Photocatalytic properties of nanocrystalline TiO<Subscript>2</Subscript> thin films doped with Tb

In this work photocatalytic properties of TiO₂ thin films doped with different amount of Tb have been described. Thin films were prepared by high energy reactive magnetron sputtering process. Comparable photocatalytic activity has been found for all doped TiO₂ thin films, while different amounts of Tb dopant (0.4 and 2.6 at. %) results in either an anatase or rutile structure. It was found that the terbium dopant incorporated into TiO₂ was also responsible for the amount of hydroxyl groups and water particles adsorbed on the thin film surfaces and thus photocatalytic activity was few times higher in comparison with results collected for undoped TiO₂ thin films.     

Magnetism and optical properties of nanocrystalline Cu<Subscript>2</Subscript>O and TiO<Subscript>2</Subscript> powders

The optical spectra of Cu₂O and TiO₂ nanopowders have been studied, which contain information about structural defects and are of interest in the search for optimum regimes providing the synthesis of ferromagnetic nanocrystals with Curie temperatures above room temperature.     

Anomalous magnetism of the nanocrystalline oxide TiO<Subscript>2</Subscript> surface

The magnetic properties of an oxygen-deficient nanocrystalline undoped titanium dioxide synthesized by the gas-phase, electric-explosion, and chemical method have been studied. The defect state was controlled using reduction treatments in vacuum or in a hydrogen atmosphere. It is shown that the defect state of the surface of nanocrystalline oxides (for example, the existence of vacancies in the anion sublattice and other defects) has a dominant influence on the formation of the magnetic properties of the samples under study. The main contributions to the magnetism of TiO₂ nanoparticles after the reduction treatments are the paramagnetic contribution of the matrix, the paramagnetic Curie–Weiss contribution, and the contribution of the spontaneous magnetic moment provided by the existence of regions with different spin ordering. A heterogeneous magnetic state is found to exist in the TiO₂ nanopowders; for example, at low temperatures, shifted hysteresis loops are observed as a result of a possible set of magnetic states with different spin orders. It is shown that a soft compaction or grinding of nanopowders in an agate mortar lead to substantial increase in the magnetization, sometimes, by a factor of more than two, regardless of the nanopowder synthesis method and the initial phase state of TiO₂ (anatase or rutile structures). This experimental fact proves the key role of the surface defects and the magnetic moment carriers with different spin configurations localized mainly on the nanoparticle surface. The compaction changes the magnetization only in the case when the initial magnetic state has a nonlinear “quasi-superparamagnetic” character of the magnetization curve. As a result of predominant exchange interaction between the nanoparticles with a frustrated character of spin ordering on the nanoparticles surface, the ferromagnetic contribution increases as nanoparticles contact.     

Physical properties of Ba<Subscript>0.8</Subscript>Sr<Subscript>0.2</Subscript>TiO<Subscript>3</Subscript> thin films

The behavior of material constants in ferroelectric Ba_0.8Sr_0.2TiO₃ thin films is studied depending on the misfit strain at room temperature in the context of nonlinear thermodynamic potential of the phenomenological theory. Some constants are found to undergo drastic changes with the alternating strain at the interfaces. The gathered results allow one to evaluate the material constants for a specific film and to outline the direction in searching the ways to synthesize films with the needed properties.     

Spray pyrolysis-deposited TiO<Subscript>2</Subscript> thin films as high-performance lithium ion battery anodes

Focusing on additive-free electrodes, thin films are of typical interest as electrodes for lithium ion battery application. Herein, we report the fabrication of TiO₂ thin films by spray pyrolysis deposition technique. X-ray diffraction and transmission electron microscopic analysis confirms the formation of anatase TiO₂. Electrochemical evaluation of these sub-micron TiO₂ thin films exhibits high-rate performance and long cycling stability. At 1C rate (1C?=?335 mA/g), the electrode delivered discharge capacity of 247 mAh/g allowing about 0.74 lithium into the structure. The electrodes also delivered specific capacities of 122 and 72 mAh/g at 10 and 30C rates, respectively. Without conductive additives, this excellent performance can be attributed to the nanosize effect of TiO₂ particles combined with the uniform porous architecture of the electrode. Upon cycling at high rates (10 and 30C), the electrode exhibited excellent cycling stability and retention, specifically only <?0.6% capacity loss per cycle over 2500 cycles.     

