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Highlights • GIMS technique is efficient to deposit the TiO 2 film on PMMA substrate. • GIMS technique is favorable for using thermally unstable materials as a substrate. • GIMS allows to use higher power density than PMS during film deposition on PMMA. Abstract This work presents decorative TiO 2 , TiO 2 /Al layers deposited on poly(methyl methacrylate) (PMMA) substrates. We chose the Gas Injection Magnetron Sputtering (GIMS) technique for layer deposition. Choosing this technique, we expected a lower thermal load of polymer substrate than in other commonly used magnetron techniques. The pulse plasma, generated in the GIMS method, is controlled by a periodical injection of gas dosages in the region of the magnetron target. The process of deposition operated with a 1 Hz frequency of a plasma generation and the life time of plasma was ∼500 ms. Under these conditions, the energetic impact into the substrate, integrated over the time, is lower than during the continuous process, so it should not cause any damage to the polymer surface. For our experiment we deposited a thick ∼700 nm aluminum layer and thin 17–116 nm TiO 2 films, which exhibited the interference effect, on non – heated PMMA substrates. The optical properties of the prepared systems were investigated by spectroscopic ellipsometry and spectrophotometric measurements. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Although scholars have done a lot of work in studying the effect of doping on the optical properties of TiO 2 , there is no report about the co-doping of rutile TiO 2 with transitional metal element Ni and nonmetallic element N. • Due to the narrowing of band gap or appearance of the impurity states in the band-gap, both the N doping and Ni doping systems have improvements to the absorption of rutile TiO 2 in the visible wavelength. But the Ni/N co-doping system has the best optical absorption in the visible wavelength and red-shift, which likely due to the complicated impurity states in the band-gap. • The emergence of these local energy levels increase the electron transitions from VBM to the impurity levels and from the impurity levels to the CBM ion at the bottom of the conduction band enhances the light absorption properties of rutile TiO 2 , which enhances the light absorption in visible wavelength of rutile TiO 2. Abstract The first-principle method based on the density functional theory (DFT) was used to calculate the electronic structure and optical properties of pure, N-doped, Ni-doped and Ni/N co-doped rutile TiO 2 systems. The band structures, electronic density of states and spectral absorption coefficients were calculated after geometrically optimizing the above TiO 2 systems. The results show that there are impurity energy levels appear within the band gaps of Ni-, N-doped systems, which provided by N-2p orbit and Ni-3d orbit; meanwhile, more complicated impurity energy levels appear within the band gaps of N/Ni co-doped rutile TiO 2. The co-doped rutile TiO 2 has a better optical absorption efficiency and stronger absorption cut-off wavelength red-shift. Which can be caused by the hybridization of Ni-3d orbit and N-2p orbit provides local impurity levels, so that electrons transition occurred from the valence band maximum to the impurity levels and also from the impurity levels to the bottom of conduction band, which contributes to the electron transition and enhances the absorption performance of rutile TiO 2. [ABSTRACT FROM AUTHOR]

Rutile phase titanium dioxide (TiO 2 ) thin films were grown on α-Al 2 O 3 (100) substrates at different deposition temperatures (500–650 °C) by the metalorganic chemical vapor deposition method. The analyses of X-ray diffraction θ -2 θ scan indicated that the deposition temperature had an obvious influence on the crystal quality of the TiO 2 films. Single crystalline rutile TiO 2 films can be obtained from a relatively low deposition temperature of 500 °C–600 °C, and the film grown at 550 °C exhibited the best crystallinity, for which the composition and epitaxial relationship were identified. The effects of deposition temperature on the deposition rate and optical properties of the films have been investigated in detail. [ABSTRACT FROM AUTHOR]

