HREEL SPECTROSCOPY OF THIN ION-BEAM DEPOSITED C-H(D) FILMS

Several monolayers thick C:H films, H/C ratio ca 0.5, have been prepared by ion beam deposition of hydrocarbons at a Pt(111)/C carrier. HREEL spectra of films deposited at 350 K exhibit a rich structure in the C-H stretch region around 3000 cm(-1) and fingerprint region below 1600 cm(-1). The spectra confirm the presence of CH, groups at carbon in sp, sp(2), and sp(3) hybridization states in a graphitic network. Vibrational spectra of deuterated films exhibit a normal isotope shift. The nature of the deposited ion: ethane, ethylene, acetylene, benzene, has a negligible effect on the vibrational structure of the C:H films. Annealing of the films up to 1250 K successively destroys sp, sp(3), and sp(2) carbon related CH groups. Although the films are not crystalline, the angular distribution of the elastically scattered electrons is considerably peaked in the specular direction. The primary energy dependence of the V(C-H) vibration losses exhibits a resonance at 5 eV which is considered as due to a marked impact mechanism contribution to the respective spectral features.