Epitaxial growth of CaF2(1Â 1Â 1) on Cu(1Â 1Â 1) visualized by STM

The initial stages of the growth of CaF2 on Cu(1 1 1) have been studied by STM as a function of deposition temperature and coverage. No evidence for a reaction between the CaF2 molecules and the Cu substrate has been found. The islands formed at 700 K and above show uniform heights, triangular shapes with two orientations rotated by 60° and flat top surfaces. They can not be imaged at voltages below +3 V indicating their insulating character. The LEED pattern shows that the film is epitaxial, (1 1 1)- oriented and in registry with the substrate. The observations indicate that epitaxial growth of twinned crystallites of CaF2(1 1 1) takes place on Cu(1 1 1).