TiO₂ nanofilm growth by Ti ion implantation and thermal annealing in O₂ atmosphere

TiO 2 nanofilm growth by Ti ion implantation and thermal annealing in O 2 atmosphere 1 corresp first-author Corresponding author, zhouxd516@163.com Corresponding author, zhouxd516@163.com zhouxd516@163.com 1 1 1 School of Physics and Electromechnical Engineering, Zhoukou Normal University, Zhoukou 466001, China School of Physics and Electromechnical Engineering, Zhoukou Normal University, Zhoukou 466001, China TiO 2 nanofilms on surface of fused silica were fabricated by Ti ion implantation and subsequent thermal annealing in oxygen ambience. The silica glasses were implanted by 20 kV Ti ions to 1.5×10 17 ions/cm 2 on an implanter of metal vapor vacuum arc (MEVVA) ion source. Effects of annealing parameters on formation, growth and phase transformation of the TiO 2 nanofilms were studied in detail. Optical absorption spectroscopy, Raman scattering spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy and transmission electron microscopy measurements were done to figure out formation mechanism of the TiO 2 nanofilms. The formation of TiO 2 nanofilms was due to out-diffusion of the implanted Ti ions to the substrate surface, where they were oxidized into TiO 2 nanoparticles. Formation, phase, and thickness of the TiO 2 nanofilms can be well tailored by controlling annealing parameters. Ion implantation Thermal annealing TiO 2 nanofilms Characterization I. INTRODUCTION 1 Since TiO 2 -photoassisted electro-chemical water splitting was reported by Honda and Fujishima in 1972 [ 1 1 ], titanium oxides have attracted much attention due to their wide applications, such as photocatalysis for environmental treatments and hydrogen production, dye-sensitized solar cells for photovoltaics, sensors, smart windows, and display devices, etc. [ 2 2 - 5 5 2-5 ]. Conventional TiO 2 powder catalysts are disadvantageous in the needs of stirring in the reaction and separation (after reaction). TiO 2 thin films make it possible to overcome the disadvantages and extend industrial applications. A variety of techniques were used to prepare TiO 2 thin films, including sol gel processing [ 6 6 ], spray pyrolysis [ 7 7 , 8 8 ], magnetron sputtering [ 9 9 ], and chemical vapor deposition [ 10 10 ]. Photocatalytic TiO 2 films prepared by wet chemistry process (e.g., sol gel method) show good photocatalytic performance, but their mechanical durability is not good enough for practical applications such as self-cleaning glasses for window and automotive mirror. In addition, they are generally inferior for applications requiring large area films [ 11 11 ]. While applications of these TiO 2 films are limited due to their unsatisfactory stability and reliability, TiO 2 films fabricated by physical methods generally have higher film adhesion and stability for practical uses [ 12 12 ]. Nanomaterials, nanoparticles and nanofilms can be fabricated by ion implantation. Metal oxide semiconductors are produced by a solid phase growth process of metal ion implantation and subsequent thermal oxidation, such as ZnO [ 13 13 - 16 16 13-16 ] or TiO 2 [ 17 17 , 18 18 ] nanomaterials by Zn or Ti ion implantation. Nanofilms made by ion implantation, due to their formation under high temperatures, usually show good adhesion and stability. In this paper, TiO 2 nanofilms in the solid phase growth process of Ti ion implantation are formed into fused silica substrate and subsequent thermal annealing in oxygen ambience. Effects of the implantation and annealing parameters on the formation, phase and growth of the TiO 2 nanofilms are studied, so as to understand mechanisms of TiO 2 nanofilm formation. The nanofilm thickness and phase can be