Thermal desorption process and surface roughness of POCO graphite irradiated by hydrogen ion beam

Abstract

POCO graphite samples are irradiated by H + 3 ion beams with an energy of 9 keV, and the thermal desorption of methane and hydrogen are investigated by a thermal desorption spectroscopy (TDS). Surface roughness factors of the samples are also measured by the BET method. Most of the incident hydrogen ion is trapped in the graphite. The trapped hydrogen is desorbed in the form of H 2 and CH 4, and the ratio of the trapped hydrogen desorbed in the form of CH 4 is (0.4–3)%. An activation energy of the methane is estimated to be 2.3 eV. In the TDS spectra of H 2, two peaks of the desorption rate are observed. From the profile of the desorption rate, the surface density of hydrogen is estimated. The estimated activation energy is 1.2 eV. The heating temperatures corresponding to the peaks increase in the low fluence range and decrease in the high fluence range. The surface roughness is reduced with increasing hydrogen fluence. The relation of the surface roughness with the desorption rate is also discussed.