Structure and bonding at the CaF₂/Si (111) interface

High resolution core level spectroscopy with synchrotron radiation is used to determine the bonding at the epitaxial CaF2/Si (111) interface. It is found that both Ca and F bond to Si at the interface inducing core level shifts of +0.4 eV and -0.8 eV, respectively. Structural models with an atomically sharp interface are proposed where Ca bonds to the first layer Si and F to the second layer.