Influence of cobalt ion implantation on optical properties of titanium dioxide thin films

Nano-crystalline TiO₂ thin films were synthesized by using sol-gel and spin-coating techniques on glass substrates for photo-catalytic applications. Prior to deposition, a TiO₂ colloidal suspension was synthesized by microwave-induced thermal hydrolysis of the titanium tetrachloride aqueous solution. In this study, the deposited TiO₂ coating with a grain size of 13 ± 2 nm was uniform without aggregation. Co ion implantation into the as-calcined TiO₂ thin films was conducted with fluences of 1 × 10¹⁵-1 × 10¹⁶ doses/cm² at 40 keV. In addition to the emission of TiO₂, the photoluminescence study showed the presence of another Co-related optical center at 405 nm in the Co-implanted TiO₂ thin films. Due to the strong capability of forming impurity compounds between the energetic cobalt ions and TiO₂, the photoluminescence emission and UV-Vis absorption efficiencies were improved.     

Nanoporous titanium oxide synthesized from anodized Filtered Cathodic Vacuum Arc Ti thin films

This paper describes the formation of self-organized nanopores in thin films of titanium prepared using a Filtered Cathodic Vacuum Arc (FCVA) deposition system. The post-deposition anodization was performed using 0.5% (wt) NH₄F in ethylene glycol and an aqueous based solution containing 0.5% (wt) NH₄F and 1 M (NH₄)₂SO₄ electrolytes. Homogenously distributed nanopores with dimensions in the range of 10 to 20 nm were obtained. Nanoporous TiO₂ thin films were obtained after annealing the anodized samples at 600 °C for 4 h. Scanning electron microscopy (SEM) and Raman spectroscopy were used to characterize these nanoporous films. Raman measurements revealed that the rutile TiO₂ polymorph dominates these structures along with imperfect titanium oxidation resulting in the formation of defect structures, particularly when aqueous electrolyte was used for the anodization.     

退火温度对Ge-SiO2薄膜结构的影响

用射频磁控溅射制备了Ge-SiO2薄膜，在N2的保护下对薄膜进行了不同温度的退火处理。使用傅里叶变换红外光谱分析（FTIR）技术，X射线衍射谱（XRD），X射线光电子能谱（XPS）分析样品的微结构，研究样品在退火中发生的结构，组分的变化，结果表明退火温度对薄膜的结构，尤其是薄膜中的GeO含量和GeO晶粒的大小的影响是显著的，并对其做了详尽的分析讨论。     

Influence of the target composition on reactively sputtered titanium oxide films

Titanium dioxide thin films have many interesting properties and are used in various applications. High refractive index of titania makes it attractive for the glass coating industry, where it is used in low-emissivity and antireflective coatings. Magnetron sputtering is the most common deposition technique for large area coatings and a high deposition rate is therefore of obvious interest. It has been shown previously that high rate can be achieved using substoichiometric targets. This work deals with reactive magnetron sputtering of titanium oxide films from TiO_x targets with different oxygen contents.The deposition rate and hysteresis behaviour are disclosed. Films were prepared at various oxygen flows and all films were deposited onto glass and silicon substrates with no external heating. The elemental compositions and structures of deposited films were evaluated by means of X-ray photoelectron spectroscopy, elastic recoil detection analysis and X-ray diffraction. All deposited films were X-ray amorphous. No significant effect of the target composition on the optical properties of coatings was observed. However, the residual atmosphere is shown to contribute to the oxidation of growing films.     

Cr-doped TiO2 thin films deposited by RF-sputtering

Cr-doped TiO₂ thin films with different band gaps were prepared. Higher Cr doping was beneficial to the formation of the rutile-TiO₂ phase over the anatase-TiO₂ phase. A 4.8% Cr-doped thin film indicated a band gap of 2.95 eV, which was lower than the band gap of the rutile-TiO₂. Cr doping was accompanied by the formation of not only the rutile-TiO₂ phase but also the Cr₂O₃ phase, lead to the degradation of the hydrophilicity. The TiO₂ thin films with the mixed phase were not desirable to improve the hydrophilicity.     

