About the structure and bonding of laser generated carbon films by raman and electron energy loss spectroscopy

Abstract

Laser generated amorphous carbon films have been investigated by Raman and electron energy loss spectroscopy to obtain information on bonding type and structure of carbon. Frequency shifts of the dominant first-order Raman lines and a strongly diminished π electron signal in the plasmon region as well as in the K absorption edge clearly indicate a fraction of sp3 bonds in the carbon films. Our model of disordered carbon containing sp2 and sp3 bonding fractions consists of small graphitic islands linked by a tetrahedrally bound network. Calculations within a force constant description confirm a fraction of 4… 20% sp3 bonds depending on the preparation history of the samples. A size of L ≤ 50 A of the graphitic clusters has been estimated by analysis of the intensity ratio of the shifted G and D Raman lines. Different graphitic target materials cause laser generated carbon films with a varying amount of sp3 bonds.