TiO2 Film Thickness Research Articles

Optimizing deposition parameters and characterizing TiO2 thin films for future memristor applications

Titanium dioxide (TiO2) thin films were deposited on glass substrates using Spray Pyrolysis technique, with variations in multiple deposition parameters. The molarity of the precursor was altered within a small range from 0.09 M–0.15 M. The deposition temperature was systematically adjusted from 200 °C to 400 °C while the ratio between precursor and chelating agent varied between 1:1,1:2 and 1:3. The thickness of TiO2 films were found to be in the range of 216 nm to 14.9 μm. Structural analysis conducted by XRD confirmed the formation of anatase TiO2 thin films. Optical studies using UV-Visible spectrophotometer determined the absorption and indirect bandgap ranging from 299 nm to 326 nm and 3.08 eV to 3.44 eV respectively. Electrical studies carried out evaluated the leakage currents and DC resistivity for all individual films with the input voltage applied from ± 0.5 V to ± 5V. Impedance studies were conducted by varying input voltages from 0.2V–3V for each film, so as to examine the resultant impedance, dielectric constant, dielectric loss, conductivity, admittance and modulus spectra. The obtained results were analysed to optimise the deposition parameters for designing future memristors with specific individual or combined characteristics, such as high ON/OFF, switching speed, endurance and retention.

Using TiO2 to capture hot electrons for self-powered position-sensitive photodetection.

As environmental issues arise, the demand for self-powered position-sensitive detectors (PSDs) is increasing because of their advantages in miniaturization and low power consumption. Finding higher efficiency schemes for energy conversion is paramount for realizing high-performance self-powered PSDs. Here, a surface plasmon-based approach was used to improve the energy conversion efficiency, and a plasmon-enhanced lateral photovoltaic effect (LPE) was observed in PSD with TiO2/Au nanorods (NRs)/Si structure. The Au NRs convert absorbed light energy into electricity by generating hot electrons, which are efficiently captured by the TiO2 layer, and the PSD is capable of generating position sensitivity as high as 251.75 mV/mm when illuminated by a 780 nm laser without any external power supply, i.e. about five times higher than similar sensors in previous studies. In addition, the position sensitivity can be tailored by the thickness of TiO2 films. The enhancement mechanism is investigated by a localized surface plasmon (LSP)-driven carrier diffusion model. These findings reveal an important strategy for high sensitivity and low energy cost PSDs while opening up new avenues for energy harvesting self-powered position sensors.

Investigating resistive and gas sensing properties of TiO2, CuO and TiO2-CuO thick films

New inventions in modern research work related to material science always based on the preparation of a well adhered film (thin or thick) of suitable base material on a suitable substrate and investigating their functional characteristics. In our work we used TiO2 and CuO as base materials. In our work, we prepared thick films of TiO2, CuO and TiO2-CuO films of variable percentage. All the films were prepared on a suitably small electrode pattern Printed Circuit Board. Then the I-V characteristic of all prepared thick film was investigated by simple lab prepared two probe method. Variation in resistive properties of each film was investigated. Also, gas sensing performance of each film was investigated.

Effect of titanium alkoxide on structure, morphology, and biocompatible properties of sol-gel synthesized TiO2 films

The purpose of this work was to study the influence of the nature of titanium alkoxide, used as a precursor for the synthesis of TiO2 films by the sol-gel method, on the crystal structure and morphology of coatings, as well as their biological compatibility. TiO2 coatings were synthesized on silicon substrates using the dip-coating method. Titanium alkoxides with different molecular weights were used as precursors: titanium tetraethoxide, titanium tetraisopropoxide, and titanium tetrabutoxide. The influence of the nature of the titanium precursor on the morphology and thickness of TiO2 films was determined using scanning electron microscopy. The structural properties of the coatings were studied by X-ray diffraction and Raman spectroscopy. Cell viability assay was performed on TiO2/Cu-Si(111) structures to evaluate the ability of TiO2 coatings synthesized from different precursors to prevent the release of toxic ions from the substrate. The biological compatibility of TiO2 films with various surface morphologies and structures was assessed based on the chorioallantoic membrane assay. It has been demonstrated that the type of titanium alkoxide utilized has a substantial influence on the morphology and crystal structure of TiO2 films produced through the sol-gel method. Furthermore, the structural properties of the coatings consequently impact their biological compatibility. Coatings synthesized from titanium tetrabutoxide exhibited the highest protective properties and biological compatibility.