退火温度对TiO2薄膜结构与光学性能的影响

研究退火温度对薄膜相结构、表面化学组成、形貌及光学性能的影响.采用射频磁控溅射法在单晶硅片和石英玻璃片上负载TiO2薄膜,通过X射线衍射(XRD)、原子力显微镜(AFM)、X光电子能谱(XPS)和紫外可见光谱(UV-vis)对其进行表征.结果表明,常温制备400℃以下退火的TiO2薄膜为无定形结构,400℃以上退火的TiO2薄膜出现锐钛矿相,600℃以上退火的TiO2薄膜开始出现金红石相,退火温度在1000℃以上时样品已经完全转变为金红石相;高温退火薄膜的组成为TiOx;随着退火温度的升高,薄膜透射率下降,折射率和消光系数有所增加.     

Photocatalytic properties of titanium dioxide sputtered on a nanostructured substrate

The effective one-step physical approach is demonstrated for the fabrication of anatase titanium dioxide nanotubes through r.f. magnetron sputtering of TiO₂ on a highly ordered nanoporous anodic alumina template. The nanostructured TiO₂ benefited from the combination of unique properties of both the sputtering technique that provided well-controlled environment for the fabrication of anatase phase TiO₂ and the porous anodic alumina (PAA) that provided uniform and ordered nanopores. The photocatalytic properties of TiO₂ films were characterized following the degradation of methylene blue molecules under UV light irradiation. The photocatalytic activity of the nanostructured TiO₂ films has been found to be approximately twice higher in comparison with the flat TiO₂ films fabricated at the same conditions.     

Comparison of hydrophilic properties of TiO2 thin films prepared by sol-gel method and reactive magnetron sputtering system

This article reports on preparation, characterization and comparison of TiO₂ films prepared by sol-gel method using the titanium isopropoxide sol (TiO₂ coating sol 3%) as solvent precursor and reactive magnetron sputtering from substoichiometric TiO_2 − x targets of 50 mm in diameter. Dual magnetron supplied by dc bipolar pulsed power source was used for reactive magnetron sputtering. Depositions were performed on unheated glass substrates. Comparison of photocatalytic properties was based on measurements of hydrophilicity, i.e. evaluation of water contact angle on the film surface after UV irradiation. It is shown, that TiO₂ films prepared by the sol-gel method exhibited higher hydrophilicity in the as-deposited state but has significant deterioration of hydrophilicity during aging, compared to TiO₂ films prepared by magnetron sputtering. To explain this effect AFM, SEM and high resolution XPS measurements were performed. It is shown that the deterioration of hydrophilicity of sol-gel TiO₂ films can be suppressed if as-deposited films are exposed to the plasma of microwave oxygen discharge.     

Effect of oxygen concentration and system geometry on the current-voltage relations during reactive sputter deposition of titanium dioxide thin films

Current-voltage relations at different magnetron sputtering systems and gas mixtures were studied during reactive sputter deposition of titanium dioxide thin films. The main goal of this work was to investigate the influence of reactive gas mixture (Ar + O₂) and system geometry on the electrical characteristics of the discharge. The geometries utilized were the conventional magnetron sputtering, hollow cathode magnetron sputtering and triode magnetron sputtering. A change in the system geometry leads to a change in the electric field distribution, which alters the working range of the discharge voltage and magnetron efficiency. It is noticed that the discharge voltage at constant current can be reduced when the geometry is altered from conventional magnetron to hollow cathode magnetron or triode magnetron, at the same time the magnetron efficiency is increased when hollow cathode magnetron or triode magnetron are used instead of conventional magnetron sputtering.     

Structures and properties of titania thin films annealed under different atmosphere

The effects of crystallinity, phase and oxygen vacancies on optical and photocatalytic properties of titania (TiO₂) thin films were systematically studied. The as-deposited amorphous titania films were prepared by reactive sputtering titanium metal targets in argon–oxygen plasma at 100 °C and subsequently annealed at various temperatures of 400–800 °C in air, vacuum and H₂ atmosphere. The results indicate that in general the crystallinity of the annealed films is enhanced with the increasing annealing temperature. At the same temperature, the H₂ annealed films achieve better crystallinity but containing more oxygen vacancies than the films annealed in air and in vacuum. In H₂ or in vacuum, the concentration of oxygen vacancies in the annealed films increases with increasing temperature, while in air it remains constant. Oxygen vacancies in titania film not only facilitate phase transformation but also lower the band gap of titania, and make the film visible-light responsive. Photocatalytic properties of the TiO₂ films were characterized in UV and visible light irradiation by following the Ag reduction and degradation of methylene blue. The films annealed at 600–700 °C in H₂ possess the best film crystallinity and the proper concentration of oxygen vacancies and exhibit the best photocatalytic performance under both UV and visible light.     

