Thin Titania Research Articles

Charge carrier transport in silicon heterojunctions with a thin titanium oxide layer

Charge carrier transport in silicon heterojunctions with a thin titanium oxide layer

Nanometer – Thick titanium film as a silicon migration barrier

Diffusion of silicon atoms to the topmost film surface poses significant challenges in various technological applications. In an effort to address this issue, titanium films with varying thicknesses were deposited on a silicon substrate to evaluate the efficacy of a thin titanium barrier film in blocking silicon migration to the upper film surface. Subsequently, the films were subjected to a 1-hour heating process in air at an oxidizing temperature of 430 K. Atomic force microscopy and Raman spectroscopy were employed to characterize the morphological and structural changes among the investigated films. X-ray photoelectron spectroscopy was utilized to explore variations in chemical composition, determine oxidation states, and measure the thicknesses of the thin titanium oxide layers. The findings revealed that titanium films with a thickness < 50 nm experienced silicon diffusion to their upper film surface. Moreover, an increase in the thickness of the oxide layers over the titanium film on the silicon substrate significantly reduced the migration of silicon to the titanium film surface. At 430 K, the study found that oxide layers at least 6.87 nm thick formed on a 35-nm thick titanium layer, which together successfully prevented silicon migration to the top surface of the film.

Photonic post-processing of a multi-material transparent conductive electrode architecture for optoelectronic device integration.

Emerging flexible optoelectronic devices require multi-material processing capabilities to fully enable the use of temperature-sensitive substrates and materials. This report demonstrates how photonic sintering enables the processing of materials with very different properties. For example, charge carrier transport/blocking metal-oxides, and transparent conductive silver nanowire-based electrodes ought to be compatible with low-energy and high-throughput processing for integration onto flexible low-temperature substrates. Compared to traditional post-processing methods, we show a rapid fabrication route yielding highly-stable hybrid electrode architectures on polyethylene terephthalate (PET). This architecture consists of an interconnected silver nanowire network encapsulated with a thin crystalline photo-sensitive titanium dioxide (TiO2) coating, allowing both layers to be treated using independent photonic post-processing sintering steps. The first step sinters the nanowires, while the second completes the conversion of the top metal-oxide layer from amorphous to crystalline TiO2. This approach improves on the fabrication speed compared to oven processing, while delivering optical and electrical characteristics comparable to the state of the art. Optimized transparency values reach 85% with haze values down-to 7% at 550 nm, while maintaining a sheet resistance of 18.1 Ω sq.-1. However, this hybrid architecture provides a much stronger resilience to degradation, which we demonstrate through exposure to harsh plasma conditions. In summary, this study shows how carefully-optimized photonic curing post-processing can provide more-stable hybrid architectures while using a multi-material processing technique suitable for high-volume manufacturing on low-temperature substrates.

One-dimensional porous silicon photonic crystals for chemosensors: Geometrical factors influencing the sensitivity

One-dimensional photonic crystals with microcavity were prepared to be used as optical chemosensors. The experimental reflectance of the as-etched devices immersed in solvent solutions appear greater than the theoretical one. The fitting procedure of the experimental data using the transfer matrix method together with the Looyenga effective medium approach reveals that the deviation of the experimental data occurs because of the expansion-contraction effect of the high and low porosity layers, respectively, caused by the presence of the solvent into the porous matrix and is proportional to the solvent effective refractive index. Due to this phenomenon, the sensitivity of the as-etched photonic crystals increases about two times but is not stable because of the aging effect. To avoid this effect, the photonic crystal structures were passivated by thermally silicon oxide growing, gold thin film and titanium oxide deposition. After thermal treatment in an air environment, the optical response achieves its stabilization even after long storage times, thus showing the importance of the passivation procedure. Among them, the passivation by TiO2 shows better performance and lower loss in sensitivity in comparison to the as-etched devices.

Reliable bi-functional nickel-phosphate /TiO2 integration enables stable n-GaAs photoanode for water oxidation under alkaline condition

Hydrogen is one of the most widely used essential chemicals worldwide, and it is also employed in the production of many other chemicals, especially carbon-free energy fuels produced via photoelectrochemical (PEC) water splitting. At present, gallium arsenide represents the most efficient photoanode material for PEC water oxidation, but it is known to either be anodically photocorroded or photopassivated by native metal oxides in the competitive reaction, limiting efficiency and stability. Here, we report chemically etched GaAs that is decorated with thin titanium dioxide (~30 nm-thick, crystalline) surface passivation layer along with nickel-phosphate (Ni-Pi) cocatalyst as a surface hole-sink layer. The integration of Ni-Pi bifunctional co-catalyst results in a highly efficient GaAs electrode with a ~ 100 mV cathodic shift of the onset potential. In this work, the electrode also has enhanced photostability under 110 h testing for PEC water oxidation at a steady current density Jph > 25 mA·cm−2. The Et-GaAs/TiO2/Ni-Pi║Ni-Pi tandem configuration results in the best unassisted bias-free water splitting device with the highest Jph (~7.6 mA·cm−2) and a stable solar-to-hydrogen conversion efficiency of 9.5%.

