Characterization of pulsed laser deposited a-C films by means of reflection electron energy loss spectroscopy

Amorphous carbon films have been deposited by ablating a high purity graphite target using a KrF excimer pulsed laser. Both the laser energy density (up to 15 J/cm(2)) and the substrate temperature (up to 900 K) were varied. Reflection electron energy loss spectra have been carried out in an ultra high vacuum surface analysis apparatus. The loss spectra were processed by removing the elastic peak contribution and the secondary electron background. The optical functions were deduced using a procedure based on the assumption that surface effects are negligible with respect to the bulk one;. The loss spectra are dominated by the presence of the pi and pi + sigma plasma resonances, whose energy positions and shapes are significantly affected by the different preparation conditions. In particular, it has been trade possible to determine, on the basis of reflection electron energy loss (REEL) data only, the sp(2)/sp(3) bonding ratio. Overall, these results are also relevant for th: correlation between the details of the preparation method and the material electronic properties. (C) 2001 Elsevier Science B.V. All rights reserved.