Photoaccumulating film systems based on TiO<Subscript>2</Subscript>/MoO<Subscript>3</Subscript> and TiO<Subscript>2</Subscript>/MoO<Subscript>3</Subscript>:V<Subscript>2</Subscript>O<Subscript>5</Subscript> nanoheterostructures

The thin-film photocatalysts TiO₂/MoO₃ and TiO₂/MoO₃:V₂O₅ obtained by a combination of sol–gel and sintering techniques were studied using the photooxidation of probing dyes, EPR spectroscopy, X-ray diffraction analysis, and electron microscopy. It was shown that due to charge accumulation caused by UV irradiation, these photocatalysts retain their oxidative activity and ability for self-sterilization in the dark for a long time after irradiation was terminated (up to 5 h for TiO₂/MoO₃:V₂O₅).     

Influence of substrate temperature on certain physical properties and antibacterial activity of nanocrystalline Ag-doped In<Subscript>2</Subscript>O<Subscript>3</Subscript> thin films

Nanocrystalline Ag-doped indium oxide (AIO) thin films, by employing a much simplified spray pyrolysis technique in different substrate temperatures (300, 350, 400 and 450°C), were fabricated for the first time. The deposited films were subjected to various characterization studies, to explore certain features like the influence of various deposition temperatures on physical and antibacterial properties. XRD results showed that all the samples exhibited preferential orientation along the (2 2 2) plane. The variation in the crystalline size with increasing substrate temperature was explained on the basis of the Zener pinning effect. The electrical sheet resistance (R _sh) was found to decrease sharply with increasing substrate temperature and attained a minimum value \((62{\Omega } /\Box \)) at 400°C and then started increasing for higher deposition temperatures. Further, PL emission spectra of the samples in the visible range ascertained the possibility of applicability of the same in nanoscale optoelectronic devices. From the studies, it was found that at 400°C deposition temperature, one could expect better antibacterial efficiency against Escherichia coli. The influence of the shape and size of AIO nanograins on the antibacterial activity was analysed using scanning electron microscopy images.     

Methane sensor based on SnO<Subscript>2</Subscript>/In<Subscript>2</Subscript>O<Subscript>3</Subscript>/TiO<Subscript>2</Subscript> nanostructure

Two sets of samples of SnO₂/In₂O₃/TiO₂ system have been fabricated with different concentrations of component materials. In the first set TiO₂ with rutile structure was used, while in the second set it has the structure of anatase. Thin films (up to 50 nm) of obtained mixtures were deposited. Their sensitivity and selectivity with respect to methane (CH4) were studied. Nanostructure on the basis of 70%SnO₂ — 10%In₂O₃ — 20%TiO₂(anatase) exhibits sufficient sensitivity to methane.     

Preparation and optical properties of nanocrystalline thin films in the ZnO-TiO<Subscript>2</Subscript> system

Nanocrystalline compound thin films of ZnO-TiO₂ with different Zn/Ti atomic ratios were prepared by radio frequency magnetron reactive sputtering. The optical constants and the optical band gap were investigated using spectroscopic ellipsometry and the optical absorption spectrum. It was found that the cubic ZnTiO₃ phase can be obtained with the atomic ratio of Zn to Ti of about 1:1, and transforms to rhombohedral ZnTiO₃ phase and a phase mixture of rhombohedral ZnTiO₃ and ZnO with increasing Zn content. The refractive index decreases with the increase of Zn content, and the extinction coefficient in the visible range is near zero. The optical band gap was derived from the modeling of ellipsometry data and extinction coefficient spectra, and compared with that obtained from optical absorption spectrum, and it was found that the optical band gaps obtained by these three methods are consistent with each other. PACS 42.70.-a; 68.55.Jk; 78.20.Ci; 81.15.Cd     

Nonlinear dielectric response of epitaxial Ba<Subscript>0.6</Subscript>Sr<Subscript>0.4</Subscript> TiO<Subscript> 3</Subscript> thin films

