Titanium Dioxide Thin Films Research Articles

Zr-Ti getter film integration in MEMS vacuum packaging

Titanium, zirconium, and Zr-Ti alloy thin films were evaporated under UHV. AFM, TEM and SEM observations showed that grain size at the surface of the films varies with their thickness and composition. The single-metal films exhibit larger grain than alloy films. The highest density of grain boundaries is found for Zr-Ti film with a balanced content in Zr and Ti. For the three types of films, the grain boundary density at the surface decreases when increasing the film thickness. The gettering properties of the films were studied by activation annealing in the range of 200 °C–400 °C by in situ sheet resistance monitoring and by integrating them into MEMS packages sealed at 300 °C. In both cases, the sorption of gases was found to increase with the surface density of grain boundaries. In the specific activation conditions of MEMS packaging, it is shown that reducing the film thickness from 400 nm to 50 nm enhances gas sorption by the Zr-Ti getter and for the first time, the activation of a getter film thinner than 100 nm integrated in a MEMS package was demonstrated.

Biofunctionalization of Porous Titanium Oxide through Amino Acid Coupling for Biomaterial Design.

Porous transition metal oxides are widely studied as biocompatible materials for the development of prosthetic implants. Resurfacing the oxide to improve the antibacterial properties of the material is still an open issue, as infections remain a major cause of implant failure. We investigated the functionalization of porous titanium oxide obtained by anodic oxidation with amino acids (Leucine) as a first step to couple antimicrobial peptides to the oxide surface. We adopted a two-step molecular deposition process as follows: self-assembly of aminophosphonates to titanium oxide followed by covalent coupling of Fmoc-Leucine to aminophosphonates. Molecular deposition was investigated step-by-step by Atomic Force Microscopy (AFM) and X-ray Photoemission Spectroscopy (XPS). Since the inherent high roughness of porous titanium hampers the analysis of molecular orientation on the surface, we resorted to parallel experiments on flat titanium oxide thin films. AFM nanoshaving experiments on aminophosphonates deposited on flat TiO2 indicate the formation of an aminophosphonate monolayer while angle-resolved XPS analysis gives evidence of the formation of an oriented monolayer exposing the amine groups. The availability of the amine groups at the outer interface of the monolayer was confirmed on both flat and porous substrates by the following successful coupling with Fmoc-Leucine, as indicated by high-resolution XPS analysis.

Formation and manipulation of 2D colloidal crystals driven by convective currents and electrostatic forces

Colloidal crystal plays a major role in novel optical devices such as waveguides, photonic crystals, and colloidal crystal lasers, among others. It has been known that colloidal crystals may self-assemble due to optical, electric, or chemical potentials, and light-induced thermal effects, such as thermophoresis and convective currents. In this work, the formation and manipulation of a self-limiting assembly of monolayer colloidal crystals using a 20 nm absorbing thin film of titanium and a CW-laser emitting at 1070 nm is reported. The colloidal particles, dragged by thermally induced convective currents, self-assembling over the titanium thin film around the laser focal spot. The self-assembled monolayer colloidal crystal tends to form a circular shape. Using numerical simulation, we obtained a potential well associated with the convective currents that spatially govern the radial extension of the monolayer colloidal crystal. We also show, that by changing the pH of the solution i.e., by tuning the electrostatic interaction, the monolayer colloidal crystal can be formed or destroyed. In addition, it was possible to create a larger monolayer colloidal structure covering an area of 600 μm2 using an array of six laser spots.

Assessment of back-side activation of titania thin film using a fixed-bed photocatalytic-reactor: Kinetic study, operating cost and ANN modeling

This work is concerned with construction, application and modeling of a thin-film fixed photocatalytic bed multi lamp photo-reactor as an organic pollutant treatment system. Five photocatalytic units were located in a cylindrical vessel with a recycling current. In each unit, a thin layer of titania nanoparticles was coated on the outer surface of a quartz tube which a UV lamp was installed inside it. By this configuration, the UV lamps irradiation can approach directly to the photocatalyst particles before penetration into the reaction media. The effect of initial pH, initial DR16 (as model pollutant) dosage, H2O2 (as auxiliary oxidant) concentration and number of applied activated photocatalytic units were studied. The process was monitored via the kinetic rate constant and operating cost factors. The photocatalytic degradation of DR16 molecules in the constructed multi lamp photo-reactor followed a pseudo-first-order kinetic, and well described by the Langmuir-Hinshelwood equation. Under the initial pH of 3, 150 mg/L of H2O2 and illumination of the five lamps, complete degradation of the target pollutant was achieved after 60 min. Under these conditions, the rate constant and operating cost were 0.078 min−1 and 1.13 US$/m3 respectively. The real photon flux inside the reactor and quantum efficiency of the photocatalytic degradation of DR16, using five turned on lamps, were evaluated as 10.84 × 10−6 (einstein.s−1) and 0.009 respectively Also, the photocatalytic process was well modeled (with mean square error of 16.81 ×10−5) by a three layered feed forward back propagation artificial neural network consists of trainlm as training function, 7 hidden neurons and tansig-tansig as transfer functions calibrated at 156th epoch.