CO Oxidation Catalyzed by Au Dispersed on SBA-15 Modified with TiO2 Films Grown via Atomic Layer Deposition (ALD)

It has been established that gold, when in nanoparticle (NP) form and in contact with reducible oxides, can promote oxidation reactions under mild conditions. Here, we report results from our exploration of the catalytic oxidation of carbon monoxide using catalysts where Au NPs were combined with thin titanium oxide films deposited on SBA-15 using atomic layer deposition (ALD). Both orders of deposition, with TiO2 added either before or after Au dispersion, were tested for two titania film thicknesses amounting to about half and full TiO2 monolayers. The resulting catalysts were characterized using various techniques, mainly electron microscopy and N2 adsorption–desorption isotherms, and the kinetics of the oxidation of CO with O2 were followed using infrared absorption spectroscopy. A synergy between the Au and TiO2 phases as it relates to the bonding and conversion of CO was identified, the tuning of which could be controlled by varying the synthetic parameters. The ALD of TiO2 films proved to be an effective way to maximize the Au-TiO2 interface sites, and with that help with the activation of molecular oxygen.

Polymer-based TiO2 membranes: An efficient route for recalcitrant dye degradation

Methyl orange (MO) is a poisonous, carcinogenic, and genotoxic azo dye with high chemical stability, high solubility in water, and very low biodegradability. The removal is difficult by conventional water purification methods. The degradation of MO with photocatalytic membrane reactors loaded with TiO2 nanoparticles(NPs) is reported in some publications, and the degradation efficiency is less than 50%. The present study presents the use of titanium dioxide nanoparticles deposited on the surface of nanofiltration membranes to assess the photocatalytic degradation of reactive dye. The morphological analyses showed the presence of a thin titanium dioxide layer on the surface of the membranes. In addition, the photocatalytic membranes with 0.25 wt% of TiO2 showed an interesting photocatalytic activity over four hours, with 82.3% of the MO degraded. The degradation followed a pseudo-second-order kinetics model, and the reusability of the prepared membranes was also verified.

Fabrication of Step‐Scheme Heterojunction between Layered MoO3/TiO2 for Photocatalytic H2 Evolution and Study on the Mechanism

AbstractThe intimate contact of components in a heterojunction photocatalyst is essential in determining the photocatalytic performance. To build a face‐to‐face interface in a 2D–2D heterojunction is an effective strategy to improve the charge carrier separation and utilization efficiency. In this work, the fabrication of a Step‐scheme heterojunction on thin titania (TiO2) nanosheets with few‐layered MoO3 structures is reported. With a decoration of a low dose of MoO3 layer by ball milling method, TiO2 (B) shows a three‐fold increase in the hydrogen evolution rate. The reaction mechanism and driving force of charge transfer in the S‐scheme heterojunction photocatalyst are investigated and discussed. Such 2D‐2D heterojunction improves photocatalytic reaction rate because photogenerated electrons and holes at the interface can be quickly transferred to the surface. In situ XPS and PL demonstrates that the presence of MoO3 promotes the electron‐hole pair separation via the Step‐scheme heterojunction. Temperature programmed desorption of hydrogen shows that the heterojunction structure facilitates the desorption of hydrogen molecules. The approach used in this work to fabricate 2D–2D assembled structure thus improve the photocatalytic activity can be applied to other 2D metal oxides and sulfides, among others.

The Anodization of Thin Titania Layers as a Facile Process towards Semitransparent and Ordered Electrode Material.

