From step fluctuations to nanostructure energetics on Nb(011)

Abstract

Using the spectroscopy of step edge fluctuations observed by low-energy electron microscopy, we measure the stiffness 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) ∼ 320 meV/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 ∼75 pN exerted on the step by the dislocation. Second, from the observed equilibrium of steps with facets we determine the free energy of 27 meV/nm with which step edges bind to the ⟨111⟩edges of {011} facets.

Acknowledgements

The research was supported by the US DOE, under grant DEFG02-91ER45439, and the LEEM was maintained and operated in the Center for Microanalysis of Materials, supported by grant DEFG02-02ER46011, in the Materials Research Laboratory of the University of Illinois.