Effects of low energy argon ion irradiation on the carbon 1s photoelectron line of highly oriented pyrolytic graphite

The effect of argon ion irradiation on the line-shape of high-resolution aluminium Kα X-ray excited carbon 1s photoemission from highly oriented pyrolytic graphite is described and comparisons made with related work. Irradiation with argon ions with 46 eV kinetic energy, an energy sufficient to penetrate the surface layer but not create lattice vacancies, did not broaden the carbon 1s photopeak. Irradiation with argon ions with 56 eV, an energy above the threshold for surface penetration and lattice vacancy creation, caused broadening of the carbon 1s line. The intensity of the argon 2p line indicated a maximum in the trapped argon concentration as a function of 56 eV argon ion dose. Irradiation with 70 eV argon ions gave similar photoemission results to those obtained after 56 eV argon ion irradiation but with a lower dose required to achieve a similar level of carbon 1s line broadening. The evidence suggests that broadening of the photopeak is primarily due to vacancy defects.