In the present work, hydrothermal method was followed to synthesize Undoped and Dy3+ doped TiO2 nanoparticles. The as-prepared pure and doped nanoparticles were investigated by the characterization techniques, as such X-ray diffraction (XRD), Transmission Electron Microscopy (TEM), Energy dispersive X-ray analysis (EDAX), Ultraviolet–Visible (UV–Vis) spectroscopy, Fourier Transform Infrared Spectroscopy (FT-IR), and Dielectric Spectroscopy. The crystallography and grain size have been studied using XRD and TEM Analysis. X-ray diffraction and energy dispersive X-ray spectroscopy results showed that the as prepared nanoparticles were without any impurity. With the doping of Dysprosium ion, the grain size increases. UV–Visible Spectra reveals the optical properties and the optical band gap calculated using Kubelka- Munk plot was found to be 3.45 eV for pure TiO2 and decreases to 3.39 eV due to doping. The results indicate that the size of the nanoparticles increases with decreasing bandgap when dopant added. The development of the anatase phase TiO2 is affirmed by XRD and FT-IR. The Dielectric properties and A.C Conductivity measurements along with frequency were done for synthesized samples. [ABSTRACT FROM AUTHOR]

Oxide-based films and nanostructures have emerged as important materials for a wide range of applications such as photovoltaics, optoelectronics, gas sensing and electronics. To develop an appropriate understanding of the properties of these oxides, it is necessary to address the material preparation methods and defect probing issues. This work reports on the synthesis processes of TiO 2 based transparent conductive films, their stoichiometry control and defect identifying, in relation with their electrical and optical properties. Un-doped and TiO 2 :Nb films were deposited by RF co-sputtering from TiO 2 and Nb 2 O 5 targets in Ar plasma. The chemical species present in the plasmas used in deposition process were investigated by optical emission spectroscopy, which was later on correlated with the defects structure of the films. Analysis by X-ray photoelectron spectroscopy shed more light on the nature of the vacancies and on the effect of the latter on the optical and electrical properties of the films. In terms of results, we measured electrical resistivity in the range 10 − 2 –10 − 3 Ω cm for the intrinsically and extrinsically doped films (films doped with oxygen vacancies and Nb + 5 respectively) while the lowest resistivity was obtained for intrinsically-extrinsically co-doped TiO 2 films (7.4 × 10 − 4 Ω cm). The films transparency was also actively determined by the defects in the lattice and highly transparent films (65–85% in the visible range) were obtained by controlling the density of defects. The approach adopted in this work for the generation of oxygen vacancies could be useful for other oxide-based films, where the oxygen vacancies-dependent properties are crucial, for room temperature ferromagnetism and photocatalytic applications. [ABSTRACT FROM AUTHOR]

In this study, Carbon Nanotubes (CNT) synthesized with Chemical Vapour Deposition (CVD) were reinforced with 0.1, 0.2, 1 and 2% weight in Titanium dioxide (TiO2). Structural characterization of samples was analyzed by Scanning Electron Microscope (SEM). Electrical conductivities of samples, based on temperature, were surveyed. Optical properties were determined using UV-VIS spectrometer. Increase in CNT rate in composites caused electrical conductivity both room and rising temperature. Furthermore, CNT caused the increases in ability of TiO2's to absorb UV beam, and the reduces on forbidden energy gap (Eg). [ABSTRACT FROM AUTHOR]

Titanium dioxide - doped magnesium oxide (TiO2:MgO) films prepared on glass substrates using a pulse laser technique (PLD) at substrate temperature 373 K with thicknesses t=400 nm. The pure TiO2 and (TiO2:MgO) films are investigated by X-ray diffraction and optical absorption spectroscope. The X-ray diffraction measurements show that the pure TiO2 films are a polycrystalline and contain tetragonal structure in anatase phase. The TiO2 structure has been changed to rutile phase after doped with 3% wt MgO and back to anatase phase after doped with 5 % wt MgO. TiO2 film doped with (7%, 10%) MgO have amorphous structure. The optical properties of the TiO2:MgO show that the absorption coefficient increasing with increase the MgO concentration while, the optical band-gap decreased to be (3eV) were obtained for 10% MgO films. [ABSTRACT FROM AUTHOR]

This paper presents the results of an experimental investigation on the optical properties of the TiO2and TixCyOznanopowders, produced by the pulsed plasma chemical method. Pulsed plasma chemical synthesis is realized on the laboratory stand, including a plasma chemical reactor (6 l) and TEA-500 electron accelerator. The parameters of the electron beam are as follows: 400–450 keV electron energy, 60 ns half-amplitude pulse duration, up to 200 J pulse energy, and 5 cm beam diameter. In TiO2sample, obtained using the pulsed plasma chemical method, the particles can be divided into two groups: 100–500 nm large spherical particles and tiny complex particles (sized less than 100 nm). For TixCyOz sample, the morphology of the particles is mainly presented with irregular fragment shape. The average size of the particles is ranged from 200 to 300 nm. The band gap for all synthesized samples is within 2.94–3.35 eV. [ABSTRACT FROM AUTHOR]

Water is regarded as a poor absorber of solar energy. This affects the efficiency of solar thermal systems. The addition of nanoparticles to heat transfer fluids used in solar thermal systems can enhance their optical properties. These new-generation heat transfer fluids are known as nanofluids. The present study investigates the stability and optical properties of three nanofluids, including aluminum oxide (13 nm and <50 nm) and titanium dioxide (21 nm) nanofluids. The stability of the nanofluids was observed through a photo-capturing method and zeta potential measurements. Ultraviolet-visible (UV-Vis) spectrophotometer was used to measure the absorbance and transmittance of the prepared nanofluids. The effect of factors such as type of particle, type of surfactant, and pH of the solution on the optical properties of the nanofluids was also investigated. We found that the titanium dioxide nanofluid had better optical properties but lower stability compared to aluminum oxide nanofluids. [ABSTRACT FROM AUTHOR]

Titanium dioxide (TiO) ultrathin films with different thicknesses below 20 nm were grown by atomic layer deposition (ALD) on silicon substrates at 300 °C. Spectroscopic ellipsometry (SE) measurements were operated to investigate the effect of thickness on the optical properties of ultrathin films in the spectra range from 200 to 1000 nm with Forouhi-Bloomer (F-B) dispersion relation. It has been found that the refractive index and extinction coefficient of the investigated TiO ultrathin film increase while the band gap of TiO ultrathin film decreases monotonically with an increase in film thickness. Furthermore, with the purpose of studying the temperature dependence of optical properties of TiO ultrathin film, the samples were annealed at temperature from 400 to 900 °C in N atmosphere. The crystalline structure of deposited and annealed films was deduced by SE and supported by X-ray diffraction (XRD). It was revealed that the anatase TiO film started to transform into rutile phase when the annealing temperature was up to 800 °C. In this paper, a constructive and effective method of monitoring the phase transition in ultrathin films by SE has been proposed when the phase transition is not so obvious analyzed by XRD. [ABSTRACT FROM AUTHOR]

In this research, vanadium doped TiO 2 (VTO) thin film was deposited on glass substrate using sol–gel dip coating method. The structure, morphology, surface roughness, surface composition, optical and electrical properties of the thin films were investigated by X-ray diffraction, field emission scanning electron microscopy, atomic force microscopy, energy-dispersive X-ray spectroscopy, UV-VIS NIR spectrophotometer and MEGGER resistivity meter, respectively. The X-ray diffraction showed that the VTO thin film had a polycrystalline structure. The optical and electrical results indicated that vanadium addition decreased the band gap of the TiO 2 thin film from 3.71 to 3.65 eV and resistivity from 16.7 × 10 7 to 1.7 × 10 7 Ωcm. [ABSTRACT FROM AUTHOR]

Graphene and TiO were synthesized using electrochemical exfoliation and co-precipitation methods, respectively. An ex situ approach was adopted for the graphene/TiO composites. The conformation of graphene in the TiO samples was examined through X-ray diffraction. Optical properties of the as-synthesised composites such as optical absorption, extinction coefficient, refractive index, real dielectric constant, imaginary dielectric constant, dissipation factor, and optical conductivity were measured using UV-Vis spectroscopy. The varying concentration of graphene in TiO affects the optical properties which appear different for 10 wt.% as compared to 5 wt.% graphene/ TiO composite. The composites exhibit an absorption peak at 300 nm with a decrease in band gap for 10 wt.% as compared to 5 wt.% graphene/TiO composite. The maximum optical conductivity for the graphene/TiO composite of 10 wt.% was found to be 1.86·10 Ω·m at 300 nm. [ABSTRACT FROM AUTHOR]