Tunable rapid electron transport in titanium oxide thin films

Rapid electron transport triggers many novel physical phenomena and becomes a critical point for high-speed electronics. Two-dimensional electron gas (2DEG) has drawn great attention due to its high electron mobility, and this has been observed in different materials, such as semiconductor, oxide interfaces, and 2D materials. In this paper, we report, for the first time, the existence and electrical manipulation of 2DEG in the Schottky quantum well, which was formed in the titanium oxide thin films. We take the asymmetry interface electron scattering effect into consideration when studying the electrical transport properties of our multilayer thin films. We found electrons would be transferred from the low-mobility semiconducting and metallic conductive channels to the high-mobility 2DEG conductive channel with an in-plane applied electric field. Therefore, electron concentration and mobility of the 2DEG formed in the Schottky quantum well could be tuned, and the nano-devices exhibited non-linear voltage–current curves. The differential resistivity of the nano-devices could decrease by two orders with increasing electric field at room temperature. Weak electron localization of electrons was experimentally observed in our nano-devices at low temperature, which further demonstrated the existence of 2DEG in the Schottky quantum well. Our work will provide us new physics about the rapid electron transport in the multilayer thin films and bring novel functional devices for the modern microelectronic industry.

Resistive switching characteristics of W/TiO2/ITO devices

Materials with resistance-switching properties are proving to be promising for the novel non-volatile memories-resistive random-access memory (ReRAM). Despite extensive research on electric field-induced resistance switching, there are diverse opinions about its reliability and working mechanism. In this work, we analysed the impact of SET and RESET voltages on the switching characteristics and the possible current conduction mechanism of W/TiO2/ITO devices. By simple solution processing and spin coating, titanium dioxide thin films were grown on ITO, glass, silicon, and quartz substrates. The precursor and solvent used for the synthesis of the active layer were titanium isopropoxide and ethanol, respectively. Polycrystalline films with an anatase structure were formed after annealing at 400 °C with a 20 nm average crystallite size, as evidenced by X-ray diffraction patterns. The crystalline nature of the fabricated film has been found to improve on annealing. Using Raman spectroscopy, the chemical bonding states of the film were studied. A UV–visible spectrometer study confirms that anatase TiO2 possesses an indirect band gap transition with a 3.42 eV band gap. The device shows reversible, reproducible, stable, and bipolar resistance-switching behaviour as indicated by current–voltage (I-V) measurements, and it was found that there exists a minimum voltage (∼-4 V) to set the device into an ON state. Compared to crystalline TiO2, theamorphous active layer offers much better switching characteristics, such as good cyclic endurance with a Roff-Ronratio ∼ 10.The current–voltage characteristics were fitted to various carrier transport mechanismssuch as Ohmic conduction, Schottky emission (SE), Space-charge-limited conduction (SCLC), and Poole-Frenkel emission (PF). Among these, the ohmic and SE mechanisms were detected at low and high fields, respectively. Schottky barrier modulation at the metal-oxide interface has been identified as the motive for switching.

Improving the performance of perovskite solar cells by electron beam evaporation processing

Electron transport layer (ETL) plays an important role in the development of high performance perovskite solar cells (PSC). Here, we first compared the optical and surface morphology characteristics of titanium dioxide (TiO₂) thin films prepared by electron beam evaporation (EB) and hydrothermal (HT) method, as well as the device performance of perovskite solar cells, and then studied the effect of electron beam evaporation TiO₂ film thickness on the performance of perovskite solar cells. It was found that the morphology of TiO₂ ETL prepared by electron beam evaporation was more uniform and compact, and the surface root mean square roughness was lower than that of hydrothermal method, and the quality of the film was better. And the average transmittance of TiO₂ ETL prepared by electron beam evaporation was 94.67%. Compared with hydrothermal method, the PCE of TiO₂-based PSC devices based on electron beam evaporation was increased by 60%. The thickness of TiO₂ ETL was adjusted by electron beam evaporation, and a good surface morphology of the film was obtained. When the thickness was 75 nm, the ETL of the prepared PSC showed the best device performance, and the PCE reached 9.00%, showing excellent performance.