well tailored by controlling the implantation and annealing parameters. II. EXPERIMENTAL 1 A. Sample preparation 2 High purity silica slides (20 mm×20 mm×1 mm) were implanted by 20 kV Ti ions to 1.5×10 17 ions/cm 2 on an implanter of metal vapor vacuum arc (MEVVA) ion source. The samples were kept rotating in a horizontal plane during ion implantation, with the sample holder being cooled by circulating water. The implanted samples were annealed under O 2 atmosphere in a conventional tube furnace. Group 1 of the samples were annealed for 2 h at 500 ℃, 600 ℃, 700 ℃, 800 ℃, 900 ℃ and 1000 ℃. Group 2 were annealed at 800 ℃ for 2, 4 and 6 h. B. Sample characterization 2 Optical absorption spectra of the samples were measured on a UV-vis-NIR dual-beam spectrophotometer (Varian Cary5000) in wavelength range of 200–800 nm. Surface morphologies of the implanted samples before and after thermal annealing were examined by using a scanning electron microscopy (SEM, FEI Sirion). Raman scattering spectra were measured using a micro-Raman microscope (Jobin-Yvon LabRAM HR) equipped with a cooled CCD detector under a backscattering geometry to identify the crystalline phase of TiO 2 . The excitation source was the blue line (488 nm) of an Ar + laser powered at 5 mW, with its scan density varying from 100 to 1200 cm -1 . Microstructural characterization of the as-implanted and annealed samples was performed on a JEOL 2010 (HT) transmission electron microscope (TEM) operated at 200 kV. X-ray photoelectron spectroscopy (XPS) analysis was done on a Kratos XSAM800 XPS system with Mg K α (1253.6 eV) as the radiation source under a vacuum of 6×10 -7 Pa. III. RESULTS AND DISCUSSION 1 A. Optical absorption spectra of Ti ions implanted samples versus annealing temperature 2 Figure 1 Figure 1 shows optical absorption spectra of the as-implanted sample and the samples annealed for 2 h at 500–1000 ℃. In the absorption spectra of the as-implanted sample, the background absorption increases drastically in the UV and visible regions. This is due to absorption of implantation-induced point defects and the Ti nanoparticles formed in silica substrate. Annealed at 500 ℃, the background absorption reduces drastically due to the defect annihilation by thermal annealing. Also, an abrupt absorption edge appears, due to presence of anatase TiO 2 [ 19 19 , 20 20 ], which was formed upon post-implantation annealing at 500 ℃. For all the annealed samples, the spectra present a trend that the absorption edges shift to longer wavelength with the increase of annealing temperature, implying an increase in mean sizes of the TiO 2 nanoparticles. It is interesting to note that the sample annealed at 1000 ℃ differs obviously from other annealed samples in spectrum with a greater shift of absorption edge to longer wavelength. This remarkable shift of absorption edge suggests that phase transformation of TiO 2 from anatase to rutile may occur at 1000 ℃. Such shifts of the maximum absorption and absorption edge induced by the phase transformation are similar to the results in Refs. [ 20 20 , 21 21 ]. B. SEM images of Ti ions implanted samples versus annealing temperature 2 Surface morphologies of the samples were investigated by SEM. Figure 2 Figure 2 shows the SEM images of the Ti ions implanted samples annealed for 2 h at 500, 600, 700, 800, 900 and 1000 ℃. On the whole, the surface morphology changes obviously for the samples annealed at different temperatures. At 500 ℃, some small-sized nanoparticles began to appear, indicating the TiO 2 nanoparticles formed at 500 ℃. At 600 ℃, a smooth and homogenous film was formed, with many near-spherical nanoparticles distributed compactly on the substrate surface. The sizes of TiO 