Abstract
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 $\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\beta}}$ in the temperature range 1050\char21{}1340 K. $\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\beta}}(\ensuremath{\theta},T)$ is of magnitude $\ensuremath{\sim}300\phantom{\rule{0.3em}{0ex}}\mathrm{meV}∕\mathrm{nm}$ at 1200 K, almost independent of step orientation $\ensuremath{\theta}$, 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 ${D}_{s}={10}^{\ensuremath{-}4\ifmmode\pm\else\textpm\fi{}0.5}\phantom{\rule{0.2em}{0ex}}\mathrm{exp}(\ensuremath{-}0.65\ensuremath{\mp}0.1\phantom{\rule{0.3em}{0ex}}\mathrm{eV}∕{k}_{B}T)\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{2}∕\mathrm{s}$ 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 $0.65{T}_{m}$ 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 $0.75{T}_{m}$ is consistent with the known cohesive energy.
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