Sol-gel coatings generally consist of thin films deposited on solid substrates from a liquid solution. These thin films generally find applications in modifying the reflectivity of the substrate' s surface, altering its rigidity, or modifying its surface chemistry. 
The films are generally deposited by dip-coating, but may also be deposited using spin coating or other thin film deposition techniques. 
To achieve uniform defect-free deposition, the substrate must be free of dust and other particles and it must be uniformly wetting to the sol-gel solution used to deposit the film. The most common application is to deposit the film on a substrate that is completely wetting to the solution being applied. 

Sol-gel coatings are frequently based on organo-silane precursor molecules, containing a hydrolysable silicon termination and an organic segment. These molecules are generally designed to cross-link and polymerize as the coating dries and cures. Generally, their polymerization includes the possibility of their grafting via silanol bonds to exposed sites on the glass surface. As such, it is interesting to clean a bare glass substrate to expose its native silanol groups. Other substrates may be used for sol-gel deposition. These may include polymer and ceramic substrates. Their cleaning will be briefly addressed at the end of the chapter. 

The cleaning procedures will be presented in two separate categories, the first dealing with particle removal, and the second with exposing the active silanol sites at the glass surface.  Subsequent curing and drying of the coating, designed to give the coating its required mechanical and optical properties, will not be discussed in this section.