2 nanopartices increase with the annealing temperature, with the mean diameter of particles being 25.3, 37.6 and 45.8 nm at 600 ℃, 700 ℃ and 800 ℃, respectively. At 900 ℃, however, the TiO 2 nanoparticles in the surface aggregated and formed cross-linked particles of about 61.4 nm in diameter, as shown in Fig. 2(e) Fig. 2(e) . The surface morphology underwent a big change at 1000 ℃, and the TiO 2 nanoparticles in the substrate surface became embedded and undistinguished, as shown in Fig. 2(f) Fig. 2(f) . Interestingly, evolution of surface morphologies of the samples as a function of annealing temperature in Fig. 2 Fig. 2 is well related with the results from optical absorption spectra ( Fig. 1 Fig. 1 ). The increase in both the particle size and crystal quality as a function of annealing temperature leads to the absorption edge shift towards longer wavelength. The abrupt shift of absorption edge observed at 1000 ℃ is just a result of structure change characterized by SEM, and the change may be due to the phase transformation from anatase to rutile. C. Formation and phase of TiO 2 nanocrystals: Raman scattering spectroscopy and XPS measurements 2 The Raman spectroscopy measurements were made to identify and analyze the formation and phase of TiO 2 nanocrystals after thermal annealing. Figure 3 Figure 3 shows Raman spectra of the bare silica, the as-implanted sample and the Ti ions implanted samples annealed for 2 h at 500–1000 ℃. Some Raman peaks of SiO 2 can be observed in the bare silica sample. However, Raman spectrum of the as-implanted silica became almost featureless due to extensive structural damage induced by ion implantation. The structure of silica is partially recovered by subsequent thermal annealing, and the Raman peaks of SiO 2 in the annealed samples can be observed again. A Raman peak centered at about 140 cm -1 appears at 600 ℃. This can be assigned as E g mode of TiO 2 in anatase phase [ 22 22 , 23 23 ]. The Raman peak height increases with temperature from 600 ℃ to 900 ℃, indicating the increased crystallinity and amount of the anatase phase TiO 2 . However, for the sample annealed at 1000 ℃, the spectrum shape changed, with three Raman peaks centered at 605, 440 and 230 cm -1 . These can be ascribed to the two-phonon scattering of A 1g and E g modes, and the second-order effect of the rutile phase TiO 2 , respectively [ 24 24 ]. Thus, the anatase-to-rutile phase transformation taking place at the high temperature is confirmed. The formation and evolution of the anatase phase in the annealed samples is consistent with the evolution of optical absorption spectra in Fig. 1 Fig. 1 and SEM in Fig. 2 Fig. 2 . The increase in size and crystal quality of the nanoparticles as a function of annealing temperature leads to the red-shift of the absorption edge and the intensification of the E g Raman mode. However, the absorption edge of TiO 2 in the sample annealed at 500 ℃ was observed, while the crystalline phase in the same sample was not detected by Raman spectroscopy. It is well known that optical absorption spectrum usually gives average structural information, whereas Raman scattering spectrum as a local probe is sensitive to crystallinity and microstructures of materials. That the Raman peaks could not observed implies that annealing at lower temperatures produced not enough TiO 2 nanocrystals, which can be verified by the SEM image in Fig. 2(a) Fig. 2(a) . Also, the nanocrystals are not of good crystallinity, though the absorption edges of TiO 2 were confirmed by optical absorption measurement. By carefully analyzing the change of E g modes centered at 140 cm -1 of the anatase phase TiO 2 as a function of annealing temperature, we found that the