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 used to deplete fluorine from a cleaved CaF2(111) surface. Calcium left behind on the surface reorganizes itself in islands. A shape transition for the islands from a compact shape to an elongated shape has been observed for islands larger than ∼20 nm in diameter. Some cleavage steps show preferential fluorine erosion, which leads to the formation of very long calcium nanowires of uniform width ∼15 nm parallel to the step edge. The observed island and wire morphology is explained by energy minimization of strained commensurate islands.

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