UV-Vis and Photoluminescent Spectra of TiO_2 Films

1　IntroductionThestudyofTiO2 photocatalysthasbeenfocusedontheapplicationtopurificationandtreatmentofairandwater[1,2 ] .ManymethodshavebeenusedtoprepareTiO2filmssuchassol gelprocess ,CVD ,sputteringandsoon[2 -4] .Amongthem ,reactivesputteringisoneofthemostunitizedmethodsforobtaininguniformthinfilmswithawell controlledstoichiometry[3 ,5] .Whenonecon sidersphotocatalyticapplications ,animportantaspectofTiO2 film ,besidesthecrystallinephase (anatase) ,isthepresenceofoxygenvacancy[6] .Takedaet…     

Cu<Subscript>2</Subscript>ZnSnS<Subscript>4</Subscript> thin films prepared by sulfurizing different multilayer metal precursors

Cu₂ZnSnS₄ (CZTS) thin films were successfully fabricated on glass substrates by sulfurizing Cu-Sn-Zn multilayer precursors, which were deposited by ion beam sputtering and RF magnetron sputtering, respectively. The structural, electrical and optical properties of the prepared films under various processing conditions were investigated in detail. Results showed that the as-deposited CZTS thin films with the precursors by both ion beam sputtering and RF magnetron sputtering have a composition near stoichiometric. The crystallization of the samples, however, has a strong dependence on the atomic percent of constituents of the prepared CZTS films. A single phase stannite-type structure CZTS with a large absorption coefficient of 10₄/cm in the visible range could be obtained after sulfurization at 520°C for 2 h. The samples relative to the RF magnetron sputtering showed a low resistivity of 0.073 Ωcm and band gap energy of about 1.53 eV. The samples relative to the ion beam sputtering exhibited a resistivity of 0.36 Ωcm and the band gap energy is about 1.51 eV. Supported by the National Natural Science Foundation of China (Grant No. 10574106), the Planned Science and Technology Project of Guangdong Province (Grant No.2003C05005) and the Natural Science Fund of Zhanjiang Normal University (Grant No.200801)     

Photocatalytic activities of amorphous TiO<Subscript>2</Subscript>-Cr thin films prepared by magnetron sputtering

Chrome-doped titanium oxide films were prepared by reactive magnetron sputtering method. The films deposited on glass slides at room temperature were investigated by atom force microscope, X-ray diffractometer, X-ray photoelectron spectroscopy, UV-Vis spectrophotometer, the photoluminescence （PL） and ellipse polarization apparatus. The results indicate that TiO2-Cr film exists in the form of amorphous. The prepared films possess a band gap of less than 3.20 eV, and a new absorption peak. The films, irradiated for 5 h under UV light, exhibit excellent photocatalytic activities with the optimum decomposition rate at 98.5% for methylene blue. Consequently, the thickness threshold on these films is 114 nm, at which the rate of photodegradation is 95% in 5 h. When the thickness is over 114 nm, the rate of photodegradation becomes stable. This result is completely different from that of crystalloid TiO2 thin film.     

The micro-structural studies of Ni-BaTiO<Subscript>3</Subscript> nanocomposite films by TEM and EELS

Epitaxial BaTiO3 films with embedded metallic Ni nanocrystal (Ni-BaTiO3) were successfully fabricated on SrTiO3 (001) single-crystalline substrate through the laser molecular beam epitaxial (L-MBE) technique.High resolution transmission electron microscopy (HRTEM) and electron energy loss spectrum (EELS) with Kramers-Kronig analysis methods were employed to characterize the microstructures,elementary distribution and the electron structure of these films.HRTEM results suggested that the structure of BaTiO3 was tetragonal with lattice parameters of a=0.399 nm and c=0.403 nm.Energy dispersive X-Ray spectroscopy (EDX) confirmed metallic Ni nanocrystal embedded successfully in BaTiO3 epitaxial films.The Ni-BaTiO3 composite films were compound of the epitaxial BaTiO3 (110) layers alternating with Ni NCs array (111) layers.Furthermore,the existence of the misfit dislocations induced by the embedding of Ni nanoparticles was also clearly demonstrated by the HRTEM images.The Ni L2,3 edges of EELS revealed that Ni NCs in their metallic state were embedded uniformly in the BaTiO3 matrix.A chemical shift of about 7 eV regarding L3 edges in the Ni EELS was also observed.The optical band gap of BaTiO3 in these films was about 3.84 eV,higher than 3.55 eV for pure BaTiO3 films at room temperature.     

Synthesis and characterization of (PEO)<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>−(V<Subscript>0.85</Subscript>Mo<Subscript>0.15</Subscript>)<Subscript>2</Subscript>O<Subscript>5</Subscript> nanocomposite films

(PEO) _x −(V_0.85Mo_0.15)₂O₅(x=0,0.5,1.0) nanocomposite films were prepared by a modified sol-gel method. The structure of the films was analyzed by XRD, and the DC electrical conductivity. Cyclic voltammogram and optical spectral transmittance were investigated. The results show that the (V_0.85Mo_0.15)₂O₅ xerogel has a layered structure and its interlayer space increased from 1.3181 nm at x=0 to 1.7897 nm at x=1.0. The introduction of MoO₃ improved the DC electrical conductivities of the films due to the generation of V₄₊ to maintain the electrical neutrality of the oxides. PEO intercalated in the interlayer of (V_0.85Mo_0.15)₂O₅ oxides has interaction with the oxides, enhancing the amount of Li⁺ ions inserted into the interlayer of the oxides. Moreover, the intercalation of PEO into the interlayer of (V_0.85Mo_0.15)₂O₅ oxides improved the cathodic electrochromic property in near ultraviolet region and anodic electrochromic property in visible range. JIANG Cong-sheng: Born in 1963 Supported by the Science Foundation of Hubei Province (Grant No. 2001ABB083)     

Effect of pre-heating temperature on structural and optical properties of sol-gel derived Zn<Subscript>0.8</Subscript>Cd<Subscript>0.2</Subscript>O thin films

Zn_0.8Cd_0.2O thin films prepared using the spin-coating method were investigated. X-ray diffraction, scanning electron microscopy, and UV-Vis spectrophotometry were employed to illustrate the effects of the pre-heating temperature on the crystalline structure, surface morphology and transmission spectra of Zn_0.8Cd_0.2O thin films. When the thin films were pre-heated at 150 °C, polycrystalline ZnO thin films were obtained. When the thin films were pre-heated at temperatures of 200 °C or higher, preferential growth of ZnO nanocrystals along the c-axis was observed. Transmission spectra showed that thin films with high transmission in the visible light range were prepared and effective bandgap energies of these thin films decreased from 3.19 eV to 3.08 eV when the pre-heating temperature increased from 150 °C to 300 °C.     

Preparation and Properties of IrO2 Thin Films Grown by Pulsed Laser Deposition Technique

Highly conductive IrO2 thin films were prepared on Si （100） substrates by means of pulsed laser deposition technique from an iridium metal target in an oxygen ambient atmosphere. Emphasis was put on the effect of oxygen pressure and substrate temperature on the structure, morphology and resistivity of IrO2 films. It was found that the above properties were strongly dependent on the oxygen pressure and substrate temperature. At 20 Pa oxygen ambient pressure, pure polycrystalline IrO2 thin films were obtained at substrate temperature in the 300-500℃ range with the preferential growth orientation of IrO2 films changed with the substrate temperature. IrO2 films exhibited a uniform and densely packed granular morphology with an average feature size increasing with the substrate temperature. The room-temperature resistivity variations of IrO2 films correlated well with the corresponding film morphology changes. IrO2 films with the minimum resistivity of （42 ±6）μΩ·cm was obtained at 500℃.     

