Electron transport properties in Nb and NbN cluster-assembled films produced by a plasma–gas–condensation cluster source

Nb and NbN cluster-assembled films were produced by a plasma–gas–condensation cluster deposition apparatus and examined by transmission electron microscopy, electrical resistivity, and ultraviolet photoemission spectroscopy. The electron diffraction patterns of the Nb and NbN clusters displayed body-centered-cubic and NaCl-type diffraction rings, respectively. The electrical sheet resistance, R□, of both Nb and NbN cluster-assembled films, however, showed no superconductivity down to 2 K. We found a linear relation in the log R□ versus T−1/4 plot for the Nb cluster assembly, suggesting an electron localization effect. For the NbN cluster-assembly, on the other hand, R□ showed a semiconductor type temperature dependence, which is consistent with the valence electron spectra.