Annealing effect on the physical properties of TiO2 thin films deposited by spray pyrolysis.

Titanium dioxide (TiO2) thin films were deposited on glass substrates at 350 °C using the spray pyrolysis technique. As deposited and annealed thin films were characterized by X-ray diffraction, scanning electron microscopy, UV-VIS spectroscopy, and photodetection. Unlike the as deposited samples which were amorphous, annealed samples show an anatase phase. Films were absorbent in the UV region and the band gap energy decreases from 3.78 eV to 3.4 eV with annealing. The photoresponse of TiO2 photodetectors was recorded under UV (λ1 = 365 nm, λ2 = 254 nm) and visible light illumination by reversible switching (ON/OFF) cycles using DC electrical characterization. Photosensitive properties such as reproducible photosensitivity, responsivity, and detectivity were also studied.

Reflectance investigation on dielectric reflectors using ethanol, methanol and isopropanol as solvents in the synthesis process

Dielectric reflectors are made up of a range of solvents in the wet chemical sol–gel based synthesis technique. The unexpected scarcity of solvents such as ethanol complicates matters, influencing the optical characteristics of the created multilayer structure. To eliminate the need for solvents, a new method for generating dielectric reflectors employing a variety of solvents must be created. We provide here an experimental inquiry on the synthesis and fabrication procedure of dielectric reflectors employing different solvents such as ethanol, methanol, and isopropanol that has not been reported previously to the best of our knowledge. The fabricated reflectors are characterized with AFM for roughness analysis and found 26, 5, and 1.2 nm for the solvent ethanol, methanol, and isopropanol respectively. Cross-sectional FE-SEM analysis supported the fabrication of titania and silica thin films with bright and dark colours on the dielectric reflectors. When ethanol was employed as the solvent, reflectance analysis using UV–vis spectroscopy approach showed 100 % reflectivity in the near-infrared region, and when methanol and isopropanol were used, improved reflectance as well as shift in the stop band were observed respectively.

Modeling, optimization and characterization of titanium dioxide thin film prepared by the spin-coating method using the experimental design for an application of photocatalytic degradation of methylene blue

This work focuses on modeling and optimizing the deposition of a TiO2 film on ITO glass using the spin-coating method and experimental design. The parameters studied include the concentration of the solution, speed and duration of rotation, drying temperatures and time, and calcination temperature and time. Results show that optimal conditions are achieved at 457 g/l concentration, 1020 rpm speed, 43 s duration of rotation, 100 °C drying temperature for 30 s, and 500 °C calcination temperature for 2 h. XRD, FTIR, EDX, and SEM analyses of the TiO2/ITO film indicate crystallization in the anatase phase with a 29.3 nm crystal size and around 80% deposition quality, with good surface adhesion and a thickness of approximately 30 nm. The photocatalytic activity of the thin film for the decomposition of methylene blue (MB) in water was also studied. Results showed a 70% degradation of MB after 4.5 h, which was confirmed by absorption spectra and discoloration of MB. Additionally, the degradation reaction of MB by TiO2 followed the pseudo-first-order, with good agreement between the kinetic study and a high degradation rate constant (k1deg = 0.2919 (h−1)), indicating a rapid process. Finally, a photodegradation mechanism of MB was reported.

Humidity-driven degradation of sputtered molybdenum oxide and molybdenum–titanium-oxide thin films

IR measurements reveal the enhanced hydrolysis resistance of molybdenum titanium oxide compared to molybdenum oxide when exposed to controlled humidity conditions.

