Raman and thermal desorption spectroscopy analyses of amorphous graphite-like carbon films with incorporated xenon

Structural and thermodynamic properties of xenon incorporated in amorphous carbon films deposited by means of a sputtering system free of vacuum pumping during the deposition were investigated by visible Raman (Vis-Raman) scattering and thermal desorption spectroscopy (TDS), respectively. Vis-Raman measurements, carried out before and after the xenon desorption, revealed a polycrystalline material rich in C-sp(2) sites that form randomly dispersed nanosized graphite clusters (nanocrystals) of approximately 1 nm. After xenon desorption, a compensating mechanism, activated by the thermal heating, promotes a more ordered C-sp(2) network as revealed by the linewidths of both D and G bands, as well as by the I-D/I-G ratio evolution. The TDS thermograms show that the xenon onset effusing temperature is approximately 120 degrees C. Besides, they also revealed two different regimes, at low and at high temperatures, associated with desorption of xenon atoms trapped either in an interconnecting void network or within the graphite nanocrystals. From the latter regime, the xenon diffusion free energy (activation energy) was determined to be 1.2 eV (115.7 kJ/mol) on the basis of the diffusion-limited desorption standard model. (C) 2014 Elsevier Ltd. All rights reserved.