OBSERVATIONS OF SURFACE AND PROJECTED BULK PHONONS IN EPITAXIAL OVERLAYERS - THE CU(100) AND CU(100)/CO SYSTEM

The phonon spectra of both clean and cobalt covered Cu(100) have been studied with helium atom scattering, and the results compared with those previously obtained with EELS for nickel and iron overlayers on Cu(100) [1,2]. In the GAMMA-M direction on clean Cu(100), both Reyleigh and bulk band edge phonons were observed. In the GAMMA-X direction, surface Rayleigh modes with dispersion similar to that obtained in EELS [3] occurred together with a previously unobserved, higher energy mode. No change in phonon dispersion was found for cobalt covered Cu(100).