Effect of annealing on TiO2 nanoparticles

TiO₂ nanoparticles have been prepared by simple chemical precipitation method and annealed at different temperatures. The as-prepared TiO₂ are amorphous, and they transform into anatase phase on annealing at 450 °C, and rutile phase on annealing at 900 °C. The X-ray diffraction results showed that TiO₂ nanoparticles with grain size in the range of 21–24 nm for anatase phase and 69–74 nm for rutile phase have been obtained. FESEM images show the formation of TiO₂ nanoparticles with small size in structure. The FTIR and Raman spectra exhibited peaks corresponding to the anatase and rutile structure phases of TiO₂. Optical absorption studies reveal that the absorption edge shifts towards longer wavelength (red shift) with increase of annealing temperature.     

Non-contact atomic force microscopy imaging of TiO2(100) surfaces

Atomically resolved non-contact fm mode atomic force microscopy images have been obtained from TiO₂(100) surfaces. The 1×1 surface is observed, as well as the 1×3 phase previously imaged with STM. The morphology of the latter reconstruction consists of (110) microfacets. An additional reconstruction with 1×3 symmetry is observed, which is assigned to a phase intermediate between the 1×1 and 1×3-microfacet terminations.     

Effects of annealing on laser-induced damage threshold of TiO2/SiO2 high reflectors

The mechanism of improving 1064 nm, 12 ns laser-induced damage threshold (LIDT) of TiO₂/SiO₂ high reflectors (HR) prepared by electronic beam evaporation from 5.1 to 13.1 J/cm² by thermal annealing is discussed. Through optical properties, structure and chemical composition analysis, it is found that the reduced atomic non-stoichiometric defects are the main reason of absorption decrease and LIDT rise after annealing. A remarkable increase of LIDT is found at 300 °C annealing. The refractive index and film inhomogeneity rise, physical thickness decrease, and film stress changes from compress stress to tensile stress due to the structure change during annealing.     

H_2气氛退火处理对Nb掺杂TiO_2薄膜光电性能的影响

采用电子束沉积方法,以钛酸锶(SrTiO3)为衬底制备铌(Nb)掺杂TiO2薄膜并研究后续H2气氛退火处理对其薄膜样品光电性能的影响.结果发现H2气氛热退火处理能有效改善Nb掺杂TiO2薄膜的导电率,最佳电阻率达到5.46×10-3Ω·cm,在可见光范围内的透光率为60%—80%.导电性能的改善与H2气氛退火处理后多晶薄膜的晶粒尺寸变大和大量的氧空位形成及H原子掺杂有关.     

Composite SiO2/TiO2 and amine polymer/TiO2 nanoparticles produced using plasma-enhanced chemical vapor deposition

Plasma-enhanced chemical vapor deposition was used to conformally coat commercial TiO₂ nanoparticles to create nanocomposite materials. Hexamethyldisiloxane (HMDSO)/O₂ plasmas were used to deposit SiO₂ or SiO_xC_yH_z films, depending on the oxidant concentration; and hexylamine (HexAm) plasmas were used to deposit amorphous amine-containing polymeric films on the TiO₂ nanoparticles. The composite materials were analyzed using Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). These analyses reveal film composition on the nanoparticles was virtually identical to that deposited on flat substrates and that the films deposit a conformal coating on the nanoparticles. The performance of the nanocomposite materials was evaluated using UV-vis spectroscopy to determine the dispersion characteristics of both SiO_x and HexAm coated TiO₂ materials. Notably, the coated materials stay suspended longer in distilled water than the uncoated materials for all deposited films.     

Thermal stability of HfO2/Si（001） films prepared by electron beam evaporation in ultrahigh vacuum using atomic oxygen

HfO2 films on silicon substrates have been prepared by electron beam evaporation in ultrahigh vacuum using atomic oxygen.Synchrotron radiation photon-electron spectroscopy was used to investigate the thermal stability of HfO2 films under an ultrahigh vacuum environment.At the temperature of 750℃,HfO2 films begin to decompose.After being further annealed at 850℃ for 3 min,HfO2 films decomposes completely,partially to form Hf-silicide and partially to form gaseous HfO.Two chemical reactions are responsible for this decomposition process.A small amount of Hf-silicide,which is formed at the very beginning of growth,may result in the films grown subsequently to be loosened,and thereby leads to a relatively low decomposition temperature.     