Comparison of SiO2/TiO2 photocatalysts with different thicknesses synthesized by fluidized bed atomic layer deposition

SiO2/TiO2 core/shell particles are effective photocatalysts, whose performance strongly depends on TiO2 film thicknesses. Fluidized bed atomic layer deposition (FBALD) can precisely control film thickness at the sub-nanometer scale. In this work, TiO2 films with different thicknesses are deposited on SiO2 particles via different ALD cycles at 180 °C in a fluidized bed reactor. TEM images indicate that complete and uniform nanoscale TiO2 films (0.7–6.4 nm, corresponding to 5–50 ALD cycles) are formed on SiO2 surface. The TiO2 film with about 3.9 nm is found to exhibit the highest photocatalytic characteristics by degrading rhodamine-B (RhB) and tetracycline (TC), and the photocatalytic activity is further maintained above 90% after 6 cycles of photocatalytic reaction. Suitable TiO2 film thickness shows minimal charge transfer resistance, resulting in enhanced photon adsorption and separation of electrons and holes, thus improving photocatalytic performance. This work provides an effective way to tune the photocatalytic performance via FBALD.

Transparent and hard TiO2/Au electromagnetic shielding antireflection coatings on aircraft canopy PMMA organic glass

This research addresses the critical need for a highly stable and transparent electromagnetic shielding coating for aircraft PMMA windows and canopies, crucial for safeguarding against electromagnetic interference and enhancing aircraft stealth capabilities. The study presents the novel design, deposition and investigation of transparent coatings, specifically TiO2/Au, on PMMA organic glass cockpit canopies. Optimization of TiO2 and Au film thicknesses is achieved through simulation using TFcalc software, incorporating polarization and optical constants data obtained in this study. The experiments reveal that the deposition of TiO2/Au/TiO2 on PMMA results in fogging, reducing transparency, while novel TiO2/Au coating does not exhibit this issue. The TiO2/Au configuration, featuring a TiO2 layer approximately 30 nm thick and an Au film ranging from 11 to 15 nm in thickness, demonstrates outstanding attributes, including a remarkable transparency level of approximately 70–80% and robust electromagnetic interference shielding efficiency within the range of 19–29 dB across S, C, X, and Ku bands of electromagnetic waves. These exceptional performance characteristics position it as an ideal choice for aviation applications. The synergy of the stable Au and durable TiO2 components, with their high hardness and self-cleaning properties, extends its potential utility to a diverse array of applications.

Quantifying recombination and charge carrier extraction in halide perovskites via hyperspectral time-resolved photoluminescence imaging

Identifying sources of nonradiative recombination and quantifying charge carrier extraction in halide perovskite solar cells are important in further developing this thin-film technology. Steady-state and time-resolved photoluminescence (TRPL), in combination with analytical modeling, have emerged as non-destructive tools to achieve the desired results. However, the exact location of the recombination and charge carrier extraction losses in devices is often obscured by various competing processes when photoluminescence measurements are analyzed. Here, we show via absolute-photon-calibrated hyperspectral photoluminescence and TRPL imaging how surface passivation and inhomogeneities at interfaces impact the photoluminescence quantum yields and minority carrier lifetimes. Laser illumination from the perovskite and glass/TiO2 sides allows us to disentangle changes in surface recombination velocity from the charge carrier extraction at the electron transport layer. We find that charge extraction is spatially modulated due to an inhomogeneous mesoporous (mp)-TiO2 film thickness. Our results show that the mp-TiO2 layer is not fully optimized since the electronic properties are spatially modified, leading to lateral changes in quasi-Fermi-level splitting, minority carrier lifetime and, consequently, a reduction in open-circuit voltage.

