Properties Of TiO2 Thin Films Research Articles

Influence of calcination temperature on optical and structural properties of TiO2 thin films prepared by means of sol-gel and spin coating

Influence of calcination temperature on optical and structural properties of TiO2 thin films prepared by means of sol-gel and spin coating

Insights into the annealing process of sol-gel TiO2 films leading to anatase development: The interrelationship between microstructure and optical properties

The microstructure and optical properties of TiO2 thin films, prepared by the sol-gel dip coating technique on glass substrates, were inspected. After deposition, the films were annealed at several temperatures in the 400–850 °C range and the resulting nanostructured films were studied by different techniques showing that their structural and optical characteristics evolved significantly with the increased annealing temperature. The analysis of these results by the assumption of the Tauc Lorenz model and the use of Wemple–DiDomenico equation leads to a correlation between microstructural aspects and optical characteristics of the films. Thus, crystallization processes (nucleation, growth and phase transformation) and the evolution of films texture and thickness with increasing annealing temperatures are related with the variation of the refractive index, average gap and extinction coefficient during annealing. Finally, the free-carrier concentration in the films, estimated from the Spitzer–Fan model, ranged from 1.44 × 1019 cm−3 to 3.07 × 1019 cm−3 with the changing annealing temperature, which is in agreement with those obtained in similar anatase thin films from electrical measurement techniques.

Influence of annealing on X-ray radiation sensing properties of TiO2 thin film

A recent study shows that the titanium dioxide (TiO2) thin film synthesised by a chemical bath deposition technique is a very useful material for the X-ray radiation sensor. In this work, we reported the influence of annealing on the X-ray radiation detection sensitivity of the TiO2 film. The films were annealed at 333 K, 363 K, 393 K, 473 K, and 573 K for 1 hour. Structural analyses showed that the microstrain and dislocation density decreased whereas the average crystallite size increased with annealing. The band gap of the films also decreased from 3.26 eV to 3.10 eV after annealing. The I-V characteristics record under the dark condition and under the X-ray irradiation showed that the conductivity increased with annealing. The influence of annealing on the detection sensitivity was negligible if the bias voltage applied across the films was low (within 0.2 V‒1.0 V). At higher bias voltage (>1.0 V), the contribution of electrons excited by X-ray became less significant which affected the detection sensitivity.

Improvement of the photocatalytic activity of TiO2 using Colombian Caribbean species (Syzygium cumini) as natural sensitizers: Experimental and theoretical studies

Natural dyes composed by anthocyanins extracted from natural Caribbean species S. cumini, were employed to evaluate their effects on the photocatalytic properties of TiO2 thin films. The qualitative and quantitative analyses of the anthocyanins were carried out using high-performance liquid chromatography with photodiode array detection (HPLC-DAD). From the chemical characterization of the S. cumini extract three main anthocyanins were identified and the most abundant compound was delphinidin-3,5-diglucoside (44%). The total anthocyanin content expresses as delphinidin chloride (TAEDC) per mL of the extract was equal to 124 ± 5 μg TAEDC/mL. After the identification, a sensitization process was performed and verified by infrared spectroscopy (IR) and absorption diffuse reflectance. Afterwards, the Methylene Blue photodegradation process was studied under visible light irradiation on the S. cumini-sensitized TiO2 material (TiO2/S. cumini). The results indicated that the photocatalytic activity of the sensitized material TiO2/S. cumini was ∼3 times greater than unmodified TiO2 thin films, which let us to propose that the extract from Caribbean Colombian S. cumini could have a great potential as source of photosensitizers for photocatalytic applications. Finally, the electronic structure of each anthocyanin found in the extract (delphinidin-3,5-diglucoside, malvidin-3-5-diglucoside and petunidin-3-5-diglucoside) and their interaction with a TiO2 model was studied by means of the density functional theory (DFT).

