Preparation and characterization of TiO2 thin film by thermal oxidation of sputtered Ti film

Titanium dioxide (TiO₂) thin films were successfully prepared on quartz substrate by thermal oxidation of sputtered titanium film in air. The structure, composition, morphology and optical properties of oxidized TiO₂ films were characterized by Raman spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, atomic force microscopy and UV-visible spectroscopy. Meanwhile, the photocatalytic activity of the films was evaluated on the basis of the degradation of methyl orange solution under UV irradiation. Ti films after oxidation present mainly in TiO₂ form with a larger amount of adsorbed O₂, and oxidation temperature has a strong impact on the crystal structure and properties of the films. A phase transformation of anatase to rutile for oxidized TiO₂ films occurred in the temperature range of 700–800 °C. The energy band gap of oxidized TiO₂ films decreased first and then increased with annealing temperature. Furthermore, TiO₂ film oxidized at 600 °C exhibited the best photocatalytic activity due to suitable crystal phase and size. These results might contribute to the synthesis of metal oxide thin films with expectant structural morphology and properties by thermal oxidation methods.     

Control of the Ti diffusion in Pt/Ti bottom electrodes for the fabrication of PZT thin film transducers

For the achievement of microactuators based on piezoelectric thin films, a Pt/Ti/Si bottom electrode is widely used. This study presents the experimental results for Ti out-diffusion in Pt and Si for both sputtered Pt/Ti and Pt/TiO_x electrodes. These results have been compared before and after a rapid thermal annealing (RTA). The diffusion has been characterized by secondary ion mass spectroscopy (SIMS) analysis using Cs⁺ as a primary ion source. The Pt orientation has been observed by XRD measurements. Ti thin films (20 nm) have been sputtered in pure Ar whereas TiO_x films have been obtained by reactive sputtering in a mixture of Ar/O₂ (90/10). Finally, the Pt (100 nm) has been sputtered without vacuum breaking. After RTA (400°C, 30 s, in N₂), the Pt film exhibited a (1 1 1) orientation for both Ti and TiO_x adhesion films. The roughness of the Pt film measured by AFM with TiO_x underlayer was 80% less than that of the Pt/Ti bi-layer. The TiO_x film, as shown by SIMS analysis, has drastically reduced the diffusion of Ti in both Pt and Si. This phenomenon is accompanied by a very low Pt roughness. These results are analyzed in terms of diffusion and regrowth mechanisms inside the Pt film.     

Low temperature TiO2 rutile phase thin film synthesis by chemical spray pyrolysis (CSP) of titanyl acetylacetonate

Rutile phase TiO₂ thin films have been synthesized using chemical spray pyrolysis of titanyl acetylacetonate TiAcAc in ethanol at 500 °C. The first part of the paper focuses on the thermal decomposition behavior of the precursor by simultaneous thermogravimetry and differential thermal analysis (TG/DTA) coupled with differential scanning calorimetry (DSC). The second part of the paper focuses on the evolution of TiO₂ thin films and their structural transformation with substrate temperature. XRD revealed amorphous TiO₂ thin film at low substrate temperatures (<350 °C) and on high substrate temperatures anatase (3.84 g/cm³) or rutile (4.25 g/cm³) crystalline structure was obtained. The lattice constant, grain size, microstrain and the dislocation density of the film were obtained from the peak width. FTIR spectra of both anatase and rutile TiO₂ revealed stretching vibration of the Ti–O bond for tetrahedral and octahedral surroundings of the titanium atom. Scanning electron micrograph showed the compactness of the rutile film.     

Photocatalytic activity of TiO2/Ti composite coatings fabricated by mechanical coating technique and subsequent heat oxidation

Titanium (Ti) coatings were fabricated on alumina (Al₂O₃) balls by mechanical coating technique (MCT) with Ti powder. The Ti coatings were then oxidized to titanium dioxide (TiO₂) coatings at different temperatures. The oxidation behavior and microstructure evolution of these coatings were investigated. The results showed that the inner and surface layers of the Ti coatings were oxidized simultaneously. When oxidizing at a relatively low temperature for a short time, TiO₂/Ti composite coatings were obtained. Increasing the oxidation temperature or time increased the thickness of the TiO₂ layer and eventually Ti coatings were totally oxidized to TiO₂ coatings. During oxidation, TiO₂ needles formed at a lower temperature grew to generate columnar crystals. The photocatalytic activity of these coatings was examined. Compared with TiO₂ coatings, the TiO₂/Ti composite coatings showed much higher photocatalytic activity. The highest activity was observed for the TiO₂/Ti composite coatings prepared by MCT and subsequent oxidation at 1073 K for 15 h and then the thickness of the TiO₂ layer was 27 μm.     

