Step edge fluctuations on clean Ni(111) are investigated using low-energy electron microscopy. When interpreted as capillary waves the fluctuations yield values of the surface mass diffusion coefficient $D_s$ and the step edge stiffness $\tilde{\beta }$ in the temperature range 1050–1340 K. $\tilde{\beta }(\theta ,T)$ is of magnitude $\sim 300\mathrm{meV}∕\mathrm{nm}$ at 1200 K, almost independent of step orientation $\theta$, and decreases with increasing temperature $T$. At the lower temperatures, the decay of capillary modes depends on wave vector $q$ as $q^3$, as expected for surface diffusion over terraces next to the step. Also, the deduced surface diffusion coefficient $D_s={10}^{-4\pm 0.5}\exp (-0.65\mp 0.1\mathrm{eV}∕k_{B}T){\mathrm{cm}}^2∕\mathrm{s}$ is consistent with that on similar surfaces when scaled to homologous temperatures by the melting temperature $T_m$, in keeping with a recently suggested universality. A component of step relaxation driven by bulk diffusion above $0.65T_m$ is reasonably consistent with bulk diffusion results obtained much earlier using radio tracer methods. This result is contrasted with earlier discussions that postulate a regime of high-temperature surface diffusion with a large activation energy and very large prefactor. Sublimation detected here by step edge flow near $0.75T_m$ is consistent with the known cohesive energy.

• Received 16 August 2005

DOI:https://doi.org/10.1103/PhysRevB.73.035418