TeO2 Thin Films Research Articles

TeO2: A Prospective High‐k Dielectric

Herein, high‐k dielectric behavior of TeO2 thin films is investigated. The films are prepared using pulsed laser deposition on indium tin oxide (ITO)–glass substrates. Increasing the growth temperature has improved the surface roughness, transparency, and bandgap of the films. Films grown at 500 °C display nanocrystalline nature which is reflected in the increase of bandgap to 4.7 eV and is higher than the bulk value of α‐TeO2 (3.7 eV). The nanocrystalline TeO2 films in the metal–insulator–metal configuration show a stable high permittivity of ≈19 with low leakage current (J < 1 × 10−7 A cm−2) and good voltage stability (α = 509 ppm V−2). Field‐effect modulation is observed in the metal–oxide–semiconductor stack configuration with tellurium as a semiconductor. The study suggests nanocrystalline TeO2 as a low‐temperature processable high‐k material with high transparency for transistor applications.

Observation of metallic TeO2 thin film with rutile structure on FeTe surface

Observation of metallic TeO2 thin film with rutile structure on FeTe surface

Dependence of structure and energy band gap on sensing properties of WO3:TeO2 thin films deposited by spray pyrolysis

In this paper, the sensing properties of WO3:TeO2 thin films deposited by spray pyrolysis using the oxide precursors with three different molar percentages of WO3 (0.15 M): TeO2 (0.05 M), WO3 (0.1 M): TeO2 (0.1 M) and, WO3 (0.05 M): TeO2 (0.15 M) are studied for before and after annealing at T = 773 K. The CO2 gas sensing properties of the WO3: TeO2 thin films at different molar percentages were investigated and experimental results showed that the sensing response of thin films strongly depends on the structure, morphology, and energy gap. The sensing response of thin films in terms of CO2 concentration for all compounds before and after annealing is linear and also the gradient of the curves increases after annealing. These changes in WO3 (0.15 M): TeO2 (0.05 M) are significant compared to other samples. Influences of TeO2 on the structures and morphology of the binary compounds of WO3: TeO2 thin films were investigated. X-ray diffraction results show that after annealing at T = 773 K, the WO2.92, TeO2, and H2Te2O6 phases were formed. FE-SEM images show that annealing at T = 773 K plays an important role in the morphology of the WO3: TeO2 thin films. The UV–Vis spectroscopy results showed that the bandgap of thin films decreases after annealing at T = 773 K.

Plasmon-enhanced photoluminescence from TiO2 and TeO2 thin films doped by Eu3+ for optoelectronic applications.

In this work we study the luminescence properties of europium-doped titanium dioxide and tellurium oxide thin films enhanced by gold plasmonic nanostructures. We propose a new type of plasmon structure with an ultrathin dielectric film between plasmonic platform and luminescent material. Plasmonic platforms were manufactured through thermal annealing of the gold thin film. Thermal dewetting of gold film results in spherical gold nanostructures with average dimensions of 50 nm. Both, luminescent TiO2:Eu and TeO2:Eu films were deposited by RF magnetron sputtering from mosaic targets. The morphology of the gold nanostructures was investigated by SEM and TEM, while the composition of oxides film was analyzed by XPS. Luminescence properties were studied on the basis of excitation and emission spectra. The experiments show that the additional dielectric layer enhances the luminescence intensity. Such structures could be potential candidates as phosphors in white LEDs.

Study of structural properties and J-V voltametric cyclic of MoTe2 binary thin films: Phase transition from MoO3-TeO2 to 2H-MoTe2