Synthesis of Sn doped ZnO/TiO2 nanocomposite film and their application to H2 gas sensing properties

Tin doped Zinc oxide/Titanium oxide nanocomposite (TZO/TiO₂) was prepared by two methods: TiO₂ nanotube (Nt) arrays are grown by anodic oxidation of titanium foil and TZO films was deposited on the TiO₂ Nt obtained by hydrothermal process. The morphological characteristics and structures of ZnO/TiO₂ and TZO/TiO₂ were examined by (scanning elecron miscroscopy) SEM, (X rays diffraction) XRD and (energy dispersive spectroscopy) EDS analysis. The diameter of TiO₂ Nts was ranged from 40 nm to 90 nm with wall thicknesses of approximately 10 nm. The anatase structure of Titania, the hexagonal Zincite crystal of zinc oxide and tetragonal structure of tin oxide were identified by XRD. EDS analysis revealed the presence of O, Zn, Ti and Sn elements in the obtained deposits.These nanocomposites have been used as active layer in hydrogen gas sensing application. The hydrogen sensing characteristics of the sensor was analyzed by measuring the sensor responses in the temperature of 100 °C and 160 °C. The highest gas response is approximately 1.48 at 160 °C.The sensing mechanism of the nanocomposite sensor was explained in terms of H₂ chimisorption on the highly active nanotube surface.     

A study of ultrasonic spray pyrolysis deposited rutile-TiO2-based metal-semiconductor-metal ultraviolet photodetector

This work uses ultrasonic spray pyrolysis deposition to grow the TiO₂ film on a Si substrate. The TiO₂ film was annealed at 800 °C for 2 h to form rutile phase. X-ray diffraction, Raman spectrum, X-ray photoelectron spectroscopy were used to characterized rutile phase TiO₂. The optical characteristics like refractive index, extinction coefficient and absorption coefficient were measured. The rutile TiO₂-based metal-semiconductor-metal ultraviolet photodetector was fabricated and investigated, including current-voltage characteristic, photoresponsivity, external quantum efficiency, response time, noise equivalent power, and detectivity.     

The significant effect of film thickness on the properties of chalcopyrite thin absorbing films deposited by RF magnetron sputtering

In this paper, thickness dependent structural, surface morphological, optical and electrical properties of RF magnetron sputtered CuIn_0.8Ga_0.2Se₂ (CIGS) thin films were studied using X-ray diffraction (XRD), Transmission electron microscopy (TEM), Field emission scanning electron microscopy (FE-SEM), Atomic force microscopy (AFM), UV–vis–NIR spectrophotometer and Keithley electrical measurement unit. The peak intensity along (112) plane as well as crystallite size was found to increase with thickness. However, for higher film thickness >1.16 μm, crystallinity reduced due to higher % of Cu content. TEM analysis confirmed pollycrysallinity as well as chalcopyrite phase of deposited films. The band gap was found to decrease with increase in thickness yielding a minimum value of 1.12 eV for film thickness 1.70 μm. The I–V characteristics showed the ohmic behavior of metal semiconductor contact with higher conductivity for film thickness 1.16 μm.     

Structural and optoelectronic properties of nanostructured TiO2 thin films with annealing

About 480 nm thick titanium oxide (TiO₂) thin films have been deposited by electron beam evaporation followed by annealing in air at 300–600 °C with a step of 100 °C for a period of 2 h. Optical, electrical and structural properties are studied as a function of annealing temperature. All the films are crystalline (having tetragonal anatase structure) with small amount of amorphous phase. Crystallinity of the films improves with annealing at elevated temperatures. XRD and FESEM results suggest that the films are composed of nanoparticles of 25–35 nm. Raman analysis and optical measurements suggest quantum confinement effects since Raman peaks of the as-deposited films are blue-shifted as compared to those for bulk TiO₂ Optical band gap energy of the as-deposited TiO₂ film is 3.24 eV, which decreases to about 3.09 eV after annealing at 600 °C. Refractive index of the as-deposited TiO₂ film is 2.26, which increases to about 2.32 after annealing at 600 °C. However the films annealed at 500 °C present peculiar behavior as their band gap increases to the highest value of 3.27 eV whereas refractive index, RMS roughness and dc-resistance illustrate a drop as compared to all other films. Illumination to sunlight decreases the dc-resistance of the as-deposited and annealed films as compared to dark measurements possibly due to charge carrier enhancement by photon absorption.     

