Microengineered CVD Diamond Surfaces : Tribology and Applications

Abstract: Recent developments in thin film synthesis of diamond have facilitated a host of new technical applications. These are motivated by the many attractive properties of diamond, for example high hardness, chemical inertness, transparency and heat conductivity. Unfortunately, these properties also make it difficult to fashion complex geometries. Other problems are the severely limited choice of suitable substrate materials and large surface roughness. To reduce these complications, a technology denoted replication and bodybuilding has been developed. The basic principle is to grow the diamond film onto a mold and then build a mechanical support on top of the diamond film. Then the mold is removed. Thereby, a diamond surface with the desired 3D geometry and the same surface roughness as the mold is created.Three potential applications for devices built using the replication and bodybuilding concept have been explored. Grinding tools for hard materials have proved superior to conventional technology in rate of removal as well as in resulting surface finish. Diamond surfaces have also been crafted into ultra-durable dies for injection molding of hard particle reinforced polymers. Initial testing of an abrasive diamond device, intended to make CMP processes more economical and easier to control has successfully been carried out.Diamond and diamond-like carbon is well-known for being “low-friction materials”, but are here demonstrated to actually be “high-friction materials” with the ability to disguise themselves in certain environments, most notably with the aid of water molecules. The mechanisms involved in these variations have been investigated. Using NEXAFS it is shown that high friction sliding is accompanied by changes in the material structure. These changes are induced by surface roughness as well as by strong adhesive forces.Highly hydrogenated carbon coatings, on the other hand, affording super-low friction coefficients (<0.01) under certain circumstances, will suffer an increase in friction in the presence of water.