| AVS 62nd International Symposium & Exhibition | |
| Applied Surface Science | Monday Sessions |
| Session AS-MoA |
| Session: | Practical Surface Analysis I: Interpretation Challenges |
| Presenter: | Filippo Mangolini, Ecole Centrale de Lyon - LTDS, France |
| Authors: | F. Mangolini, Ecole Centrale de Lyon - LTDS, France J. Hilbert, University of Pennsylvania J.B. McClimon, University of Pennsylvania J.R. Lukes, University of Pennsylvania R.W. Carpick, University of Pennsylvania |
| Correspondent: | Click to Email |
Silicon oxide-doped hydrogenated amorphous carbon (a-C:H:Si:O) 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 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 [1]. However, a-C:H:Si:O exhibits much lower susceptibility to oxidative degradation, and higher thermal stability compared to a-C:H. This makes a-C:H:Si:O attractive for many applications, including next generation hard disk drives, which require overcoat materials that are thermally stable up to temperatures above 500ºC. Although it is well-established that a-C:H:Si:O 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 X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy study was performed. Changes in the surface chemistry and bonding configuration of a-C:H:Si:O (e.g., silicon oxidation state, carbon hybridization state) were accessed in situ at temperatures up to 450ºC. 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 [2]. This allowed quantitative evaluation of the carbon hybridization state in the film as a function of the annealing temperature. Upon high vacuum annealing, two thermally-activated processes could be determined to take place in a-C:H:Si:O by assuming a Gaussian distribution of activation energies with mean value E and standard deviation σ: a) ordering and clustering of sp2 carbon (E±σ= 0.22±0.08 eV); and b) conversion of sp3- to sp2-bonded carbon (E±σ= 2.7±1.0 eV). The experimental results are in qualitative agreement with the outcomes of molecular dynamics simulations performed using the ReaxFF potential. To determine the environmental dependence of the surface structural evolution of a-C:H:Si:O, the results of the in situ XPS/NEXAFS investigation were compared to those for a-C:H:Si:O samples heated in air, showing a strong effect of atmospheric oxygen. These results provide guidance for designing modified materials able to meet ever-increasing performance requirements of coatings for demanding applications.
1. F. Mangolini, F. Rose, J. Hilbert, R.W. Carpick, Applied Physics Letters, 103, 161605, 2013
2. F. Mangolini, J.B. McClimon, F. Rose, R.W. Carpick, Analytical Chemistry, 86, 12258, 2014