LEED STRUCTURE ANALYSES OF THE CLEAN AND FULLY HYDROGEN-COVERED W(110) and Mo(110) SURFACES

Abstract

We present a comparative low energy electron diffraction (LEED) structure analysis for the clean as well as hydrogen-saturated (110) surfaces of tungsten and molybdenum. Both clean surfaces exhibit some contraction of the first interlayer spacing, i.e. -3.1% for W and -4.0% for Mo, whereas deeper layer distances remain practically bulklike. The only structural consequence of a hydrogen monolayer adsorbed is the reduction of the first interlayer distance contraction to approximately half its value of the clean surface, i.e. to -1.7% for W and -2.0% for Mo . Our results give no evidence for an adsorbate-induced reconstruction of either surface and thus discard the widely accepted model of a hydrogen-induced lateral shift of the top layer of W (110). Hydrogen itself is found to be adsorbed in threefold-coordinated hollow sites at a height of about 1.2 Å and 1.1 Å above the first substrate layer of W and Mo , respectively.

A theoretical study of hydrogen adsorption and diffusion on a W(1 1 0) surface

“…Our results show that the TF site is the most stable site, which is consistent with Arnold and Scheffler's LEED and DFT studies and the DFT-LDA study [16][17][18]. The structural parameters are also consistent with Arnold and Scheffler's study and the DFT-LDA study [17,18].…”

“…They insisted that the first layer of the W substrate is reconstructed moving toward the 1 1 0 direction. Recently, this adsorption structure model was questioned by LEED I-V experiments and density functional theory (DFT) calculations by Arnold and Scheffler [16,17]. They found little reconstruction of the first layer of the W substrate, and that the TF sites are the most stable hydrogen adsorption sites.…”

Atomic and electronic properties of the Pb/Mo(110) adsorption system

“…These results are in good agreement with earlier theoretical studies [15][16][17][18] as well as LEED measurements. 12 The results presented in Table I show that the increase in the slab thickness above seven layers does not change considerably the atomic structure of the surface. Therefore, in the rest part of this work the Mo͑110͒ surface has been described by a slab composed of seven atomic layers.…”

“…Taking into account the corresponding experimental result of 3.15 Å provided by LEED measurements, 12 …”

Increasing the specularity of surface scattering of conduction electrons caused by adsorption of a hydrogen monolayer on the W(110) surface

“…It means that the value of "pure" effect, in fact, is even greater. In addition, we note that the lack of surface reconstruction under the hydrogen adsorption on the tungsten (110) surface also contributes to the manifestation of this effect [11].…”