Novel Infrared Thermal Annealing Device

M. J. Gladys and D. J. O'Connor

School of Mathematical and Physical Sciences, University of Newcastle, Callaghan, NSW, Australia.

Abstract

Pd(001)-(2x2)p4g-Al surface consists of 0.5ML of Al diffusing into the second layer during annealing and causing a p4g clock reconstruction. This is a unique bimetallic alloy due to the ability of the Al to be lifted from the second layer with the absorption of O2 and when the oxygen is removed with hydrogen. The removal of oxygen will happen without H2 as well but you need to anneal to a higher temperature and in the process the Al diffuses. Using hydrogen allows the removal of the oxygen at lower temperatures and hence keeps the Al on the surface. The surface is heated and the remaining Al diffuses into the second layer and again produces the clock reconstruction. This cyclic process has been found to be repeatable continuously. STM studies have revealed that the diffusion takes place mid terrace rather than at a terrace edge. A model has been derived to calculate the activation energy for this process using Ficks second law with a special boundary condition on the second atomic layer. Furthermore, using Low Energy Ion Scattering (LEIS), the activation energy for the diffusion of Al from the first to the second atomic layer has been measured to be 0.41± 0.02eV. This value strongly suggests that Pd atoms segregating to the surface is the dominating process. The activation barrier between the second and third layers was also measured to be 2.0 ± 0.4eV which suggests diffusion of the Al into the bulk via the vacancy mechanism.