intensity, frequency and linewidth (FWHM) of the E g Raman mode are strongly dependent on the annealing treatment. The linewidth of Raman peaks indicates that the TiO 2 nanofilms are of high crystallinity. The intensity of E g Raman mode increases with annealing temperature, accompanied by a downshift in frequency and a decrease in linewidth. The sample annealed at 900 ℃ exhibits a large downshift in frequency and an obvious decrease in the linewidth. A similar behavior of frequency shift and linewidth decrease of E g Raman mode was observed in TiO 2 nanoparticles fabricated by other methods [ 24 24 - 28 28 24-28 ]. Mechanisms proposed to interpret this behavior include the phonon confinement effect [ 24 24 , 29 29 ], internal stress/surface tension effects [ 28 28 , 30 30 ], and nonstoichiometry due to oxygen deficiency [ 25 25 , 26 26 ]. The pressure effect mechanism usually leads to large frequency shifts, and Raman measurements as a function of the external pressure shows that the Raman modes undergo a downshift in frequency with increasing pressure [ 31 31 ]. For instance, the pressure effect induced by the surrounding particles or the interface stress has been successfully used to elucidate the frequency shift of the Raman peaks observed in TiO 2 and PbTiO 3 nanoparticles [ 32 32 ]. The size-induced pressure effect may act in a manner similar to an external pressure on the TiO 2 nanoparticles. The smaller the nanoparticles are, the larger the contribution of pressure is, hence the frequency downshift of the E g annatase mode [ 28 28 ]. In our experiment, the size of TiO 2 nanoparticles increases with annealing temperature, and the pressure releases gradually with heat treatment, which can lead to the frequency up-shift (towards to higher frequency) of the E g mode according to the size-induced pressure effect. However, instead of up-shift, a frequency downshift with increasing annealing treatment was observed, implying that the pressure effect can be ruled out. In addition, according to the phonon confinement effects, the increase in crystallite size can cause downshift in frequency and decrease in linewidth of the E g Raman mode, thus the phonon confinement effects should be taken into account to explain the change of E g Raman mode. Also, non-stoichiometry observed in nanophase TiO 2 samples prepared by other methods [ 24 24 - 26 26 24-26 ] plays an important role in frequency shift of Raman peaks, in which the frequency downshifts with decreasing oxygen deficiency. Although the TiO 2 samples used in this work are prepared by Ti-ion implantation and subsequent annealing in an oxygen atmosphere, oxygen deficiency, as the most common form of nonstoichiometry in TiO 2 , can not be ruled out. Moreover, the downshift in frequency of the E g annatase mode with increasing annealing temperature (the decrease of oxygen deficiency) is well consistent with the results reported by other authors [ 24 24 - 26 26 24-26 ]. The oxygen defiency decreases with increasing annealing temperature. Therefore, the nonstoichiometry should be taken into account in explaining changes in the E g Raman mode in our TiO 2 films. To further confirm the formation of TiO 2 nanofilms and measure the atomic ratio of Ti and O, the XPS spectra of the implanted samples annealed at 800 ℃ was measured ( Fig. 4 Fig. 4 ). The peaks centered at 458.7 eV and 464.5 eV binding energies correspond to the 2 p 3/2 and 1/2 core levels of Ti 4+ , and the peaks centered at 530.0 eV and 532.6 eV correspond to the binding energies of Ti-O and Si-O, respectively, agreeing well with the values reported by other authors [ 3 3 ]. The atomic ratio of Ti and O was calculated as 1:1.82, proving the nonstoichiometry of TiO 2 . The color of the annealed samples changes from light-blue to almost white at 900 ℃, indicating a decrease in oxygen vacancies [ 30 30 ] and a change of films thicknesses according to interference phenomena in thin films. D. Mechanism for the formation of TiO 2 nanofilms: TEM Characterization 2 To figure out growth process and formation mechanism of the TiO 2 nanofilms, the TEM study on microstructure of the samples was carried out. Figure 5 Figure 5 shows the cross sectional TEM images of the as-implanted sample and the sample annealed at 800 ℃ for 2 h. A dark layer with tiny Ti nanocrystals below the surface was observed in the as-implanted sample ( Fig. 5(a) Fig. 5(a) ). After annealing at 800 ℃ for 2 h, a nanofilm in thickness of 10 nm was formed on the sample surface ( Fig. 5(b) Fig. 5(b) ). The selected area electron diffraction (SAED) pattern confirms the formation of an anatase phase TiO 2 nanofilm. Meanwhile, the Ti atoms in the silica substrate aggregate into larger nanocrystals according to the SAED pattern. This indicates that during annealing in O 2 atmosphere, the implanted Ti atoms diffused out to the silica surface and were oxidized into TiO 2 nanoparticles. Meanwhile, the embedded Ti nanocrystals form larger ones due to the Ostwald ripening effect. The solid phase growth process of TiO 2 nanofilms by ion implantation and subsequent thermal oxidation is similar to the results reported on Zn-implanted silica and sapphire to form high-quality ZnO nanofilms on the substrate surface [ 14 14 - 16 16 14-16 ]. The formation of metal oxide semiconductor by metal ion implantation and subsequent thermal oxidation was due to out-diffusion of the implanted Ti ions to the substrate surface, where they were oxidized into TiO 2 . E. Growth of the TiO 2 nanofilms: Influence of the annealing time 2 The annealing time was increased to 4 h and 6 h, so as to further study the growth process and formation mechanism of the TiO 2 nanofilms. The cross sectional TEM images of the Ti ions implanted samples annealed at 800 ℃ for 4 h and 6 h are shown in Fig. 6 Fig. 6 . In Fig. 6(b) Fig. 6(b) , almost all the Ti atoms diffused out of the substrate to form a thicker TiO 2 nanofilm with a thickness of 50 nm, and the TiO 2 nanocrystals increased greatly in size. It should be mentioned that the TiO 2 nanofilms have a slow growth rate of about 0.15 nm/min to ensure the high crystal quality and high density of the formed nanofilms. Figure 7 Figure 7 shows SEM images of the samples annealed at 800 ℃ for 4 h and 6 h. The film of 6-h annealing has flatter film surface and larger nanocrystal size than the film of 4-h annealing. Combining the TEM with SEM results, annealing time was expected to affect the surface morphology, structure and thickness of the formed TiO 2 nanofilms when the samples were annealed at 800 ℃. Thickness of TiO 2 nanofilms increases with annealing time until all of the Ti atoms diffuse out of the substrate to form a thicker TiO 2 nanofilm. As discussed above, the absorption edge and phase transformation of TiO 2 are annealing temperature dependent, and the thickness of the TiO 2 nanofilms is annealing time dependent. IV. CONCLUSION 1 In summary, TiO 2 nanofilms were fabricated on fused silica substrate by a solid phase growth process of Ti-ion implantation and subsequent thermal annealing in an O 2 atmosphere. The growth mechanism and phase transformations of TiO 2 nanofilms were discussed. The grain sizes and the crystallographic phase of TiO 2 nanofilms can be tailored. A higher annealing temperature produced a larger nanograin size, and the anatase-to-rutile phase transformation occurred at annealing temperatures higher than 1000 ℃. The thickness of the TiO 2 