Synthesis of epitaxial structures with two-dimensional si layers embedded in a CaF$_2$ dielectric matrix

The possibility of fabricating two-dimensional Si layers on a CaF$_2$/Si(111) film by molecular beam epitaxy is studied. The growth conditions, under which the regions of two-dimensional Si layers are formed, are found. Raman spectroscopy, transmission electron microscopy, photoluminescence, and electron paramagnetic resonance (EPR) studies have shown that regions of two-dimensional Si layers are formed in epitaxial structures prepared by the deposition of one to three biatomic Si layers on the CaF$_2$/Si(111) film surface at a temperature of $550^\circ$. The Raman spectra of these structures exhibit a narrow peak at $418$ cm$^{-1}$, which is due to light scattering on vibrations of Si atoms in the plane of a two-dimensional Si layer intercalated with calcium. The EPR spectra of multilayer structures with regions of two-dimensional Si layers embedded in CaF$_2$ demonstrate an isotropic signal with an asymmetric Dyson shape and the $g$-factor $g = 1.9992$ under illumination. Consequently, this signal can be attributed to photoinduced conduction electrons in extended two-dimensional Si islands. These results may be useful for understanding the mechanisms of the formation of two-dimensional materials on CaF$_2$/Si(111) substrates.