Sputtered oxides used for passivation layers of amorphous InGaZnO thin film transistors

Four sputtered oxide films (SiO₂, Al₂O₃, Y₂O₃ and TiO₂) along with their passivating amorphous InGaZnO thin film transistors (a-IGZO TFTs) were comparatively studied in this paper. The device passivated by an Al₂O₃ thin film showed both satisfactory performance (μ_FE=5.3 cm²/V s, I_on/I_off>10⁷) and stability, as was probably related to smooth surface of Al₂O₃ thin films. Although the performance of the a-IGZO TFTs with a TiO₂ passivation layer was also good enough (μ_FE=3.5 cm²/V s, I_on/I_off>10⁷), apparent V_th shift occurred in positive bias-stress tests due to the abnormal interface state between IGZO and TiO₂ thin films. Sputtered Y₂O₃ was proved no potential for passivation layers of a-IGZO TFTs in this study. Despite unsatisfactory performance of the corresponding a-IGZO TFT devices, sputtered SiO₂ passivation layer might still be preferred for its high deposition rate and excellent transparency which benefit the mass production of flat panel displays, especially active-matrix liquid crystal displays.     

Effect of substrate biasing and temperature on AlN thin film deposited by cathodic arc ion

Aluminum nitride (AlN) films have been grown in pure N₂ plasma using cathodic arc ion deposition process. The films were prepared at different substrate bias voltages and temperatures. The aim was to investigate their influence on the Al macro-particles, structural and optical properties of deposited films. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, Scanning electron microscope (SEM) and Rutherford backscattering spectrometry (RBS) were employed to characterize AlN thin films. XRD patterns indicated the formation of polycrystalline (hexagonal) films with preferential orientation of (002), which is suppressed at higher substrate bias voltage. FTIR and Raman spectroscopic analysis were used to assess the nature of chemical bonding and vibrational phonon modes of AlN thin films respectively. FTIR spectra depicted a dominant peak around 850 cm^?1 corresponding to the longitudinal optical (LO) mode of vibration. A shift in this LO mode peak towards higher wavenumbers was observed with the increase of substrate bias voltage and temperature, showing the upsurge of nitrogen concentration in the deposited film. Raman spectra illustrated a peak at 650 cm^?1 corresponding to E₂ (high) phonon mode depicting the c-axis oriented (perpendicular to substrate) AlN film. SEM analysis showed the AlN film deposited at higher substrate bias voltage contains fewer amounts of Al macro-particles.     

Synthesis and characterization of TiO2-doped Polyaniline nanocomposites by chemical oxidation method

Polyaniline (PANI)/TiO₂ nanocomposite samples with various dopant percentages of TiO₂ were synthesized at room temperature using a chemical oxidative method. The samples were characterized by ultraviolet-visible spectrometer, Fourier transform infrared (FTIR) spectrometer, X-ray diffraction (XRD), scanning electron microscopy (SEM), EDAX and conductivity measurements. Incorporation of TiO₂ nanoparticles caused a slight red shift at 310 nm in the absorption spectra due to the interactions between the conjugated polymer chains and TiO₂ nanoparticles with π–π^? transition. FTIR confirmed the presence of TiO₂ in the molecular structure. In PANI/TiO₂ composites, two additional bands at 1623 cm^?1 and 1105 cm^?1 assigned to Ti–O and Ti–O^–C stretching modes were present. It can be concluded that Ti organic compounds are formed with an alignment structure of TiO₂ particles. XRD patterns revealed that, as the TiO₂ percentage was increased, the amorphous nature disappeared and the composites became more strongly oriented along the (1 1 0) direction, which showed the tetragonal structure of nanocrystalline TiO₂. SEM studies revealed the formation of uniform granular morphology with average grain size of 200 nm for (50%) PANI/TiO₂ nanocomposite samples.     

Effects of annealing technique and TiO2 seed layer on the phase composition of 0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 film

The lead magnesium niobate–lead titanate (PMN–PT) thin films with and without the TiO₂ seed layer were prepared by a pulsed laser deposition (PLD) deposited on Pt/Ti/SiO₂/Si substrates. The films were treated by two-step annealing and normal annealing with rapid thermal annealing (RTA). The effects of two-step annealing and the TiO₂ seed layer on the phase composition of PMN–PT films were studied. The results show that the PMN–PT film with TiO₂ seed layer can gain a pure perovskite phase with a high (1 0 0) preferential orientation after the two-step annealing technique.     

