1. Physical Vapor Deposition:

In physical vapor deposition (PVD), the depositing material will be transferred from solid, liquid or gas phase precursors into a vapor phase by different vaporization methods and condensed on a suitable substrate kept at different substrate temperatures after the transport as a molecular beam in vacuum or by diffusion through a diluted background gas (working gas atmosphere). In the case of chemical compounds deposition, they are usually decomposed during their vaporization and undergoes a chemical reaction on the surface of the substrate during the film growth with a suitable reactive gas. Regarding the vaporization methods we can classify the PVD as thermal evaporation and sputtering methods. The properties of the deposited films are determined essentially by the growth conditions during their deposition.

Although many factors influence the growth processes and modify the structure of the films, there are, in general, three stages essential in the thin film deposition processes: nucleation, coalescence, and growth processes.

● Thermal Evaporation:

The thermal evaporation of a solid precursor takes place by heating the source, kept on a high melting point source holder. Above the melting point, the vaporization of the melt increases with increasing temperature in an exponential manner and a vapor beam will be spread into the vacuum chamber having a low residual pressure. The most simple evaporation sources are resistance based heating sources [1].