Relaxation and thermal expansion of Ru(0001) between 300 and 1870 K and the influence of hydrogen

The surface structure of Ru(0001) 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. (C) 2001 Elsevier Science B.V. All rights reserved.