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

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

Characterization of cadmium sulfide/titania heterostructure films by utilizing microstructure and optical characteristics

Engineering and controlling the bandgap of semiconducting metal oxide (TiO₂) to enhance photoactivity under visible light is challenging. Impact of the changing CdS thickness (50–150 nm) on the structure and optical properties of the CdS/TiO₂ heterostructure films (HSFs) which fabricated by pulsed laser deposition (PLD) was observed. XRD, FE-SEM, AFM, UV–vis and PL spectroscopy measurements were utilized to characterize structural and optical behaviors of the films. XRD measurement shows gradual increments of the lattice constants of the films with the increase of CdS thickness. The mean values of the calculated lattice constants and cell volume (V) were a=b=0.3785 nm, c=0.9475 nm and V=13.58 nm³ respectively. The average of crystallite sizes estimated for TiO₂ and CdS/TiO₂ at various CdS thickness is 12.20, 13.49, 24.24 and 43.10 nm. FESEM images prove the high quality nanocrystalline nature of the films without cracks and dislocation. The root means square roughness of the films was increased with the increase of CdS thickness as showed by AFM images. UV–vis measurement reveals an improvement in the optical absorbance of HSFs in the range of 380–550 nm due to presence of CdS. Interestingly, the PL intensity was enhanced by a factor of nineteen compare to pure TiO₂ attributed to the charge carrier recombination in the band gap. The current results suggest that possibility to improve the optical and structural properties of the TiO₂ films and also it possible to fabricate high quality CdS/TiO₂ HSFs by variation of the CdS thickness.     

Effect of annealing on the structural and optical properties of laser ablated nanostructured barium tungstate thin films

High quality BaWO₄ thin films are successfully deposited on quartz substrate for a duration of 30 min using pulsed laser ablation technique and using a laser radiation of wavelength 355 nm and the effect of thermal annealing on the structural and optical properties is studied by using techniques like X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy, micro-Raman, FTIR and UV–visible spectroscopy. All the films show monoclinic crystalline structure with (2 0 2) plane as the preferred orientation of crystal growth. From the XRD analysis it is found that the optimum annealing temperature for better crystallization of the BaWO₄ film is 700 °C and there is no phase change observed with annealing temperature. The presence of the characteristic bands for the BaWO₄ in the Raman spectra of the films suggests the formation of BaWO₄ crystalline phase in all the films. SEM and AFM analyses show that as the annealing temperature increases the connectivity between individual grains increases and shows an ordered packing. The geometrical optimization and energy calculation of the title compound were done using the Gaussian 09 software package and the calculations were carried out using the CAM-B3LYP functional combined with standard Lanl2Dz basis set. The thickness of the films was calculated using lateral SEM images and also from optical transmission spectral data using PUMA software.     

Synthesis of highly selective and sensitive Cu-doped ZnO thin film sensor for detection of H2S gas

Copper (Cu) doped zinc oxide (ZnO) thin films were successfully prepared by a simple sol-gel spin coating technique. The effect of Cu doping on the structural, morphology, compositional, microstructural, optical, electrical and H₂S gas sensing properties of the films were investigated by using XRD, FESEM, EDS, FTIR, XPS, Raman, HRTEM, and UV–vis techniques. XRD analysis shows that the films are nanocrystalline zinc oxide with the hexagonal wurtzite structure and FESEM result shows a porous structured morphology. The gas response of Cu-doped ZnO thin films was measured by the variation in the electrical resistance of the film, in the absence and presence of H₂S gas. The gas response in relation to operating temperature, Cu doping concentration, and the H₂S gas concentration has been systematically investigated. The maximum H₂S gas response was achieved for 3 at% Cu-doped ZnO thin film for 50 ppm gas concentration, at 250 °C operating temperature.     

Ni and Ti silicide oxidation for CMOS applications investigated by XRD,XPS and FPP

Although silicide oxidation was studied 20 years ago, the interest of obtaining a robust process for new application appears significant today. Indeed, for the new architectural development process are required dense and narrow spaces. This paper focuses to bury a silicide layer under a protective layer such as silica in order to keep constant the physical and electrical properties of silicide after oxidation. Earlier works show the possibility to oxidize preferably the silicon (Si) in metal contained silicide rather than a pure crystalline Si at high temperatures. Thus, we first tried to reproduce and study these conditions and once acquired, targeted to decrease the oxidation temperature in order to fit with industrial requirements. Titanium (Ti) and Nickel (Ni) are chosen for their metallurgical interest and their integration capability in devices. Thus, four different group/phases (TiSi, TiSi₂, Ni₂Si, NiSi) of silicide were targeted by adjusting the temperature. In situ X-ray diffraction (XRD), photoelectron spectroscopy and sheet resistance (four point probe) measurements were carried out simultaneously before and after oxidation of silicide to characterize the phase and chemical composition. After silicide formation last three phases (TiSi₂, Ni₂Si, NiSi) were confirmed by XRD and G1(Ti/Si) was unknown, where only for NiSi was observed the low sheet resistance (≈7.3 Ω/□) and resistivity (18 μΩ·cm). After (dry, wet and plasma) oxidation, the phases of TiSi₂ and Ni₂Si changed and only NiSi was observed the constant phase, even pure SiO₂ was noted on NiSi after wet oxidation.     