Photoelectrocatalytic Processes of TiO2 Film: The Dominating Factors for the Degradation of Methyl Orange and the Understanding of Mechanism.

Various thicknesses of TiO2 films were prepared by the sol-gel method and spin-coating process. These prepared TiO2 films exhibit thickness-dependent photoelectrochemical performance. The 1.09-μm-thickTiO2 film with 20 spin-coating layers (TiO2-20) exhibits the highest short circuit current of 0.21 mAcm-2 and open circuit voltage of 0.58 V among all samples and exhibits a low PEC reaction energy barrier and fast kinetic process. Photoelectrocatalytic (PEC) degradation of methyl orange (MO) by TiO2 films was carried out under UV light. The roles of bias, film thickness, pH value, and ion properties were systematically studied because they are the four most important factors dominating the PEC performance of TiO2 films. The optimized values of bias, film thickness, and pH are 1.0 V, 1.09 μm, and 12, respectively, which were obtained according to the data of the PEC degradation of MO. The effect of ion properties on the PEC efficiency of TiO2-20 was also analyzed by using halide as targeted ions. The "activated" halide ions significantly promoted the PEC efficiency and the order was determined as Br > Cl > F. The PEC efficiency increased with increasing Cl content, up until the optimized value of 30 × 10-3 M. Finally, a complete degradation of MO by TiO2-20 was achieved in 1.5 h, with total optimization of the four factors: 1.0 V bias, 1.09-μm-thick, pH 12, and 30 × 10-3 M Cl ion content. The roles of reactive oxygen species and electric charge of photoelectrodes were also explored based on photoelectrochemical characterizations and membrane-separated reactors. Hydrogen peroxide, superoxide radical, and hydroxyl radical were found responsible for the decolorization of MO.

UV-activated room temperature oxygen gas sensor based on TiO2-decorated bridging GaN nanowires

A reliable and high-performance oxygen (O2) sensor based on TiO2-decorated bridging Gallium Nitride nanowires (TiO2/GaN NWs) was fabricated, which operates under ultraviolet (UV) irradiation at room temperature (RT). The TiO2/GaN NWs were prepared by direct-bridge growth of GaN NWs across the trench of GaN coated sapphire substrate, followed by titanium (Ti) sputtering and thermal oxidation. The morphology characteristic shows that TiO2 nanoparticles (NPs) are anchored uniformly on the surface of GaN NWs. The sensors with various TiO2 film thickness (0, 2, 5, 10 nm) were measured at RT under 365 nm UV illumination with O2 concentrations varying from 1% to 25%. Experimental results show that when the TiO2 film thickness is 5 nm, the O2 response reaches its maximum and the limit of detection (LOD) as low as 0.45% O2. Moreover, the 5 nm TiO2/GaN NWs sensor were also measured under different wavelengths (λ = 280, 365, 450 nm) UV illumination and found that the lower light wavelength, the higher O2 sensing. In addition, the sensor has excellent repeatability, selectivity and long-term stability, thus has a wide application in the field of O2 gas sensing.

Exploring the impact of electron transport layer thickness and morphology on perovskite infiltration and photoresponse in HTM-free self-powered photodetector