The effects of O2/Ar ratio on the structure and properties of hafnium dioxide (HfO2) films

HfO₂ films at various O₂/Ar flow ratios were prepared by reactive dc magnetron sputtering. The effects of O₂/Ar ratio on the structure and properties of HfO₂ films were studied using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and UV-Visible spectroscopy. The results showed that the HfO₂ films were amorphous at different O₂/Ar ratios, and the atomic ratio of O/Hf in the HfO₂ films at high O₂/Ar ratio was nearly to 2:1. The peaks of Hf4f and O1s shifted to higher binding energy with increasing the oxygen flow proportion. The HfO₂ films at high O₂/Ar ratio had high transmissivity at the range of 400-1100 nm.     

Structural, thermal and optical characterization of TiO2:ZrO2 thin films prepared by sol-gel method

We have studied the structural and optical properties of thin films of TiO₂, doped with 5% ZrO₂ and deposited on glass substrate (by the sol-gel method). The dip-coated thin films have been examined at different annealing temperatures (350 to 450 °C) and for various layer thicknesses (63-286 nm). Refractive index and porosity were calculated from the measured transmittance spectrum. The values of the index of refraction are in the range of 1.62-2.29 and the porosity is in the range of 0.21-0.70. The coefficient of transmission varies from 50 to 90%. In the case of the powder of TiO₂, doped with 5% ZrO₂, and aged for 3 months in ambient temperature, we have noticed the formation of the anatase phase (tetragonal structure with 14.8 nm grains). However, the undoped TiO₂ exhibits an amorphous phase. After heat treatments of thin films, titanium oxide starts to crystallize at the annealing temperature 350 °C. The obtained structures are anatase and brookite. The calculated grain size, depending on the annealing temperature and the layer thickness, is in the range (8.58-20.56 nm).     

The effect of sputtering gas pressure on structure and photocatalytic properties of nanostructured titanium oxide self-cleaning thin film

Titanium oxide thin films were deposited by DC reactive magnetron sputtering on ZnO (80 nm thickness)/soda-lime glass and SiO₂ substrates at different gas pressures. The post annealing on the deposited films was performed at 400 °C in air atmosphere. The results of X-ray diffraction (XRD) showed that the films had anatase phase after annealing at 400 °C. The structure and morphology of deposited layers were evaluated by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The surface grain size and roughness of TiO₂ thin films after annealing were around 10-15 nm and 2-8 nm, respectively. The optical transmittance of the films was measured using ultraviolet-visible light (UV-vis) spectrophotometer and photocatalytic activities of the samples were evaluated by the degradation of Methylene Blue (MB) dye. Using ZnO thin film as buffer layer, the photocatalytic properties of TiO₂ films were improved.     

Effect of sputtering pressure and post-annealing on hydrophilicity of TiO2 thin films deposited by reactive magnetron sputtering

A series of TiO₂ thin films was deposited onto glass substrates without intentional heating or biasing by magnetron sputtering of a titanium target using Ar/O₂ reactive mixtures over a broad range of total sputtering pressures from 0.12 Pa to 2.24 Pa. Each of the film types was deposited by the threshold poisoned mode at a specific given oxygen flow rate monitored in-situ by optical emission spectroscopy. Both the sputtering pressure and thermal annealing are the key factors for the TiO₂ films to yield fast-response superhydrophilicity with a water contact angle of 5°. The mechanism of superhydrophilicity for the TiO₂ films deposited by high-pressure sputtering will be discussed based on empirical studies of X-ray diffractometry, high-resolution scanning microscopy and atomic force spectroscopy.     

Gas sensing mechanism of TiO2-based thin films

Two classes of thin film gas sensors have been studied: TiO₂ doped with Cr or Nb and TiO₂-SnO₂ mixed systems. Thin films have been prepared by the reactive sputtering from mosaic targets. It is demonstrated that titanium dioxide doped with Nb and Cr should be considered as a bulk sensor. Its performance is governed by the diffusion of point defects, i.e. very slow diffusion of Ti vacancies for TiO₂: 9.5 at% of Nb and fast diffusion of oxygen vacancies in the case of TiO₂: 2.5 at% Cr sensor. The corresponding response times are 55 min for TiO₂: 9.5 at% of Nb and 20 s for TiO₂: 2.5 at% Cr. In turn, sensors based on TiO₂-SnO₂, particularly those of the SnO₂-rich composition, belong to the group of surface sensors.     

