It was found that small temperature changes caused steps on the NiAl(110) surface to move. It was shown that this step motion occurred because mass was transferred between the bulk and the surface as the concentration of bulk thermal defects such as vacancies changed with temperature. Since a change in island area with temperature change scaled strictly with the island step-length, thermally generated defects were created/annihilated very near to the surface steps. The sample temperature was oscillated, and measurements were made of the amplitude and phase-lag of the system response. That is, the change in island area normalized to its perimeter. By using a 1-dimensional model of defect diffusion through the bulk, in a direction perpendicular to the surface, the migration and formation energies of the bulk thermal defects were determined. During surface smoothing, it was shown that there was no flow of material between islands on the same terrace and that all of the islands in a stack shrank at the same rate. It was concluded that smoothing occurred via mass transport through the bulk of the crystal, rather than via surface diffusion. Based upon the measured relative sizes of the activation energies for island decay, defect migration and defect formation, it was concluded that attachment/detachment at steps was the rate-limiting step in smoothing.

Surface Dynamics Dominated by Bulk Thermal Defects - the Case of NiAl(110). K.F.McCarty, J.A.Nobel, N.C.Bartelt: Physical Review B, 2005, 71[8], 085421 (12pp)

Figure 7

Pre-Exponential for Interdiffusion in β-NiAl