Atomic separation in a solid is about 0.3nm. The thin film thickness can range from nanometers (monolayers) to microns. Monolayers has high surface to volume ratio. Thin film properties are different from the bulk; however when hundreds of atomic layers forms micron layers, their properties are similar to that of "bulk". Typically there is a critical thickness above which it behaves essentially as a bulk material. Variety of forms of thin films are possible based on their crystal structure, grain size, composition, defects, electro- chemical-mechanical-optical properties, adhesion, stress resulted etc.

Gas Kinetics and Vacuum Technology
In order to understand deposition techniques, we must first know some basics of gas kinetics and vacuum physics. The vacuum ranges can be broadly defined as follows: