Ultraviolet photoelectron spectra of mass-selected copper clusters: Evolution of the 3dband

Ultraviolet photoelectron spectra (UPS) have been measured for bare unsupported copper clusters in the 1–410 atom size range as mass selected from a supersonic, negatively charged, cluster ion beam. Using an ${\mathrm{F}}_2$ excimer laser at 7.9 eV, the UPS patterns display the evolution of the 3d band structure as a function of cluster size. Clusters larger than a few atoms were found to display an increasingly sharp feature at the onset of the 3d band similar to that seen for bulk copper UPS at low photon energies, suggesting that these larger clusters may already be crystalline.