Graphitic clusters in hydrogenated amorphous carbon induced by keV-ion irradiation

Abstract
Energy gap and hydrogen concentration have been measured in hydrogenated amorphous carbon (a-C:H) after bombardment with 100 keV He+ and 300 keV Ar+ ion beams, up to ion fluences 3×1016 ions/cm2. a-C:H films have been obtained by ion irradiation at low ion fluences of polystyrene layers and with a subsequent low-temperature annealing (400 °C, 10 min). Experimental values for the energy gap (2.5–0.5 eV) and hydrogen concentration (7.4×1022–1.8×1022 H atoms/cm3) have been interpreted in terms of a graphitic cluster structure with a different size (3–20 Å). We were able to determine experimentally the value of the bond integral ‖β‖ and we found it in good agreement with the calculated one for graphite.