The electronic and optical properties of Mn-S co-doped anatase TiO2 were calculated using the plane-wave-based ultrasoft pseudopotential density functional method within its generalized gradient approximation (GGA). The calculated results show that the band gap of Mn-S co-doped TiO2 is larger than that of the pure TiO2, and two impurity bands appear in the forbidden band, one of which above the valence band plays a vital role for the improvement of the visible light catalytic activity. The Mn-S co-doped anatase TiO2 could be a potential candidate for a photocatalyst because of its enhanced absorption ability of visible light. [ABSTRACT FROM AUTHOR]

This work investigates the structural and optical properties of mixed ZnO/TiO 2 ceramics synthesized at 900 °C by the conventional solid state sintering method. We doped different weights of TiO 2 powder (x = 1–7 wt%) to prepare the ceramic pellets. Then we studied the effect of TiO 2 content on crystalline properties, grain size and residual stress using X-ray diffraction. XRD patterns revealed the alloying of hexagonal ZnTiO 3 and spinel Zn 2 TiO 4 phases as the doping rate x (wt%) increased. The growth of ZnO grains in wurtzite structure was favored along the (100) direction with coefficient texture 2.27 for a TiO 2 amount x = 1wt%. Grain sizes were obtained in the range 33–73 nm. We used Williamson-Hall (W–H) analysis and size–strain plot (SSP) method to study the individual contributions of crystallite sizes and lattice strain on the peak broadening of the ZnO/TiO 2 composites. Strain, stress and energy density values were calculated by assuming a uniform deformation model (UDM). We investigated the optical properties of the ceramics by Absorbance and Reflectance measurements at room temperature in the wavelength range 200–1000 nm. The results suggested that the addition of TiO 2 to ZnO powder led to a high transparency in the visible range and two absorption edges in the UV region. Interestingly, it was seen slight enhancement of the band gap from 3.1 eV to 3.18 eV for the first edge while the second one was enhanced from 4.8 eV to 5.05 eV as the TiO 2 doping concentration increased from 1 wt% to 7 wt% respectively. [ABSTRACT FROM AUTHOR]

The electronic and optical properties of S- and/or Ce-(co)doped anatase titanium dioxide (TiO2) are investigated using density functional theory plus U (DFTU) calculations. The optimized total energy suggests that TiO2 codoping by Ce and S favours the configuration of one substitutional Ce atom occupied on a Ti site with one substitutional S atom either on its nearest neighboring O or Ti site. The calculated results show that all doping configurations exhibit remarkable red-shift and excellent photocatalytic properties compared with pure TiO2. These reinforced features can mainly be ascribed to the appearance of S states in the top of valence band (VB) and Ce states in the bottom of conduction band (CB) as well as the contribution from the increasing octahedral dipole moments. The synergetic effects of cationic Ce and anionic S can extend optical absorption edge, which results in higher absorption coefficient in the visible light region than that of the anionic S monodoping and cationic Ce monodoping case; in the same time, decreasing the codoping concentration leads to reduced optical absorption. Additionally, Ce and S as cations incorporating into TiO2 lattices can induce stronger redox potential with a lower defect formation energy under O-rich condition compared with other doping systems. [ABSTRACT FROM AUTHOR]

The high-temperature modification of micron-sized grains of titanium dioxide with nanoparticles of Al 2 O 3 , ZrO 2 , SiO 2 , TiO 2 , ZnO, and MgO was performed. The influence of these types of nanoparticles on the diffuse reflectance spectra of modified pigments in the range of 350–2000 nm and their changes after irradiation by 30 keV electrons were investigated. It was determined that the modification does not lead to significant changes in the diffuse reflection spectra of the TiO 2 pigments. The type of oxide nanoparticles, the size of the ionic radii and the valence of the cations do not noticeably influence the radiation stability of the modified pigment, as determined by the intensity of the absorption bands in the visible and near infrared regions of the spectrum. The determining factor in the increase of the radiation stability of the modified pigments is the specific surface area of the nanopowders. [ABSTRACT FROM AUTHOR]

The effects of electronic and local structures on the optical properties of C-doped anatase TiO 2 (101) surface were investigated. When C is at Ti or interstitial site, a planar CO 3 unit is observed and leads to the decrease of band gap. While for C substituted at O site, although it introduces impurity states, the intrinsic band gap does not change. Furthermore, the dipole moment is calculated to explore the effect of local crystal structure on the photocatalytic ability. The results show that the dipole moment can promote the separation of charge carriers and enhance the photocatalytic activity. [ABSTRACT FROM AUTHOR]

