Interface formation and epitaxy of CaF 2 on CoSi 2(111)Si(111)

Abstract

XPS, UPS and LEED have been used to study the interface formation and epitaxy of very thin CaF 2 films (⩽63 A ̊ ) on thin layers of CoSi 2 (∼ 70 A ̊ ) , formed by solid phase epitaxy on Si(111). XPS core levels (Si 2s, Co 2p, Ca 2p, F 1s) and Si(KLL) Auger transition indicate that both Ca and F are bonded to Si atoms only, whether the CoSi 2 surface is Si or Co-rich. At room temperature CaF 2 grows layer-by-layer on CoSi 2(111), and no ordered surface structure is observed by LEED. XPS valence bands reveal that the electronic structure of CoSi 2 is not affected by the formation of the CaF 2 upper layer. Upon annealing thin layers of CaF 2 in the 550–650°C range, LEED shows good (1 × 1) patterns of CaF 2 (111). The thin epitaxial films are stable up to ∼ 650° C. Above this temperature the CaF 2 valence band undergoesrapid changes indicating a degradation of the insulator layer.