Influence of substrate on structural, morphological and optical properties of TiO2 thin films deposited by reaction magnetron sputtering

Titanium dioxide (TiO2) films have been prepared by DC reaction magnetron sputtering technique on different substrates (glass, SiO2, platinum electrode-Pt, Silicon-Si). X-ray diffraction (XRD) patterns showed that all TiO2 films were grown along the preferred orientation of (110) plane. Samples on Si and Pt substrates are almost monophasic rutile, however, samples on glass and SiO2 substrates accompanied by a weak anatase structure. Atomic force microscopy (AFM) images revealed uniform grain distribution except for films on Pt substrates. Photoluminescence (PL) spectra showed obvious intrinsic emission band, but films on glass was accompanied by a distinct defect luminescence region. Raman spectroscopy suggested that all samples moved to high wavenumbers and films on glass moved obviously.

UV assisted photoelectrocatalytic degradation of reactive red 152 dye using spray deposited TiO2 thin films

TiO2 thin films have been deposited onto glass and FTO coated glass substrates using spray pyrolysis method. The effect of substrate temperature on the structural, morphological and photoelectrocatalytic properties of TiO2 thin films are studied. The photoelectrochemical (PEC) study shows that, both short circuit current (Isc) and open circuit voltage (Voc) are (Isc = 0.475 mA and Voc = 0.395 V) relatively higher at 400 °C substrate temperature. The structure and morphology of TiO2 thin films are studied by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM). XRD study reveals that the films are polycrystalline in nature with tetragonal crystal structure. FE-SEM images show that the substrate surface is well covered with a uniform grain like morphology. Photoelectrocatalytic degradation of reactive red 152 dye in aqueous solutions is studied. The end result shows that the degradation percentage of reactive red 152 using TiO2 photoelectrode has reached 70% under ultraviolet light illumination after 120 min.

Effect of ytterbium doping concentration on structural, optical and photocatalytic properties of TiO2 thin films

Abstract Ytterbium (Yb) doped TiO 2 thin films have been synthesized by sol-gel spin-coating technique. Films with different Yb concentrations such as 0.5, 1, 2, 4 wt% were deposited and the impact of the dopant concentration on their physicochemical properties was evaluated. The films were characterized by X-Ray diffraction, transmission electron microscopy, Raman spectroscopy, UV–Vis transmittance spectroscopy and photoresponse. The results showed that the incorporation of ytterbium modified the properties of TiO 2 films. The photocatalytic efficiency of TiO 2 :Yb films was determined using methylene blue (MB) as the generic pollutant. Compared to undoped TiO 2 , 1 wt% Yb doped films exhibited higher photocatalytic activity toward MB degradation under UV light. When the amount of Yb dopant concentration was increased, there was a negative effect on the photosensitivity and photocatalysis.

Optical and electrical properties of sol-gel spin coated titanium dioxide thin films

In this work; TiO2 thin films were deposited on glass and stainless steel substrates by sol-gel spin coating method. The films deposited on glass were annealed at different temperatures (Ta) in the range of 200 to 500 0C and that are deposited on steel substrate were annealed at 800 0C. The optical properties of TiO2 thin films were studied by using UV-VIS spectroscopy and photoluminescence (PL) spectroscopy. The transmittance on the average was found to ≥ 80 % and is found to sensitive to Ta. The PL spectra exhibited the strong emission band associated with band- to- band transition around 390 nm and the two weak bands at 480 and 510 nm associated to the oxygen defects and surface defects respectively. The current-voltage (I-V) characteristics of the Al/TiO2/steel capacitors were studied and analysed with application of various current mechanisms. Analysis reveals that the conduction in Al/TiO2/steel capacitors is governed by Poole-Frenkel mechanism.

Electrochromic properties of TiO2 thin films grown by thermionic vacuum arc method

Titanium dioxide (TiO2) thin films were deposited on fluorine tin oxide/glass and indium tin oxide/glass substrates by thermionic vacuum arc in this work. The deposited films phases were identified as anatase and rutile from X-ray Diffractions. The bandgap of the samples has been found ~3.0eV. The electrochromic properties of TiO2 thin films were investigated using cyclic voltammograms, chronoamperometry and chronocoulometric studies. Electrochemical cation intercalation was promoted using 0.1M LiClO4 in propylene carbonate. Inserted/extracted charge, diffusion coefficient, coloration efficiency, optical modulation, and reversibility was calculated. Best results were obtained for TiO2/FTO sample with 18.6cm2/C coloration efficiency. Deposited TiO2 thin films optical and morphological studies also covered.

