Electrical Properties Of TiO2 Research Articles

Investigation of optical and electrical properties of TiO2, SiO2, and Ag single and multilayer thin films using spectroscopic ellipsometry and spectrophotometry methods: prepared by spin coating and DC magnetron sputtering

In this work, spectroscopic ellipsometry was used to study the optical and electrical properties of TiO2 and SiO2 thin films deposited by spin-coating at different coating rotation speeds and annealed at various temperatures. In addition, Ag thin films of different thicknesses were deposited by DC magnetron sputtering at ambient temperature. In this method, the optical band gap for TiO2 thin films is between 3.15–3.85 eV, and for SiO2 thin films, it is between 3.2–3.8 eV. The optical properties, including reflectance, transmittance, and absorbance, of TiO2, SiO2, and Ag thin films in the form of single and multilayer thin films in the wavelength range of 200–2500 nm, were investigated using an ultraviolet-visible-near infrared (UV–vis-NIR) dual-beam spectrophotometer. In the TiO2/Ag/SiO2 multilayer thin film, the rejection was 58.6% −73.6% in the NIR wavelength range (800–2500 nm), and a transmittance of 40%–45% was achieved in the visible light range (400–700 nm).

Computational and experimental investigation of the structure, morphology, optical and electrical properties of TiO2 and caffeine adsorbed TiO2 in methyl ammonium lead iodide

Effects of caffeine and titanium dioxide (TiO2) in methylammonium lead iodide (MAPbI3/CH3NH3PbI3) as a photon absorber are studied. XRD showed high crystallinity of TiO2:Caffeine:MAPbI3 with larger crystallite size of ∼3.9 nm compared to TiO2:MAPbI3 with ∼3.6 nm. Large grain size of ∼550 µm was obtained for TiO2:Caffeine:MAPbI3 compared to ∼256 µm of TiO2:MAPbI3. Rod-like structures were observed though TiO2:Caffeine:MAPbI3 morphology and was smoother compared to TiO2:MAPbI3. Reduced bandgap energy of ∼2.3 eV was observed from TiO2:Caffeine:MAPbI3 and PL quenching indicated the possibility of reduction of the electron-hole recombination. TiO2:Caffeine:MAPbI3 showed better electrical conductivity compared to TiO2:MAPbI3. Density functional theory calculations showed increased charge transfer/redistribution which accounts for the slight enhanced electrical conductivity for TiO2:Caffeine:MAPbI3. The density of state calculations suggests the formation of unoccupied states and O 2p, Ti 3p, N 2p and C 2p as major contributors to the electronic and electrical properties of TiO2:Caffeine.

Advanced Nanostructured Coatings Based on Doped TiO2 for Various Applications

For many years, TiO2-based materials and improving their properties in order to expand their application areas have been the focus of numerous research groups. Various innovative approaches have been proposed to improve the photocatalytic and gas-sensing properties of TiO2 nanostructures. In this review, we aim to synthesize the available information in the literature, paying special attention to the sol–gel technology, which is one of the most frequently used methods for TiO2 synthesis. The influence of dopants on the structural, morphological, optical, and electrical properties of TiO2 and the way to modify them in a controlled manner are briefly discussed. The role of shallow and/or deep energy levels within the TiO2 bandgap in the electron transport behavior of doped TiO2 is emphasized. Selected research on photocatalytic applications in water disinfection, wastewater treatment, and self-sterilizing coatings that contribute to improving the quality of human life and environmental preservation is highlighted. A survey of biosensors that are closely related to medical applications such as cancer detection, implantology, and osteogenesis is also provided. Finally, the pressing problems that need to be solved in view of the future development of TiO2-based nanostructures are listed.

Investigating the chemical and physical aspects: optical and electrical properties of TiO2, TiO2: Fe, and Fe/ TiO2 (111) through DFT analysis

Investigating the chemical and physical aspects: optical and electrical properties of TiO2, TiO2: Fe, and Fe/ TiO2 (111) through DFT analysis

Fabrications of Electrospun Mesoporous TiO2 Nanofibers with Various Amounts of PVP and Photocatalytic Properties on Methylene Blue (MB) Photodegradation.

