Influence of High-Fluence Proton Irradiation on the Optical Absorption and Microstructure of Rutile
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Influence of High-Fluence Proton Irradiation on the Optical Absorption and Microstructure of Rutile Tiecheng Lu 1,3*, Sha Zhu 2 and Lumin Wang2 1 Department of Physics, Sichuan University, Chengdu 610064, P.R. China Key Laboratory of Radiation Physics and Technology (Sichuan University), Ministry of Education, P.R. China 2 Department of Nuclear Engineering and Radiological Sciences, University of Michigan, Ann Arbor, Michigan 48109, USA 3 International Center for Material Physics, Chinese Academy of Sciences, Shenyang 110015,P. R. China ABSTRACT Rutile (TiO2) single crystals of (110) or (001) orientation were irradiated by high fluence protons with the energy of 0.5, 4.9 and 18 MeV and with the fluence of 1×1018 and 1.9×1022 m-2. UV-VIS-IR, LRS and HRTEM were used to analyze the optical absorption and microstructure of samples. The UV-VIS-IR results showed that proton irradiation induces two absorption peaks centered at 760 and 1700 nm respectively, even high fluence irradiation induces absorption plateau at 600~2500 nm. LRS results showed that the related intensity of common vibration modes is different for different planes. Proton irradiation induces the vibration frequency and related intensity change for inherent LRS modes, and several new vibration modes also appear. High fluence proton irradiation induced large defect clusters, i.e. stacking faults, which is demonstrated by HRTEM observation. The optical absorption mechanism also has been discussed. INTRODUCTION Rutile, which possesses varied physical properties and unique photochemical characteristics, has created great interest in the field of water photoelectrolysis and photochemical cell since water photoelectrolysis can be achieved without decomposition of the rutile electrode [1]. For solar application, however, TiO2 is not suitable because its gap is 3 eV, too far away from the u.v. region to absorb solar energy significantly. But TiO2 remains high on the list of numerous materials since it has been regarded as the most stable material for a long time. So what really counts is decreasing its gap or increasing the optical absorption in the visible region by increasing the number of defects. Therefore the properties of defects in doped TiO2 have been extensively studied [2-4]. Recently, dye-sensitization has become a new modification method for solar application because organic dye has strong optical absorption in the u.v. region [5-6]. However, organic dye is unstable and subject to ageing. In fact, defects can also be introduced deliberately by irradiation [7-14]. Unfortunately, few papers have been reported the influence of neutron and/or proton irradiation on the optical properties of rutile [13,14]. As for material modification by ion beams, proton implantation or irradiation is an important and valuable method because proton projectile depth and implantation dose can be controlled accurately. In
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addition, the implanted ions, as well as the induced defects by implantation, can be introduced in exact layers of material. In this pap
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