Micro spherical anatase phase TiO2 thin films for room temperature operated formaldehyde gas sensor applications

A highly sensitive and selective gas sensor is crucial for detecting hazardous gases in the environment at room temperature (RT). Titanium dioxide (TiO2) shows promise as an excellent candidate for gas sensing due to its superior sensitivity and stability, even in robust conditions. TiO2 could potentially replace volatile organic compound (VOC) gas sensors. This study employed the spray pyrolysis technique to deposit titania thin films. The precursor solution was sprayed onto substrates at temperatures ranging from 375 °C to 450 °C in 25 °C increments. A temperature-dependent study was conducted on TiO2 thin films to examine their structural, optical, and topographical properties. Films deposited at 400 °C and above exhibit a crystalline anatase phase. Higher deposition temperatures resulted in the decreased band gap of TiO2 films. TiO2 films showed excellent response to formaldehyde concentrations (1–25 ppm) and high selectivity over other reducing gases (methanol, ethanol, butanol, toluene, xylene), even at room temperature. Microstructural, optical, and morphological analyses provided valuable insights into the gas sensing mechanism, enhancing understanding of film functionality.

INFLUENCE OF NIOBIUM, CERIUM AND IRON IMPURITIES ON PROPERTIES OF TITANIUM DIOXIDE FILMS

This article investigates the effect of some few metallic impurities that can be referred to as dopants introduced into TiO2 thin films as a host composite material. It also gives a guide on how to choice these impurities and how their influence on TiO2 thin films can be determined by measuring their n-type and p-type conductivities and their insulating characteristics or properties. It discusses three rare earth metals of niobium, cerium, and iron. It further explains how they give rise to donor and acceptor characteristics, oxygen vacancy concentrations and influence structural changes in titanium dioxide thin films. The thin films exhibit varying conductivity, structure, electronic transport, morphology and stability.

Aqueous Photoelectrochemical CO2Reduction to CO and Methanol over a Silicon Photocathode Functionalized with a Cobalt Phthalocyanine Molecular Catalyst

AbstractWe report a precious‐metal‐free molecular catalyst‐based photocathode that is active for aqueous CO2reduction to CO and methanol. The photoelectrode is composed of cobalt phthalocyanine molecules anchored on graphene oxide which is integrated via a (3‐aminopropyl)triethoxysilane linker to p‐type silicon protected by a thin film of titanium dioxide. The photocathode reduces CO2to CO with high selectivity at potentials as mild as 0 V versus the reversible hydrogen electrode (vs RHE). Methanol production is observed at an onset potential of −0.36 V vs RHE, and reaches a peak turnover frequency of 0.18 s−1. To date, this is the only molecular catalyst‐based photoelectrode that is active for the six‐electron reduction of CO2to methanol. This work puts forth a strategy for interfacing molecular catalysts to p‐type semiconductors and demonstrates state‐of‐the‐art performance for photoelectrochemical CO2reduction to CO and methanol.

Aqueous Photoelectrochemical CO2 Reduction to CO and Methanol over a Silicon Photocathode Functionalized with a Cobalt Phthalocyanine Molecular Catalyst.

We report a precious-metal-free molecular catalyst-based photocathode that is active for aqueous CO2 reduction to CO and methanol. The photoelectrode is composed of cobalt phthalocyanine molecules anchored on graphene oxide which is integrated via a (3-aminopropyl)triethoxysilane linker to p-type silicon protected by a thin film of titanium dioxide. The photocathode reduces CO2 to CO with high selectivity at potentials as mild as 0 V versus the reversible hydrogen electrode (vs RHE). Methanol production is observed at an onset potential of -0.36 V vs RHE, and reaches a peak turnover frequency of 0.18 s-1 . To date, this is the only molecular catalyst-based photoelectrode that is active for the six-electron reduction of CO2 to methanol. This work puts forth a strategy for interfacing molecular catalysts to p-type semiconductors and demonstrates state-of-the-art performance for photoelectrochemical CO2 reduction to CO and methanol.

Aluminum Doped Titanium Dioxide Thin Film for Perovskite Electron Transport Layer

Aluminum (Al) doped titanium dioxide thin film with different Al doping concentration (Al = 0 mol%, 1 mol%, 3 mol%, 5 mol% and 7 mol%) were deposited using solution spin coating technique and the effect of Al concentration on the structural, morphological and optical properties were examine. All samples were annealed at 450°C for 1 hour. XRD reveal that the films exhibits anatase crystal phase at (101) peak orientation. Based on the FESEM and AFM image it is found that, surface morphology of the film was significantly affected with different doping concentration. Al doped titanium dioxide with 3 mol% Al concentration shows the highest transmittance compared to others samples. Consequently, it is shown that different Al doping concentration plays vital roles in producing an optimum Al doped titanium dioxide thin films samples.

