Relaxation and thermal expansion of Ru(0 0 0 1) between 300 and 1870 K and the influence of hydrogen

The surface structure of Ru(0 0 0 1) has been studied between 300 and 1870 K using X-ray diffraction. At 300 K, the outermost layer is contracted by 2.2(4)%, in agreement with the value determined by low-energy electron diffraction studies, but about half that predicted by ab initio calculations. H-adsorption appears to introduce disorder through an increased surface Debye–Waller factor and an increased step density, but does not significantly alter the interlayer spacing. Temperature-dependent studies of the clean surface structure indicate a thermal expansion of the first three interlayer distances that is slightly smaller than that of the bulk, accompanied by increasing vibrational motion comparable to that of the bulk.