Quantum characterization of some cluster-based materials

Three kinds of cluster-based materials are prepared by evaporation and iner t gas condensation method. Their structures and properties are examined by transmission electron microscopy, Raman scattering, STM/STS, optical spectr oscopy, etc. Some important results are obtained. (1) surface phonon modes of quasi-free Si clusters are observed when Si clusters softly land onto th e mother skeleton of the porous silicon and/or through grazing angle collis ions with the walls of the pores; (2) very sharp peaks of conductance reson ances are obtained when the STM tip is right on the top of the Au cluster d eposited on the H-terminated silicon crystal, and (3) large blue shifts and photoluminescence from violet to orange with main peaks in the blue range are observed from Ge cluster-based nanofilms at an excitation wavelength of 370 nm. Mechanisms are discussed including the quantum confinement effect of the Ge cluster cores, radiation transition from oxygen difficiency cente rs in the oxide surface layers, and exciton confinement in the interfacial layers bt tween the crystalline cores and thr oxide shells.