Photoanodes consisting of titania nanotubes (TNTs) grown on transparent conductive oxides (TCO) by anodic oxidation are being widely investigated as a low-cost alternative to silicon-based materials, e.g., in solar light-harvesting applications. Intending to enhance the optical properties of those photoanodes, the modification of the surface chemistry or control of the geometrical characteristics of developed TNTs has been explored. In this review, the recent advancement in light-harvesting properties of transparent anodic TNTs formed onto TCO is summarized. The physical deposition methods such as magnetron sputtering, pulsed laser deposition and electron beam evaporation are the most reported for the deposition of Ti film onto TCO, which are subsequently anodized. A concise description of methods utilized to improve the adhesion of the deposited film and achieve TNT layers without cracks and delamination after the anodization is outlined. Then, the different models describing the formation mechanism of anodic TNTs are discussed with particular focus on the impact of the deposited Ti film thickness on the adhesion of TNTs. Finally, the effects of the modifications of both the surface chemistry and morphological features of materials on their photocatalyst and photovoltaic performances are discussed. For each section, experimental results obtained by different research groups are evoked.

Surface analysis of titanium disks with strontium coating.

Peri-implantitis is one of the most common complications after dental implant placement. Researchers have demonstrated that the peri-implantitis tends to occur around dental implants with a rough surface rather than those with a smooth surface. We aimed to investigate the ability of a smooth titanium (Ti) surface containing strontium (Sr) to enhance bone formation as a result of strontium's capacity to support osteoblast proliferation and differentiation. A thin titanium oxide film was formed on an as-mirror polished Ti surface by dipping in 5% sodium hypochlorite (NaOCl) solution for 24 h, followed by thermal treatment at 350°C. The Ti surface was then treated with 1% strontium nitrate (Sr(NO3)2) solution and turned in spin coater. The surface morphology, chemical composition, and release of strontium ions (Sr2+) were evaluated. The results demonstrate that strontium in the form of Sr2+ was successfully doped into the titanium dioxide (TiO2) film by this simple chemical treatment.

Design of thin DLC/TiO2 film interference coatings on glass screen protector using a neon–argon-based gas injection magnetron sputtering technique

This paper reports the results obtained from the deposition of diamond-like carbon (DLC) films on glass substrates by gas injection magnetron sputtering method. The conducted studies aimed to evaluate if the plasma discharge that is generated by varying the proportions of neon−argon (Ne−Ar) gases during pulsed injections (0%–100%) would promote the synthesis of DLC films with desirable sp3 phase by means of electron impact-induced plasma interactions. The obtained DLC films showed the presence of sp3 (CC) hybridized bonds along the Gaussian distribution curve, which revealed that a maximum sp3 content in the range of 32%–45% was obtained along the 40% injection of Ne gas, based on the analysis of the C1s core-level spectra and Raman spectroscopy. A 25% gain in hardness (H) and resistance to cracking (H3/E2) were also observed in the sp3-rich DLC sample (24.1 ± 4 GPa and 0.29 ± 0.04), thus promoting its use in various nanomechanical systems. The change in the sp3/sp2 fraction ratio, demonstrated in this research, corresponded well to a calculated model of graded optical bandgap in the range from 0.53 to 3.01 eV. However, to further minimize the parasitic reflectance from a significant share of sp2 (C=C) domains, thin titanium dioxide (TiO2) (8–36 nm) layers were deposited on the DLC surface, which provided maximum antireflective effect due to interference shift. A significant increase in visible–near-infrared transmittance (up to 87%) was observed as a result of such an interference in DLC/TIO2 bilayers. Our results have practical applications and aid in the design of functional nanocoating structures which are tremendously favored and required to improve the toughness of commercially available glass protectors in hostile environmental conditions.

The characteristics of microplasma discharge propagation over &#x0D; the titanium surface covered with a thin oxide film

The propagation and structure of a microplasma discharge initiated in vacuum by a pulsed plasma flow with a density of 1013 cm–3 on the surface of a titanium sample covered with a &#x0D; thin continuous dielectric titanium oxide film with a shickness of 2–6 nm were studied experimentally when the electric current of the discharge changes from 50 A to 400 A. &#x0D; It was found that the microplasma discharge glow visually at the macroscale has a branched structure of the dendrite type, which at the microscale consists of a large number &#x0D; of brightly glowing “point” formations – cathode spots localized on the metal surface. The resulting erosion structure on the titanium surface is visually “identical” to the structure of &#x0D; the discharge glow and consists of a large number of separate non-overlapping microcraters with characteristic sizes from 0.1–3 μm, which are formed at the sites of localization of &#x0D; cathode spots at distances of up to 20 μm from each other. It was found that the propagation of a single microplasma discharge over the titanium surface covered with a thin oxide film a &#x0D; thickness of 2–6 nm occurs at an average velocity of 15–70 m/s when the amplitude of the discharge electric current changes in the range of 50–400 A. In this case, the microplasma &#x0D; discharge propagation on the microscale has a “jumping” character: the plasma of “motionless” burning cathode spots, during their lifetime 1 μs, initiates the excitation of new &#x0D; microdischarges, which create new cathode spots at localization distances of 1–20 μm from the primary cathode spots. This process repeated many times during a microplasma dis-&#x0D; charge pulse with a duration from 0.1 ms to 20 ms.

