Formation of large carbon cluster ions at graphite (HOPG) surfaces by laser irradiation

The formation process of carbon cluster ions by the irradiation of CO2 laser and N2 laser on the different surfaces of graphite (HOPG) has been investigated. Large cluster ions Cn+ (44 ≤ n ≳ 160) were observed by the first irradiation of CO2 laser pulse on a cut surface of which normal axis is perpendicular to the c-axis of the graphite, whereas only small cluster ions were obtained by the irradiation on cleaved surfaces. The N2 laser produced only small cluster ions on the cut and cleaved surfaces. The formation mechanism of the large cluster ions is considered to be the condensation of carbon vapor in gaps between graphite crystallites being exposed at the cut surface.