Surface mass diffusion and step stiffness on an anisotropic surface; Mo(0 1 1)

Results of step fluctuation experiments for Mo(0 1 1), using low-energy electron microscopy, are re-examined using recently developed procedures that offer accurate coefficients of surface mass diffusion. By these means, surface diffusion Ds is documented at T/Tm ∼ 0.5, while the crossover to relaxation driven by bulk vacancy diffusion is inferred for T/Tm ∼ 0.6. Here, Tm is the melting temperature Tm = 2896 K. We obtain Ds = 4 × 10−4 exp(−1.13 eV/kBT) cm2/s for the temperature interval 1080-1680 K. Possible indications of diffusion along step edges appear for T/Tm ∼ 0.4. The same measurements of step fluctuation amplitudes determine also the step stiffness, which by symmetry is anisotropic on Mo(0 1 1). It is shown that three independent procedures yield mutually consistent step stiffness anisotropies. These are (1) step fluctuation amplitudes; (2) step relaxation rate anisotropies; and (3) the observed anisotropies of islands in equilibrium on the Mo(0 1 1) surface. The magnitude of the step stiffness obtained from step edge relaxation is consistent with earlier measurements that determine diffusion from grain boundary grooving.