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We performed a photoemission study on the (a-Si)/Si(111) homojunction with a thin intralayer of calcium fluoride (one monolayer). The intralayer and the amorphous silicon were grown in situ on cleaved Si(111) single crystals. From the core-level analysis we found a valence-band discontinuity of 0.35 eV due to the electrostatic dipole induced by the intralayer ionic bonds. Our results show that the intralayer forms an abrupt interface with Si and that the overlayer valence band has a lower binding energy than the substrate one. This implies that the most probable interface configuration is Si(111)-Ca-F-(a-Si), confirming the results of previous works on the CaF&/Si(111) interface.

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