Hydrothermal preparation and photocatalytic water splitting properties of ZrW<Subscript>2</Subscript>O<Subscript>8</Subscript>

ZrW₂O₈ was prepared by adjusting Zr:W mole ratio and HCl concentration in hydrothermal reaction processes. The obtained sample was crystallized in α-ZrW₂O₈ phase (cubic, P2₁3), with band gap energy of 4.0 eV. The properties of photocatalytic water splitting were examined under UV light irradiation. The average rate of H₂ evolution over 0.3wt% Pt/ZrW₂O₈ in the presence of CH₃OH as electron donor (ED) was 23.4 μmol/h, while the average rate of O₂ evolution over ZrW₂O₈ in the presence of AgNO₃ as electron scavenger (ES) was 9.8 μ mol/h. Moreover, H₂ was evolved over 0.3wt% Pt/ZrW₂O₈ from pure water splitting at a rate of 5.2 μ mol/h. The study indicated that the band structure of ZrW₂O₈ was suitable for reducing H⁺ to H₂ and oxidizing H₂O to O₂. The band structure and photocatalytic water splitting properties of ZrW₂O₈, different from either ZrO₂ (5.0 eV) or WO₃ (2.7 eV), were attributed to the hybridization of W5d and Zr4d in conduction band (CB) as well as the change in crystal structure.     

溶胶凝胶法制备透明氧化铝薄膜及光学性能

以异丙醇铝为先驱体,采用溶胶凝胶方法制备了透明氧化铝薄膜;并采用DTA-TG,XRD, UV-vis分光光度计和PL光谱等测试手段对氧化铝薄膜进行表征.研究结果表明, 氧化铝薄膜(膜厚为100 nm) 在紫外到近红外范围内具有高的透射性,750 ℃热处理后氧化铝薄膜的光透射性最好;氧化铝薄膜在360-600 nm波长范围具有一个宽的蓝色发光带,且氧化铝膜的光致发光强度和峰位与热处理温度和激发光波长有关, 在345 nm 波长激发下,500 ℃热处理后氧化铝薄膜的发光强度最强;氧化铝薄膜的蓝色发光由氧空位缺陷(F+色心)引起.     

Effect of pH value on the micro-structures and optical properties of nano-crystalline CuInS<Subscript>2</Subscript> by solvothermal method

Copper indium disulfide (CuInS₂) nano-particles were synthesized by solvothermal method at 150 °C using copper (I) chloride, indium (III) chloride, thiourea and ethanol as raw materials, and characterized by X-ray diffraction(XRD), field-emission scanning electron microscope (FESEM), and UV-Vis spectra. The effects of pH value on its micro-structures and optical properties were investigated. The results show that, with the pH value increasing, the particle size of the nano-crystalline CuInS₂ increases, and its band gap becomes narrower under alkaline condition. The band gaps of CuInS₂ nano-particles are from 1.52 eV to 1.93 eV, which makes them promising candidates as absorber materials for photovoltaic applications.     

Preparation and enhanced daylight-induced photo-catalytic activity of transparent C-Doped TiO<Subscript>2</Subscript> thin films

The transparent C-doped TiO₂ nanostructure films were fabricated on the silicate glass substrates by sol-gel spin-coated method. The as-prepared films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), UV-visible absorption spectra (UV-vis) and X-ray photoelectron spectroscopy (XPS). The photocatalytic activity was evaluated via the photo-catalytic oxidation of methylene blue in aqueous under daylight irradiation at room temperature. The results show that the daylight-induced photocatalytic activities of the as-prepared films are improved by the C-doping. The calcination temperatures significantly affect the morphology, microstructure and photocatalytic activity of the as-prepared samples. At 723 K, the C-doped TiO₂ films exhibit the highest photocatalytic activity due to the synergetic effects of good crystallization, appropriate oxygen vacancies and strong absorption in the near UV and visible-light region.     

Enhanced Ferroelectric Polarization in Laser-ablated Bi<Subscript>4</Subscript>Ti<Subscript>3</Subscript>O<Subscript>12</Subscript> Thin Films by Controlling Preferred Orientation

