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Preparation and Characterization of Cobalt Doped ZnO and TiO2 Shaoguang Yang, Silas T. Hung, Herman H.Y. Sung, A.B. Pakhomov, C.Y. Wong Magnetic Innovation Center (MAGIC), Material Characterization and Preparation Facility, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, HONG KONG.

ABSTRACT Synthesis and characterization of transparent Co-doped ZnO and TiO2 diluted magnetic semiconductor (DMS) films are described. The films are prepared by single sputtering deposition. They are ferromagnetic at temperatures as high as 350 K. The films were characterized by X-ray diffraction (XRD), X-ray photoemission spectroscopy (XPS), X-ray fluorescence (XRF). Optical transparency was measured on UV/VIS spectrometer. The Codoped ZnO films had wurtzite structure similar to ZnO with the (002) preferential texture. Neither XRD nor XPS showed any presence of pure Co or CoO in the samples. The Co-doped TiO2 samples were amorphous, and some unoxidized Co was found in the films.

INTRODUCTION ZnO and TiO2 are wide gap semiconductors, which have been widely studied as optical materials. The wurtzite ZnO is transparent in the visible wavelength range due to a large band gap (3.3eV), the energy gap of this material can be extended up to ~4eV [1]. It is a promising candidate for ultraviolet laser device [2]. TiO2 has three types of crystal structures: rutile, anatase and brookite. For many technologically important properties, such as excellent optical transmittance in the visible and near-infrared region, high refractive index, and high dielectric constant [3, 4, 5], TiO2 has been investigated for several decades. Recently, diluted magnetic semiconductors (DMS) have been studied intensively as they are regarded the key materials for spin electronics [6]. Magnetic field controlled light polarization has been observed in experiments with DMS [7, 8]. (Ga,Mn)As, which has attracted much attention, has a ferromagnetic transition at the critical (Curie) temperature of 110K [9]. Theoretical analysis has predicted room temperature ferromagnetism in ZnO doped with transition metal [10]. Very recently, several experiments have illustrated the room temperature DMS is Co-doped ZnO [11] and TiO2 anatase [12], and rutile [13] systems, making roomtemperature magnetic and optical hybrid devices possible based on a single compound. In this work, we prepare Co-doped ZnO and TiO2 by sputtering method. We present comparative analysis of the magnetic and optical properties, and the structure of these materials.

SAMPLE PREPARATION AND CHARACTERIZATION The Zn1-xCoxO and Ti1-xCoxO2 samples were prepared by RF magnetron sputtering. Composite sputtering targets used in the deposition were prepared by mixing and compression Co3O4 and ZnO or Co3O4 and TiO2 powders at appropriate atomic ratios, followed by annealing at 1000 oC K9.14.1 Downloaded from https://www.cambridge.org/core. Columbia University Libraries, on 19 Jul 2017 at 14:11:42, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. http