Nanoporous TiO2 thin film based conductometric H2 sensor

Nanoporous titanium dioxide (TiO₂) based conductometric sensors have been fabricated and their sensitivity to hydrogen (H₂) gas has been investigated. A filtered cathodic vacuum arc (FCVA) system was used to deposit ultra-smooth Ti thin films on a transducer having patterned inter-digital gold electrodes (IDTs). Nanoporous TiO₂ films were obtained by anodization of the titanium (Ti) thin films using a neutral 0.5% (wt) NH₄F in ethylene glycol solution at 5 V for 1 h. After anodization, the films were annealed at 600 °C for 8 h to convert the remaining Ti into TiO₂. The scanning electron microscopy (SEM) images revealed that the average diameters of the nanopores are in the range of 20 to 25 nm. The sensor was exposed to different concentrations of H₂ in synthetic air at operating temperatures between 100 °C and 300 °C. The sensor responded with a highest sensitivity of 1.24 to 1% of H₂ gas at 225 °C.     

纳米TiO2薄膜的低温制备

采用液相沉积法,在90℃下制备了纳米锐钛矿型TiO2薄膜.采用XRD、UV透射光谱、薄膜表面接触角的测量、厚度的测量及亚甲基蓝降解等手段研究了TiO2薄膜的性能.结果表明所制备的TiO2薄膜具有较好的超亲水特性及光催化活性,在可见光范围内具有较好的透明性,其平均透光率在80%以上.     

Fabrication of TiO2 thin film memristor device using electrohydrodynamic inkjet printing

In this paper, we are reporting the fabrication of memristor device (Ag/TiO₂/Cu) using electrohydrodynamic inkjet printing technology. The titanium oxide (TiO₂) active layer was deposited using electrohydrodynamic atomization technique. The metal electrodes were patterned by using electrohydrodynamic printing technique. The crystalline nature, surface morphology and optical properties of as deposited TiO₂ films were characterized using X-ray diffraction (XRD), scanning electron microscope (SEM) and UV-visible spectroscopic analysis respectively. XRD and SEM studies revealed that the presence of anatase TiO₂ with uniform deposition. The optical transmittance of the deposited TiO₂ films was observed to be 87% in the visible region. The fabricated memristor device (Ag/TiO₂/Cu) exhibits bipolar resistive switching behavior within the low operating voltage (± 0.7 V). Our results ensure that the printed technology provides breakthrough solution in the electronic memory device fabrication.     

纳米TiO2薄膜紫外吸收特性的研究

选用不同材料做衬底,使用溶胶-凝胶法制备纳米TiO2薄膜,并采用XRD、AFM、UV、SPS对薄膜进行表征.在500℃以上焙烧2h后,即可获得锐钛矿型TiO2薄膜,粒径15nm左右,紫外吸收光谱分析表明,薄膜在220～350nm处有较强的紫外吸收.     

High transparent sol-gel derived nanostructured TiO2 thin film

In this investigation, high transparent nanostructured TiO₂ thin film has been prepared by a dip-coating method. The prepared sol was obtained through the hydrolysis of titanium isopropoxide under the selected pH. The transmission of film as an optical parameter was characterized by spectrophotometer. With respect to other experimental results, a high transmission spectrum without any fluctuation in visible wavelength region has been recorded. According to transmission spectrum of film the refractive index and extinction coefficient has been determined. Experimental result has shown that the prepared film has high transmission and good optical parameters. SEM and AFM have been applied for morphology characterization of the film surface.     

Low temperature preparation of TiO2 nanodot film on substrates

Herein, we report a photoinduced transition of hydrophobicity to high hydrophilicity of TiO₂ nanodot films in applications of cell sheet engineering. A phase-separation-induced self-assembly process was adopted to prepare a TiO₂ nanodot gel film on a substrate. Subsequently, a hydrothermal treatment (with ethanol/water at 140 °C for 2 h) was used to convert the nanodot gel film to TiO₂ nanodot solid film. The resulting TiO₂ dots were amorphous with adjustable size and density. The amorphous TiO₂ nanodot film showed a conversion from a good hydrophobic surface, with a water contact angle (WCA) of 67.6 ± 2.0°, to a highly hydrophilic one, with a WCA of 5.3 ± 2.0° (i.e. almost superhydrophilic) after UV irradiation. A good reversibility was also observed.     

