THERMAL ROUGHENING OF CU(115) - AN ENERGY-RESOLVED HELIUM-ATOM-BEAM SCATTERING STUDY

The structure of the Cu(115) surface has been investigated in the temp erature range between 160 and 700 K with energy-resolved helium-atom-b eam scattering. The ''power-law'' diffraction pro tiles found in previ ous helium-scattering experiments without energy analysis are shown to be the result of inelastic (phonon) scattering. In our energy-resolve d measurements, the line shapes of the elastically scattered intensity can be described by a two-dimensional Lorentzian. This asserts that o n this surface a possible crossover of the height difference correlati on function to the expected logarithmic behavior might only occur for distances larger than about 100 Angstrom (perpendicular to the average step direction).