The structural phase transition and ionic exchange in two-dimensional transition metals oxides have very important effect on their physical properties. The MoO3-TeO2 binary compounds can be used to improve these properties. In binary compounds, this exchange occurs easily due to the formation of an oxygen vacancy. In this paper, the MoO3 - TeO2 binary compounds thin films have been deposited by spray pyrolysis technique at Ts = 400 °C and structural phase transition from MoO3-TeO2 to 2H-MoTe2 has been investigated. The molar concentration of [MoO3 - TeO2] in initial solution was changed at molar ratios (a) MoO3 (0.05 M) - TeO2 (0.15 M), (b) MoO3 (0.1 M) -TeO2 (0.1 M) and (c) MoO3 (0.15 M) - TeO2 (0.05 M). The structural and electrochromic properties of MoO3 - TeO2 thin films have been studied before and after annealing at T = 500 °C. The X-ray diffraction results of the films showed that, before annealing, the amorphous phase and after annealing at T = 500 °C, the MoO2, Te2O5, H6TeO6 and MoTe2 phases were formed. The FE-SEM images after annealing showed that, the morphology of films including nanoparticles which are almost uniformly distributed, is polygon structures. The electrochromic results showed that higher number of particles and holes in the surface of the electrochromic layers lead to the higher charge exchange rate and then the coloration. Also, in the hysteresis curve of J-V voltametric cyclic, MoO3-TeO2 compound with molar concentration of (a) MoO3 (0.05 M) - TeO2 (0.15 M) has higher area than other compounds and the diffusion coefficient of this sample has been studied before and after annealing at T = 500 °C.

Investigation of structural, optical and thermoelectric properties of 2H–MoTe2 and MoO3–TeO2 thin films

Easy synthesis of two-dimensional chalcogenide materials sach as MoTe2 and WTe2 is an important challenge for researchers. In this paper, we are showed that using Mo and Te oxides percursors as inexpensive initial materials and spray pyrolysis method, the MoO3–TeO2 thin film binary compounds, and the important two-dimensional structure of 2H–MoTe2 are prepared. . In this method, through the preparation of thin films of the MoO3–TeO2 binary composition by changing the molar concentration of Mo and Te in a solid-state reaction process, with molar ratios (a) MoO3 (0.05 M) -TeO2 (0.15 M), (b) MoO3 (0.1 M) -TeO2 (0.1 M) and (c) MoO3 (0.15 M) -TeO2 (0.05 M), we can obtain the 2H–MoTe2 phase. After synthesis of MoO3–TeO2 and 2H–MoTe2 compounds, structural and optical characterization of thin films, as well as thermoelectric properties of the prepared thin films were studied before and after annealing at T = 500 °C. X-ray diffraction results showed that the structure of thin films before annealing is amorphous structure, and after annealing at T = 500 °C for synthesis c: MoO3 (0.15 M) -TeO2 (0.05 M), the two-dimensional structure of 2H–MoTe2 was formed. The images of the field emittion scanning electron microscope (FE-SEM) showed that the morphology of the nanoparticles is the pseudo-spherical shape, rod and polygon, indicating the presence of particles in different phases at before annealing and flat – like form after annealing. The results of UV–Vis spectrometry showed that the energy gap of thin films varied in the range of 2.3–2.87 eV. The nanoparticle bonding structure was also studied by FT-IR spectroscopy. Studies on the thermoelectric properties of thin films before and after annealing showed that for synthsis (c): MoO3 (0.15 M) -TeO2 (0.05 M) with formation of the 2-H-MoTe2 phase, the seebeck coefficient was larger than other samples, and the majority carrier are holes. Also, ZT increases with decreasing molar concentration of TeO2 and reached to 1.32 at room temperature for synthesis c: MoO3 (0.15 M) -TeO2 (0.05 M).

An extensive study on the structural evolution and gamma radiation stability of TeO2 thin films

The influence of post deposition thermal annealing on the structure and gamma radiation sensing properties of thermally evaporated TeO2 thin films was studied. The as-deposited films showed amorphous nature, the crystallization into the mixed phase (tetragonal and orthorhombic) occurs on annealing at 350°C and the crystallization into the pure tetragonal structure occurs at higher annealing temperatures. The grain size in the TeO2 films grew with the increase in annealing temperature. Among the thin films investigated, the films annealed at 150°C showed the highest response and sensitivity to gamma radiation. The results also indicate the significance of the post deposition thermal annealing up to the temperature of 150°C in improving the gamma radiation sensing properties of the TeO2 films.