Based on Landau-Devonshire (LD)-type phenomenological thermodynamic theory, the electric field dependence of the dielectric properties of tetragonal single-domain barium strontium titanate(Ba_1-xSr_xTiO₃) films on cubic substrates is theoretically investigated by taking into account the high order terms of the polarization. At room temperature, the nonlinear dielectric responses of epitaxial Ba_0.6Sr_0.4TiO₃ films are provided by adjusting the film thickness and growth temperature. The strong nonlinearity of relative dielectric constant and pyroelectric coefficient are attained around critical film thickness on MgO (69 nm) and LaAlO₃ (132 nm) substrates or critical growth temperature on MgO (337 °C) substrate with respect to epitaxy-induced lattice misfit and thermal stresses during deposition. This can be explained that small compressive stresses are effective to support high nonlinearity of dielectric constant and pyroelectric coefficient for Ba_0.6Sr_0.4TiO₃ films irrespective of whether they are on compressive substrate or tensile substrate. It is also predicted that a large tunability may be achieved by altering processing conditions, such as the film thickness and growth temperature for different substrates. Our theoretical results are in good agreement with the experimental data reported in literature.     

Phase composition and structure of nanocrystalline powders based on ZrO<Subscript>2</Subscript>(Y) and Al<Subscript>2</Subscript>O<Subscript>3</Subscript> obtained by plasma spray pyrolysis

It is shown that a nonequilibrium solid solution ZrO₂(3Y, Al) with tetragonal structure is formed in systems based on ZrO₂(3Y) with Al₂O₃ as a second component. A delay in the γ → α Al₂O₃ transformation and a reduction in the size of the coherently scattering domain of modifications are observed in systems based on Al₂O₃ with ZrO₂(Y) as a second component.     

Optoelectronics properties of TiO<Subscript>2</Subscript>:Cu thin films obtained by sol gel method

In this research, Cu-doped TiO₂ thin films have been successfully deposited onto a glass substrate by Sol–gel technique using dip coating method. The films were annealed at different annealing temperatures (400–500 °C) for 1 h. The structural, optical and electrical properties of the films were investigated and compared using X-ray Diffraction, UV–visible spectrophotometer and 4-point probe method. Optical analysis by mean transmittance T(λ) and absorption A(λ) measurements in the wavelength range between 300 to 800 nm allow us to determine the indirect band gap energy. DRX analysis of our thin films of TiO₂:Cu shows that the intensities of the line characteristic of anatase phase increasing in function of the temperature.     

Optical and electrical properties of nanocrystalline TiO<Subscript>2</Subscript>:Pd semiconducting oxides

Electrical and optical properties of TiO₂:Pd thin films deposited from Ti-Pd mosaic targets sputtered in reactive oxygen plasma have been studied. The properties were investigated for thin films with the Pd amount of 5.5 at. %, 8.4 at. % and 23 at. %. Based on resistivity measurements a drop from 10³ down to almost 10⁻³Ωcm has been recorded when the Pd amount was varied from 5.5 at. % to 23 at. %, respectively. Moreover, it was shown that doping with different amounts of Pd results in the possibility of obtaining both types of electrical conduction: n-type for the TiO₂ with 5.5 at. % and 8.4 at. % of Pd and p-type for the TiO₂ with 23 at. % of Pd thin films. From optical measurements it has been found that as the Pd amount was increased the transmission through the thin films was reduced and position of the fundamental absorption edge was shifted toward a longer wavelength range of up to 600 nm. The optical band gap was calculated for direct and indirect transitions from optical absorption spectra. Structural properties were characterized by X-ray diffraction (XRD) and atomic force microscopy (AFM). The XRD patterns displayed occurrence of the crystalline, TiO₂-rutile for lower Pd amounts (5.5 at. %, 8.4 at. %), while the TiO₂:Pd (23 at. %) thin films displayed XRD-amorphous behaviour. Images obtained from AFM displayed dense, nanocrystalline structure with homogenous distribution of crystallites. Additionally performed secondary ion mass spectroscopy investigation confirmed homogenous distribution of Pd in the whole thickness of the prepared thin films.     

Modeling the structure and spectral properties of sensitizing black dye for nanocrystalline TiO<Subscript>2</Subscript> solar cells

Spectral and electronic properties of a sensitizing black dye; a 4,4′,4′′-tricarboxy-2,2′:6′,2′-terpyridine)tris(isocyanato) ruthenium(II) complex; for nanocrystalline TiO₂ solar cells have been investigated by modern methods of quantum chemistry. The light absorption mechanism in the lowest excited triplet states of the dye was studied. The efficiency of electron injection into nanocrystalline TiO₂ is shown to depend on both the nature of charge-transfer states and asymmetric deformation of an excited triplet term of the black dye.     

