Structure of the hydrogen covered Cu(110) surface studied with thermal energy helium scattering

Abstract

The adsorption of atomic hydrogen on the Cu(110) surface has been studied with thermal energy helium scattering. Upon hydrogen adsorption the structure exhibits a variety of structures: At temperatures above 140 K the helium diffraction spectra show a clear (1 × 2) structure even at very low H coverages. This phase is the well known (1 × 2) Cu(110)-H “missing row” reconstructed phase. Based on an analysis of the specularly reflected He-intensity as a function of hydrogen coverage we have characterized the nucleation and growth of this phase. After the formation of small reconstructed areas the development of the reconstructed phase proceeds via the growth of these nuclei into large (1 × 2) Cu(110)-H islands indicating an attractive interaction between adsorbed H atoms within the reconstructed unit cells. Adsorption at temperatures below 80 K yields a sequence of adsorbate phases as a function of hydrogen exposure: at low exposures a (1× 4) phase is observed. With increasing hydrogen exposure the (1 × 4) structure changes continuously into a well ordered (1 × 3) phase, which then evolves into a (1 × 2) phase at higher exposures. This (1 × 2) structure is only poorly ordered and transforms upon further hydrogen exposure into a (1 × 1) structure. This sequence of adsorbate phases, as well as the continuous transition between them, suggests a repulsive interaction between the adsorbed H atoms. All adsorbate phases formed at surface temperatures T s below 120 K undergo an irreversible transition into a disordered phase upon heating to 120 K < T s < 140 K. Heating above T s = 140 K irreversibly yields the (1 × 2) “missing row” phase.