RESEARCH ACTIVITIES   Electrical Transport Properties of Nanocrystal (Nanoclusters) Assemblies   45. O. Mamezaki, M. Fujii, and Shinji Hayashi, "Internal Photoemission from Ag Nanoparticles Embedded in Al2O3 Film,” Japanese Journal of Applied Physics, Vol. 40, No. 9A, pp.5389-5393, September (2001). Photocurrent properties of Al2O3 films containing Ag particles a few nanometers in diameter were studied. In the dark, the films exhibit T-1/2 dependence of ln (σ), where σ and T are the conductivity and temperature, respectively. This dependence indicates that the electron transport is carried out by thermally activated electron tunneling between Ag nanoparticles. Under UV-light irradiation, the photocurrent produced in the films was observed. The photocurrent could be well explained by the internal photoemission from Ag nanoparticles and/or electrodes. 15. Minoru Fujii, Osamu Mamezaki, Shinji Hayashi and Keiichi Yamamoto, "Current Transport Properties of SiO2 Films Containing Ge Nanocrystals,” Journal of Applied Physics, Vol. 83, No. 3, pp.1507 - 1512, February (1998). The electrical transport properties of SiO2 films ( ≥ 3 μm in thickness) containing Ge nanocrystals have been studied. We found that the films exhibit T−1/2 dependence of ln(σ) under relatively low electric fields independent of the volume fraction of Ge in the films, where T and σ are the temperature and the conductivity, respectively. The observed electrical properties could be well explained by the theory developed by Šimánek [Solid State Commun. 40, 1021 (1981)] which considers the tunneling of thermally activated carriers between neighboring nanocrystals.  14. Minoru Fujii, Takeshi Kita, Shinji Hayashi and Keiichi Yamamoto, "Current Transport Properties of Ag-SiO2 and Au-SiO2 Composite Films: Observation of Single Electron Tunneling and Random Telegraph Signals,” Journal of Physics: Condensed Matter, Vol. 9, No. 41, pp. 8669-8677, October (1997). Current-transport properties of extremely thin composite films of and (about 9 to 15 nm in thickness) were studied. The observation of the sample cross-section by high-resolution transmission electron microscopy revealed that only a few Ag (Au) nanocrystals exist across the films. In spite of the simple device structure (i.e. just sandwiching the granular film between Al electrodes) and very large electrodes , Coulomb blockade (CB) and Coulomb staircase (CS) structures have been clearly observed at low temperatures. As the temperature rose, the CB and CS structures smeared out and random telegraph signals due probably to a charge trapped at the interfaces between the nanocrystals and matrices were observed. 9. Minoru Fujii, Yoku Inoue, Shinji Hayashi and Keiichi Yamamoto, "Hopping Conduction in SiO2 Films Containing C, Si and Ge Clusters,” Applied Physics Letters, Vol. 68, No. 26, pp. 3749-3751, June (1996). emperature dependence of electrical characteristics of SiO2 films doped with C, Si, and Ge were studied. The conductivity σ was found to vary with the temperature as lnσ∝T−1/4 over a wide temperature range, indicative of the conduction by the variable range hopping (VRH) mechanism. Since the previous optical studies for the same films indicate the existence of clusters in the films, it is very likely that the VRH through localized states associated with clusters dominates the conduction process, irrespective of the kind of group IV elements.