Lateral and vertical evolution of the compositional and morphological profiles in nanostructured photocatalytic titania thin films

Thin films of nanostructured titania comprising different levels of lateral and vertical microstructural order and surface chemistry were prepared via the anodization of titanium. We segmented and demystified the contributions that lead to nanostructured titania and affected its photocatalytic behaviour to: (1) specific compositional (less dominant) and (2) specific (surface) morphological differences (substantial), in the as-achieved films. To shed more light on the contributions, we partitioned these films by chemically and morphologically distinctive constituents; (1) top porous non-stoichiometric titania, (2) mid tubular nanoformations, and (3) bottom dense titania.Morphology of the films was described using electron microscopy, and synchrotron grazing incidence X-ray scattering/diffraction. Narrow range of synthetic conditions allowed preparing of ordered, macroscopically homogeneous nanotubes for photovoltaics. Interestingly, somewhat different, distorted tubular nanoformations were better suited for the photo-degradation of salicylic acid (fit by pseudo-second order). In this case, rutile traces in anatase tubular formations were commonly observed, synergistically boosting photodegradation. Broad characterisations reasons the photodegradation in order of importance to: (1) controlling the evolution of type of porosity and presence of defects in the films, (2) controlling the ratio and vertical profile of anatase-to-rutile, and (3) observing the surface chemistry changes, i.e. the presence of substoichiometric titania.

Aero-TiO2 Prepared on the Basis of Networks of ZnO Tetrapods

In this paper, new aeromaterials are proposed on the basis of titania thin films deposited using atomic layer deposition (ALD) on a sacrificial network of ZnO microtetrapods. The technology consists of two technological steps applied after ALD, namely, thermal treatment at different temperatures and etching of the sacrificial template. Two procedures are applied for etching, one of which is wet etching in a citric acid aqua solution, while the other one is etching in a hydride vapor phase epitaxy (HVPE) system with HCl and hydrogen chemicals. The morphology, composition, and crystal structure of the produced aeromaterials are investigated depending on the temperature of annealing and the sequence of the technological steps. The performed photoluminescence analysis suggests that the developed aeromaterials are potential candidates for photocatalytic applications.

Preparation and characterization of titanium dioxide using PLD at various energy of pulsed laser

Because of its distinctive optical and electrical characteristics, titanium dioxide (TiO2) thin films are one of the significant and promising semiconductor materials for environmental and energy applications. The effect of the laser pulse energy of Nd:YAG on the properties of TiO2 thin film grown on silicon and quartz substrates using the laser pulse deposition technique by the crystal structure, surface area, crystalline structure, average particle size, and porosity were summarised. The nano-thin film with the optimum condition has been prepared with a pulse laser energy of 900 mJ. The optical properties have been investigated using UV–vis spectrophotometer, morphological properties have been studied using atomic force microscopy and field emission scanning electron microscopy, and structural properties have been examined using x-ray diffractometer and Raman spectrometer. The tests and measurements have shown a crystalline structure, and the distribution of the grains was regular in the film. Raman spectroscopy showed two diffraction peaks corresponding to anatase Eg and rutile Eg. This observation is typically used in dye-sensitised solar cells, separation sensor devices, and more.

Investigation of thermally induced changes on structure, morphology and stoichiometry of sputter deposited titanium oxide thin films

We report here tailoring the properties of amorphous titanium oxide (a-TiOx) thin films by changing substrate heating as well as post-annealing. The a-TiOx thin films have been deposited on silicon substrates by direct current magnetron sputtering at a sputter power of 50 W without and with substrate heating (200°C) with no additional oxygen sources. After deposition, the films were annealed in vacuum for 1 hour at 300°C, 400°C, and 500°C. The influence of substrate heating and post-deposition annealing on the structure and surface morphology of the films along with their chemical states has been investigated. X-ray reflectivity analysis revealed that films deposited at 200°C were denser and thinner with low roughness than those deposited without substrate heating. Grazing incidence X-ray diffraction analyses showed that the films before and after annealing were amorphous; except for the ones deposited without substrate heating and were annealed at 500°C which showed slight crystallinity. From field emission scanning electron microscopy and atomic force microscopy images, distinct variations in the morphology of the films were also observed when films were deposited at 200°C X-ray photoelectron spectroscopy analysis showed that the a-TiOx films were oxygen deficient. It was observed that Ti was found in Ti4+ and Ti3+ states in the films and that the proportion of Ti4+ increased when the films were annealed at 500°C. Therefore, the structure, morphology, and chemical states of a-TiOx thin films can be tailored with substrate heating and post-annealing.