Cluster generation by laser ablation

We produced niobium clusters over a wide size range (Nbn: 1 n 1000) by a laser ablation method in a low-pressure condensation source. Mass spectra of the neutral clusters, positive and negative ion clusters were measured by a time-of-¯ight mass spectrometer with a high mass resolution and a wide mass range. Similarity and difference in their mass spectra were examined to understand the cluster generation process in different charged states. # 2001 Elsevier Science B.V. All rights reserved