Dissertation > Excellent graduate degree dissertation topics show

Study of Electronic Structure and Magnetism in ZnO-based Diluted Magnetic Semiconductors

Author: HuFengChun
Tutor: WeiShiQiang
School: University of Science and Technology of China
Course: Synchrotron Radiation and Applications
Keywords: X-ray absorption fine structure Diluted magnetic semiconductors Co -doped ZnO films Co, Cu doped ZnO Local Structure Solubility Magnetic mechanism
CLC: TN304.21
Type: Master's thesis
Year: 2009
Downloads: 245
Quote: 0
Read: Download Dissertation

Abstract

In this thesis, the use of synchrotron radiation X-ray absorption fine structure (XAFS) technology, combined with a variety of other experimental means of joint research from both experimental and theoretical aspects of the structure and performance of the different methods of preparation of the transition metal doped ZnO-based diluted magnetic semiconductor system . Sol - gel (sol-gel) method and pulsed laser deposition (PLD) method, a series of transition metal-doped and co-doped samples were prepared equilibrium growth and non-equilibrium growth. XAFS the method detailed study of the different preparation methods and doping conditions, changes in the local structure of the transition metal atoms in ZnO medium and doping atoms in the local structure of Zn atoms in the matrix. Dopant atoms occupying, the coordination environment of the local structure information, parse the presence of transition metal matrix ZnO and solubility. The combination of superconducting quantum interference device (SQUID) and vibrating sample magnetometer (VSM) gives the magnetic properties, microstructure explore ferromagnetism sources and Mechanism for the preparation of high-performance ZnO-based semiconductor The experimental and theoretical basis. Co clusters in Zn _1-x Co _x O dilute magnetic semiconductor thin film, the use of XAFS and XRD studies of pulsed laser deposition (PLD) on Si ( 100) the prepared Zn _{substrate 1-x} O, the Co. _{x (x = 0.02, 0.05, 0.10) diluted magnetic semiconductor films local structure and magnetic properties. The results showed that in a low content of Zn _0.98 Co _0.02 O film sample, Co mainly in the form of alternate bits exist, while in the higher content of Zn _{0.95 < / sub> Co _0.05 the O and Zn0.90Co0.10O film samples, part of the Co atoms to the metal on Co clusters precipitation. Magnetic measurement results show that the Co atom magnetic moment MS is significantly reduced with the increase of the Co concentration, Co clusters is superparamagnetic. Zn _0.98 Co _0.02 O film samples, due to the formation of oxygen vacancies in the substitutional Co atoms generated strong local structure distortions induced by the intrinsic weak ferromagnetism. 2 co-doped Cu ions Zn _0.95 Co _0.05 O dilute magnetic semiconductor solubility and structure the use of XAFS technical studies sol - gel prepared Co , Cu-doped Zn _0.95-x the of Cu _x Co _0.05 O (0 ≤ x ≤ 0.08) dilute magnetic semiconductor (dilute magnetic semiconductors the DMS ) material. For all samples, the Co K-edge XAFS results show that the incorporation of Co ^{2 ion completely replace Zn ^{2 ion position and causing the expansion of the lattice. While the Cu K-edge XAFS and XRD results show that the the Cu ion doped samples burning at 1073K CuO matter. Warp after sintering of the high temperature (1473K), is doped at a low Cu concentration (x ≤ 0.02), Cu ion substitution position of the Zn dopant concentration, while at higher Cu (x ≥ 0.05), and there is still a small amount of Cu as CuO phase presence. By XAFS results estimate the Cu ions Zn _0.95 Co _0.05 O DMS solubility of about 0.04. Meanwhile, OK edge XANES spectra showed that the series of samples burning 1073K under a large number of alternate bits formula Co exist in dimer form; under calcining the samples in alternate bit formula Co, Cu ions are uniformly dispersed in the ZnO lattice. These results for the synthesis of co-doped ZnO-based DMS materials provided experimental guidance. 3 Zn _0.95-x}}} Co, Cu _{x _0.05 O nano polymer structure and performance by the sol - gel process Zn < sub> 0.95-x} Cu _x Co _0.05 O dilute magnetic semiconductor materials. The magnetic measurements showed that the samples with weak ferromagnetism. XAFS, XRD and XPS results showed that the Co completely substitutional dispersed ZnO lattice, and resulted in the expansion of the local structure and twisted. Lower Cu Doping concentration (x ≤ 0.02), Cu ions substitutional form exists, and is doped at a higher Cu concentration x ≥ 0.05, part of the Cu ions form of CuO phase. The analysis showed that the structural distortion and the sample in the pressuring process the formation of grain boundary defects Zn _0.95 Co _0.05 O weak room temperature ferromagnetic source of. For Zn _0.95-x the of Cu _x Co _0.05 O co-doping of Cu (2) state instead of the location of ZnO in Zn , but because of its 3d orbital by Co 3d orbital hybridization to migrate to the direction of the energy gap formed localized impurity, and not with the O 2p orbital full hybrid and therefore can not effectively induced ferromagnetic interaction. This indicates that the Cu ^{2 / Zn ^{2 alternative not only a necessary condition for a ferromagnetic. The microstructure analysis showed that Zn _0.95-x Cu _x Co _0.05 O magnetic properties of the sample from the Zn _0.95 Co _0.05 O substrate surface formed of Cu-O of nanophase or CuO particles and other second phase.}}}

Related Dissertations

CLC: > Industrial Technology > Radio electronics, telecommunications technology > Semiconductor technology > General issues > Material > Compound semiconductor > Oxide semiconductor
© 2012 www.DissertationTopic.Net Mobile