Electron-beam action induced CaSi₂ crystal nucleation and growth at the CaF₂ epitaxy on Si

The effects of electron-beam irradiation (electron energy 20 keV, current density 50 μA/m²) on CaF₂ films epitaxially grown on Si(111) has been studied with reflection high-energy electron diffraction (RHEED) and Raman spectroscopy (RS). It was found that the electron beam action leads to the CaSi₂ layer synthesis as during the epitaxial growth of СаF₂ films and with irradiation after formation of CaF₂ films. The radiation-induced phenomena of CaSi₂ crystal growth were investigated, both directly during the epitaxial CaF₂ growth on Si (111) and film irradiation with fast electrons on Si(111) after its formation of CaF₂ films with keeping the specified film thickness, substrate temperature and radiation dose. Irradiation in the process of the epitaxial CaF₂ film growth leads to the formation of CaSi₂ nanowhiskers oriented along the direction <110>. The electron irradiation of the formed films, under similar conditions, leads to the homogeneous nucleation of CaSi₂ crystals and their proliferation as inclusions in the CaF₂ film. It was shown that both approaches lead to the formation of CaSi₂ crystals of the 3R polymorph in the irradiated region of a 10 nm thick CaF₂ layer. The crystal structures of CaSi₂ was found to depend on thickness of deposited СаF₂ films: it is trigonal rhombohedral modification tr3 for thin (<20nm) СаF₂ films and trigonal rhombohedral modification tr6 for thicker one.

The reported study was funded by RFBR and ROSATOM, project number 20-21-00028