Atomic-level carbon thin film as the lubricant layer on Si

摘要

Carbon monolayer film on a Si wafer was characterized in terms of bonding structure and tribological properties, and examined in terms of the degree of tribological contribution of the surface topmost layer Amorphous hydrogenated carbon (a-C:H) films of 0.7-2.7 monolayers were prepared by plasma chemical vapor deposition(CVD) and characterized using X-ray photoelectron spectroscopy (XPS), Raman scattering(RS) and surface enhanced Raman spectroscopy (SERS), to determine that the film is composed of a-CH and diamondlike carbon. The carbon on the substrate interface was partially bound with Si to form SiC, and was difficult to move during sliding. A sliding test on a carbon monolayer with a TiC/alumina composite pin indicated a drastic decrease of the coefficient of friction from 0.88 to 0.30, but the coefficient of friction was not as low as that of the Ag-coated Si, 0.003, due to sliding with the diamond pin. This difference was attributed to the mobility of the coated atoms during sliding. The bias voltage Vb for preparation of the film by plasma changed the percentage of sp{sup}3 in the structure and the hydrogen content in the film but did not significantly change the coefficient of friction. The experimental results showed that a monolayer of a-C:H film has a rather small interaction with the pin material, as compared with Si. With increasing overcoat thickness, the coefficient of friction increased near the bulk material. The durability of the a-C:H-coated surface against ablation, or the number of sliding cycles before the surface is damaged, was significantly greater than that for uncoated Si, beyond our expectation. These results suggest that the chemical interaction between the surface monolayer and the pin material or the substrate is a very important factor in terms of friction. They also revealed that the extremely thin overcoat was useful to protect the surface of a magnetic memory hard disk for practical use.