A Study Of Fabrication, Microstructure And Magnetic Properties For Diluted Magnetic Semiconductors Nanowire Of Co_xSn_1-xO₂

Diluted magnetic semiconductors (DMS) have been considered as the main materials to make the electronic devices by using spin degrees of freedom and hence are promising for application. The previous DMS were obtained by doping magnetic impurities into host semiconductors, mostly II-VI and III-V compounds. Room temperature ferromagnetism in DMS has been reported by several groups. Up to now most of the effort has been focused on the preparation and characterization of thin film and bulk materials, little work has been done on the fabrication of one-dimensional DMS nanostructures. Spin effects in nanoscale semiconductors are still largely unexplored, however, and many essential advances in this field would be facilitated by the development of facile methods for the preparation of high-quality DMS nanostructures. SnO₂ is a very interesting oxide semiconductor with a wide band gap of～3.6 eV. Its high optical transparency, electrical conductivity and chemical sensitivity make it a very attractive material for solar cells, catalysis and gas-sensing applications. In this thesis SnO₂ and Co_xSn_1-xO₂ nanowires were successfully fabricated by chemical vapor deposition (CVD) method. The X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray (EDX), transmission electron microscopy (TEM), selected area electron diffraction (SAED) and vibrating sample magnetometer (VSM) were used to investigate the microstructure, morphology, magnetic properties of SnO₂ and Co_xSn_1-xO₂ nanowires.The main results are as following:1. SnO₂ nanowires have been deposited on the Si wafer by the catalyzer assisted CVD method. The as-grown nanowires are homogeneous in diameter with the diameters varying from 50nm to 200nm. The length of nanowires can reach several hundred microns.2. The morphology of nanowires is sensitively influenced by the fabrication conditions, especially catalyzer, the flux of O₂ and Ar respectively.3. The growth mechanism of the SnO₂ nanowires has been suggested to be dominated by gas-liquid-solid (VLS) process. The diameter of the as-grown nanowires is restricted by the size of catalyzer granule.4. CoxSnl-xO2 nanowires have been also deposited on the Si wafer by the CVD method. The diameter of the Co_xSn_1-xO₂ nanowires is the similar to that of SnO₂ nanowires obtained under the same fabrication conditions, because of the restriction of cataluzer drop, While the length is much small, indicating that the growth is restrained by doping of cobalt.5. The Co_xSn_1-xO₂ nanowires samples exhibit an evident hysteresis loop at RTtemperature by the VSM test. Magnetic moment per Co atom reaches 1.8μB, andsharply decrease with the increase of the doping content.6. XRD study shows that no peak of Co clusters are found in the instrument's sensitivity in the Co_xSn_1-xO₂ nanowires samples. It is believed that RTFM does not come from Co clusters, but is the intrinsic property of the nanowires.