The superior chemical and electrical properties of TiO2 are considered to be suitable material for various applications, such as photoelectrodes, photocatalysts, and semiconductor gas sensors; however, it is difficult to commercialize the applications due to their low photoelectric conversion efficiency. Various solutions have been suggested and among them, the increase of active sites through surface modification is one of the most studied methods. A porous nanostructure with a large specific surface area is an attractive solution to increasing active sites, and in the electrospinning process, mesoporous nanofibers can be obtained by controlling the composition of the precursor solution. This study successfully carried out surface modification of TiO2 nanofibers by mixing polyvinylpyrrolidone with different molecular weights and using diisopropyl azodicarboxylate (DIPA). The morphology and crystallographic properties of the TiO2 samples were analyzed using a field emission electron microscope and X-ray diffraction method. The specific surface area and pore properties of the nanofiber samples were compared using the Brunauer-Emmett-Teller method. The TiO2 nanofibers fabricated by the precursor with K-30 polyvinyl pyrrolidone and diisopropyl azodicarboxylate were more porous than the TiO2 nanofibers without them. The modified nanofibers with K-30 and DIPA had a photocatalytic efficiency of 150% compared to TiO2 nanofibers. Their X-ray diffraction patterns revealed anatase peaks. The average crystallite size of the modified nanofibers was calculated to be 6.27-9.27 nm, and the specific surface area was 23.5-27.4 m2/g, which was more than 150% larger than the 17.2 m2/g of ordinary TiO2 nanofibers.

Effects of Sn4+ and Ta5+ dopant concentration on dielectric and electrical properties of TiO2: Internal barrier layer capacitor effect

The (Sn1/2Ta1/2)xTi1-xO2.0125 (SnT–TO) ceramics with x = 1.0–5.0 % were prepared by a standard mixed–oxide method. The sintered ceramics showed highly dense microstructures with a single phase of rutile–TiO2 structure. The lattice parameters of the SnT–TO enlarged with increasing x. All the SnT–TO ceramics exhibited a high dielectric permittivity (ε′ > 104) due to the substitution of Ta5+. The ε′ value at 1 kHz increased with increasing the mean grain size. Furthermore, an ultra–low loss tangent (tanẟ<0.05) and low temperature coefficient (<±15 %) were achieved over a wide temperature range, which were attributed to the large grain boundary resistance owing to the substitution of isovalent Sn4+ ions. Hence, the SnT–TO ceramics were suitable for applications in ceramic capacitors. The semiconducting grains and insulating grain boundaries were confirmed using an impedance spectroscopy. The grain resistance increased with increasing Sn4+ ions. In addition, the DC bias dependence of the dielectric properties increased with increasing co–doping concentration. According to the microstructure analysis, dielectric response, and electrical properties, the origin of the high–performance colossal dielectric properties of SnT–TO was well described by the interfacial polarization based on the internal barrier layer capacitor effect.

Self-powered, transparent, flexible, and solar-blind deep-UV detector based on surface-modified TiO2 nanoparticles

Titanium oxide (TiO2) has been widely used as a low-cost, chemically stable, and biologically inert semiconductor for many applications. However, there are a limited number of studies on the application of TiO2 for deep-UV photodetection, which has potential environmental and military applications. In this study, we introduce a facile sol–gel method followed by post-modification with acetic acid (HAc) to prepare wide-bandgap anatase TiO2 (3.83 eV) for use as a solar-blind deep-UV photoabsorber. The beneficial effects of simple post-modification on the structural, optical, and electrical properties of TiO2 were comprehensively investigated. When TiO2 nanoparticles are functionalized by an appropriate number of HAc, O vacancies in TiO2 are significantly reduced while the bandgap is increased with reduced particle size. As a result, the HAc-modified TiO2-based deep-UV photodetector exhibits high specific detectivity, fast response time, and R254:R365 rejection at zero bias. Furthermore, the device displays good stability with a nearly constant photoresponse even after one month of storage and under stringent bending strain. The average visible transmittance of the device reaches as high as 80%. The results suggest that the device can be used as an efficient TiO2-based solution-processable solar-blind deep-UV photodetector, with self-powered operability, wearability, and transparency.