nanofilms is annealing time dependent, and it is determined by all of the Ti atoms which diffuse out of the substrate to form a thicker TiO 2 nanofilms through subsequent thermal annealing under O 2 atmosphere. Thus, the formation, phase and growth of the TiO 2 nanofilms can be well tailored by controlling the annealing parameters (temperature and time). The results indicate that the TiO 2 nanofilms fabricated by this approach have great potential for various optical, sensing and catalytic applications. References A Fujishima and K Honda . Electrochemical Photolysis of Water at a Semiconductor Electrode . Nature , 1972 , 238 : 37 - 38 . DOI: 10.1038/238037a0 http://doi.org/10.1038/238037a0 Electrochemical Photolysis of Water at a Semiconductor Electrode T Fröschl , U Hörmann , P Kubiak , et al . High surface area crystalline titanium dioxide: potential and limits in electrochemical energy storage and catalysis . Chem Soc Rev , 2012 , 41 : 5313 - 5360 . DOI: 10.1039/c2cs35013k http://doi.org/10.1039/c2cs35013k High surface area crystalline titanium dioxide: potential and limits in electrochemical energy storage and catalysis X B Chen and S S Mao . Titanium dioxide nanomaterials: synthesis, properties, modifications, and applications . Chem Rev , 2007 , 107 : 2891 - 2959 . DOI: 10.1021/cr0500535 http://doi.org/10.1021/cr0500535 Titanium dioxide nanomaterials: synthesis, properties, modifications, and applications F X Liang , T L Kelly , L B Luo , et al . Self-cleaning organic vapor sensor based on a nanoporous TiO2 interferometer . ACS Appl Mater Interfaces , 2012 , 4 : 4177 - 4183 . DOI: 10.1021/am300896p http://doi.org/10.1021/am300896p Self-cleaning organic vapor sensor based on a nanoporous TiO2 interferometer Y Y Song , Z D Gao , J H Wang , et al . Multistage coloring electrochromic device based on TiO2 nanotube arrays modified with WO3 nanoparticles . Adv Funct Mater , 2011 , 21 : 1941 - 1946 . DOI: 10.1002/adfm.201002258 http://doi.org/10.1002/adfm.201002258 Multistage coloring electrochromic device based on TiO2 nanotube arrays modified with WO3 nanoparticles H Choi , E Stathatos and D D Dionysiou . Sol-gel preparation of mesoporous photocatalytic TiO2 films and TiO2/Al2O3 composite membranes for environmental applications . Appl Catal B-Environ , 2006 , 63 : 60 - 67 . DOI: 10.1016/j.apcatb.2005.09.012 http://doi.org/10.1016/j.apcatb.2005.09.012 Sol-gel preparation of mesoporous photocatalytic TiO2 films and TiO2/Al2O3 composite membranes for environmental applications I Stambolova , M Shipochka , V Blaskov , et al . Sprayed nanostructured TiO2 films for efficient photocatalytic degradation of textile azo dye . J Photoch Photobio B , 2012 , 117 : 19 - 26 . DOI: 10.1016/j.jphotobiol.2012.08.006 http://doi.org/10.1016/j.jphotobiol.2012.08.006 Sprayed nanostructured TiO2 films for efficient photocatalytic degradation of textile azo dye I Stambolova , V Blaskov , M Shipochka , et al . Effect of post-synthesis acid activation of TiO2 nanofilms on the photocatalytic efficiency under visible light . J Phys Conf Ser , 2014 , 558 : 012055 . DOI: 10.1088/1742-6596/558/1/012055 http://doi.org/10.1088/1742-6596/558/1/012055 Effect of post-synthesis acid activation of TiO2 nanofilms on the photocatalytic efficiency under visible light M B Casu , W Braun , K R Bauchspiess , et al . A multi-technique investigation of TiO2 films prepared by magnetron sputtering . Surf Sci , 2008 , 602 : 1599 - 1606 . DOI: 10.1016/j.susc.2008.02.030 http://doi.org/10.1016/j.susc.2008.02.030 A multi-technique investigation of TiO2 films prepared by magnetron sputtering H F Sun , C Y Wang , S H Pang , et al . Photocatalytic TiO2 films prepared by chemical vapor deposition at atmosphere pressure . J