Defect and disorder reduction by annealing in hydrogenated tetrahedral amorphous carbon

Hydrogenated tetrahedral amorphous carbon (ta-C:H) is a form of diamond-lik e carbon with a high sp(3) content (>60%), grown here using a plasma beam s ource. Information on the behaviour of hydrogen upon annealing is obtained from effusion measurements, which show that hydrogen does not effuse signif icantly at temperatures less than 500 degrees C in films grown using methan e and 700 degrees C in films grown using acetylene. Raman measurements show no significant structural changes at temperatures up to 300 degrees C. At higher temperatures, corresponding to the onset of effusion, the Raman spec tra show a clustering of the sp(2) phase. The density of states of ta-C:H i s directly measured using scanning tunnelling spectroscopy. The measured gr adients of the conduction and valence band tails increase up to 300 degrees C, confirming the occurrence of band tail sharpening. Examination of the p hotoluminescence background in the Raman spectra shows an increase in photo luminescence intensity with decreasing defect density, providing evidence t hat paramagnetic defects are the dominant non-radiative recombination centr es in ta-C:H. (C) 2000 Elsevier Science S.A. All rights reserved.