Evidence of surface defects in ultrathin tetrahedral amorphous carbon films probed by x-ray absorption spectroscopy
S.S. Roy, R. McCann, P. Papakonstantinou, G.A. Abbas and J.A. McLaughlin
University of Ulster, UK
Tetrahedral carbon, NEXAFS, Ultrathin, Raman
The ta-C films with thickness in the range of 1-10 nm were obtained by FCVA and investigated by NEXAFS and Raman spectroscopies. The C=C bonds were quantitatively determined from the area of pi* peak in the C-K edge of NEXAFS spectra. It was clearly revealed that the relative concentration of C=C bonds is similar with film thickness above 2 nm. Evidence of the surface defects was established on films 1 nm thick. The C K edge NEXAFS analysis further showed that the content of the surface defect (mainly C–H bonds) decreased with the increase thickness (Fig. 1).
Raman parameters such as G peak width, ID/IG ratio, critically analyzed in terms of film thickness. The intensity of the Raman G peak increased with film thickness (Fig. 2). The ta-C film, showed a very small changes in baseline slope in the entire ultra thin region with the DLC component dominating, which suggests superior film properties.
In this study we demonstrate that the combined study of normalized Raman and NEXAFS spectra is very useful in determining the role of thickness in the structure of ta-C films.
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Nanotech 2006 Conference Program Abstract