Electronic and Atomic Structures of the Nano-material Studied by X-ray Absorption Spectroscopy and Scanning Photoelectron Microscopy

• Main Authors: Jau-Wern Chiou, 邱昭文
• Other Authors: Way-Faung Pong
• Format: Others
• Language: en_US
• Published: 2005
• Online Access: http://ndltd.ncl.edu.tw/handle/21284270437068326293

博士 === 淡江大學 === 物理學系博士班 === 93 === The development of third generation synchrotron radiation sources has provided powerful spectroscopic techniques for probing the electronic structures of nanomaterials. Primarily five techniques namely; X-ray absorption spectroscopy (XAS) (mainly X-ray absorption near edge structure, XANES), X-ray photoelectron spectroscopy (XPS), scanning photoelectron microscopy (SPEM), X-ray magnetic circular dichroism (XMCD), and X-ray emission spectroscopy (XES), have been extensively employed to understand the unoccupied as well as occupied states of electronic structures of nanomaterials; carbon nanotubes (CNTs), ZnO & Zn1-xCoxO nanorods, GaN nanowires, and AlN nanotips. Angle-dependent measurements were performed to understand the local electronic structures of the tips and sidewalls of highly aligned CNTs and ZnO nanorods. It suggests that increase in tip intensities is quite uniform over an energy range wider than 10 eV and the tip surfaces of the highly aligned ZnO nanorods are terminated by O atoms and the nanorods are oriented in [000 ]. An analysis of XANES spectra at O K- and Zn K-edge of ZnO nanorods at various diameters showed enhancement of surface states with decrease of diameter. Spectroscopic studies on Zn1-xCoxO nanorods showed that the ferromagnetism is strongly associated with the transfer of electrons from deep defect states to valence-band Co 3d orbitals. A comparison of the XANES spectra at N (Ga) K-edge revealed that the GaN nanowires have smaller (larger) intensity than that of GaN thin film, which suggests an increase of the N (Ga) negative (positive) effective charge in the nanowires. Apart from this, a comparison of the electronic structures was carried on AlN nanotips grown on p- and n-type Si substrates and the SPEM study indicates that the former have larger density of states than the latter near Fermi level.