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IR-spectroscopy of CO adsorption on mixed-terminated ZnO surfaces

Research paper by Maria Buchholz, Xiaojuan Yu, Chengwu Yang, Stefan Heißler, Alexei Nefedov, Yuemin Wang, Christof Wöll

Indexed on: 14 Mar '16Published on: 06 Jan '16Published in: Surface Science (including Surface Science Letters)



Abstract

The adsorption of CO on two different mixed-terminated, single-crystal surfaces of zinc oxide, ZnO(10<img height="12" border="0" style="vertical-align:bottom" width="8" alt="View the MathML source" title="View the MathML source" src="http://origin-ars.els-cdn.com/content/image/1-s2.0-S0039602815004392-si1.gif">1−0) and ZnO(11<img height="12" border="0" style="vertical-align:bottom" width="8" alt="View the MathML source" title="View the MathML source" src="http://origin-ars.els-cdn.com/content/image/1-s2.0-S0039602815004392-si2.gif">2−0), was investigated by employing infrared reflection absorption spectroscopy (IRRAS) using p- and s-polarized light. For both surfaces, one negative CO band was observed only for p-polarized light, indicating that CO is bound to the surface Zn2 + sites in a nearly upright geometry. In addition, we observed a substantial coverage-induced frequency shift for CO adsorption on both ZnO surfaces. For ZnO(10<img height="12" border="0" style="vertical-align:bottom" width="8" alt="View the MathML source" title="View the MathML source" src="http://origin-ars.els-cdn.com/content/image/1-s2.0-S0039602815004392-si1.gif">1−0), the ν(C-O) band shows a red shift of 16 cm− 1 when increasing the CO coverage from 0.5 ML (2185 cm− 1) to 1 ML (2169 cm− 1). On the ZnO(11<img height="12" border="0" style="vertical-align:bottom" width="8" alt="View the MathML source" title="View the MathML source" src="http://origin-ars.els-cdn.com/content/image/1-s2.0-S0039602815004392-si2.gif">2−0) surface, for isolated CO molecules, a frequency of 2192 cm− 1 was detected. The CO band shifts to 2170 cm− 1 at full monolayer. On both surfaces, the coverage-dependent frequency shift is attributed to a combination of dynamic and substrate-mediated static adsorbate–adsorbate interactions.

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