Cluster formation in UV laser ablation plumes of ZnSe and ZnO studied by time-of-flight mass spectrometry.

The composition of nitrogen laser (wavelength 337 nm, pulse width 3 ns) induced ablation plumes from ZnSe and ZnO targets was studied at different laser fluences using a time-of-flight mass spectrometer. In the case of ZnSe, abundant ion signals corresponding to Se and ZnSe clusters, some of which were Se-rich, were detected with fluence-dependent distributions. At a laser fluence of 1250 J m[sup -2], clusters with elevated intensity were observed at sizes of 6, 13, 19, 23 and 33 ZnSe molecules (‘magic numbers’), which match quite well with the earlier observation by others of magic numbers of chemically similar ZnS produced by a conventional vaporization and quenching scheme. In the case of ZnO, we detected the presence of atomic Zn and molecular species of ZnO, as well as a series of (ZnO)[sub n]-type clusters with fluence-dependent distributions. Unlike the case of ZnSe, no magic numbers were observed for ZnO. [ABSTRACT FROM AUTHOR]