BL-7C/2012G738
Yasuhisa Tezuka 1*, Sekiya Nakamoto 1 , Yuto Yokouchi 1 , Masaya Mikami 1 , Shunsuke Nozawa 2 , Toshiaki Iwazumi 3 , Yoichi Ishiwata 4 , 1Grad. Sch. of Sci. and Tech., Hirosaki Univ., Hirosaki, Aomori, 036-8224, Japan ²Photon Factory, Inst. of Mats. Struct. Sci., Tsukuba, Ibaraki, 305-0801, Japan ³Grad. Sch. of Eng., Osaka Pref. Univ., Sakai, Osaka, 599-8531, Japan 4 Grad. Sch. of Sci. and Tech., Saga Univ., Saga, Saga, 840-8502, Japan l Introduction exhibits titanium-dioxide (TiO 2 ) Anatase larger photocatalytic activity than other polymorphs; rutile and brookite. The electronic structure should be investigated to make clear the nature of TiO 2 . We have reported X-ray Raman scattering (XRS) of several Ti-oxides [1] and anatase [2] excited around Ti K absorption edge. In this study, we investigated electronic structure of nano- particle anatase and its doping-effect with Co 2+ .
2 Experiment
Nano-particle anatase made by thermal was decomposition method. The structure and particle size (~5nm) were confirmed by X-ray diffraction and transmission electron microscope methods, respectively. XRS spectra were observed using X-ray emission (ESCARGOT) spectrometer BL-7C. at  beamline Scattered photon was analyzed using Ge(400) and detected by one-dimensional multi-channel proportional counter. The energy resolution of XRS measurements was about leV for 5keV photon. In this experiment, XRS spectra were excited at 4963.0 eV that is just below Ti K absorption edge where Ti 3d state was observed via quadrupole transition [1].
3 Results and Discussion
Figure 1 shows XRS spectra of two kinds of anatase which have different particle-sizes. The XRS spectra are plotted against energy-loss from excitation (Raman shift). These samples were made in different growth time; longer growth-time results larger particle-size. We have reported that four peaks on the right correspond to the excitation of Ti 2p3d , while three peaks on the left correspond to the excitation of Ti 2p4p , where underline denote core-hole [1]. The Ti 2p3d peaks are split by ligand-field and spin-orbit interaction as shown in the figure. The figure shows the whole 3d peaks become weak in larger sample, while 4p peaks does not change. Since the XRS spectra reflect unoccupied 3d state, the intensity change suggests increase of 3 d -electron numbers. Usually, crystal of TiO 2 has rutile structure at RT and anatase undergoes a transition to rutile phase when annealed at high temperature, while nano-particle TiO 2 has anatase structure. The fact means that bond strength become tighter with increasing particle size. The result in this study suggests increasing of hybridization between Ti and O with increasing particle-size. Fig.1 Size dependence of XRS spectra of nano-particle anatase.  Line: smaller size, Dot: larger size. anatase; Line: non-doped, Dot: Co-doped. Figure 2 shows doping-effects of XRS spectra. Black line shows XRS of non-doped sample that is same with smaller sample in Fig. 1, while blue dot shows XRS of doped samples with about 8% Co. The figure shows the t 2g peaks of L III excitation become weak in doped sample, while the t 2g peaks of L II excitation does not change very much. The Co ion is thought to be Co 2* and electrons are doped in the anatase. Usually, the doped electron enters in lowest levels of unoccupied state.  The result seems to be consistent roughly to the doping effect. Multiple scattering effects might affect in the L II scattering.