Oxidant-assisted preparation of CaMoO4 thin film using an irreversible galvanic cell method

CaMoO₄ thin films were prepared by an irreversible galvanic cell method at room temperature; the crystalline phase structure, surface morphology, chemical composition and room temperature photoluminescence property were characterized by X-ray diffraction, Raman spectroscopy, scanning electronic microscopy, X-ray photoelectron spectroscopy as well as photoluminescence spectroscopy. Our results reveal that it is very difficult to directly deposit dense and uniform CaMoO₄ thin films in saturated Ca(OH)₂ solution at room temperature by the irreversible galvanic cell method. After adding some oxidant (NaClO solution or H₂O₂ solution), the growth of CaMoO₄ grains has been promoted, and well-crystallized, dense, and uniform CaMoO₄ films were obtained. The as-prepared CaMoO₄ films exhibit a good green photoluminescence, with the excitation of various wavelengths (220 nm, 230 nm, 240 nm, 250 nm and 270 nm) of ultraviolet irradiation.     

色素增感太阳电池多孔TiO2薄膜研究

采用溶胶-凝胶法制备复合硫化镉的二氧化钛纳米多孔薄膜;用差热分析仪、X射线分析仪、紫外-可见光分光光度计对薄膜的热处理制度、吸光度以及电池的性能进行了研究.结果表明在550℃下热处理,可以形成结晶良好,吸光度较好的TiO2薄膜;试制了太阳能电池,测定了电池性能.     

Rutile-type TiO2 thin film for high-k gate insulator

We investigated rutile-type titanium dioxide (TiO₂) films for possible use as a high-k gate insulator. The TiO₂ thin films were directly deposited on Si substrates using a RF magnetron sputtering method with a sintered oxide target. A single phase of rutile-type TiO₂ whose dielectric constant of approximately 75 was obtained when the film was deposited in an inert gas atmosphere and annealed at 800 °C in an oxidizing gas atmosphere. The oxygen ions were deficient in the as-deposited film, and consequently, a sufficient oxygen supply was needed to crystallize the film to a single phase of rutile during the post-annealing. However, the interfacial SiO₂ layer between the TiO₂ and the Si substrate simultaneously grew thicker than 2 nm. As the interfacial SiO₂ grew, the leakage current was decreased and the equivalent oxide thickness was increased, in the Au/rutile-type TiO₂/Si capacitor. Therefore, we concluded that the growth of the interfacial SiO₂ layer thicker than 2 nm is inevitable to form the single phase of rutile-type TiO₂ and to decrease the leakage.     

In-situ preparation of multi-layer TiO2 nanotube array thin films by anodic oxidation method

The multi-layer TiO₂ nanotube array thin films have been formed by anodic oxidation method via adjusting the outer voltage during oxidation process in glycerol electrolyte containing 0.3% NH₄HF₂. The diameter of the nanotube array increases with the outer voltage, and the length of nanotube in every layer increases with the anodic oxidation time. These multi-layers bring new possibilities to tailor the properties of the TiO₂ nanotube array thin films formed via anodic oxidation method. Further, such multi-layer structure provide a new approach to evaluate the growth rate of TiO₂ nanotube, which will help us to understand more deeply the formation mechanism of the TiO₂ nanotubes. The growth rate of TiO₂ nanotube array is respectively 1.2 and 3.6 μm/h under the anodic voltage of 30 V and 60 V. These multi-layer TiO₂ nanotube array thin films may exhibit lots of potential applications in photoelectrochemical fields.     

The preparation and characterization of photocatalytically active TiO2 thin films and nanoparticles using Successive-Ionic-Layer-Adsorption-and-Reaction

Photocatalytically active TiO₂ thin-films were deposited on silicon wafers using the Successive-Ionic-Layer-Adsorption-and-Reaction technique and subsequent hydrothermal and/or furnace annealing. Atomic-force-microscopy images and X-ray diffraction measurements of the TiO₂ films obtained under various annealing conditions show how changes of the micro-scale surface structure depend on the post-SILAR treatment. The hydrogen evolution over various TiO₂ films was measured. Hydrothermally treated TiO₂ films show a higher photocatalytic activity and a much better mechanical stability compared to furnace-annealed films. The optical transmittance of TiO₂ thin films on glass substrates was also studied. A red shift was observed with increasing film thickness. TiO₂ nanoparticles (∼10 nm) that were peeled off from the TiO₂ films were investigated using high-resolution-transmission-electron-microscopy.     