Polycrystalline Bi₄Ti₃O₁₂ thin films with various fractions of a-axis, c-axis and random orientations have been grown on Pt(111)/Ti/SiO₂/Si substrates by laser-ablation under different kinetic growth conditions. The relationship between the structure and ferroelectric property of the films was investigated, so as to explore the possibility of enhancing ferroelectric polarization by controlling the preferred orientation. The structural characterization indicated that the large growth rate and high oxygen background pressure were both favorable for the growth of non-c-axis oriented grains in the Bi₄Ti₃O₁₂ thin films. The films with high fractions of a-axis and random orientations, i e, f (a-sxis) = 28.3% and f (random) = 69.6%, could be obtained at the deposition temperature of 973 K, oxygen partial pressure of 15 Pa and laser fluence of 4.6 J/cm², respectively. It was also noted that the variation of ferroelectric polarization was in accordance with the evolution non-c-axis orientation. A large value of remanent polarization (2Pr = 35.5 μC/cm²) was obtained for the Bi₄Ti₃O₁₂ thin films with significant non-c-axis orientation, even higher than that of rare-earth-doped Bi₄Ti₃O₁₂ films.     

Effect of pH values on photocatalytic properties of Bi<Subscript>2</Subscript>WO<Subscript>6</Subscript> synthesized by hydrothermal method

Highly crystalline orthorhombic Bi₂WO₆ powders were hydrothermally synthesized from aqueous solutions of Na₂WO₄ · 2H₂O and Bi (NO₃)₃ · 5H₂O over a wide range of pH. The effect of pH on morphologies, sizes and properties of the Bi₂WO₆ crystals was investigated. The band gaps of the as-prepared Bi₂WO₆ were determined from the onset of the absorption edge of UV-vis diffuse reflectance spectra. The methyl orange photodegradation was employed as a probe reaction to test the photocatalytic activity of the as-prepared samples under visible light irradiation. The photocatalytic activities of methyl orange degradation under visible light irradiation are strongly dependent on the pH used in the synthesis. The highest efficiency is observed at pH=7. Funded by the PCSIRT, the National Natural Science Foundation of China (Nos. 50532030 and 50625206) and the Zhejiang Provincial Natural Science Foundation of China (No. Z4080021)     

Effect of the sputtering parameters on the structure and properties of Cu<Subscript>3</Subscript>N thin film materials

Copper nitride (Cu₃N) thin films were successfully deposited on glass substrates by reactive radio frequency magnetron sputtering. The effects of sputtering parameters on the structure and properties of the films were studied. The experimental results show that with increasing of RF power and nitrogen partial pressure, the preferential crystalline orientation of Cu₃N film is changed from (111) to (100). With increasing of substrate temperature from 70 °C to 200 °C, the film phase is changed from Cu₃N phase to Cu. With increasing sputtering power from 80 W to 120 W, the optical energy decreases from 1.85 eV to 1.41 eV while the electrical resistivity increases from 1.45 ×10² Ω · cm to 2.99 × 10³ Ω · cm, respectively.     

Thermal-dynamical properties and pressure dependence of phonon spectrum of ordered Si<Subscript>50</Subscript>Ge<Subscript>50</Subscript> alloy based on <Emphasis Type="Italic">ab initio</Emphasis> methods

The phonon spectrum of ordered zincblende Si₅₀Ge₅₀ alloy is calculated by ab initio method. The energy band structure at zero pressure and the pressure dependence of phonon dispersion curves are shown up to 20 GPa. The calculation finds a pressure-induced softening of the transverse acoustic phonon mode and the mode frequency reaching zero at about 14 GPa, which indicate breaking of the symmetry and formation of a new phase under high pressure. Supported by the National Natural Science Foundation of China (Grant No. 50771090), the State Key Program for Basic Research of China (Grant No. 2005CB724404) and the Program for Changjiang Scholars and Innovative Team (Grant No. IRT0650)     

Fabrication and photocatalytic activity of Ag<Subscript>3</Subscript>PO<Subscript>4</Subscript>-TiO<Subscript>2</Subscript> heterostructural nanotube arrays