Synthesis and characterisation of Cu - Doped TiO2 nanoparticles for DSSC and photocatalytic applications

In the present work, copper-doped TiO2 nanoparticles were synthesized via sol-gel technique with different molar concentration of copper precursor (0.025 M-CT-1, 0.05 M-CT-2, 0.1 M-CT-3 and 0.2 M-CT-4). The effect of copper doping on the structural, morphological, compositional, optical and electrical properties of TiO2 was systematically analyzed for its better suitability as photoanode in Dye-Sensitized Solar Cells (DSSC) and photocatalyst in dye degradation. From structural analysis, all the synthesized samples show anatase phase with a tetragonal crystal system. The broadening and shift in the peaks of the synthesized samples show the successful incorporation of Cu ions into TiO2 lattices. All the synthesized samples exhibit spherical shape morphology with slight agglomeration. EDS analysis exhibit the purity of the synthesized nanoparticles with the presence of only Ti, O, and Cu. UV-DRS analysis reveals the decrease in reflectance of the TiO2 with increasing the Cu concentration. The bandgap values of the Cu–TiO2 decreased from 2.66 to 2.40 eV with the increase of copper concentration. From PL analysis, the peak observed at 380.20, 469.56 and 535.24 nm corresponds to the band-band PL emission, free excitons, and oxygen vacancies, respectively. Further, we have fabricated DSSC using Cu-doped TiO2 as a photoanode without treatment of any scattering layer and we have obtained the maximum efficiency of 3.90% for 0.1 M Cu–TiO2 (CT-3). Similarly, the maximum degradation efficiency of 97.12% was obtained against rhodamine-B dye with the highest regression coefficient (R2 = 0.9957) and lesser half-life degradation time (t1/2 = 47.1428 min) for CT-3. This higher efficiency was not reported elsewhere using Cu-dopant concentrations. From these observations, it was concluded that 0.1 M concentration of Cu was the optimum dopant concentration with TiO2 which was suitable for DSSC and photocatalytic applications.

Improving the electrical properties of TiOx Schottky-type diode with an extra ZrO2 insulating layer

Titanium oxide has been considered a promising candidate for Schottky-type diode application. In this paper, an alternative approach for improving electrical properties of TiO[Formula: see text]-based Schottky-type diode has been demonstrated. Compared with the Ag/TiO[Formula: see text]/Ti structure Schottky-type diode, by embedding an extra ZrO2 insulating layer between the Ag/TiO[Formula: see text] interface, an extremely high rectifying ratio of 109 can be obtained in the Ag/ZrO2/TiO[Formula: see text]/Ti structure device. The improvement of the electrical properties in the Ag/ZrO2/TiO[Formula: see text]/Ti structure device can be attributed to the localized formation of Ag metal conductive filaments in ZrO2 layer after switching on.

Photoelectrochemical performance enhancement of low-energy Ar+ irradiation modified TiO2

To evaluate the effects of surface properties of semiconductor and enhance semiconductor’s activity for photocatalytic water oxidation, low-energy Ar+ irradiation was employed to modify the rutile TiO2 (110) surface and control the formation of oxygen vacancy density in TiO2, which was subsequently used for the photoelectrochemical (PEC) oxygen evolution reaction (OER). Specifically, by controlling the substrate temperature during Ar+ irradiation, the surface morphology and oxygen vacancy density of rutile TiO2 (110) could be modified, such that the effects of surface crystallinity, optical absorption and electrical properties of TiO2 could be compared for OER. We found that the intrinsic activity of TiO2 for PEC OER does not exhibit a scaling relationship with respect to the density of oxygen vacancy, optical adsorption or charge carrier concentration. Rather, a linear relationship could be observed between the photocurrent density and the interfacial charge-transport conductivity. Furthermore, ambient pressure X-ray photoelectron spectroscopy (APXPS) was used to investigate the effect of low-energy Ar+ irradiation on the interaction between TiO2 and water. It was demonstrated that using single crystal model systems with controlled properties, this study has thus provided a clear yet detailed analysis on key factors in tuning the photoelectrochemical performance of TiO2.