紫外光辐照对TiO2纳米线电输运性能的影响及磁阻效应研究

采用溶胶凝胶法以及静电纺丝法, 利用热处理工艺, 成功制备出了多晶锐钛矿型TiO₂纳米线, 通过两线法在室温下测试单根TiO₂纳米线的V-I曲线来研究其电输运性能及磁阻效应. 结果表明: 在无光照环境下其V-I曲线为不过零点的直线, 零场电阻较大, 在磁场作用下电阻下降, 表现出负磁阻效应; 紫外光辐照环境下TiO₂纳米线载流子浓度增加使得电阻变小, 然而在磁场作用下电阻增大, 表现为正磁阻效应. 紫外光辐照导致的载流子浓度变化, 使得负磁阻转变为正磁阻, 我们将磁阻变化归结为d电子局域导致的负磁阻与能带劈裂导致的正磁阻两种机理相互竞争的结果.     

Microstructures and magnetic properties of CoPt-TiO2 nanocomposite films prepared by annealing CoPt/TiO2 multilayers

CoPt-TiO₂ nanocomposite films were synthesized by rapid thermal annealing of CoPt/TiO₂ multilayers. The effects of annealing temperature, annealing time, Ag addition and TiO₂ volume fraction on the microstructures and magnetic properties of the CoPt-TiO₂ nanocomposite films were studied. Results showed that the ordering degree of CoPt and coercivity of CoPt-TiO₂ nanocomposites increased with annealing temperature. Increasing annealing time and Ag addition were able to increase the ordering degree and coercivity of CoPt. However, complete L1₀-ordering of CoPt at 550 °C annealing was not realized by increasing annealing time up to 30 min and Ag addition up to 30 vol.%. Increasing TiO₂ volume fraction at 700 °C annealing did not lead to the change of ordering of CoPt. However, the grain structure of the films changed slightly when TiO₂ volume fraction was larger than 56%. The coercivity of the film decreased slightly with the addition of TiO₂.     

Ag/TiO2纳米材料的制备和光致变色性能研究

 采用光催化还原法在不同温度热处理的TiO2薄膜表面沉积Ag纳米颗粒,制备了Ag/TiO2纳米薄膜材料。通过UV-Vis吸收光谱表征对比了不同温度热处理的TiO2对Ag粒子光催化沉积的影响,发现500℃退火处理TiO2薄膜较利于Ag纳米粒子的光催化沉积;在650 nm红色激光照射下,500℃退火处理的Ag/TiO2样品具有明显的光致变色现象,对此变色过程中涉及的机理进行了讨论,且发现随着Ag纳米颗粒光催化沉积时间的增长,Ag/TiO2薄膜光致变色的响应速率提高,但Ag纳米颗粒过多会抑制Ag/TiO2薄膜的变色响应速率。     

Scanning tunneling microscopy of N2H4 on silicon surfaces

The chemistry of N₂H₄ on Si(100)2 × 1 and Si(111)7 × 7 has been studied using scanning tunneling microscopy. At low coverages on Si(100)2 × 1 at room temperature the adsorption sites are distributed randomly on the surface and are imaged as dark spots in the dimer row by the STM. Upon annealing the substrate at 600 K, both isolated reaction products, as well as clusters of reaction products are formed on the surface. The STM images show that the majority of the isolated reaction products are adsorbed symmetrically across the dimers. Based on previous HREELS data, these are most likely NH_x groups. However, the clusters are not well resolved. Because of this we speculate that they are not simply symmetrically adsorbed NH_x groups, but likely have a more complicated internal structure. At higher coverages, the STM images show that the predominant pathway for adsorption is with the N---N bond parallel to the surface, in agreement with HREELS studies of this system. On Si(111)7 × 7, the molecule behaves in a manner which is similar to NH₃. That is, at low coverages the molecule adsorbs preferentially at center adatoms due to the greater reactivity of these sites, while at higher coverages it also reacts with the corner adatoms.     