Non-Cryst Solids , 2008 , 354 : 1440 - 1443 . DOI: 10.1016/j.jnoncrysol.2007.01.108 http://doi.org/10.1016/j.jnoncrysol.2007.01.108 Photocatalytic TiO2 films prepared by chemical vapor deposition at atmosphere pressure J G Yu and X J Zhao . Effect of substrates on the photocatalytic activity of nanometer TiO2 thin films . Mater Res Bull , 2000 , 35 : 1293 - 1301 . DOI: 10.1016/S0025-5408(00)00327-5 http://doi.org/10.1016/S0025-5408(00)00327-5 Effect of substrates on the photocatalytic activity of nanometer TiO2 thin films A Kleiman , A Márquez , M L Vera , et al . Photocatalytic activity of TiO2 thin films deposited by cathodic arc . Appl Catal B-Environ , 2011 , 101 : 676 - 681 . DOI: 10.1016/j.apcatb.2010.11.009 http://doi.org/10.1016/j.apcatb.2010.11.009 Photocatalytic activity of TiO2 thin films deposited by cathodic arc H Amekura , N Umeda , Y Sakuma , et al . Fabrication of ZnO nanoparticles in SiO2 by ion implantation combined with thermal oxidation . Appl Phys Lett , 2005 , 87 : 013109 . DOI: 10.1063/1.1989442 http://doi.org/10.1063/1.1989442 Fabrication of ZnO nanoparticles in SiO2 by ion implantation combined with thermal oxidation F Ren , C Z Jiang and X H Xiao . Fabrication of single-crystal ZnO film by Zn ion implantation and subsequent annealing . Nanotechnology , 2007 , 18 : 285609 . DOI: 10.1088/0957-4484/18/28/285609 http://doi.org/10.1088/0957-4484/18/28/285609 Fabrication of single-crystal ZnO film by Zn ion implantation and subsequent annealing X H Xiao , F Ren , L X Fan , et al . ZnO single-crystal films fabricated by the oxidation of zinc-implanted sapphire . Nanotechnology , 2008 , 19 : 325604 . DOI: 10.1088/0957-4484/19/32/325604 http://doi.org/10.1088/0957-4484/19/32/325604 ZnO single-crystal films fabricated by the oxidation of zinc-implanted sapphire Y X Liu , Y C Liu , C L Shao , et al . Excitonic properties of ZnO nanocrystalline films prepared by oxidation of zinc-implanted silica . J Phys D Appl Phys , 2004 , 37 : 3025 - 3029 . DOI: 10.1088/0022-3727/37/21/013 http://doi.org/10.1088/0022-3727/37/21/013 Excitonic properties of ZnO nanocrystalline films prepared by oxidation of zinc-implanted silica X Xiang , M Chen , Y F Ju , et al . N-TiO2 nanoparticles embedded in silica prepared by Ti ion implantation and annealing in nitrogen . Nucl Instrum Meth B , 2010 , 268 : 1440 - 1445 . DOI: 10.1016/j.nimb.2010.01.023 http://doi.org/10.1016/j.nimb.2010.01.023 N-TiO2 nanoparticles embedded in silica prepared by Ti ion implantation and annealing in nitrogen F Ren , X D Zhou , Y C Liu , et al . Fabrication and properties of TiO2 nanofilms on different substrates by a novel and universal method of Ti-ion implantation and subsequent annealing . Nanotechnology , 2013 , 24 : 255603 . DOI: 10.1088/0957-4484/24/25/255603 http://doi.org/10.1088/0957-4484/24/25/255603 Fabrication and properties of TiO2 nanofilms on different substrates by a novel and universal method of Ti-ion implantation and subsequent annealing R Asahi , T Morikawa , T Ohwaki , et al . Visible-light photocatalysis in nitrogen-doped titanium oxides . Science , 2001 , 293 : 269 - 271 . DOI: 10.1126/science.1061051 http://doi.org/10.1126/science.1061051 Visible-light photocatalysis in nitrogen-doped titanium oxides J Zhang , M J Li , Z C Feng , et al . UV Raman spectroscopic study on TiO2. I. phase transformation at the surface and in the bulk . J Phys Chem B , 2006 , 110 : 927 - 935 . DOI: 10.1021/jp0552473 http://doi.org/10.1021/jp0552473 UV Raman spectroscopic study on TiO2. I. phase transformation at the surface and in the bulk R I Bickley , T Gonzalez-Carreno , J S Lees , et al . A structural investigation of titanium dioxide photocatalysts . J Solid State Chem , 1991 , 92 : 178 - 190 . DOI: 10.1016/0022-4596(91)90255-G http://doi.org/10.1016/0022-4596(91)90255-G A structural investigation of titanium dioxide photocatalysts T Ohsaka , F Izumi and Y Fujiki . Raman spectrum of anatase TiO2 . J Raman Spectrosc , 1978 , 7 : 321 - 324 . DOI: 10.1002/jrs.1250070606 http://doi.org/10.1002/jrs.1250070606 Raman spectrum of anatase TiO2 A Chaves , K S Katiyan and S P S Porto . Coupled modes with A1 symmetry in tetragonal BaTiO3 . Phys Rev B , 1974 , 10 : 3522 - 3533 . DOI: 10.1103/PhysRevB.10.3522 http://doi.org/10.1103/PhysRevB.10.3522 Coupled modes with A1 symmetry in tetragonal BaTiO3 W F Zhang , Y L He , M S Zhang , et al . Raman scattering study on anatase TiO2 nanocrystals . J Phys D Appl Phys , 2000 , 33 : 912 - 916 . DOI: 10.1088/0022-3727/33/8/305 http://doi.org/10.1088/0022-3727/33/8/305 Raman scattering study on anatase TiO2 nanocrystals J C Parker and R W Siegel . Raman microprobe study of nanophase TiO2 and oxidation-induced spectral changes . J Mater Res , 1990 , 5 : 1246 - 1252 . DOI: 10.1557/JMR.1990.1246 http://doi.org/10.1557/JMR.1990.1246 Raman microprobe study of nanophase TiO2 and oxidation-induced spectral changes J C Parker and R W Siegel . Calibration of the Raman spectrum to the oxygen stoichiometry of nanophase TiO2 . Appl Phys Lett , 1990 , 57 : 943 - 945 . DOI: 10.1063/1.104274 http://doi.org/10.1063/1.104274 Calibration of the Raman spectrum to the oxygen stoichiometry of nanophase TiO2 D Bersani , P P Lottici and X Z Ding . Phonon confinement effects in the Raman scattering by TiO2 nanocrystals . Appl Phys Lett , 1998 , 72 : 73 - 75 . DOI: 10.1063/1.120648 http://doi.org/10.1063/1.120648 Phonon confinement effects in the Raman scattering by TiO2 nanocrystals W H Ma , Z Lu and M Zhang . Investigation of structural transformations in nanophase titanium dioxide by Raman spectroscopy . Appl Phys A , 1998 , 66 : 621 - 627 . DOI: 10.1007/s003390050723 http://doi.org/10.1007/s003390050723 Investigation of structural transformations in nanophase titanium dioxide by Raman spectroscopy E Barborini , I N Kholmanov , P Piseri , et al . Engineering the nanocrystalline structure of TiO2 films by aerodynamically filtered cluster deposition . Appl Phys Lett , 2002 , 81 : 3052 - 3054 . DOI: 10.1063/1.1510579 http://doi.org/10.1063/1.1510579 Engineering the nanocrystalline structure of TiO2 films by aerodynamically filtered cluster deposition V Swamy , A Kuznetsov , L S Dubrovinsky , et al . Finite-size and pressure effects on the Raman spectrum of nanocrystalline anatase TiO2 . Phys Rev B , 2005 , 71 : 184302 . DOI: 10.1103/PhysRevB.71.184302 http://doi.org/10.1103/PhysRevB.71.184302 Finite-size and pressure effects on the Raman spectrum of nanocrystalline anatase TiO2 T Ohsaka , S Yamaoka and O Shimomura . Effect of hydrostatic pressure on the Raman spectrum of anatase (TiO2) . Solid State Commun , 1979 , 30 : 345 - 347 . DOI: 10.1016/0038-1098(79)90648-3 http://doi.org/10.1016/0038-1098(79)90648-3 Effect of hydrostatic pressure on the Raman spectrum of anatase (TiO2) J F Meng , G T Zou , Q L Cui , et al . Raman scattering from PbTiO3 of various grain sizes at high hydrostatic pressures . J Phys Condens Matter , 1994 , 6 : 6543 - 6548 . DOI: 10.1088/0953-8984/6/32/015 http://doi.org/10.1088/0953-8984/6/32/015 Raman scattering from PbTiO3 of various grain sizes at high hydrostatic pressures 10.13538/j.1001-8042/nst.26.030507 Supported by National Natural Science Foundation of China (No. 11405280), Foundation from Education Department of Henan Province (No. 14B140021) and the Startup Foundation for Doctors of Zhoukou Normal University (No. zksybscx201210) 2015-03-13 2015-04-19 2015-06-20 2015-06-20 2021-04-11 2015 Nuclear Science and Techniques 3 26