Shape transition of calcium islands formed by electron-stimulated desorption of fluorine from a CaF2(111) surface

Extremely low-energy electrons emitted from a heated filament have been use d to deplete fluorine from a cleaved CaF2(111) surface. Calcium left behind on the surface reorganizes itself in islands. A shape transition for the i slands from a compact shape to an elongated shape has been observed for isl ands larger than similar to 20 nm in diameter. Some cleavage steps show pre ferential fluorine erosion, which leads to the formation of very long calci um nanowires of uniform width similar to 15 nm parallel to the step edge. T he observed island and wire morphology is explained by energy minimization of strained commensurate islands. (C) 2000 American Institute of Physics. [ S0003-6951(00)00439-3].