Atomic Vibrations in the (00.1) Graphite Surface: Observation with Low-Energy Electron Diffraction and Lattice-Dynamic Calculations

Abstract

Low-energy electron diffraction has been used to measure the variation of the surface Debye temperature ${\Theta }_{\perp }$ in the [00.1] direction of graphite as a function of the energy of incident electrons. A change (hexagonal-trigonal) in the symmetry of the diffraction diagram, depending on the penetration of electrons, was observed. This change in symmetry has been made use of in selecting, from the many other values of ${\Theta }_{\perp }$ we had measured, the one associated with the first layer of the (00.1) surface of graphite, namely (690 ± 70) °K. Furthermore, the dynamics of the Born lattice has been applied to compute the Debye temperature of the first layer of the surface associated with the normal (${\Theta }_{\perp }$) and parallel (${\Theta }_{\parallel }$) directions of the (00.1) face. The computed value of ${\Theta }_{\perp }$ is in fairly good agreement with the one determined experimentally. The computed value of ${\Theta }_{\parallel }$ is close to that previously obtained by other authors using different methods of calculation.