Interface chemistry and epitaxial growth modes of SrF2 on Si(001)

Molecular beam epitaxy has been used to grow SrF{sub 2} thin films on Si(001). The growth modes have been investigated by atomic force microscopy, electron diffraction, and photoemission. Two principal growth regimes have been identified: (i) when deposition is carried out with the substrate held at a temperature of 700-750 deg. C, SrF{sub 2} molecules react with the substrate giving rise to a Sr-rich wetting layer on top of which three dimensional bulklike fluoride ridges develop; (ii) when deposition is carried out with the substrate held at 400 deg. C, a nanopatterned film forms with characteristic triangular islands. Results are compared to the growth mode of CaF{sub 2} on Si(001) under analogous deposition conditions. Morphological and structural differences between the two systems are associated with the larger lattice parameter of SrF{sub 2} with respect to CaF{sub 2}, resulting in a larger mismatch with the Si substrate.

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