Investigation on structural, optical and electrical properties of Nd doped titania films and application of optical model

The effect of dopant concentration and temperature on the structural, optical and electrical properties of TiO2 (Titania) thin films deposited through sol-gel spin coating was investigated. The X-Ray Diffractometer was used for phase analysis, UV–Vis spectrometer and Ellipsometer techniques were used for the optical measurements and Hall effect was used for the electrical characterization. Annealing temperature and dopant concentration were chosen as the parameters in the present study. The optical band gap marginally increased from 3.40 eV to 3.43 eV with increase in dopant concentration for the films annealed at 350 ֯C. The increasing trend was also observed for the films annealed at 450 °C with the optical band gap in the range 3.34 eV–3.39 eV. Using ellipsometric measurement, thickness and optical constants were obtained and we compared the refractive index values with those obtained from PARAV software. For Nd doped films, a single oscillator model was tested by using the refractive index values from ellipsometric measurement. The carrier density and plasma frequency were calculated using the Wemple Di Domenico (W-D) model. The electrical properties indicate decreased resistivity from 103 Ωcm to 101 Ωcm and increased carrier density from 1015 cm-3 to 1017 cm-3 with increase in annealing temperature. Similarly, with increase in dopant concentration at a given annealing temperature, we have observed a decreased resistivity compared to the prestine samples. However, the carrier density increased marginally with increase in dopant concentration.

A study of the effect of morphology on the optical and electrical properties of TiO2 nanotubes for gas sensing applications

In this paper, we report the results of the optical and electrical properties of TiO2 nanotubes with different morphologies for gas sensing applications. Four nanomaterials of TiO2 were prepared by electrochemical anodization using four different electrolyte solutions: 0.255 wt% NH4F with 1 wt%, 3 wt%, 6 wt% and 9 wt% of deionized water in ethylene glycol. Micrographs by scanning electron microscopy (SEM) showed different morphologies caused by the variation in the water content of the solutions. Consequently, as an effect of morphology, the photoluminescence intensity in the visible spectrum was modified. By a change of the crystalline phase of TiO2 nanotubes, the oxygen vacancies increased and affected to the optical and electrical properties of TiO2 films. These films were used for detecting gas at room temperature. Hence, we studied and analyzed the relationship of the morphology, elemental composition, phase composition, band gap energy and defect states as a function of the electrical resistance change of TiO2 nanotubes to understand and improve the sensor response.

Double Junction Characteristics of Amorphous TiO2 Thin Film Due to Various Potential Barriers

This report investigated the chemical, physical and electrical properties of TiO2 that was prepared with various oxygen gas flows and annealing temperatures to create different Schottky barriers. The thin films of the Schottky contact with double barriers were observed as increments of the capacitance. The oxygen vacancy increased at the film with the crystal structure and decreased at the film with the amorphous structure. It was confirmed that the current–voltage characteristics differ when observed in the low current area because the formation of potential barrier varies depending on the condition of the interfacing even in thin films with similar amorphous characteristics. Because the size of the potential barrier is mostly small, current is not observed in areas high at μA level, but at nA level, the electrical properties of the potential barrier could be observed more closely by the effect of relatively large potential barriers. It was found that the single and double connections were made depending on the size of the potential barrier at Schottky contact according to the after annealing treatment temperature.

Pressure-induced structural phase transition and vacancy filling in titanium monoxide TiO up to 50 GPa

Vacancy engineering can effectively modulate the optical and electronic properties of metal oxides. Here, we demonstrate that high-pressure could be a clean strategy to tune the vacancies in oxides with a high cationic vacancy content. By combining in situ synchrotron x-ray diffraction, Raman scattering, and charge transport measurements in a diamond anvil cell, we systematically study the structure and electrical properties of TiO with ∼16% ordered vacancies up to 50.2 GPa at room temperature. The monoclinic TiO transforms to the cubic phase at ∼37.8 GPa. After decompression to ambient conditions, the cubic phase survives. The vacancies are partially filled and become disordered with a concentration of approximately 12.5%. The charge transport of TiO at high pressure exhibits a metal-insulator transition, which originates from the ordered to disordered transition of vacancies under pressure. Molecular dynamics simulations suggest that the vacancies enhance the mobility of atoms in the lattice under pressure and lead to the pressure-induced amorphization and recrystallization.

