Radiation-Stimulated Formation of Two-Dimensional Structures Based on Calcium Silicide

The formation of CaSi2 polycrystalline structures under the postgrowth electron irradiation of epitaxial CaF2/Si(111) films with embedded thin Si layers was studied. The dependence on the electron exposure time was investigated for two types of structures with different film thicknesses. The optimal conditions for the formation of two-dimensional CaSi2 structures were found. Raman spectra of the structures after a 1 min electron irradiation demonstrated only one pronounced peak corresponding to the vibrations of Si atoms in the plane of the calcium-intercalated two-dimensional Si layer. An increase in the exposure time resulted in the transition from two- to three-dimensional CaSi2 structures having more complex Raman spectra with additional peaks typical of bulk CaSi2 crystals. Based on the results of microscopic studies and transport measurements, a model explaining the observed effects was proposed.