TiO2 thin films using organic liquid materials prepared by Hot-Wire CVD method

TiO₂ thin films prepared by Hot-Wire CVD method have been studied as a protecting material of transparent conducting oxide (TCO) against atomic hydrogen exposures for the fabrications of Si thin film solar cells. It was found that electrical conductivity of the films at room temperature reached a value of 0.4 S/cm. This value is 2-3 orders of magnitude higher than that of TiO₂ films prepared by RF magnetron sputtering and electron-beam evaporation methods in our previous works. The conductivity improvement seems to be partly due to the enlargement of TiO₂ crystallites.     

Superhydrophilicity of TiO2 thin films using TiCl4 as a precursor

TiO₂ thin films on soda lime glass were prepared by the sol-gel method and spin coating process using TiCl₄ as a precursor. The AFM images indicate that the surface morphology of the films is granular with 72 nm particle size. The roughness and thickness of the films are about 3 nm and 140 nm, respectively. The XRD spectrum shows polycrystalline anatase phase without any considerable impurity phase. The UV-vis spectroscopy of the films show 80-90% transmission in the visible region. The absorption edge is at 370 nm, which corresponds to 3.3 eV energy band gap. The films have a high superhydrophilicity character after being exposed to UV illumination for about 10 min. The surfaces, which were synthesized by this method, can retain their superhydrophilicity property for at least 24 h. Our results are consistent with the idea that UV-induced wetting of TiO₂ surface is caused by the removal of hydrophobic layers of hydrocarbons by TiO₂-mediated photooxidation, which leads to the attractive interaction of water with clean TiO₂ surface. TiO₂ thin films on Si(1 1 1), Si(1 0 0), and quartz substrates need less time than glass and polycrystalline Si substrates to be converted to superhydrophilic surface.     

Photodecomposition effects of graphene oxide coated on TiO2 thin film prepared by electron-beam evaporation method

Morphological, structural and photocatalytic properties of graphene oxide (GO)/TiO₂ thin-film deposited on quartz substrate were investigated. The TiO₂ film was prepared by electron-beam evaporation and the GO film by spin coating method. The photocatalytic activities of the GO/TiO₂ film were evaluated by photodecomposition of methylene blue. There was synergistic effect between TiO₂ and GO which causes a rapid photo-induced charge separation and the reduction of the recombination of electron-hole pairs under the UV-visible light irradiation. GO on TiO₂ film also promotes the properties of adsorption of the dye, photon scattering probability, and interacting surface area. As a result, it leads to the enhancement of the efficiency of the photodegradation in GO/TiO₂ film.     

Visible light enhanced TiO2 thin film bilayer dye sensitized solar cells

Visible light enhanced nitrogen-sulfur (N-S) doped titanium dioxide (TiO₂) thin films were prepared by the sol-gel method using thiourea as a dopant. The physical and chemical properties of the TiO₂ thin films were greatly influenced by the amount of thiourea added to the sol-gel solution. The greatest shift to longer wavelengths for visible light absorption was observed with 0.6 g of thiourea in the precursor solution, while 0.4 g yielded the largest particle sizes. These single-cycle dip-deposited N-S doped TiO₂ thin films were used as visible light harvesters as well as blocking layers in dye sensitized solar cells. When deposited directly on conducting fluorine doped tin oxide electrodes, photo-conversion efficiencies were reduced. However, the opposite configuration, with N-S doped thin films on top of nanoporous TiO₂, yielded an increased open-circuit voltage of 0.84 V, a short-circuit current density of 9.86 mA cm⁻², and an overall conversion efficiency of 5.88% greater than that of a standard cell. The effectiveness of the blocking layer on the cell efficiencies was analyzed by electrochemical impedance spectroscopy.     

