Seminars Archive

Jose` M. Ripalda

Abstract


Tuesday, April 3, 2000, 14:00
Seminar Room, ground floor, Building "T"
Sincrotrone Trieste, Basovizza
Core Level Spectroscopy of Amorhpus Carbon Nitride

Jos M. Ripalda
(Departamento de Fsica Aplicada, Universidad Autonoma de Madrid) ABSTRACT During the last decade, a large research effort has been focused on amorphous carbon nitride due to its exceptional mechanical and tribological properties, but the nature of carbon-nitrogen bonding in these solids has been the subject of a long controversy during these years. The origin of the difficulty lies in the large structural disorder. Most microscopy and diffraction techniques offer little insight in this case due to their lack of chemical selectivity, for that reason we have investigated this question with synchrotron radiation based spectroscopies and compared our results with ab initio calculations of chemical shifts and photoelectron multiple scattering phenomena. Our main objective has been understanding the N 1s photoemission spectra. We have studied the excitation energy dependence of the photoemission spectra and found oscillations of the N 1s photoionization cross section due to the EXAFS effect. From these oscillations we have obtained the bond lengths corresponding to each chemical shift in the N 1s spectra. Although most samples proved to be completely amorphous, in samples prepared at high temperatures we found a strong photoemission angle dependence that we attributed to photoelectron forward scattering due to preferential orientation of bonds near the surface. We have also studied most other types of N 1s core level spectra such as Auger spectra, Fluorescence spectra, and X-ray absorption spectra. All the accumulated evidence consistently points towards the following interpretation of N 1s photoemission spectra: the low binding energy peaks (398-399 eV) are due to low coordination number local structures with double and triple bonds (p bonding) while the high binding energy peaks (400-401 eV) are due to threefold coordinated nitrogen with sp2 hybridization. Diamond-like bonding seems to play a negligible role.