Methylammonium lead Iodide (MAPbI3) is emerging as the frontrunner for high-performance photo-detection due to its superior optoelectronic characteristics and ease of processing. Titanium dioxide (TiO2) is the commonly employed electron transport layer in conventional perovskite-based photodetectors. However, the fundamental understanding of the role of TiO2 morphology and its thickness on the photodetector performance is yet to be explored explicitly. This work systematically investigates the impact of morphology (mesoporous versus compact TiO2 layer) and thickness of the TiO2 layer (50 nm – 3000 nm) on the MAPbI3 photodetector performance. The devices have been fabricated in a hole transport material (HTM)-free architecture with carbon as the top contact. The heterojunction between MAPbI3 and TiO2 renders the device with self-powered capability. The influence of the perovskite sensitisation in the TiO2 electrodes, carrier recombination characteristics and charge-carrier transfer resistances have been studied using photoluminescence and impedance spectroscopy. The TiO2 layer morphology and thickness affected the MAPbI3 infiltration and film formation kinetics. Impedance and photoluminescence spectroscopies reveal that TiO2 layers, with thickness above 460 nm, negatively affected the device performance. An optimum thickness of 460 nm-mesoporous TiO2 layer exhibited a superior responsivity and rise time of 2.9 A/W and 21 ms, respectively. The poor performance at higher thicknesses is due to the increased interfacial charge transfer resistance and charge carrier recombination. This work is the first report of extensive optimisation and study on the impact of TiO2 film morphology and thickness on the MAPbI3 photodetectors. The present work will be a key for modelling and designing high-performance perovskite photodetectors.

The growth mechanisms of TiO2 film onto PET surfaces by atomic layer deposition

Atomic layer deposition (ALD) was used to coat a polyethylene terephthalate (PET) polymer substrate with TiO2 film. The TiO2 was grown onto the surface with better film coverage by using thicker ALD deposition. Further evaluation on the coated substrates indicated that the reactive sites of –C=O that existed on PET surface played a significant contribution to facilitating the initial ALD growth of the TiO2 thin film. The chemical composition of the coated substrates was characterised using energy dispersive X-ray spectroscopy, which showed that increasing the TiO2 film thickness increased the Ti element content. Two growth mechanisms, namely, diffusion growth and direct coordination through the precursor coordination with surface reactive sites of –C=O with product release occurred simultaneously in the initial growth of TiO2 coating onto PET polymer by ALD. The surface alteration of the coated ALD was characterised by Fourier transform infrared spectroscopy, which showed that the hydroxyl –OH groups emerged in the TiO2 ALD film.

A fully automatized method for the unambiguous wavelength-by-wavelength determination of the thickness and optical property of a very thin film with a transparent range

Spectroscopic ellipsometry is a powerful method with high surface sensitivity that can be used to monitor the growth of even sub-monolayer films. However, analysis of ultrathin films is complicated by the correlation between the dielectric constant and thickness. This problem is usually resolved by fixing one or the other value, limiting the information that can be extracted. Here, we propose a method to determine unambiguously the refractive index, extinction coefficient, and thickness of a film when a transparent range is available in the energy range investigated. We decompose the analysis in three steps. First, the thickness of the film is determined from the transparent range of the film. Then, knowing the thickness of the layer, an initial estimation of the refractive index and extinction coefficient is made based on a first-order Taylor expansion of the ellipsometric ratio. Finally, using this estimation, a numerical iteration is done to ensure convergence of the fit toward the solution. A theoretical example of the method is given for two different thicknesses of TiO2 films. Finally, the method is applied to the experimental data measured during the atomic layer deposition of a thin film of Hf0.5Zr0.5O2 grown on Si. The thickness, refractive index, and extinction coefficient are retrieved with high precision (respectively, 0.01 and 0.002) in the energy range of 3.5–6.5 eV. A detailed analysis is presented on the accuracy of the retrieved values and their dependency on random and systematic errors for different energy ranges.

Synthesis of TiO2 mesoporous film with the effect of 200 eV argon ion beam on its surface chemistry

This work presents an elegant and systematic method to study the effect of a 200 eV Ar ion beam on TiO2 semiconductor mesopores film. Argon ion beam (Ar+) of 200 eV energy was irradiated on the prepared TiO2 film (thickness ∼ 20 μm) at different irradiation times of 0, 150, 250, 350, and 450 s. The irradiated samples were subsequently characterized using x-ray photoelectron spectroscopy (XPS). The survey spectrum reveals the presence of elemental composition of titanium (Ti 2p), oxygen (O 1s), and carbon (C 1s). The compositional ratio of Ti3+/Ti4+ increases and lattice oxygen/Ti 2p decreases with an increase in irradiation time which confirms the creation of oxygen vacancy as the irradiation time progresses. The demonstrated oxygen vacancy induction potentials would be highly meritorious in enhancing the photocatalytic activity of the semiconductor under visible light for various applications.

