Study of impurity states in II-VI semiconductor particles by local photon-emission spectroscopy

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1.For the study of the local electronic structure of the surfaces and the microclusters, we have made a digital controlled UHV-STM which is able to record 2-dimensional map of the intensity of the photon emitted from the STM tunnel junction. An image of the photon map is recorded simultaneously with the measurements of a topography image by STM and the STS measurements. The spectral resolved photon-maps can also be obtained by using an optical band pass filter with the band width of about 50 nm and the center of the wave length of 700 and 650 nm. This apparatus is emplyed to observe the STM induced photon-maps for the film of the noble metal particles (Au and Ag) on the graphite surface. We have measured the photon images for various morphology of the film to investigate the correlation between the photon maps and the morphology of the films. We have observed that the photon map is dependent on the wave length of the collected light. We have found that the photon spectra is closely related with the geometry of the STM tip and the metal particles. The change in the spectral resolved photon map is explained in terms of the effect of the curvature radius of the STM tip on the photon spectra.2.We have studied the optical properties of the CdS microclustes. The microclustes of CdS microclusters in various sizes ranging from 1 to 2nm are prepared by precipitation technique.We have observed the size-dependnet absorption spectra for the CdS microclusters. The absorption edge for the CdS clusters increases in energy with the decrease in the cluster size. This observation is explained by the quantum size effect on the electronic levels of CdS microclustes.