Effect of Spin-Coating Cycle on the Properties of TiO2 Thin Film and Performance of DSSC

Effect of Spin-Coating Cycle on the Properties of TiO2 Thin Film and Performance of DSSC

Radiation-free superhydrophilic and antifogging properties of e-beam evaporated TiO2 films on glass

In this work, we show the unique wettability properties of TiO2 thin films deposited by e-beam evaporation on glass and treated at 500°C. The deposited materials exhibited compact non-porous structures and their non-UV activated superwetting behavior was characterized, emphasizing the better performance compared to the bare glass substrate and to a commercial self-cleaning glass (Pilkington Activ™) even in terms of antifogging and optical properties. The results demonstrate how the superhydrophilic character arises from the used deposition technique inducing a large amount of oxygen vacancies further boosted by the annealing treatment, allowing for the fabrication of a pioneering material in the area of multifunctional coatings. The superhydrophilic character was maintained even at an extremely small thickness (20nm), similarly to the adhesion of the film to the glass substrate, as confirmed by ultrasound stress tests and the cross-cut test performed according to ISO 2409 standard. The photocatalytic activity of the e-beam evaporated film was also assessed by degradation of methanol, 2-propanol and toluene under UV light in a gas phase reactor and the performance was found to be in most cases superior compared to Pilkington Activ™.

Effect of sputtering power on optical properties of prepared TiO2 thin films by thermal oxidation of sputtered Ti layers

In this research, TiO2 thin films prepared via thermal oxidation of Ti layers were deposited by RF-magnetron sputtering method at three different sputtering powers. The effects of sputtering power on structure, surface and optical properties of TiO2 thin films grown on glass substrate were studied by X-ray diffraction (XRD), atomic force microscopic (AFM) and UV–visible spectrophotometer. The results reveal that, the structure of layers is changed from amorphous to crystalline at anatase phase by thermal oxidation of deposited Ti layers and rutile phase is formed when sputtering power is increased. The optical parameters: absorption coefficient, dielectric constants, extinction coefficient, refractive index, optical conductivity and dissipation factor are decreased with increase in sputtering power, but increase in optical band gap is observed. The roughness of thin films surface is affected by changes in sputtering power which is obtained by AFM images.

Synthesis of nanostructured TiO2 thin films with highly enhanced photocatalytic activity by atom beam sputtering

Nanostructured TiO2 thin films with highly enhanced photocatalytic activity were prepared by atom beam sputtering technique. The effects of thermal annealing on the structural, morphological and photocatalytic properties of TiO2 thin films were investigated using X-ray diffraction, atomic force microscopy, field emission scanning electron microscopy, Raman spectroscopy and UV-visible absorption spectroscopy. X-ray diffraction studies showed that the as-deposited TiO2 thin films made up of anatase TiO2 nanoparticles transformed into anatase/ rutile mixed-phase TiO2 nanoparticles upon annealing. Field emission scanning electron microscopy and atomic force microscopy studies revealed growth of TiO2 nanoparticles from 16 nm to 29 nm upon annealing at 600 o C. The photocatalytic activities of the nanostructured TiO2 thin films were studied by monitoring photocatalytic degradation of methylene blue in water. Our results showed that the as-deposited nanostructured TiO2 thin films exhibited highly enhanced photocatalytic efficiency as compared to the annealed samples. The mechanism underlying the enhanced photocatalytic activity of nanostructured TiO2 thin film is tentatively proposed.

Thermal effect on the optical and morphological properties of TiO2 thin films obtained by annealing a Ti metal layer

Titanium metal layers of different thicknesses were deposited on optical glass, quartz and ceramic at 50 °C and 150 °C substrate temperatures with the help of magnetron deposition. The metal layers were converted into a rutile phase of TiO2 at different annealing temperatures. The effect of thermal annealing on the morphology and the refractive index of the thin film was investigated. The film’s quality and roughness were found to depend on the substrate’s temperature during metal film deposition and on the annealing temperature. The TiO2 thin films obtained on ceramic and glass substrates were seem to show less surface roughness at low substrate temperature as compared to the quartz substrate.