To extend the absorption capability of TiO₂ into visible light region and inhibit the recombination of photogenerated electrons and holes, we put forward an effective strategy of the coupling of TiO₂ with a suitable semiconductor that possesses a narrow band gap. Meanwhile, Ag₃PO₄-TiO₂ heterostructural nanotube arrays were prepared by the two-step anodic oxidation to obtain the TiO₂ nanotube arrays and then by a deposition-precipitation method to load Ag₃PO₄. The samples were characterized by field emission scanning electron microscopy (FESEM), energy dispersive spectrometry (EDS), X-ray diffraction (XRD), and UV-vis diffuse reflectance spectroscopy (UV-vis DRS). The experimental results showed that Ag₃PO₄ nanoparticles were uniformly dispersed on the highly ordered TiO₂ nanotube arrays, which increased the visible-light absorption of TiO₂ photocatalyst. The photocurrent density and photocatalytic degradation of methyl orange indicated that the performance of Ag₃PO₄-TiO₂ heterostructural nanotube arrays was better than that of the TiO₂ nanotube arrays, which could be attributed to the effective electron-hole separation and the improved utilization of visible light.     

Glass formation and optical band gap studies on Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-B<Subscript>2</Subscript>O<Subscript>3</Subscript>-BaO ternary system

The glass forming region of Bi₂O₃-B₂O₃-BaO ternary system was investigated. A serial of glass samples with high Bi₂O₃ content in Bi₂O₃-B₂O₃-BaO system were prepared by using conventional melting and quenching meld, and the refractive indexes and absorption spectra of samples were measured. It is found that the refractive index of samples as well as the UV absorption increase with the increase of BaO content. According to the Tauc law, optical band gap E _opg which is assumed to be the effective energy band gap E _g is calculated and decreases with the increasing BaO content, and the ratio of E _g/E _opg is 1.3.     

W掺杂量对非晶态TiO_2:W薄膜光学带隙的影响

在不同的W靶溅射功率下,用反应磁控溅射法在载玻片上制备了TiO2:W薄膜,并对样品进行了XRD,STS和UV-V is分析.结果表明试样为非晶态;W靶溅射功率为30 W时,带隙为2.75eV;W靶溅射功率为100 W时,带隙为3.02 eV;W靶溅射功率为150 W时,带隙能为2.92 eV.STS分析结果表明,在样品的禁带中产生了新的能级,能级宽度为0.83 eV.     

Orientation of Bi<Subscript>3.2</Subscript>La<Subscript>0.8</Subscript>Ti<Subscript>3</Subscript>O<Subscript>12</Subscript> ferroelectric thin films with different annealing schedules

Fatigue-free Bi_3.2La_0.8Ti₃O₁₂ ferroelectric thin films were successfully prepared on p-Si (100) substrates using metalorganic solution deposition process. The orientation and formation of 5-layers thin films were studied under different processing conditions using XRD. Experimental results indicate that increase in annealing time at 700 °C after preannealing for 10 min at 400 °C can remarkably increase (200)-orientation of the films derived from the precursor solutions with two contents of citric acid. Meanwhile, high content of citric acid increases the film thickness and is conducive to the a-orientation of the films with the preannealing, and low concentration of the solution is conducive to the c-orientation of the films without the preannealing.     

Enhanced photoelectric property of Mo-C codoped TiO<Subscript>2</Subscript> films deposited by RF magnetron cosputtering

Mo-C codoped TiO₂ films were prepared by RF magnetron cosputtering. Ultraviolet-visible spectroscopy, atomic force microscopy, X-ray photoelectron spectroscopy, energy dispersive X-ray Analysis and X-Ray Diffraction were used to study the influences of codoping on energy gap, surface morphology, valence states of elements, ions content and crystal structure, respectively. The concentration of photogenerated carriers was measured by studying photocurrent density, while catalytic property was evaluated by observing degradation rate of methylene blue under visible light. A Mo-doped TiO₂ film, whose content of Mo had been optimized in advance, was prepared and later used for subsequent comparisons with codoped samples. The result indicates that Mo-C codoping could curtail the energy gap and shift the absorption edge toward visible range. Under the illumination of visible light, codoped TiO₂ films give rise to stronger photocurrent due to smaller band gaps. It is also found that Mo, C codoping results in a porous surface, whose area declines gradually with increasing carbon content. Carbon and Molybdenum doses were delicately optimized. Under the illumination of visible light, sample doped with 9.78at% carbon and 0.36at% Mo presents the strongest photocurrent which is about 8 times larger than undoped TiO₂ films, and about 6 times larger than samples doped with Mo only.