⁸O₃ films by ¹⁶O atom beams demonstrate that oxygen desorption below about 500 K originates almost entirely from the oxygen that is 鈥渁dded鈥?to the Tb₂O₃ film and that all isotopic combinations of O₂ desorb from the bulk above 500 K, though the relative amount of ¹⁸O to ¹⁶O which desorbs above 500 K is lower than that determined from the isotopic composition of the oxidized TbO_x films. These results support the idea that oxygen desorption below 500 K originates from oxygen species that are localized at the surface and further suggest that the oxide structure only partially accommodates oxygen atoms that incorporate into lattice sites at 300 K.