Oxygen partial pressure induced effects on the microstructure and the luminescence properties of pulsed laser deposited TiO2 thin films

In this work, the influence of oxygen partial pressure on structural, morphological, and optical properties of TiO2 thin films grown on fused quartz substrate at different oxygen partial pressure by pulsed laser deposition were examined. X-Ray diffraction (XRD) patterns show the formation of TiO2 anatase phase deposited at high oxygen pressure. Atomic Force Microscopy (AFM) reveals that surface roughness of the films increases with oxygen pressure. Variation of surface morphology of films with increasing oxygen partial pressure was studied by AFM. It is observed that energy band gap of the films increases from 3.27 eV to 3.52 eV with the increase of oxygen pressure and is attributed to the decrease of oxygen defects. TiO2 thin films exhibited blue emission under the excitation of 320 nm wavelength. De-convoluted photoluminescence (PL) peaks showed that defect states are responsible for visible emission in TiO2 thin films. The intensity of PL emission associated with oxygen vacancies decreases with increasing oxygen pressure. Photometric characteristic analysis shows that the films deposited 1x10-4 mbar oxygen pressure exhibited intense blue emission with high luminescence efficacy of radiation.

Characterization of photocatalytic, wetting and optical properties of TiO2 thin films and demonstration of uniform coating on a 3-D surface in the mass transport controlled regime

Titania is a well-known self-cleaning coating for window glass, but it could also be an important industrial coating and active surface if a thicker coating with tunable properties could be applied to stainless steel objects. In this work the tunable properties of TiO2 were studied and a coating on a 3D stainless steel object with the selected microstructure was demonstrated. TiO2 thin films were deposited onto fused silica slides over a range of temperature using the direct liquid injection pulsed-pressure MOCVD technique. All depositions used the same concentration and injection rate of titanium isopropoxide in dilute toluene solution in a cold-wall reactor. The number of pulses was adjusted so that films deposited at different temperatures were the same thickness of around 2μm. Deposition below 400°C was kinetically controlled and above 400°C was mass transport controlled. XRD showed all films were anatase phase TiO2 with highly textured columnar structure in the mass transport regime. SEM, TEM, and AFM analysis showed a marked difference between films deposited in the different regimes. Columnar grain diameter and surface roughness were much smaller and growth rate much higher in the mass transport regime. Surface wettability and MB dye degradation rate under UV radiation were both markedly higher for mass transport controlled deposition. An interesting finding was hydrophilic behavior of the high temperature thin films without UV irradiation. Coating conformality of 0.91 was measured around the circumference of a stainless steel ferrule with coating thickness of 8.7μm deposited in the mass transport controlled regime.

The annealing temperature dependence of anatase TiO2 thin films prepared by the electron-beam evaporation method

In this paper, we report on titanium dioxide (TiO2) thin films deposited by an electron beam evaporation method on quartz glass substrates (15 × 15 × 2 mm3 in size), followed by post-annealing at 300 °C to 600 °C for an annealing time of up to 2 h. The substrate temperature during the film deposition was kept at 150 °C. The effect of post-growth thermal annealing on the structural and optical properties of TiO2 thin films were systematically studied as a function of annealing temperature. We found that the as-deposited TiO2 films are amorphous in structure, while the films started to crystallize into the anatase phase when annealed at temperatures ≥450 °C. An increase in annealing temperature results in a decrease of transmittance percentage and also in optical band gap energy. The refractive indices of the films were evaluated from the measured transmittance spectra using the envelope method. An increase in the refractive index with an increase of annealing temperature was observed.

Optoelectronic and photocatalytic properties of in situ platinum-doped TiO2 films deposited by means of pulsed laser ablation technique

