Flexoelectric and local heating effects on CdSe nanocrystals in amorphous As2Se3 films

Raman and photoluminescence (PL) spectra of amorphous As2Se3:Cd films show that laser irradiation can result in the local formation of CdSe nanocrystals (NCs). Due to a pronounced laser-induced drastic drop of the film viscosity, a strong local enhancement of diffusion of atoms in the laser spot area results in a material transfer from the laser spot (evidenced by SEM and AFM data) and simultaneously facilitates the formation of CdSe NCs. The difference of the PL maximum positions measured at a high laser power density Pexc and subsequently (from the same spot) at a lower Pexc value can be explained either by local heating of the sample by the high-Pexc illumination, or by the flexoelectric effect (additional strain in the CdSe NCs induced by the electric field gradient caused by the charging of the NC surface). Based on the spectral positions of the PL maximum, with the account of the Stokes shift, the average radii of the CdSe NCs formed are estimated.