Analysis of the role of fluorine content on the thermal stability of a-C : H : F thin films

The effect of fluorine incorporation on the thermal stability of hydrogenated amorphous carbon (a-C:H) films was investigated by Raman spectroscopy, infrared (IR) absorption, X-ray photoelectron spectroscopy (XPS), as well as measurements of the film thickness. Results of IR and XPS analysis suggest that the total fluorine content after annealing corresponds to the amount of fluorine bonded to carbon in the as-deposited films. The evolution of Raman spectra obtained on films before annealing indicates that progressive fluorine incorporation is accompanied by graphifisation. In particular, the decrease in the optical bandgap is interpreted as a clustering of the existing sp(2) carbon sites. Under thermal annealing, the film structures are very stable and the films do not show anv chanae in refractive index values with respect to the original as-deposited films, for all fluorine contents. This behaviour is most likely due to extended graphitisation, with no sp2 clustering. The experimental findings suggest that the strength of the CF bonding configuration promotes thermal stability of the films. (C) 2002 Elsevier Science B.V. All rights reserved. RI Valentini, Luca/D-5238-2011; Kenny, Jose/F-9372-2010