Temperature effect on structural, optical and NH<SUB align="right">3 gas sensing properties of TeO<SUB align="right">2 thin films

TeO2 thin films with different temperatures (400, 450 and 500°C) were deposited on glass substrates by thermal evaporation technique from a Te powder. XRD patterns indicate that as the temperature increases, the crystallisation improves. Observing the images obtained by SEM, it is seen that the grain size decreases as the temperature increases. The optical energy gap of the films was determined from transmittance and reflectance spectra. The optical energy gap decreased continuously from 3.95 eV to 3.80 eV with increasing temperature. Studying the effect of deposition temperature on NH3 gas measurement, it became obvious that as the deposition temperature increases, the sensitivity increases and the response and recovery times decrease.

Electrochemical and antimicrobial activity of tellurium oxide nanoparticles

Thin film of tellurium oxide (TeO2) has been synthesized by chemical vapour deposition method onto indium tin oxide (ITO) coated glass substrate without using any catalyst. XRD pattern of TeO2 thin film suggests that the structure of TeO2 changes from amorphous to crystalline (paratellurite) on dispersing into deionized water. Zeta potential measurement reveals a positive surface potential of 28.8mV. TEM images shows spherical shaped TeO2 nanoparticles having average particle size of 65nm. Electrochemical studies of TeO2/ITO electrode exhibit improved electron transfer owing to its inherent electron transfer property at pH 7.0 of phosphate buffer. Antimicrobial activity of TeO2 has been studied for gram-positive (Staphylococcus aureus and Streptococcus pyogenes) and gram negative (Escherichia coli and Klebsiella pneumoniae) bacterial and fungal strains (Aspergillus nizer and Candida albicans). These studies suggest that the TeO2 NPs inhibit the growth of E. coli, K. pneumoniae and S. aureus bacteria, whereas the same particles enhance the growth of S. pyogenes bacteria.

Ethanol sensing properties of TeO2 thin films prepared by non-hydrolytic sol–gel process

The microstructure and ethanol sensing properties of TeO2 thin films prepared by non-hydrolytic sol–gel process were investigated. Microstructural characterizations showed that TeO2 thin films were identified as tetragonal in the TeO2 structure. The films with porous cotton-shaped nanostructures were assembled by numerous TeO2 nanostrips with a diameter of 80–350nm and a length of 250–900nm. Non-hydrolytic process of TeO2 thin films was discussed. Gas sensing measurements demonstrated that the sensors based on TeO2 thin films obtained the highest response to ethanol gas at an operating temperature of 200°C. The sensors showed reversible and quick response to ethanol gas at various operating temperatures and ethanol concentrations. The high porosity and continuous crystalline network of TeO2 thin films are responsible for their excellent performance in ethanol gas sensing.

Deposition temperature effect on structural and gas sensing properties of TeO<SUB align="right">2 thin films

In this work, TeO2 thin films were investigated for use as hydrogen sulphide gas sensors. For this purpose, a TeO2 thin film has been deposited on ITO glass substrates by thermal evaporation and the influence of deposition temperature on structural and sensitivity of the TeO2 thin film for measuring H2S gas is studied. X-ray diffraction patterns indicate that as the deposition temperature increases, the crystallisation improves. Observing the images obtained by scanning electron microscope (SEM), it is seen that the grains join to each other and structural changes from granular to cluster with deposition temperature increase. Studying the effect of deposition temperature on H2S gas measurement, it became obvious that as the deposition temperature increases, the sensitivity decreases and the response and recovery times increase. The aim of this work was to study the effect of deposition temperature on structural and gas sensing properties of TeO2 thin films.

Fabrication of Yb3+/Er3+ codoped Bi2O3–WO3–TeO2 pedestal type waveguide for optical amplifiers

We report, for the first time to our knowledge, experimental results on pedestal waveguides produced with Yb3+/Er3+ codoped Bi2O3–WO3–TeO2 thin films deposited by RF Sputtering for photonic applications. Thin films were deposited using Ar/O2 plasma at 5mTorr pressure and RF power of 40W on substrates of silicon wafers. The definition of the pedestal waveguide structure was made using conventional optical lithography followed by plasma etching. Propagation losses around 2.0dB/cm and 2.5dB/cm were obtained at 633 and 1050nm, respectively, for waveguides in the 20–100μm width range. Single-mode propagation was measured for waveguides width up to 10μm and 12μm, at 633nm and 1050nm, respectively; for larger waveguides widths multi-mode propagation was obtained. Internal gain of 5.6dB at 1530nm, under 980nm excitation, was measured for 1.5cm waveguide length (∼3.7dB/cm). The present results show the possibility of using Yb3+/Er3+ codoped Bi2O3–WO3–TeO2 pedestal waveguide for optical amplifiers.