Synthesis of Thin Titania Coatings onto the Inner Surface of Quartz Tubes and Their Photoactivity in Decomposition of Methylene Blue and Rhodamine B

An evaporation-deposition coating method for coating the inner surface of long (&gt;1 m) quartz tubes of small diameter has been studied by the introduction of two-phase (gas-liquid) flow with the gas core flowing in the middle and a thin liquid film of synthesis sol flowing near the hot tube wall. The operational window for the deposition of continuous titania coatings has been obtained. The temperature range for the deposition of continuous titania coatings is limited to 105–120 °C and the gas flow rate is limited to the range of 0.4–1.0 L min−1. The liquid flow rate in the annular flow regime allows to control the coating thickness between 3 and 10 micron and the coating porosity between 10% and 20%. By increasing the liquid flow rate, the coating porosity can be substantially reduced. The coatings were characterized by X-ray diffraction, N2 chemisorption, thermogravimetric analysis, and scanning electron microscopy. The coatings were tested in the photocatalytic decomposition of methylene blue and rhodamine B under UV-light and their activity was similar to that of a commercial P25 titania catalyst.

Enhancing Si Solar Cells Efficiency by Adding SiO2 / TiO2 Thin Films Using Transfer Matrix Method

Thin film silicon solar cells are nowadays the best choice to get electricity due to their low cost compared to the crystalline solar cells. However, thin film silicon solar cells have weak absorption of incident light. To deal with such a weakness and get better efficiency of these cells, an efficient back reflector composed of multilayer thin films (Silver, Silicon dioxide (SiO2) and Titanium dioxide (TiO2)) will be used. The transmitted light from the first silicon layer will be reflected by the next layer, and the reflected light will go back to the first silicon layer. By this way, the absorbance of the silicon solar cell can be increased by an increase in the probability of the light reflection from the SiO2, TiO2 and Ag. The transfer matrix method (TMM) by Matlab program will be used to analyze the results of the reflectance, transmittance and absorbance of the thin film layer and these results can prove the efficiency of the cells by using MATLAB codes.

Method for milk whey microfiltration with filtrate pulsed backpressure and installation for its implementation

During deep processing of whey using microfiltration, the loss of membrane efficiency can take place. In this work, an installation for microfiltration of milk whey has been developed. It includes pumps, containers with liquids, throttling valves, a pressure gauge, and a microfiltration cell with a tubular ceramic membrane. A thin titanium oxide layer was deposited on the inner surface of the porous alumina tube. The outer diameter of the tubes is 10 mm, the wall thickness is 2 mm, the length of the tubes is 45 cm. A homogenized aqueous dispersion of sugar beet fiber was used as an agent that improves the performance of the installation by creating a pulsed backpressure of the filtrate. It is shown that the use of a finely ground suspension of dietary fiber during microfiltration of milk whey through a tubular ceramic membrane prevents the formation of protein deposits on the membrane and in its pores. The installation allows obtaining a suspension of dietary fiber, enriched with milk protein, as an additional product. The protein-enriched fiber suspension left over after microfiltration can be used in food production, for example, as a thickening agent in the production of yogurts.

High-performance Opening-up Dual-core Photonic Crystal Fiber Sensors Based on Surface Plasmon Resonance

Nowadays, plasmonic sensors based on photonic crystal fiber (PCF) attracted a great deal of attention in the field of optical sensing. Opening-up dual-core photonic crystal fibers based on surface plasmon resonance (SPR) are numerically demonstrated and analyzed for detecting a wide refractive index (RI) range by the finite-difference time-domain method (FDTD). Wavelength and amplitude integration methods as well as figures of merit are used to investigate the sensing performance. For improving sensing performance, a large hole between two cores in the opening-up section is introduced. The opening-up section as a sensing channel is coated with a gold film and a thin titanium dioxide ( $${TiO}_{2}$$ ) layer. By surface engineering including imposing of grating on the gold film, specification of optimized values of different layers located near the surface and sensing performance are investigated. Next, the effect of the fiber structural parameters is analyzed to enhance SPR and fundamental core mode coupling. The proposed sensor revealed maximum wavelength and amplitude sensitivities of 15,167 $$\left(\frac{nm}{RIU}\right)$$ and 207.19 $$\left({RIU}^{-1}\right)$$ , respectively. Due to the ease of infiltration of analyte and gold coating and thanks to the high wavelength and amplitude sensitivity, the sensors can be a promising candidate for physical and chemical sensing.