Annealing study of electrodeposited CuInSe<Subscript>2</Subscript> and CuInS<Subscript>2</Subscript> thin films

In this study CuInSe₂ and CuInS₂ thin films were prepared onto ITO glass substrate using the electrodeposition technique in aqueous solution. The electrodeposited films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray analysis. The annealing effects on electrodeposited precursors were investigated. The chalcopyrite structure of CuInSe₂/CuInS₂ showed an enhancement of crystallinity after subsequent selenization/sulfurization treatment in Se/S atmosphere, respectively. XRD and SEM studies revealed a dramatic improvement of the crystalline quality of CIS films after annealing treatments. Mott–Schottky measurements were used to assess the conductivity type of the films and their carrier concentration. The prepared samples underwent an etching process to remove the binary accumulated Cu_2?x(Se,S) phases shown in FESEM pictures. This etching process has shown a noticeable decrease in both, the flat band potential, V_fb (V), and the number of acceptors, N_A (cm^?3) in selenized CuInSe₂ and sulfurized CuInS₂ samples.     

Effects of thickness on the infrared optical properties of Ba<Subscript>0.9</Subscript>Sr<Subscript>0.1</Subscript>TiO<Subscript>3</Subscript> ferroelectric thin films

Using infrared spectroscopic ellipsometry (IRSE), the optical properties of the Ba_0.9Sr_0.1TiO₃ (BST) ferroelectric thin films with different film thicknesses on Pt/Ti/SiO₂/Si substrates prepared by a modified sol-gel method have been investigated in the 2.5–12.6 m wavelength range. By fitting the measured ellipsometric parameter ( and ) data with a three-phase model (Air/BST/Pt) and the classical dispersion relation for the BST thin films, the optical constants and thicknesses of the thin films have been obtained. The average thickness of the single layer decreases with increasing film thickness. The refractive index of the BST films decreases with increasing thickness in the wavelength range 2.5–11 m, and increases with increasing thickness in the wavelength range 11–12.6 m. However, the extinction coefficient of the BST films monotonously decreases with increasing thickness. It is closely associated with the crystallinity of the thin films, the crystalline size effect and the influence of the interface layer. The absorption coefficient of the BST films with different thicknesses decreases with increasing thickness. PACS 77.55.+f; 78.20.Ci; 78.30.Am; 81.70.Fy; 81.40.Tv     

Lattice structure and magnetization of LaCoO<Subscript>3</Subscript> thin films

We investigate the structure and magnetic properties of thin films of the LaCoO₃ compound. Thin films are deposited by pulsed laser deposition on various substrates in order to tune the strain from compressive to tensile. Single-phase (001) oriented LaCoO₃ layers were grown on all substrates despite large misfits. The tetragonal distortion of the films covers a wide range from -2% to 2.8%. Our LaCoO₃ films are ferromagnetic with Curie temperature around 85 K, contrary to the bulk. The total magnetic moment is below 1μ _B /Co³⁺, a value relatively small for an exited spin-state of the Co³⁺ ions, but comparable to values reported in literature. A correlation of strain states and magnetic moment of Co³⁺ ions in LaCoO₃ thin films is observed.     

Antibacterial effect of silver modified TiO<Subscript>2</Subscript>/PECVD films

This paper deals with photocatalytic activity of silver treated TiO₂ films. The TiO₂ films were deposited on glass substrates by plasma enhanced chemical vapor deposition (PECVD) in a vacuum reactor with radio frequency (RF) low temperature plasma discharge in the mixture of oxygen and titanium isopropoxide vapors (TTIP). The depositions were performed under different deposition conditions. Subsequently, the surface of TiO₂ films was modified by deposition of silver nanoparticles. Photocatalytic activity of both silver modified and unmodified TiO₂ films was determined by decomposition of the model organic matter (acid orange 7). Selected TiO₂ samples were used for tests of antibacterial activity. These tests were performed on Gram-negative bacteria Escherichia coli. The results clearly proved that presence of silver clusters resulted in enhancement of the photocatalytic activity, which was up to four times higher than that for pure TiO₂ films.