Depth profile analysis of chemical structures around lubricant/overcoat interface using plasmonic sensor

A chemical depth profile in lubricant films, carbon films, and their interfaces is an informative parameter for hard disk media because molecular features of lubricants bonded to a surface of carbon overcoats (COCs), which usually consist of a nitrogen doped layer, are important to achieve high tribological performance. However, it was difficult to analyze their interfaces with high depth resolution because thickness of lubricant films and COC films are so thin, i.e. 1.5nm and 2nm, respectively. We have developed new method using plasmonic sensors, which has measurement capability for chemical structures with depth resolution of 0.1nm by surface-enhanced Raman spectroscopy (SERS). We examined the lubricant film composed of perfluorinated polyether (PFPE) with phosphazene derivative (A2OH) on a diamond-like carbon (DLC) film. The result shows that the functional group is adsorbed on the DLC surface, where lower shift in the wave number of phenyl group is observed. The depth profile of the intensity ratio of D-peak to G-peak shows the maximum at around the surface of the DLC film. A variety of organic components in the DLC films, fabricated by a chemical vapor deposition (CVD), were observed in it. Besides, the depth profiles shows that organic materials, involving methyl, ethyl, or ethylene groups, Co(OH)x exist in the film.