Preparation of aminofunctionalized TiO2 surfaces by binding of organophosphates

Titanium dioxide (TiO₂) powder was chemically modified with 2-aminoethyl dihydrogen phosphate (AEPH₂) and with 2-aminoethyl hydrogen ammonium phosphate (AEPHNH₄) in order to achieve an aminofunctionalized high-surface-area TiO₂ carrier suitable for more complex functionalizing. AEPH₂ was found to form the monoammonium salt AEPHNH₄ with ammonium ion rather than the diammonium salt AEP(NH₄)₂. The AEPHNH₄ was thoroughly characterized by various techniques and compared with AEPH₂. Bonding of AEPH₂ and AEPHNH₄ with TiO₂ powder was studied. According to the ³¹P NMR and elemental analysis results, AEPH₂ and AEPHNH₄ form covalent chelate bidentate bonds between the phosphate group and the TiO₂, while the amino groups remain accessible, creating uniform aminofunctionalized TiO₂ surface fully occupied by AEP groups. Amount of AEP groups on TiO₂ was limited to 1.5 wt-%.     

Synthesis of anatase TiO2 nanowires by modifying TiO2 nanoparticles using the microwave heating method

Anatase TiO₂ nanowires with a diameter of 5-10 nm and length of 500 nm to 2 μm have been successfully synthesized by modifying TiO₂ nanoparticles (P25) using the microwave heating method. The microwave power, reaction pressure, and reaction time for the synthesis of TiO₂ nanowires were 500 W, 0.5-3.0 MPa (corresponding to a temperature range of 175-260), and 40-70 min, respectively. X-ray diffraction (XRD), field-emission scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), and the BET techniques were used to investigate the phase structures, morphologies, and specific surface areas of the TiO₂ nanowires. The effects of reaction time, pressure, and different post-treatment processes on the microstructures of TiO₂ nanowires were discussed. It has been shown that the microwave heating method is efficient in transforming TiO₂ nanoparticles to anatase TiO₂ nanowires.     

非聚焦电子束照射SiO2薄膜带电效应

采用考虑电子散射、俘获、输运和自洽场的三维数值模型, 模拟了低能非聚焦电子束照射接地SiO₂薄膜的带电效应. 结果表明, 由于电子的迁移和扩散, 电子会渡越散射区域产生负空间电荷分布. 空间电荷呈现在散射区域内为正, 区域外为负的交替分布特性. 对于薄膜负带电, 电子会输运至导电衬底形成泄漏电流, 其暂态过程随泄漏电流的增加趋于平衡. 而正带电暂态过程随返回二次电子的增多而趋于平衡. 在平衡态时, 负带电表面电位随薄膜厚度、陷阱密度的增大而降低, 随电子迁移率、薄膜介电常数的增大而升高;而正带电表面电位受它们影响较小.     

Effects of rapid thermal annealing on the structural properties of TiO2 nanotubes

The structural properties of TiO₂ nanotubes with rapid thermal annealing (RTA) and traditional thermal annealing in O₂ were studied by X-ray diffraction (XRD) and Raman scattering measurements. From analyzing the line width of XRD and the correlation length of the Raman peak, we demonstrate that RTA can be an effective tool for amorphous-anatase transformation in TiO₂ nanotubes. The Raman peak redshifts and reduces its line width after thermal annealing and RTA, which may involves the reduction of oxygen-related defects.     

Effect of thermal annealing on the structure and microstructure of TiO2 thin films

Nanostructured TiO₂ thin films have been prepared through chemical route using sol-gel and spin coating techniques. The deposited films were annealed in the temperature range 400–1000°C for 1 h. The structure and microstructure of the annealed films were characterized by GAXRD, micro-Raman spectroscopy and AFM. The as-deposited TiO₂ thin films are found to be amorphous. Micro-Raman and GAXRD results confirm the presence of the anatase phase and absence of the rutile phase for films annealed up to 700°C. The diffraction pattern of the film annealed at 800 to 1000°C contains peaks of both anatase and rutile reflections. The intensity of all peaks in micro-Raman and GAXRD patterns increased and their width (FWHM) decreased with increasing annealing temperature, demonstrating the improvement in the crystallinity of the annealed films. Phase transformation at higher annealing temperature involves a competition among three events such as: grain growth of anatase phase, conversion of anatase to rutile and grain growth of rutile phase. AFM image of the asdeposited films and annealed films indicated exponential grain growth at higher temperature.      