Effect of metal oxide sensing layers on the distinct detection of ammonia using surface acoustic wave (SAW) sensors

In the present work, SAW sensors coated with various metal oxides as sensitive layer have been exploited for distinct detection of ammonia. Thin films of different metal oxides (ZnO, SnO2, TeO2 and TiO2) of same thickness (40nm) were deposited under optimized parameters using rf sputtering technique for selective detection of liquor ammonia. As deposited ZnO thin film was highly c-axis oriented, whereas SnO2 thin film was polycrystalline. However the coatings of TiO2 and TeO2 thin films were amorphous. SAW sensor coated with ZnO film (ZnO/SAW) was found to be highly sensitive towards liquor ammonia as compared to other metal oxide coated SAW sensors. Effect of the thickness of ZnO sensing layer (20–80nm) has been studied on the sensing response characteristics. Mass loading and elastic loading are identified as the major contributions towards the response of SAW sensor for ammonia and their contributions were evaluated by fitting with the theory.

Oxide thin films (ZnO, TeO2, SnO2, and TiO2) based surface acoustic wave (SAW) E-nose for the detection of chemical warfare agents

Chemical warfare agents (CWA) are deadly chemicals even at low levels of concentration. In the present work, an electronic-nose (E-nose) comprising of an array of four surface acoustic wave (SAW) sensors having different chemical sensitive coatings of ZnO, TeO2, SnO2 and TiO2 is prepared for the detection of CWA. The oxide thin films are coated on the surface of SAW devices by rf sputtering technique. ZnO and SnO2 thin films are poly-crystalline with fine surface morphology whereas TeO2 and TiO2 thin films are amorphous. The E-nose shows good sensitivity toward the four simulants (dimethyl methylphosphonate (DMMP), dibutyl sulfide (DBS), chloroethyl phenyl sulfide (CEPS) and diethyl chlorophosphate (DECP)) of CWA allowing sub ppm level detection possible. Different simulants give distinct characteristic pattern when passed through the surface of E-nose. Using principal component analysis (PCA), the four different simulants of CWA are well separated from each other. Even with the incorporation of interferants (petrol, diesel, kerosene, VOCs and water vapors) in the PCA study, all four simulants are well separated showing the capability of the prepared SAW E-nose to classify simulants of chemical warfare agents efficiently.

Photonic Crystals on Erbium doped tellurite Thin Films for Broadband Enhanced Photoluminescence at Near Infrared

ABSTRACTTwo dimensional Er3+-TeO2 thin film photonics crystals (PhCs) are fabricated. These PhCs demonstrate broadband enhancement of PL emission at near Infrared (NIR). The PhC structures are written by dual beam focused ion beam (FIB). Highly uniformed patterns with smooth surfaces are observed. A pattern resolution better than hundred nanometers is achieved. PhCs arrays with photonic lattice constants from 350 nm to 1700 nm are examined in order to optimize the PL extraction efficiency. Strong photoluminescence around 1530 nm is observed by 488-532 nm lasers pumping. A confocal microscopy with spectrometer is used to capture the broadband PL signals from individual PhC array.The emission enhancement factor and spectral dependent extraction ratio are analyzed to find the interaction between PL lightwave and PhC structures. By optimize the PhC structures, 1500 um-1560 um broadband PL is successfully converted between the PL emission layer and the external cavity. A 60 % enhancement of surface extraction efficiency is achieved when PhC with periodicity a=800 nm is applied. When photonic lattice constants a are smaller than the critical periodicity 600 nm, the PL light becomes confined inside the thin film layer. Simulation is also performed by two dimensional finite difference time domain (FDTD) calculation in order to explain the experimental observed anisotropic PL enhancements.The broadband PL enhancement enables Er3+-TeO2 PhCs thin film as a potential light source for three dimensional integrated photonic circuits.

