Istituto dei materiali per l'elettronica ed il magnetismo     
Salviati G., Sekiguchi T., Lazzarini L., Rossi F., Yuan X., Zha M., Calestani D., Grillo V. Cathodoluminescence spectroscopy of SnO2, In2O3 single nanobelts and ZnO single nanotubes. G. Salviati, T. Sekiguchi, S. Heun and A. Gustafsson, Eds (eds.). Trivandrum-695 023, Kerala, India: Research Signpost, T.C., 2008.
The last two decades have witnessed the increasing interest of the scientific community on the Cathodoluminescence technique because of its unique capability to achieve in a single experiment imaging and optical spectroscopy with lateral and in-depth resolution on nanometeric scale and controlled power dependent spectroscopy. The above mentioned possibilities allow to explore a wide variety of materials as far as the study of their optical properties on a local scale and the correlation with crystal defects are needed. In this paper a short review of the major results on the study of optical transitions in functional oxides is reported. Then the basics of Cathodoluminescence are briefly schematized and finally some emblematic examples of nanoscale spectroscopy of functional oxides single nanoribbons and nanotubes performed by the authors are presented. Among the non-carbon based materials, quasi-one-dimensional single SnO2, In2O3 nanoribbons and ZnO nanotubes have been chosen to demonstrate the potentiality of the power dependent and low-energy Cathodoluminescence spectroscopy respectively attached to a conventional and to a field emission Scanning Electron Microscope. As for SnO2 samples, it is shown how power-and temperature-dependent experiments evidence a correlation between Oxygen vacancies and the yellowgreen Cathodoluminescence emission as well as a variation across the nanoribbons, related to different facets at the growth front. No near band edge emission is found. This result is assigned to a major role of surface effects with respect to bulk properties. Further, power dependent Cathodoluminescence on In2O3 single nanowires evidences an anticorrelation between the integrated intensities of two emission bands peaked at 420 and 630 nm. In-situ low temperature cathodoluminescence spectroscopy before and after e-beam irradiation on single nanowires reveales that, contrary to what reported in the literature, only the emission at 420 nm is due to Oxigen vacancies. Finally, concerning ZnO hexagonal nanotubes, it is reported how temperature-dependent Cathodoluminescence spectroscopy evidences the nanotubes are incorporated with acceptors. Side view Cathodoluminescence along the nanotubes also shows the ultraviolet emission becomes weaker and red shifts along the growth direction. The results are explained by an unintentional impurity doping during the growth process.
Subject SEM

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