We report on the effect of Pt incorporation on the microstructural, optoelectronic and catalytic properties of TiO2 thin films deposited by means of the pulsed-laser deposition (PLD) method. The structural, morphological, optoelectronic and catalytic properties of the deposited TiO2:Pt films were systematically investigated, as a function of their Pt content, by means of various techniques including X-ray diffraction, X-ray photoelectron spectroscopy (XPS), atomic force microscopy, Fourier-transform infra-red spectroscopy and ellipsometry. The in situ doping of the PLD-TiO2 films, at different Pt contents, was achieved by the concomitant laser ablation of a TiO2 target uniformly covered with Pt wires. We show that by increasing the number of Pt wires positioned on the TiO2 target from 1 to 4, the Pt concentration of the TiO2:Pt films increases from 0.05 to 0.35 at.%. While the bandgap of room-temperature (RT) deposited films was found to be insensitive to their Pt content (remaining around the 3.2 eV anatase value), the TiO2:Pt films deposited at high temperature (Td = 500 °C) were found to exhibit a significant narrowing of their bandgap (from 3.3 to 2.45 eV), when their Pt content is increased (from 3.3 to 2.45 eV). From a structural point of view, while the RT-deposited TiO2:Pt films deposited are mainly amorphous with the presence of some TiO2 nanocrystallites whose density increases as Pt content increases, while those deposited at 500 °C were found to crystallize in the anatase phase with their crystallinity improving with increasing Pt contents. XPS analyses have revealed that the incorporated Pt mainly exists in a metallic state, likely as nano-inclusions in an otherwise TiO2 matrix. By being able to monitor the optoelectronic properties of the annealed TiO2:Pt films through their Pt content, their photocatalytic activity was significantly improved with respect to that of their undoped TiO2 counterpart. The enhancement of the photocatalytic activity is believed to be due to an enhanced photoabsorption of photons because of bandgap narrowing along with a better harvesting of the separated photogenerated charges.

Tunable dielectric properties of TiO2 thin film based MOS systems for application in microelectronics

Post-deposition annealing (PDA) is an inherent part of a sol-gel fabrication process to achieve the optimum device performance, especially in CMOS applications. Annealing removes the oxygen vacancies and improves the structural order of the dielectric films. The process also reduces the interface related defects and improves the interfacial properties. Here, we applied a sol-gel spin-coating technique to prepare high-k TiO2 films on the p-Si substrate. These films were fired at 400 °C for the duration of 20, 40, 60 and 80 min to know the effects of annealing time on the device characteristics. The current-voltage (I-V) and capacitance-voltage (C-V) characteristics of annealed TiO2 films were examined in Al/TiO2/p-Si device configuration at room temperature. The 60 min annealed film gives the optimum performance and contained 69.5% anatase and 39.5% rutile phase with refractive index 2.40 at 550 nm. The C-V and I-V characteristic showed a significant dependence on annealing time such as variation in dielectric constant and leakage current. This allows us to tune the various electrical properties of MOS systems. The accumulation capacitance (Cox), dielectric constant (κ) and the equivalent oxide thickness (EOT) of the film fired for 60 min were found to be 458 pF, 33, and 4.25 nm, respectively with a low leakage current density (3.13 × 10−7 A/cm2) fired for 80 min at −1 V. The current conduction mechanisms at high bias voltage were dominated by trap-charge limited current (TCLC), while at small voltages, space charge limited current (SCLC) was more prominent.

STRUCTURE AND PHOTO- FUNCTIONAL PROPERTIES OF TiO2 THIN FILM PREPARED BY RF HELICON MAGNETRON SPUTTERING

Fabrication of titanium dioxide (TiO2) thin film (200nm) has been done by using RF helicon magnetron sputtering from metallic Ti target under changing of O2 flow rate and substrate temperature. Film structure was measured by X-ray diffraction (XRD). The films were examined by an X-ray photoelectron spectroscopy (XPS) to study the structure; atomic force microscopy (AFM) and field-emission scanning electron microscope (FE-SEM) were employed to investigate the surface morphology and the cross section of films, respectively. Optical properties and optical band gap were calculated by using UV-VIS spectrophotometer. Photocatalytic activity was evaluated by light induced degradation of methylene blue (MB) solution using UV and Vis light. TiO2 thin film with a rutile phase at substrate temperature 100oC and O2 flow rate to 0.5 - 1.0sccm can be obtained, also an anatase phase can be fabricated when set substrate temperature to 300 oC and O2 flow rate to 2.5sccm. Obtained films showed a high dense with smooth surface and high crystalline. Maximum degradation rate (about 85%) of MB has been indicated at anatase phase under UV light irradiation, while under Vis light irradiation rutile and anatase mixture phase showed a maximum degradation rate (about 15%). In this work, the morphological, structural, optical, and photocatalytic properties of TiO2 thin films that were fabricated by RF helicon magnetron sputtering under change of O2 flow rate and substrate temperature have been investigated. It is expected that the change of substrate temperature and/or O2 flow rate will make ability to control the film structure.