FORMATION OF LARGE CARBON CLUSTER IONS AT GRAPHITE (HOPG) SURFACES BYLASER IRRADIATION

The formation process of carbon cluster ions by the irradiation of CO2 laser and N-2 laser on the different surfaces of graphite (HOPG) has been investigated. Large cluster ions C-n(+) (44 less than or equal to n greater than or similar to 160) were observed by the first irradiat ion of CO2 laser pulse on a cut surface of which normal axis is perpen dicular to the c-axis of the graphite, whereas only small cluster ions were obtained by the irradiation on cleaved surfaces. The N-2 laser p roduced only small cluster ions on the cut and cleaved surfaces. The f ormation mechanism of the large cluster ions is considered to be the c ondensation of carbon vapor in gaps between graphite crystallites bein g exposed at the cut surface.