紫外光辐照对TiO2薄膜光学性能的影响

 采用电子束热蒸发技术在不同工艺下制备了TiO2薄膜,利用椭偏仪和分光光度计研究了紫外光辐照后薄膜光学特性的变化。实验结果表明：不同工艺下制备的TiO2薄膜经相同条件的紫外光辐照后,其折射率均有所下降,折射率的变化量随着沉积速率上升、基底温度上升、工作真空度下降分别有增大的趋势。薄膜的透射率在紫外光辐照后有一定下降。相同工艺条件下制备的TiO2薄膜,其折射率随着辐照时间的增加,先迅速降低,随后又有所增加,但均低于辐照前薄膜的折射率。     

Deposition and characterization of binary Al2O3/SiO2 coating layers on the surfaces of rutile TiO2 and the pigmentary properties

Binary Al₂O₃/SiO₂-coated rutile TiO₂ composites were prepared by a liquid-phase deposition method starting from Na₂SiO₃·9H₂O and NaAlO₂. The chemical structure and morphology of binary Al₂O₃/SiO₂ coating layers were investigated by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, TG-DSC, Zeta potential, powder X-ray diffraction, and transmission electron microscopy techniques. Binary Al₂O₃/SiO₂ coating layers both in amorphous phase were formed at TiO₂ surfaces. The silica coating layers were anchored at TiO₂ surfaces via Si-O-Ti bonds and the alumina coating layers were probably anchored at the SiO₂-coated TiO₂ surfaces via Al-O-Si bonds. The formation of continuous and dense binary Al₂O₃/SiO₂ coating layers depended on the pH value of reaction solution and the alumina loading. The binary Al₂O₃/SiO₂-coated TiO₂ composites had a high dispersibility in water. The whiteness and brightness of the binary Al₂O₃/SiO₂-coated TiO₂ composites were higher than those of the naked rutile TiO₂ and the SiO₂-coated TiO₂ samples. The relative light scattering index was found to depend on the composition of coating layers.     

Methylene blue photoelectrodegradation under UV irradiation on Au/Pd-modified TiO2 films

In this work TiO₂ thin films were modified with gold/palladium (Au/Pd) bimetallic paticles by sputtering method. TiO₂ films were deposited on ITO (SnO₂:In) by Doctor Blade method and post-anneling. The properties of the films were studied through measurements of XRD (X-ray diffraction) and AFM (atomic force microscopy). The degradation of methylene blue was studied by UV-irradiated pure TiO₂ and Au/Pd-modified TiO₂ in aqueous solution. Langmuir-Hinshelwood model was used to obtain kinetic information. Photocatalytic study indicated that Au/Pd-modified TiO₂ photocatalytic activity was better than TiO₂ pure; the best half-life time for Au/Pd-modified TiO₂ in photodegradation was 2.8 times smaller than TiO₂ pure; finally the efficiency in methylene blue photodegradation was improved from 23% to 43% when Au/Pd-modified TiO₂ films were used.     

Substrate effects on the oxygen gas sensing properties of SnO2/TiO2 thin films

In this study, SnO₂/TiO₂ thin films are fabricated on SiO₂/Si and Corning glass 1737 substrates using a R.F. magnetron sputtering process. The gas sensing properties of these films under an oxygen atmosphere with and without UV irradiation are carefully examined. The surface structure, morphology, optical transmission characteristics, and chemical compositions of the films are analyzed by atomic force microscopy, scanning electron microscopy and PL spectrometry. It is found that the oxygen sensitivity of the films deposited on Corning glass 1737 substrates is significantly lower than that of the films grown on SiO₂/Si substrates. Therefore, the results suggest that SiO₂/Si is an appropriate substrate material for oxygen gas sensors fabricated using thin SnO₂/TiO₂ films.     

Enhancement in the photoluminescence of ZnS nanowires by TiO2 coating and thermal annealing

Influences of the TiO₂ coating and thermal annealing on the photoluminescence (PL) properties of ZnS nanowires were investigated. ZnS nanowires were synthesized by thermal evaporation of ZnS powder and then coated with TiO₂ by using the sputtering technique. The PL emission of ZnS nanowires can be significantly enhanced without nearly changing the wavelength of the emission by coating them with a TiO₂ layer with an appropriate thickness and then annealing them in an Ar atmosphere. The optimum TiO₂ coating layer thickness for the highest PL emission enhancement was found to be about 6.5 nm. The PL emission of the ZnS-core/TiO₂-shell coaxial nanowires is degraded by annealing in an oxygen atmosphere whereas it is enhanced by annealing in an argon atmosphere.