Adsorption of hydrogen on Fe(110) at cryogenic temperatures investigated by low energy electron diffraction

Abstract

A cryosample holder was constructed and used to investigate the adsorption system H/Fe(110) at temperatures down to 35 K. We find a new 2×2-2H superstructure with a graphitic arrangement of adatoms which reversibly transforms to the well-known c(2×2) phase at a critical temperature of about 80 K. We give arguments that in both phases hydrogen induces the same type of a weak substrate reconstruction. Also, we propose a structural model according to which the c(2×2) phase is equivalent to the 2×2 phase, however, with additional local disorder imposed by thermally fluctuating occupation of neighboring threefold coordinated sites by the adatoms.