Photo-electrocatalytic performance of poly(3,4-ethylenedioxythiophene)/TiO2 nano-tree films deposited by oCVD/CVD for H2 production

The hydrogen production from photo-electrocatalytic water splitting attracts extensive attention as a direct way to convert solar energy into chemical fuels. In this work, innovative photo-anodes composed of TiO2 which has a preferable growth orientation [211] conjugated with PEDOT as bi-layers are prepared by a dry process strategy, combining oxidative and metalorganic chemical vapor deposition (CVD). Pure anatase, dendritic TiO2 films of variable thickness are obtained at 500 °C by varying the deposition time. Increase of films thickness from 474 to 2133 nm results in morphologies that evolve from dense and angular structures to isolated and nanostructured tree-like columns with a concomitant decrease of the charge transfer resistance due to the enhancement of active facets of anatase structure. The PEDOT/TiO2 bi-layer with an overall thickness of 1350 nm and a 50 nm thick upper-PEDOT layer exhibits the highest photocurrent response (0.26 mA cm−2 at 1.8 V/RHE), a fast photocurrent response under illumination, and the best hydrogen yield up to 4.1 µmol cm-2h−1 with electronic conductivity being three order of magnitude higher than pristine TiO2.

Growth and characterization of screen printed TiO2–CuO thick films for optoelectronic applications

We herein report, the deposition of pure and CuO doped TiO2 thick films on glass slides by a cost effective screen printing process, which were then sintered to obtain desired stochiometric composition. Different analytical approaches were used to reveal the precise structural, morphological, optical and electrical characteristics information of pure TiO2 and TiO2–CuO thick films. X-ray diffraction (XRD) patterns exhibit the formation anatase phase of TiO2 and monoclinic phase of CuO. Raman spectra show four TiO2 anatase phase modes only in 100–800 cm−1 region. Infrared (IR) transmittance spectra of these samples recorded in 4000–400 cm−1 region also showed weak, very weak and medium intensity stretching and bending modes of O–Ti–O and Ti–O–Ti bond groups of TiO2 only in 700–400 cm−1 region which further supported the formation of TiO2 anatase phase only. Scanning electron microscopy (SEM) images indicate porous surfaces morphology, irregular shaped as well as size polygonal and spherical shaped particles with tendency to form aggregates along with the EDS analysis that confirms proper composition of the films. The optical band gap energies were derived from diffused reflectance spectroscopy and photoluminescence (PL) spectra. They showed a red shift in peak positions which caused reduction in band gap energy. The CIE diagram clearly depicted blue-green and white emissions. I–V characteristics has been used for calculation of the diode parameters such as ideality factor (n) and barrier height (Φb). The extracted results such as band gap, particle size and electrical parameters suggest that the TiO2–CuO thick films can be used in photovoltaic applications.

Surface deformation studies of TiO2 thin films by double exposure laser holographic interferometry

Double exposure laser holographic interferometry is implemented to investigate the surface deformation of an stainless steel (SS) 304 substrate during the deposition of titanium dioxide (TiO2) thin films on it. The TiO2 thin film is synthesized by the potentiostatic mode in the electrodeposition process. The in-situ analysis of the stress on the substrate and the thickness of the deposition is evaluated by non-destructive holographic interferometry. The holography interference fringes are computed and show that the TiO2 film thickness increases with an escalation in deposition time, but the stress on the substrate decreases.