Microstructure and optical and electrical properties of TiO 2 nanotube thin films prepared by spin‐coating method

Titanium dioxide nanotubes prepared by hydrothermal method and the TiO2 films and TiO2 nanotube film were prepared by spin-coating method. The TiO2 nanotube film and a part of TiO2 film were annealed at 150°C for 1 h, while the another part of TiO2 film was annealed at 500°C. The high-resolution transmission electron microscopy analysis indicated that the TiO2 nanotubes prepared by hydrothermal method have been crystallised and the lattice plane indices corresponded to anatase {200}, and the TiO2 nanotube grown along the 〈100〉 direction. The atomic force microscopy results show that the surface morphology of the TiO2 film annealed at 150°C was smooth and uniform (0.62 nm in roughness) compared to the surface morphology of TiO2 film annealed at 500°C (roughness is 2.41 nm). For the TiO2 nanotube film, the nanotube fragments were uniformly dispersed in the base and the complete films have been prepared and the roughness was reached to 6.4 nm. The optical properties showed that the visible light transmittance of the TiO2 nanotube film was larger (larger than 95%) than the TiO2 film. The electrical properties showed that square resistance of TiO2 nanotube film was smaller than that of TiO2 film.

Influence of synthesis route on structural, optical, and electrical properties of TiO2

TiO2 samples with two different morphology were synthesized via sol–gel and hydrothermal techniques. The effect of synthesis procedure on structural, morphological, optical, and electrical properties was studied. Rietveld analysis revealed that anatase phase having tetragonal structure dominates at room temperature. The presence of anatse phase of TiO2 was further confirmed by the analysis of various peaks obtained from the Raman spectra. The field-emission scanning electron microscopy (FESEM) and transmission electron microscopy micrographs depicted the formation of two different kinds of morphologies with average particle size ranging from 9.87 to 11.35 nm. The FESEM micrographs showed homogeneous particle distribution for sol–gel synthesized sample, whereas it depicted rod-like structure in the sample synthesized via hydrothermal technique. The X-ray photoelectron spectroscopy analysis clearly indicated the presence of appropriate chemical composition and valency states of Ti and O element in TiO2 samples. The optical bandgap was estimated from the UV–visible spectra and found to be in corroboration with the reported values. The conductivity spectra were analyzed using Jonscher power law. The values of activation energy suggested that the conduction mechanism is thermally activated. The conductivity isotherms were scaled through Ghosh scaling model. In the sol–gel synthesized sample, the conduction mechanism was found to be independent of temperature in the entire measured temperature range; however, the hydrothermally synthesized sample depicted that the conduction mechanism is temperature-dependent in the measured temperature range. This discrepancy was understood in terms of structural changes and charge trapping within the structure.

Synthesis of visible light responsive iodine-doped mesoporous TiO2 by using biological renewable lignin as template for degradation of toxic organic pollutants

The visible light responsive I-doped mesoporous TiO2 (I/TiO2-T) catalysts were synthesized by facile hydrolysis method with lignin as a template. The resulting I/TiO2-T catalysts synthesized from different amounts of I as a dopant and lignin as a template were characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), transmission electron microscopy (TEM), UV–vis diffuse spectroscopy (DRS), Fourier transform infrared spectroscopy (FTIR), photoluminescence (PL), and electrochemical impedance spectroscopy (EIS). The photocatalytic activities of the resulting catalysts were investigated by the degradation of p-chlorophenol under artificial visible light irradiation. The results showed that the lignin-templated TiO2 with a suitable amount of I-doping (I/TiO2-T) had higher catalytic activity than the catalyst prepared form I-doped TiO2 without lignin template (I/TiO2). Complete degradation of p-chlorophenol was achieved by I/TiO2-T with suitable amount of I-doping at 60 min. However, 95.7, 10.7, and 5.5% of the p-chlorophenol was degraded with I/TiO2, TiO2-T, and P25 catalysts, respectively, under 140 min visible light irradiation. The enhanced catalytic activities of the samples with template and I-doping may be due to the small grain size and high specific surface area of the catalysts. The band gap and the electrical properties of TiO2 also could be adjusted with I-doping. The I-doped TiO2 with the extrinsic I5+-to-Ti4+ and the iodine-to-oxygen donor defects could be excited by visible irradiation for efficient pollutants degradation. A possible photocatalytic mechanism for the degradation of the pollutants with I/TiO2-T under visible light irradiation was also proposed.