Residual stresses and Raman shift relation in anatase TiO2 thin film

Anatase TiO₂ film (100-1000 nm thick) grown on glass, sapphire (0001), and Si (100) substrates by pulsed dc-magnetron reactive sputtering were evaluated for stress and strain analysis using Raman spectroscopy and curvature measurement techniques. The X-ray analysis revealed that films prepared for this study were purely anatase, and the measurements indicate that the film exhibit that (101) is the preferred growth orientation of the crystallites, especially for the film thicker than 100 nm. Curvature measurements and Raman spectroscopy, with 514.5 nm excitation wavelength, phonon line shift were used for stress analysis. A comparison between Raman lineshapes and peak shifts yields information on the strain distribution as a function of film thickness. The measurements of residual stresses for crystalline anatase TiO₂ thin film showed that all thin film were under compressive stress. A correlation between Raman shifts and the measured stress from the curvature measurements was established. The behavior of the anatase film on three different substrates shows that the strain in film on glass has a higher value compared to the strain on sapphire and on silicon substrates. The dominant 144 cm^− 1E_g mode in anatase TiO₂ clearly shifts to a higher value by 0.45-5.7 cm^− 1 depending on the type of substrate and film thickness. The measurement of the full width at half maximum values of 0.59-0.80 (2θ°) for the anatase (101) peaks revealed that these values are greater than anatase powder 0.119 (2θ°) and this exhibits strong crystal anisotropy with thermal expansion.     

Reactive sputtering of SiO2-TiO2 thin film from composite Six/TiO2 targets

Coatings of SiO₂-TiO₂ films are frequently used in a number of optical thin film applications. In this work we present results from depositing films with variable Si/Ti ratios prepared by reactive sputtering. The different Si/Ti ratios were obtained by varying the target composition of composite single targets. Compared to co-sputtering this facilitates process control and composition uniformity of the films. Varying the oxygen supply during sputter deposition can result in films ranging from metallic/substoichiometric to stoichiometric oxides. Transmittance spectra of the different films are presented and the optical constants are determined from these spectra. Furthermore, the deposition process, films structure and composition of the films are discussed. The study shows that by choosing the right composition and working in the proper oxygen flow range, it is possible to tune the refractive index.     

Hydrophilicity of anatase TiO2/Cr-doped TiO2 thin films with different band gaps

Based on the concept that the electron-hole separation effect caused by a different band-gap structure would improve its hydrophilicity, anatase-TiO₂/Cr-doped TiO₂ thin films were synthesized by DC magnetron sputtering. The optical band gaps of TiO₂ thin films decreased from 3.23 to 2.95 eV with increasing Cr-doping content. Multilayer TiO₂ thin films with different band gaps exhibited a superhydrophilicity under UV illumination. In particular, in anatase TiO₂ (3.23 eV)/4.8% Cr-doped TiO₂ (2.95 eV), the hydrophilicity, which indicated a contact angle of less than 20°, lasted for 48 h in the dark after UV illumination was discontinued. This outstanding result has rarely been reported for TiO₂ thin films, which confirmed that the prominent superhydrophilicity of anatase TiO₂/Cr-doped TiO₂/glass could be attributed to the retardation of electron-hole recombination caused by the band-gap difference.     

退火温度对P离子注入TiO2薄膜材料物理与生物学性能的影响

利用离子注入技术在TiO2薄膜中注入P元素,然后分别在不同温度进行退火处理,得到一系列钛氧化物掺杂材料.随着退火温度的上升,P注入的TiO2薄膜材料电阻降低,与水的接触角在70度左右波动.通过LDH及血小板粘附实验,发现高温退火样品的血液相容性得到改善.     

微米级石英空心小球表面TiO2薄膜的制备及其降解性能的研究

在粒径大小为57～74μm之间的石英空心小球表面成功的镀上一层TiO2薄膜.XRD显示600℃退火时TiO2薄膜结晶性能较好,退火700℃以上开始出现金红石相.镀TiO2薄膜石英空心小球较好的解决了TiO2纳米粉在溶液光降解中易出现的团聚问题.小球衬底的粒径较大,有利于解决TiO2粉状催化剂易出现的难以回收再利用的问题.利用对甲基橙的光降解试验来评估薄膜的催化降解性能,结果表明镀膜小球的光催化性能比TiO2纳米粉的光催化性能要好.