The real-time gamma radiation dosimetry with TeO2 thin films

A detailed study of the effect of gamma radiation on the current–voltage characteristics of the TeO2 thin films of different thicknesses, prepared by thermal evaporation in a vacuum, has been carried out for a much wider range of the gamma radiation doses than made here-to-fore. Subsequently, for the thin films of different thicknesses at different applied voltages, the variations of the current density with dose have been obtained. The current density increases near linearly with the gamma radiation dose up to a critical radiation dose, a dose value higher for the thicker films and decreases thereafter. The sensitivities of these TeO2 thin films at different applied voltages have been found to be in the range 1.2–37.0 nA/cm2/μGy. Correspondingly, the detection limits have also been estimated and have been found to be in the range 0.22–2.16 mGy. Clearly, the TeO2 thin films have high potential for their use as real-time gamma radiation dosimeters in monitoring the gamma radiation doses under a variety of practical situations involving low level to high level of the doses.

Effect of thermal annealing time on optical and structural properties of TeO2 thin films

Abstract TeO 2 thin films were deposited on quartz substrates by rf reactive sputtering technique from a Te metal target. The obtained samples were annealed in an argon atmosphere at 450 °C for different annealing times up to 90 min. X-ray diffraction studies revealed that the as-grown samples were amorphous and there was no appreciable change in structure for a short annealing time. Thin films became polycrystalline with the tetragonal ( α -phase) structure of tellurium dioxide crystal with the increase of the thermal annealing time. The refractive index and optical energy gap of the films were calculated by modelling transmittance spectra. The optical energy gap decreased continuously from 3.83 eV to 3.71 eV with increasing thermal annealing time.

Preparation and Characterization of BaO–TeO2 Thin Films Obtained from Tellurium(VI) Alkoxide by a Sol–Gel Method

BaO–TeO2 thin films were prepared from tellurium(VI) alkoxide by a sol–gel method and their structure was investigated by X‐ray diffractometry, Fourier transform infrared spectrometry, and 125Te static nuclear magnetic resonance. Their crystallization temperature (Tc), optical transmittance, and dielectric constant were measured, and their refractive index was calculated from the transmission spectra. The results indicate that the BaO–TeO2 thin films were composed of TeO6 and TeO4 units, and had a Tc of ∼520°C, refractive index of ∼1.79, dielectric constant of ∼20. These films had a Tc higher than the glass prepared by a melt‐quench method, but their refractive index and dielectric constant were lower. These differences may be due to differences in their structural units.

Effect of gamma radiation on optical and electrical properties of tellurium dioxide thin films

Gamma radiation induced changes in the optical and electrical properties of tellurium dioxide (TeO2) thin films, prepared by thermal evaporation, have been studied in detail. The optical characterization of the as-deposited thin films and that of the thin films exposed to various levels of gamma radiation dose clearly show that the optical bandgap decreases with increase in the gamma radiation dose up to a certain dose. At gamma radiation doses above this value, however, the optical bandgap has been found to increase. On the other hand, the current vs voltage plots for the as-deposited thin films and those for the thin films exposed to various levels of gamma radiation dose show that the current increases with the gamma radiation dose up to a certain dose and that the value of this particular dose depends upon the thickness of the film. The current has, however, been found to decrease with further increase in gamma radiation dose. The observed changes in both the optical and electrical properties indicate that TeO2 thin films can be used as the real time gamma radiation dosimeter up to a certain dose, a quantity that depends upon the thickness of the film.

Theoretical studies on a TeO2/ZnO/diamond-layered structure for zero TCD SAW devices

High-frequency surface acoustic wave (SAW) devices based on diamond substrate are useful because of their very high SAW velocity. In the present work, SAW propagation characteristics, such as phase velocity, coupling coefficient and temperature coefficient of delay (TCD) of a TeO2/ZnO/diamond-layered structure, are examined using theoretical calculations. The ZnO/diamond bi-layer structure is found to exhibit a high positive TCD value. A zero TCD device structure is obtained after integration with a TeO2 over layer having a negative TCD value. Introduction of a non-piezoelectric TeO2 over layer on the bi-layer structure (ZnO/diamond) increases the coupling coefficient. A relatively low thickness of TeO2 thin film (∼(1.6–3.1) × 10−3λ) is required to achieve temperature-stable SAW devices based on diamond.