Silicon oxide-doped diamond-like carbon (SiOx-DLC) coatings are fully amorphous thin-film materials consisting of two interpenetrating networks, one being a hydrogenated amorphous carbon (a-C:H) network and the other a silica glass (SiOx) network. At temperatures above 150�C, pure a-C:H films undergo a rapid degradation that starts with the evolution of hydrogen and is followed by the conversion of sp3 bonds to sp2. However, SiOx-DLC exhibits much lower susceptibility to oxidative degradation, and much higher thermal stability compared to a-C:H. This makes SiOx-DLC an attractive material for many applications, including for the development of next generation hard disk drives which require novel overcoat materials that are thermally stable up to temperatures above 500�C. Even though it is well-established that SiOx-DLC possesses superior thermal stability and oxidation resistance relative to a-C:H, the scientific basis for this behavior is not understood. To investigate this, a combined in situ XPS and NEXAFS study was performed. Changes in the surface chemistry and bonding configuration of SiOx-DLC (e.g., silicon oxidation state, carbon hybridization state) could be accessed in situ at temperatures up to 450�C. A novel methodology for processing NEXAFS spectra, which makes it possible to account for the presence of a carbonaceous contamination layer on an air-exposed material, was developed. This allowed quantitative evaluation of the carbon hybridization state in the film as a function of the annealing temperature. These experimental results could be well fit with a thermal activation-based model that describes the structural transformations occurring in vacuum in SiOx-DLC as a function of time and temperature. To determine the environmental dependence of the surface structural evolution of SiOx-DLC, the results of the in situ XPS/NEXAFS investigation were compared to those for SiOx-DLC samples heated in air, showing a strong effect of atmospheric oxygen.

In situ XPS and NEXAFS investigation of the thermally-induced structural evolution of advanced amorphous carbon-based surfaces

248th National Meeting (2014)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.