Structure of the Sputtered Coating

The perpendicular orientation of the main crystal structure in Type I films is not the desirable orientation for effective lubrication, but coatings with this structure are consistently found to give excellent lubrication in vacuum, with friction coefficients better than 0.05. It is clear that some mechanism must exist by which the crystais 

All the highly crystalline Type I sputtered films are more or less porous, with densities of the order of 3,8 gm cm , compared with a typical value of 4.92 gm cm quoted for fully dense single crystals. Fleischauer et al pointed out that the ease with which the crystals can bend to a basal plane orientation will depend on the crystal size and the density of packing. They also suggested that an increased degree of pre-etching of the substrate would increase the number of reactive sites available for crystal formation, and therefore the density of crystal packing, as well as the 

In recent years there has been considerable interest in the production and properties of sputtered films in which the dominant crystal orientation is with the basal planes parallel to the substrate surface. These are often loosely described as Type II films but their technology has been developing rapidly, and they cannot yet be considered as being at all precisely defined. Fleischauer reported in 1983 the preparation of both Type I and Type II films, but the different conditions which produced the two different films were not known. The films were produced with different targets, and the deposition rate for the Type II films was slower. He speculated that conditions which favour the closest approach to M0S2 stoichiometry would favour the formation of Type temperatures might be responsible. 

Type II films appear to be more reliably produced by certain co-sputtered materials, and by ion beam bombardment, and these are discussed in Section 10.7. 

---