Mechanisms and effects of wear on amorphous carbon thin films.

摘要

Amorphous carbon thin films, which are commonly used as protective layers for magnetic hard disks, experience wear during the operation of a hard disk. During sliding between these carbon films and the read-write head's slider tribochemical reactions occur, which have been predicted to remove carbon oxides. The tribochemical reactions have been investigated in this study through the use of a novel mass-spectroscopy tribotester. We have observed that the dominant species produced during sliding is CO{dollar}sb2{dollar}, in both dry nitrogen and oxygen environments, and that the generation rate is ten times higher in oxygen. With the use of this tester, we have also investigated the effect of the slider material, which consists of alumina titanium-carbide {dollar}rm(Alsb2Osb3{dollar}-TiC), on the carbon dioxide evolution. By depositing a thin barrier coating of carbon (50A) on the slider surface, we found that the production of carbon dioxide was an order of magnitude lower than with uncoated sliders. Thermogravimetric analysis (TGA) of the slider material corroborates its role in enhancing the gasification of carbon.; We have also explored the effect of wear on the microstructural features of carbon. With the aid of transmission electron spectroscopy (TEM) and electron-energy loss spectroscopy (EELS), we have found that the graphitic content of the amorphous carbon layer increases in the initial stages of wear. We also explored the temperatures achieved during sliding by comparing the microstructure of the worn carbon to that of unworn thermally-annealed carbon. Using additional techniques of Raman spectroscopy and NEXAFS, we found analogous less-randomly ordered microstructures at anneal temperatures of 300-500{dollar}spcirc{dollar}C.; We also explored the role of the magnetic layer (cobalt-platinum-chromium alloy) in the graphitization of amorphous carbon. With in situ heating and cooling TEM observations of the carbon/magnetic layer interface, we found that the microstructure of the carbon becomes more graphitic at low temperatures when in the presence of the magnetic layer. Crystallization temperatures of amorphous carbon, determined by calorimetry, occur in the range of 500-600{dollar}spcirc{dollar}C when the carbon is in contact with this layer. TEM observations suggest carbon diffuses into the magnetic layer upon heating and precipitates as graphite upon cooling.; We conclude that the wear mechanism includes frictional heating combined with metal-induced graphitization.