INTERFACE FORMATION AND EPITAXY OF CAF2 ON COSI2(111)-SI(111)

XPS, UPS and LEED have been used to study the interface formation and epitaxy of very thin CaF2 films (≤63 A ̊) on thin layers of CoSi2 (∼ 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 CoSi2 surface is Si or Co-rich. At room temperature CaF2 grows layer-by-layer on CoSi2(111), and no ordered surface structure is observed by LEED. XPS valence bands reveal that the electronic structure of CoSi2 is not affected by the formation of the CaF2 upper layer. Upon annealing thin layers of CaF2 in the 550-650°C range, LEED shows good (1 × 1) patterns of CaF2 (111). The thin epitaxial films are stable up to ∼ 650°C. Above this temperature the CaF2 valence band undergoesrapid changes indicating a degradation of the insulator layer. © 1990.