Potential evaluation of an annular thermoelectric cooler driven by a dye-sensitized solar cell

For round shaped cooling space, a dye-sensitized solar cell (DSSC) is used to drive annular thermoelectric cooler (ATEC) to solve the performance deterioration caused by geometric mismatch, in which ATEC considers Seebeck effect, Peltier effect and Thomson effect. Considering all kinds of irreversible losses between DSSC and ATEC, the mathematical formula of performance parameters of hybrid system is derived. The effects of Schottky barrier height, thickness of TiO2 film, thickness of ATEC, number of thermoelectric elements and annular parameter of the ATEC on the cooling capacity and coefficient of performance (COP) of the coupling system are analyzed theoretically. The theoretical calculation results show that the maximum cooling capacity and COP of the hybrid system are 68.75 W/m2 and 0.071, respectively. In addition, it can be found that the positive Thomson effect had a positive influence on the thermoelectric cooling system. The findings of this work have the potential to provide fresh light of solar-driven annular thermoelectric cooler matching with actual round shaped cooled spaces.

Crystalline Structure, Morphology, and Adherence of Thick TiO2 Films Grown on 304 and 316L Stainless Steels by Atomic Layer Deposition

Titanium dioxide (TiO2) thin films are widely used in transparent optoelectronic devices due to their excellent properties, as well as in photocatalysis, cosmetics, and many other biomedical applications. In this work, TiO2 thin films were deposited onto AISI 304 and AISI 316L stainless steel substrates by atomic layer deposition, followed by comparative evaluation of the mixture of anatase and rutile phase by X-ray diffraction, Raman maps, morphology by SEM-FEG-AFM, and adhesion of the films on the two substrates, aiming to evaluate the scratch resistance. Raman spectroscopy mapping and X-ray diffraction with Rietveld refinement showed that the films were composed of anatase and rutile phases, in different percentages. Scratch testing using a diamond tip on the TiO2 film was employed to evaluate the film adherence and to determine the friction coefficient, with the results showing satisfactory adherence of the films on both substrates.

Enhancing the photocatalytic properties of doped TiO2 nanowires grown by seed-assisted thermal oxidation

In the present paper, an investigation of the structural, optical, and photo-catalytical properties of TiO2 nanowires (NWs) was conducted. The NWs were synthesized on a Si substrate by thermal oxidation of a thick (4 µm) Ti film covered by a thin (∼ 5 nm) Au film. The annealing process at 750 °C produced a 1.7 μm thick NWs TiO2 layer over a 3 μm thick TiO2 film. Characterization techniques show that TiO2 NWs are in rutile phase and have gold nanoparticles on top. Fe-doped TiO2 NWs were synthesized to increase photoactivity in the visible range. The doping was performed using an unusual strategy, that is, implanting Fe+ ions into the Ti layers before the growth of the TiO2 NWs. The defectiveness introduced by the ion implantation is avoided and precise control of the doping is achieved. The photocatalytic properties were studied by following the degradation of methylene blue. In order to increase the photo-degradation rate under UV light of undoped NWs, two different strategies have been followed: 1) deposition of Pt nanoparticles on the front or on the rear side of the samples, and 2) thermal annealing in a reductive environment. A three-fold activity enhancement is obtained and discussed. Photocatalytic activity in the visible range was also measured for the Fe-doped samples, showing good activity, which was further improved by using the same strategies implemented under UV irradiation.

Structural and Optical Properties of TiO<sub>2</sub> Thin Films prepared by the Dip-Coating Method: Effect of Thickness and Annealing Temperature

In this work, the Sol-Gel dip-coating technique is used to report the effect of thickness and annealing temperature on structural and optical properties of TiO2 thin films. To study the effect of the annealing temperature, the prepared samples were annealed at different temperatures: 300, 400, and 500 °C for 1 h. By increasing the annealing temperature, an amelioration of the crystalline quality is observed. The best crystalline quality was obtained at 500 °C. Additionally, the band gap value Eg, evaluated from transmission spectra, does not vary with the increasing of the annealing temperature. All the films with different thicknesses present crystalize in the Anatase structure, and the crystallite size value does not practically change with thickness increase. It was also found that the TiO2 film band gap value decreases with the film thickness increase, demonstrating the possibility of band gap tuning by varying the TiO2 film thickness.