Hydrogen Adsorption on Fe Monolayer Grown on Ni(111) Investigated by Scanning Tunneling Microscopy

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The adsorption of hydrogen on an Fe monolayer on a Ni(111) substrate at room temperature has been investigated by scanning tunneling microscopy. The epitaxial fcc-Fe(111) monolayer grows from the step edge of the Ni(111) substrate. Equilateral triangular lines consisting of dark spots aligned along the $\langle 1\bar{1}0\rangle$ direction with a spacing of 0.5 nm are observed on the Fe monolayer and considered to be due to the misfit-induced atomic vacancies in the first layer of the Ni substrate. The dark spots at the apexes of triangles become larger with the initial adsorption of hydrogen, and the triangular lines on the same line become a broad ditch with the reconstruction of the Fe monolayer and a bright Fe cluster on the surface with further hydrogen adsorption. The hydrogen-induced agglomeration of vacancies in the Ni substrate and the reconstruction of the Fe monolayer near the vacancies result in the formation of the broad ditch and bright cluster.
2007-08-30