Balancing Charge Extraction for Efficient Back‐Contact Perovskite Solar Cells by Using an Embedded Mesoscopic Architecture

AbstractAs the performance of organic–inorganic halide perovskite solar cells approaches their practical limits, the use of back‐contact architectures, which eliminate parasitic light absorption, provides an effective route toward higher device efficiencies. However, a poor understanding of the underlying device physics has limited further performance improvements. Here a mesoporous charge‐transporting layer is introduced into quasi‐interdigitated back‐contact perovskite devices and the charge extraction behavior with an increased interfacial contact area is studied. The results show that the incorporation of a thin mesoporous titanium dioxide layer significantly shortens the charge‐transfer lifetime and results in more efficient and balanced charge extraction dynamics. A high short‐circuit current density of 21.3 mA cm–2 is achieved using a polycrystalline perovskite layer on a mesoscopic quasi‐interdigitated back‐contact electrode, a record for this type of device architecture.

Highly sensitive dual-core symmetrical side-polished modified D-shaped SPR based PCF refractive index sensor with deeply etched micro openings

A novel dual side-polished photonic crystal fiber (DSP-PCF) refractive index (RI) sensor is proposed for the RI detection range of 1.30−1.35. An active plasmonic metal gold (Au) is deposited on a polished flat fiber surface to generate plasmons so that it can detect the change in RIs of its surrounding medium. A thin titanium dioxide (TiO2) layer is coated to assist the adhesion of Au layer with silica-based fiber. To enhance the sensitivity, silicon nitride (Si3N4) is deposited on the top of Au to make it as a dielectric sensing layer. Simulation outcomes demonstrate that the maximum wavelength sensitivity (WS), amplitude sensitivity (AS) and RI resolution reach the highest value of 35,000 nmRIU−1, 350 RIU−1 and 4.347×10-6RIU, respectively, for DSP-PCF. Additionally, the obtained WS for DSP-PCF is far better than the recently reported PCF sensors in the above mentioned RI detection range to the best of our knowledge. With these significant outcomes over the wide analyte RI range, the proposed sensor opens new possible study windows in the field of organic chemicals and biological sensing.

Photoactive Titanium Dioxide Films with Embedded Gold Nanoparticles for Quantitative Determination of Mercury Traces in Humic Matter-Containing Freshwaters

Mercury detection in humic matter-containing natural waters is often associated with environmental harmful substances for sample preparation. Herein we report an approach based on photoactive titanium dioxide films with embedded gold nanoparticles (AuNP@TiO2 dipstick) for chemical-free sample preparation and mercury preconcentration. For this purpose, AuNPs are immobilized onto a silicon wafer and further covered with a thin photoactive titanium dioxide layer. The AuNPs allow the preconcentration of Hg traces via amalgamation, while TiO2 acts as a protective layer and, at the same time, as a photocatalyst for UV-C radiation-based sample pretreatment. Humic matter, often present in natural waters, forms stabile complexes with Hg and so hinders its preconcentration prior to detection, causing a minor recovery. This problem is solved here by irradiation during Hg preconcentration onto the photoactive dipstick, resulting in a limit of detection as low as 0.137 ng L−1 using atomic fluorescence spectrometry (AFS). A 5 min preconcentration step is sufficient to obtain successful recovery of Hg traces from waters with up to 10 mg L−1 DOC. The feasibility of the approach was demonstrated by the determination of Hg traces in Danube river water. The results show no significant differences in comparison with standard cold vapor-atomic fluorescence spectrometry (CV-AFS) measurements of the same sample. Hence, this new AuNP@TiO2 dipstick provides a single-step sample preparation and preconcentration approach that combines sustainability with high analytical sensitivity and accuracy.

X-ray Photoelectron Spectroscopy and Resonant X-ray Spectroscopy Investigations of Interactions between Thin Metal Catalyst Films and Amorphous Titanium Dioxide Photoelectrode Protection Layers

The use of electrochemistry, X-ray photoelectron spectroscopy, and resonant X-ray spectroscopy has unlocked the paradox of interfacial hole conduction through amorphous TiO2 (a-TiO2) to deposited N...