Effects of post-deposition annealing on the structure and optical properties of Y2O3 thin films

Y₂O₃ thin film waveguides were prepared by RF magnetron sputtering. The effects of post-deposition annealing on the structure and optical properties have been investigated. The structural evolution of Y₂O₃ films with annealing temperature was investigated by X-ray diffraction (XRD). Spectroscopic ellipsometry was employed to determine the optical properties of Y₂O₃ films annealed at various temperatures. It was found that with increasing annealing temperature, the refractive index (n) of Y₂O₃ films increases. The optical band gap of Y₂O₃ films shifts to higher energy after higher temperature annealing, which is likely due to the reduction of defects and the change of crystalline structure in Y₂O₃ films.     

The optical properties of nanoporous structured titanium dioxide and the photovoltaic efficiency on DSSC

This study examined the characterization of nanoporous structured titanium dioxide and its application to dye-sensitized solar cells (DSSCs). TEM revealed nanopore sizes of 10.0 nm with a regular hexagonal form. When nanoporous structured TiO₂ was applied to DSSC, the energy conversion efficiency was enhanced considerably compared with that using nanometer sized TiO₂ prepared using a hydrothermal method. The energy conversion efficiency of the DSSC prepared from nanoporous structured TiO₂ was approximately 8.71% with the N719 dye under 100 mW cm⁻² simulated light. FT-IR spectroscopy showed that the dye molecules were attached perfectly to the surface and more dye molecules were absorbed on the nanoporous structured TiO₂ than on the nano-sized TiO₂ particles prepared using a conventional hydrothermal method. Electrostatic force microscopy (EFM) showed that the electrons were transferred rapidly to the surface of the nanoporous structured TiO₂ film.     

Superhydrophilic anatase TiO2 film with the micro- and nanometer-scale hierarchical surface structure

Nanosized anatase TiO₂ film on the ITO glass has been fabricated via spin coat process, with sodium dodecylbenzenesulfonate modified TiO₂ nanoparticles, which is synthesized by a sol-hydrothermal method, and also characterized mainly by means of field emission scanning electron microscopy (FESEM). The results show that the as-prepared anatase TiO₂ film exhibits superhydrophilic characteristic although it is not exposed to ultraviolet irradiation. The high roughness resulting from hierarchical surface structure is responsible for its superhydrophilicity. This work would provide a new route to fabricate newly nanostructured semiconductor films.     

Influence of annealing treatments for ZnO-doped Zr0.8Sn0.2TiO4 thin films by RF magnetron sputtering

Zirconium tin titanium oxide doped 1 wt.% ZnO thin films on n-type Si substrate were deposited by rf magnetron sputtering at a fixed rf power of 300 W, a substrate temperature of 450 °C, a deposition pressure of 5 mTorr and an Ar/O₂ ratio of 100/0 with various annealing temperatures and annealing times. Electrical properties and microstructures of 1 wt.% ZnO-doped (Zr_0.8Sn_0.2)TiO₄ thin films prepared by rf magnetron sputtering on n-type Si(100) substrates at different annealing temperatures (500 °C-700 °C) and annealing times (2 h-6 h) have been investigated. The structural and morphological characteristics analyzed by X-ray diffraction (XRD) and atomic force microscope (AFM) were sensitive to the treatment conditions such as annealing temperature and annealing time. At an annealing temperature of 600 °C and an annealing time of 6 h, the ZnO-doped (Zr_0.8Sn_0.2)TiO₄ thin films possess a dielectric constant of 46 (at f = 10 MHz), a dissipation factor of 0.059 (at f = 10 MHz), and a low leakage current density of 3.8 × 10^− 9 A/cm² at an electrical field of 1 kV/cm.     

Microstructure of sol-gel derived TiO2 thin films characterized by atmospheric ellipsometric porosimetry

Adsorption of water vapor during ellipsometric measurements was performed in-situ for the characterization of sol-gel derived TiO₂ thin films. The data obtained were compared with complementary results derived from scanning electron microscopy and photocatalytic degradation measurements. Results indicate that a less permeable surface layer encapsulates the porous interior of the films which may become more accessible by defects such as cracks. Atmospheric ellipsometric porosimetry provides a valuable tool for the microstructural characterization of sol-gel films.