Laser annealing of epitaxial CaF2 films on Si

Highlights: • Pulsed laser annealing of the CaF₂/Si(111) film leads to morphology changes. • Round-shaped nanohills are formed on the epitaxial film. • The nanohills contain cavities filled with Si₂F₆ gas. Nanosecond time-resolved reflectivity and transmission changes in CaF₂/Si(111) structures were measured to study the phase transitions, surface modification and radiolysis induced by nanosecond ruby laser pulses. The Si lattice heating up to the melting point leads to the nanohills formation on the surface of the structure, the height of which does not exceed 100 nm with the average base diameter of 360 nm and the surface density of 2• 10⁸cm^{– 2}. The Raman scattering and energy-dispersive X-ray spectroscopy data indicate that the nanohills contain cavities inside them, and they are filled with the gas of Si₂F₆ molecules. The shell of the nanohills, obviously, consists of calcium oxide.