Surface Debye Temperatures of the (100), (111), and (110) Faces of Platinum

The intensity of back-diffracted low-energy electrons (15–350 eV) from the clean (100), (111), and (110) surfaces of platinum single crystals was measured. From the temperature dependence of the (00) reflection in the range of 25°—700°C, the Debye—Waller factor and the root-mean-square displacements of surface atoms perpendicular to the surface planes were determined. The measured root-mean-square displacement 〈uz2〉½ was found to be a sensitive function of electron energy. The properties of the surface planes were determined from the intensity data taken at the lowest electron energy. Using the Debye model in the high-temperature approximation, the Debye temperatures and the frequencies of lattice vibration were calculated. The root-mean-square displacement of surface platinum atoms perpendicular to the surface plane is about twice as great as that in the bulk. This effect gives rise to surface Debye temperatures which are much smaller (107°—118°K) than the bulk value (234°K).