DEVELOPMENT OF GLANCING ANGLE CEMS AND ANALYSIS OF TIN OXIDES BASED SEMICONDUCTORS.

我们的研究目的是开发一种可用于分析透明半导体和气体传感器材料较薄表面层中锡态的掠角转换电子穆斯堡尔光谱（GACEMS）。由于^<119>Sn穆斯堡尔效应后发射的内部转换电子（19.6 keV）范围很大（固体中约为2mum），因此传统方法对薄表面的灵敏度很小。为GACEMS设计了一个背向散射气体流量计数器，使^<119>Sn的伽马射线能够以低掠射角（<5^0）照射到表面。由于测量时间长，对测量系统也进行了改进，通过检测不同能量的转换电子，可以同时得到三到四个光谱。另一方面，用点电荷近似法和穆斯堡尔谱法重新估计了锡掺杂In_2O_3 （ITO）粉末和薄膜中锡的化学态。结果表明，在ITO晶格中除了两个电活性Sn^<4+>外，还存在7倍和8倍配位的Sn^<4+>。穆斯堡尔谱估计的载流子密度与实测值吻合较好。研究了注入Au和Fe离子的SnO_2薄膜的气敏性能，并用CEMS对其进行表征。并对CEMS在各个领域的应用进行了综述。

The purpose of our research is to develop a glancing angle conversion electron Mossbauer spectroscopy (GACEMS), which can be applied to the analysis of tin states in the thinner surface layrs of transparent semiconductors and gas sensors materials. Since the range of internal conversion electrons (19.6 keV) emitted after ^<119>Sn Mossbauer effect is large (about 2 mum in solid), the sensitivity of thin surface by a conventional method was small. A back scattered gas flow counter for GACEMS was designed so that the gamma rays of ^<119>Sn could be irradiated on the surface at low glancing angles (<5^0). Since the measuring time was so long, the measuring system was also improved so as to get three or four spectra simultaneously by detecting the conversion electrons with different energy. On the other hand, the chemical states of Sn in Sn-doped In_2O_3 (ITO) powders and films were reestimated by a point charge approximation and Mossbauer spectrometry. It was found that there are 7-and 8-fold coordinated, electrically inactive Sn^<4+> species in the ITO lattice in addition to two electrically active Sn^<4+> species. The estimated carrier densities by Mossbauer spectra were in good agreement with the measured values. Gas sensor properties of SnO_2 films implanted with Au and Fe ions also were studied, and will be characterized by CEMS.Further, the applications of CEMS to various fields have been reviewed.