Titanium Dioxide: From Engineering to Applications

Titanium dioxide (TiO2) nanomaterials have garnered extensive scientific interest since 1972 and have been widely used in many areas, such as sustainable energy generation and the removal of environmental pollutants. Although TiO2 possesses the desired performance in utilizing ultraviolet light, its overall solar activity is still very limited because of a wide bandgap (3.0–3.2 eV) that cannot make use of visible light or light of longer wavelength. This phenomenon is a deficiency for TiO2 with respect to its potential application in visible light photocatalysis and photoelectrochemical devices, as well as photovoltaics and sensors. The high overpotential, sluggish migration, and rapid recombination of photogenerated electron/hole pairs are crucial factors that restrict further application of TiO2. Recently, a broad range of research efforts has been devoted to enhancing the optical and electrical properties of TiO2, resulting in improved photocatalytic activity. This review mainly outlines state-of-the-art modification strategies in optimizing the photocatalytic performance of TiO2, including the introduction of intrinsic defects and foreign species into the TiO2 lattice, morphology and crystal facet control, and the development of unique mesocrystal structures. The band structures, electronic properties, and chemical features of the modified TiO2 nanomaterials are clarified in detail along with details regarding their photocatalytic performance and various applications.

Enhancement of Electrical Properties of TiO2−x Oxide Semiconductor by d-Orbital Ordering Using Swift Heavy Ni-Ion Irradiation at Room Temperature

The electrical properties of radiofrequency (RF)-sputtered TiO2−x films have been investigated as a function of Ni-ion irradiation dose at room temperature. The prepared TiO2−x films were irradiated with 130-MeV swift heavy Ni ions in the range from 5 × 1011 ions/cm2 to 1 × 1013 ions/cm2. Increasing the Ni-ion irradiation dose dramatically enhanced the mobility in the TiO2−x films from 2.2 cm2/V s to 1.24 × 102 cm2/V s, while the carrier concentration did not vary. To explain this change in the electrical properties of the TiO2−x films, we investigated various physical properties, namely the physical structure, molecular orbital ordering in the conduction band, and shallow/deep trap states in the band-edge area below the conduction band. We suggest that the improvement in mobility originates from the ordering of the Ti 3d orbital in the conduction band. In addition, increase of the Ni-ion irradiation dose changed two distinct band-edge states below the conduction band.

Enhanced Optical and Electrical Properties of TiO2 Buffered IGZO/TiO2 Bi-Layered Films

In and Ga doped ZnO (IGZO, 100-nm thick) thin films were deposited by radio frequency magnetron sputtering without intentional substrate heating on a bare glass substrate and a TiO2-deposited glass substrate to determine the effect of the thickness of a thin TiO2 buffer layer on the structural, optical, and electrical properties of the films. The thicknesses of the TiO2 buffer layers were 5, 10 and 15 nm, respectively. As-deposited IGZO films with a 10 nm-thick TiO2 buffer layer had an average optical transmittance of 85.0% with lower resistivity (1.83×10(-2) Ω cm) than that of IGZO single layer films. The figure of merit (FOM) reached a maximum of 1.44×10(-4) Ω-1 for IGZO/10 nm-thick TiO2 bi-layered films, which is higher than the FOM of 6.85×10(-5) Ω-1 for IGZO single layer films. Because a higher FOM value indicates better quality transparent conducting oxide (TCO) films, the IGZO/10 nm-thick TiO2 bi-layered films are likely to perform better in TCO applications than IGZO single layer films. (Received January 19, 2016; Accepted March 20, 2016)