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

1.为了研究表面和微团簇的局部电子结构，我们制作了一个数字控制的UHV-STM，它能够记录从STM隧道结发射的光子强度的二维图。光子图的图像与STM和STS测量的地形图像同时记录。采用带宽约为50 nm，中心波长为700 nm和650 nm的带通滤光片也可获得光谱分辨光子图。该装置用于观察石墨表面贵金属粒子（Au和Ag）薄膜的STM诱导光子图。我们测量了不同形态薄膜的光子图像，以研究光子图与薄膜形态之间的相关性。我们已经观察到光子图依赖于所收集光的波长。我们发现光子光谱与STM尖端的几何形状和金属粒子密切相关。光谱分辨光子图的变化可以用STM尖端曲率半径对光子光谱的影响来解释。我们研究了CdS微团簇的光学性质。采用沉淀法制备了1 ~ 2nm大小的CdS微团簇。我们观察了CdS微团簇的尺寸依赖性吸收光谱。CdS团簇的吸收边能量随团簇尺寸的减小而增大。这一现象可以用CdS微团簇电子能级上的量子尺寸效应来解释。

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.