Effect of hydrogen on the surface relaxation of Pd(100), Rh(100), and Ag(100)

Abstract

Hydrogen induced surface relaxations of Pd(100), Rh(100), and Ag(100) have been studied by density functional theory calculations. We find that the first interlayer spacings of Pd(100) and Rh(100) expand almost linearly with hydrogen coverage. This result is used to estimate the amount of remaining hydrogen atoms on the surface samples investigated in previous low-energy electron diffraction studies, unusually large top-layer expansions of which have been suggested due to hydrogen contamination. The estimated H coverages of 0.5-1.1 ML, unexpectedly high for the samples claimed as clean, indicates that Pd(100) and Rh(100) are extremely susceptible to H contamination, requiring a more careful surface cleaning process. Hydrogen adsorption could result in a significantly large top-layer expansion in Ag(100), but such H effect is not realized in experiment since a dissociative adsorption of H-2 on Ag(100) is energetically improbable.