• influences film properties as: chemical reactivity, electrical conduction, mechanical behaviour,
• vacancies: (the absence of an atom - see picture below) in case there are a lot of vacancies, the film is porous

• dislocations = line defects, edge or screw (see picture below); play an important role in mechanical deformations, important also for epitaxy; dislocations can be avoided in a crystal, while vacancies can't

• grain boundaries = heterogeneous regions where various processes are accelerated and electronic transport impeded; separates the grains (crystalline regions) in a polycrystalline film

Chemical composition:

• contaminations: metals from sputtering, water from vacuum leaks
• chemical bonds: films should possess strong chemical bonds, not easily broken or strained; the bonds are observable in optical absorption spectra