Thin layers of titanium dioxide were fabricated by direct inkjet patterning of a reverse micelles sol-gel composition onto soda-lime glass plates. Several series of variable thickness samples were produced by repeated overprinting and these were further calcined at different temperatures. The resulting layers were inspected by optical and scanning electronic microscopy and their optical properties were investigated by spectroscopic ellipsometry in the range of 200-1000 nm. Thus the influence of the calcination temperature on material as well as optical properties of the patterned micellar titania was studied. The additive nature of the deposition process was demonstrated by a linear dependence of total thickness on the number of printed layers without being significantly affected by the calcination temperature. The micellar imprints structure of the titania layer resulted into significant deviation of measured optical constants from the values reported for bulk titania. The introduction of a void layer into the ellipsometric model was found necessary for this particular type of titania and enabled correct ellipsometric determination of layer thickness, well matching the thickness values from mechanical profilometry. [ABSTRACT FROM AUTHOR]

In this study pure and aluminum (Al) doped TiO2 films were prepared by using sol-gel spin coating process. The structural, surface morphological and optical properties of these films have been investigated. X-ray diffraction (XRD) with a Cu-Kα irradiation was used to identify the phase structures of the films. Optical properties of undoped and Al-doped TiO2 films were determined by using UV-VIS spectrophotometer and its attachment of diffuse reflectance. Transmittance and reflectance values of the films were measured in the wavelength range of 350-700 nm. The optical parameters (band gap, refractive index, etc.) of the films were then calculated based on these data. The results show that optical bandgap the film is effectively enhanced by Al doping. The results open an approach to create a new semiconductor material for the engineering applications especially for gas sensing and photocatalytic applications. [ABSTRACT FROM AUTHOR]

The electronic states and formation energies of four types of lattice point defects in rutile TiO2 are studied using the first-principles calculations. The existence of oxygen vacancy leads to a deep donor defect level in the forbidden band, while the Ti interstitial forms two local states. It is predicted that oxygen vacancy prefers to combine with Ti-interstitial to form VO-Tii dimer by a partial 3d electron transfer from the Tii to its neighboring VO. The charge distribution between a Ti interstitial and its neighboring Ti ions partially shields the Coulomb interactions. Lastly, optical properties of these defective lattices are discussed. [ABSTRACT FROM AUTHOR]

Highlights: [•] The calculated band gap of the TiO2(110) surface is improved by LSDA+ U calculation. [•] LSDA calculation for the TiO2(011) surface has reproduced the experimental band gap. [•] The same value of U cannot provide a universal correction for different TiO2 surfaces. [ABSTRACT FROM AUTHOR]

This work investigates surface reconstruction, electronic structure, and optical properties of the rutile TiO2(011)-2×1 surface using means of density functional theory calculations. For the surface reconstruction of the rutile TiO2(011) surface, a theoretical simulation with forming from bulk truncation to the 2×1 reconstruction was carried out. The calculated band structure shows a direct band gap at Г point, and the band gap of 2.08eV reproduces the experimental measurement value ~2.10eV very well. Analysis of the density of states reveals that no surface state was introduced into the forbidden gap. Not coincidentally, the calculated optical absorption edge at about 2.01eV further clarifies the band gap narrowing and such an intrinsic band gap nature effectively pushes the optical absorption edge into the visible light. Hence, our theoretical calculations provide evidence that the rutile TiO2(011)-2×1 surface possesses high photocatalytic activity. [ABSTRACT FROM AUTHOR]

Abstract: The nanocomposite thin films of titanium dioxide (TiO2)–lead phthalocyanine (PbPc) have been prepared on glass substrates by the electron beam evaporation technique. The optical properties of TiO2/PbPc nanocomposite thin films have been investigated using a spectrophotometric measurement of the absorbance and transmittance at normal incident of light in the wavelength region 300–800nm. Surface morphology of thin films has been characterized using field emission scanning electron microscopy (FESEM). The UV–vis analysis has been performed to determine the type of electronic transition and the optical energy band gap. The analysis of the spectral behavior of the absorption coefficient in the intrinsic absorption region reveals that the absorption mechanism is due to direct transition. Moreover, by studying the absorption coefficient spectra just below the fundamental absorption edge, the width of band tails of localized states (Urbach energy), steepness parameter and width of the defect states have been evaluated. The obtained results of this novel nanocomposite (TiO2/PbPc) support the desirable features for the optoelectronic devices. [Copyright &y& Elsevier]