Effects of silver substrates on the visible light photocatalytic activities of copper-doped titanium dioxide thin films

Novel copper-doped titanium dioxide (Cu-doped TiO₂) thin films on silver (Ag) substrates with different thicknesses were prepared by sol–gel and magnetron sputtering methods. The influences of the Ag substrate thickness on the morphology and performance of the films were investigated by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, photoluminescence spectroscopy, UV–visible spectroscopy, and photocatalytic degradation testing with methylene blue aqueous solution under visible light irradiation. The results indicated that Ag substrates with an optimal thickness of 30 nm not only maintained the tiny nanocrystals but also greatly improved dispersion of the nanoparticles on the surface of the nanofilms. Furthermore, during the calcination process, part of the Ag atoms diffused from the substrates into the Cu–TiO₂ films and substituted for the Cu ions to form Ag–TiO₂. A proper Ag substrate thickness (30 nm) greatly improved the photocatalytic properties of TiO₂ with photocatalytic efficiency, reaching approximately 86% in 300 minutes under visible light irradiation. However, an excess of Ag substrate not only led to the Cu ion separating out in the form of CuO but also resulted in the agglomeration of TiO₂ particles on the surface, which were detrimental to photocatalytic activities.     

P-silicon thin film fabricated by magnetron sputtering and aluminium induced crystallization for Schottky silicon solar cells

Solar cells consist of n-Si wafer and p-Si polycrystalline thin film, which was solely fabricated by magnetron sputtering, and aluminium induced crystallization, are presented in this paper. Firstly, the material and electrical properties of the fabricated p-Si thin films including the crystallization ratio, grain size, morphology, carrier density and mobility were studied by Raman spectroscopy, X-ray diffraction (XRD), scanning electron microscopy and Hall Effect measurement, respectively. The p-Si polycrystalline thin film formed under optimal process conditions had the crystallization ratio of ~ 99% and the grain size of ~ 64.6 nm, determined from the data of Raman spectroscopy and XRD. The hole concentration in the fabricated p-Si polycrystalline thin films was mainly in the order of 10¹⁷ cm⁻³ to 10¹⁹ cm⁻³, and their corresponding mobility values ranged from 15 cm²/V s to 65 cm²/V s. Then solar cells with the device structure of Al electrode/n-Si wafer/p-Si thin film/Al electrode were fabricated, and their electrical properties were measured both under dark and illumination conditions by the semiconductor performance tester and solar simulator. The measured J-V curves under dark condition confirmed the creation of a p-n junction with the ideality factor of 1.55, rectification ratio of 410 at ± 1 V, and the reverse saturation current of 246 nA/cm². The efficiency of 2.19%, with an open circuit voltage of 448 mV and a short circuit current density of 11.2 mA/cm², was achieved under AM1.5G standard illuminations.     

XPS analysis and characterization of thin films Cu2ZnSnS4 grown using a novel solution based route

A new technique to grow single phase Cu₂ZnSnS₄ (CZTS) thin films for solar cells applications using a chemical route is presented; this consist in sequential deposition of Cu₂SnS₃ (CTS) and ZnS thin films followed by annealing at 550 °C in nitrogen atmosphere, where the CTS compound is prepared in one step process by simultaneous precipitation of Cu₂S and SnS₂ performed by diffusion membranes assisted CBD (chemical bath deposition) technique and ZnS by conventional CBD technique.Measurements of X-ray diffraction (XRD), Raman spectroscopy and scanning electron microscopy (SEM) were used to identify the phases present in the CTS and CZTS films as well as to study their structural and morphological properties. Further, the oxidation states and the chemical composition homogeneity in the volume were studied by X-ray photoelectron spectroscopy (XPS) analysis. Oxidation states and results regarding structural and morphological characterization of CZTS films prepared using the novel technique are compared with those results obtained from single phase CZTS films prepared by sequential evaporation of metallic precursors in presence of elemental sulfur. XRD and Raman spectroscopy studies were used to verify that the CZTS films prepared by the novel method do not present secondary phases.