Solid state magnetic resonance investigation of the thermally-induced structural evolution of silicon oxide-doped hydrogenated amorphous carbon

Due to their increased stability in extreme environments, relative to amorphous hydrogenated carbons (a-C:H), amorphous thin film silicon oxide-doped hydrogenated amorphous carbons (a-C:H:Si:O) are being commercially developed as solid lubricants and protective coatings. Although various properties of a-C:H:Si:O have been investigated, no definitive structure of a-C:H:Si:O has ever been proposed, nor has its thermally-induced structural evolution been thoroughly studied. The aim of this work is to better understand the structure of a-C:H:Si: O through solid-state nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) spectroscopies. Deeper insights into the thermally-driven structural evolution are obtained by annealing a-C:H:Si: O between 50 degrees C and 300 degrees C under anaerobic conditions and taking NMR/EPR measurements after each step. EPR results show that the number of paramagnetic defects decreases by 70% with annealing at 300 degrees C. H-1 NMR shows the hydrogen concentration decreases with annealing temperature from 2 x 10(22) g(-1), and then levels off at approximately 0.7 x 10(22) g(-1) for anneals between 200 degrees C and 300 degrees C. The carbonesiliconeoxygen network exhibits some structural reorganization, seen directly as a slight increase in the sp(2)/sp(3) ratio in the C-13 NMR with annealing. These results combined with relaxation data are interpreted according to a two-component structure largely defined by differences in hydrogen and defect contents. (C) 2016 Elsevier Ltd. All rights reserved.