Abstract: Electronic and optical properties of compensated and noncompensated (Cr, N) codoped TiO2 have been investigated using density functional theory with plane wave basis set and pseudopotential. To investigate the formation of defect pair in the codoped models, defect pair binding energy was calculated. Compensated codoped model has two Cr atoms doped at Ti sites, one N atom at O sites along with an oxygen vacancy that gave stable configuration, better electronic and optical properties. Defect pair binding energy of this model showed that, individual defects would bind each other leading to stable configuration compared to mono-doped models. Band structure results showed that compensated (Cr, N) codoping introduced substantially broaden intermediate states in the forbidden band along with narrowed band gap. Furthermore, the Fermi level was shifted from top of the valence band to middle of the forbidden band describing half metallic character. Cr doping changed the nature of N 2p states from unoccupied to occupied which will improve electron–hole pair separation. Optical properties comparison showed that all doped models effectively shifted the absorption edge of TiO2 towards visible light. Compensated (Cr, N) codoped TiO2 has better optical properties and covered wide absorption band in the visible light region, attributed to the stable configuration, narrowed band gap and widely distributed states in the band gap. Our results provide reasonable explanation of the experimental findings. [Copyright &y& Elsevier]

Titanium dioxide thin films were deposited on crystalline silicon substrates by electron beam physical vapor deposition. The deposition was performed under vacuum ranging from 10-5 to 10-6 Torr without process gases, resulting in homogeneous TiO2-x layers with a thickness of around 100 nm. Samples were then annealed at high temperatures ranging from 500°C to 800°C for 4 hours under nitrogen, and their structural and optical properties along with their chemical structure were characterized before and after annealing. The chemical and structural characterization revealed a substoichiometric TiO2-x film with oxygen vacancies, voids, and an interface oxide layer. It was found from X-ray diffraction that the deposited films were amorphous and crystallization to anatase phase occurred for annealed samples and was more pronounced for annealing temperatures above 700°C. The refractive index obtained through spectroscopic ellipsometry ranged between 2.09 and 2.37 in the wavelength range, 900 nm to 400nm for the as-deposited sample, and jumped to the range between 2.23 and 2.65 for samples annealed at 800°C. The minimum surface reflectance changed from around 0.6% for the as-deposited samples to 2.5% for the samples annealed at 800°C. [ABSTRACT FROM AUTHOR]

We developed a mathematical analysis method of reflectometry data and used it to characterize the internal structure of TiO2/SiO2/Si and Ti/SiO2/Si stacks. Atomic concentration profiles of all the chemical elements composing the samples were reconstructed from the analysis of the reflectivity curves measured versus the incidence angle at different soft x-ray reflection (SXR) photon energies. The results were confirmed by the conventional techniques of hard x-ray photoelectron spectroscopy (HXPES) and high-resolution transmission electron microscopy (HRTEM). The depth variation of the chemical composition, thicknesses and densities of individual layers extracted from SXR and and HXPES measurements are in close agreement and correlate well with the HRTEM images. [ABSTRACT FROM AUTHOR]

This paper revisits dual-layer ultrathin film optics, which can be used for functional graded refractive index thin film stack. We present the detailed derivation including s-polarized and p-polarized light under arbitrary incidence angle showing the equivalence between the dual-layer ultrathin films and a negative birefringent thin film and also the approximations made during the derivation. Analysis of the approximations shows the influence of thickness of dual-layer thin films, the incidence angle and desired refractive index of the birefringent film. Numerical comparison between the titanium dioxide/aluminum oxide based dual-layer ultrathin film stack and the equivalent birefringent film verifies the theoretical analysis. The detailed theoretical study and numerical comparison provide a physical insight and design guidelines for dual-layer ultrathin film based optical devices. [ABSTRACT FROM AUTHOR]