The surface evolution of highly-oriented pyrolytic graphite, bombarded with 1keV Ar+ to doses of between 5 x 1011 and 1013/cm2 during annealing, was investigated by scanning tunnelling microscopy and atomic force microscopy in the tapping mode. Hillocks were observed by using scanning tunnelling microscopy and atomic force microscopy after ion bombardment. The height of a hillock, as measured by scanning tunnelling microscopy was larger than that measured by atomic force microscopy. The ion-bombarded surface recovered in 3 stages during annealing. The first stage was at 473 to 873K, the second stage was at 873 to 1473K and the third stage was at 1473 to 1873K. In the first stage, many of the ion-induced hillocks recovered rapidly and irregular dome-like protrusions formed due to the recombination of mobile interstitial clusters with immobile vacancies and the aggregation of interstitial clusters. In the second stage, the hillocks recovered slightly and dome-like protrusions aggregated into larger dome-like protrusions. In the third stage, the hillocks recovered completely and dome-like protrusions changed from irregular shapes to regular circles (with the monatomic step-height of graphite) due to a change from irregular C interstitial clusters to a complete extra plane in graphite. Hexagonal hollows were also formed and became larger circular hollows above 1623K (with the monatomic step-height of graphite) due to vacancy clusters formed by the migration of vacancies and the collapse of the neighboring layers in graphite.

Evolution of Ar+-Damaged Graphite Surface during Annealing as Investigated by Scanning Probe Microscopy. B.An, S.Fukuyama, K.Yokogawa, M.Yoshimura: Journal of Applied Physics, 2002, 92[5], 2317-22