From step fluctuations to nanostructure energetics on Nb(011)

Using the spectroscopy of step edge fluctuations observed by low-energy electron microscopy, we measure the stiffness β̃θ) of surface steps on Nb(011) thin single crystal films as a function of step orientation θ. From this we determine also the step free energy (line tension) β(θ)∼320meV/nm. The results are supported by observed equilibrium shapes of islands on the surface. The measured β is employed to analyse configurations of nanostructures reported here for two significant examples. First, for the glide of a threading edge dislocation through a field of parallel steps we determine the maximum absolute 'plucking' force of ∼75pN exerted on the step by the dislocation. Second, from the observed equilibrium of steps with facets we determine the free energy of 27meV/nm with which step edges bind to 〈111〉 the edges of {011} facets.