Hydrogen superstructures on Co nanoislands and Cu(111)

SURFACE SCIENCE

卷:602

Article

Sicot, M.¹ 

[1] Eindhoven Univ Technol, Dept Appl Phys, Ctr Nanomat, NL-5600 MB Eindhoven, Netherlands

关键词: Scanning tunneling microscopy;    Chemisorption;    Physisorption;    Surface structure;    Cobalt;    Copper;    Hygrogen atom;    Hydrogen molecule;   

DOI  :  10.1016/j.susc.2008.10.012

来源: Elsevier

【 摘 要 】

Surface structures and related electronic properties of flat Co nanoislands supported on Cu(111) are studied before and after adsorbing different doses of molecular hydrogen at 10 K by low-temperature scanning tunneling microscopy/spectroscopy (STM/STS) at 5 K. It is found that the adsorption process on Co consists in two steps. First, H-2 dissociatively chemisorbs on Co, forming an atomic H adlayer. Subsequently, molecules impinging on that H-terminated Co surface are physisorbed. When adsorbing a low dose of hydrogen on the Co/Cu(111) system, STM analysis shows that the chemisorbed hydrogen adlayer on Co forms a p(2 x 2) superstructure. On Cu surface however, no superstructure is observed. When adsorbing a high dose of H-2, hydrogen-induced superstructures are observed on both Co and Cu surfaces. These superstructures are ascribed to the presence of physisorbed molecules as revealed by the STS spectra. A (3 x 3) superstructure is observed on Co and a mixture of (2 x 2) and (3 x 3) is identified on Cu. A model describing the adsorption sites of molecules is proposed: H-2 molecules occupy on-top sites when arranged as a (2 x 2) phase and they occupy on-top and bridge sites when arranged as a Q x 3) phase. Besides, STM-induced desorption is used to desorb atomic hydrogen from selected Co nanoisland surface. The desorption is visualized in terms of a disappearance of the p(2 x 2) superstructure. (C) 2008 Elsevier B.V. All rights reserved.

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