Orientation variation of surface strain

Expansion of the surface layers of a facetted hemispherical nanocrystal of Pb is reported at a temperature just below the melting point. Inversion of the coherent x-ray diffraction pattern yields quantitative three-dimensional maps of the deformation of the crystal from its equilibrium lattice spacing. Most of the surface of the crystal has a clear outward displacement, which decays exponentially into the bulk. This is suppressed on the (111) facet itself and is stronger on the spherical regions, suggesting that it arises from the orientational variation of the underlying surface stress.