Absorbing TiOx thin film enabling laser welding of polyurethane membranes and polyamide fibers

We report on the optical properties of thin titanium suboxide (TiO_x) films for applications in laser transmission welding of polymers. Non-absorbing fibers were coated with TiO_x coatings by reactive magnetron sputtering. Plasma process parameters influencing the chemical composition and morphology of the deposited thin films were investigated in order to optimize their absorption properties. Optical absorption spectroscopy showed that the oxygen content of the TiO_x coatings is the main parameter influencing the optical absorbance. Overtreatment (high power plasma input) of the fiber surface leads to high surface roughness and loss of mechanical stability of the fiber. The study shows that thin substoichiometric TiO_x films enable the welding of very thin polyurethane membranes and polyamide fibers with improved adhesion properties.     

Microstructure and Optical Properties of Tantalum Modified TiO<Subscript>2</Subscript> Thin Films Prepared by the Sol–Gel Process

Tantalum doped TiO₂ thin films ((TiO₂)_1−x (Ta₂O₅) _x , x=0, 0.1%, 0.3%, 0.5%, 0.8%) were prepared on ITO-coated substrates by means of the sol–gel method and spin coating technology followed by rapid thermal annealing treatment (RTA). The effects of various processing parameters, including Ta content (x=0–0.8%) and annealing temperature, on the growth and properties of thin films were investigated. Structural characteristics by X-ray diffraction analysis indicated that the doping of Ta₂O₅ in the TiO₂ without change the anatase structure of TiO₂ thin films. The optical transmittance of (TiO₂)_1−x (Ta₂O₅) _x thin films decrease from 50% down to 20% with increasing the Ta₂O₅ concentrations from x=0.00 to x=0.8%. The absorption coefficient shows energy gap were decreased with increasing Ta₂O₅ content from 2.932 eV for x=0.00 to 2.717 eV for x=0.8%. Doping TiO₂ with Ta₂O₅ can lower its band gap and shift its optical response to the visible region.     

Electrical and optical properties of reactive sputtered TiO x thin films for uncooled IR detector applications

Nanostructured titanium oxide (nano-TiO _x ) thin films for uncooled IR detectors were fabricated by dc reactive magnetron sputtering and post-deposition annealed in oxygen atmosphere. The crystalline structure and surface morphology were characterized by glancing incidence X-ray diffraction (GIXRD) and field emission scanning microscopy. The results of GIXRD measurements indicate that TiO _x thin film deposited at room temperature is amorphous. A mixture of anatase and rutile nanocrystalline structure phase were present in oxygen annealed TiO _x thin film. A weak absorption peak around 438 cm^?1 corresponding to Ti–O stretching vibration is observed by Fourier transform infrared spectroscopy with annealed TiO _x thin film. The X-ray photoelectron spectra reveals Ti³⁺ and Ti⁴⁺ ions are coexisting in TiO _x films. The optical spectra of the films indicate that the optical absorption edge of the nano-TiO _x film exhibits a red shift compared to the as-deposited film. Furthermore, compared to bulk TiO _x , a blue shift was observed in both of the deposited and annealed films due to quantum size effect. The dependence of resistivity on temperature reveals both the absolute value of temperature coefficient of resistivity (TCR) and activation energy of TiO _x thin film increase significantly after annealing in oxygen.     

Influence of Nd dopant amount on microstructure and photoluminescence of TiO2:Nd thin films

TiO₂ and TiO₂:Nd thin films were deposited using reactive magnetron sputtering process from mosaic Ti–Nd targets with various Nd concentration. The thin films were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM) and spectroscopic techniques. Photoluminescence (PL) in the near infrared obtained upon 514.5 nm excitation was also examined. The relationship between the Nd concentration, structural, optical and photoluminescence properties of prepared thin films was investigated and discussed. XRD and TEM measurements showed that an increase in the Nd concentration in the thin films hinders the crystal growth in the deposited coatings. Depending on the Nd amount in the thin films, TiO₂ with the rutile, mixed rutile–amorphous or amorphous phase was obtained. Transmittance measurements revealed that addition of Nd dopant to titania matrix did not deteriorate optical transparency of the coatings, however it influenced on the position of the fundamental absorption edge and therefore on the width of optical band gap energy. All TiO₂:Nd thin films exhibited PL emission that occurred at ca. 0.91, 1.09 and 1.38 μm. Finally, results obtained for deposited coatings showed that titania with the rutile structure and 1.0 at.% of Nd was the most efficient in VIS to NIR photon conversion.     

A.c. photoconductivity and optical properties of bulk polycrystalline and amorphous In x Se1−x thin films

The a.c. photoconductivity of bulk polycrystalline In _x Se_1–x and the optical properties of amorphous In _x Se_1–x thin films were investigated. The effect of heat treatment on the absorption coefficient of InSe thin films was also studied. The spectral response of the photoconductivity of polycrystalline In _x Se_1–x related to the near-edge absorption spectrum, shows a well-defined maximum corresponding to the width of the forbidden gap. Polycrystalline In _x Se_1–x realizes the behaviour of photoconductors which are sensitive in a spectral range between 400 and 1700 nm. Optical absorption of amorphous In _x Se_1–x thin films was recorded as a function of photon energy and the data were used to deduce the value of optical energy gap of the films. It was found that the optical energy gap decreased with increasing indium content in both bulk polycrystalline and amorphous thin films. The effect of heat treatment on the optical gap of the film has been interpreted in terms of the density of states model of Mott and Davis.     

Measurement of Thermal Conductivity of TiO2 Thin Films Using 3ω Method

TiO₂ film has been used in many industrial components such as laser filters, protection mirrors, chemical sensors, and optical catalysts. Therefore, the thermal properties of TiO₂ thin films are important in, e.g., reducing the thermal conductivity of ceramic coatings in gas turbines and increasing the laser damage threshold of antireflection coatings. The thermal conductivity of four kinds of TiO₂ thin films, prepared by dc magnetron sputtering, was measured using the 3 method in the temperature range from 80 K to room temperature. The results showed that the thermal conductivity of TiO₂ thin films strongly depends on the thickness and the microstructure of the films. The films with smaller grain size and thinner thickness have smaller thermal conductivities.     

Effects of ion energy on internal stress and optical properties of ion-beam sputtering Ta2O5 films

Abstract

The effects of ion-beam energy on the internal stress and optical properties of tantalum pentoxide (Ta₂O₅) thin film have been investigated. Ta₂O₅ thin films were deposited on unheated glass substrates by ion-beam sputter deposition (IBSD) with different ion-beam voltage V _b. The mechanical properties, internal stress and surface roughness, and the optical properties, refractive index and absorption, were studied directly after deposition. The refractive index, extinction coefficient and surface roughness were found to depend on the ion-beam energy. The internal stresses were measured by the phase-shifting interferometry technique. The film stress was also found to be related to V _b, and a high compressive stress of -0.560 GPa was measured at V _b = 750 V. Ta₂O₅/SiO₂ multilayer coatings had smaller average compressive stress than single-layer Ta₂O₅ film.     

Preparation and properties of Bi2−x As x S3 thin films by solution-gas interface technique

The solution gas interface technique by which thin films of Bi_2−x As _x S₃ were deposited is described in this paper. The semiconducting properties of the interface grown Bi_2−x As _x S₃ thin films are studied. The optical absorption, dark resistivity and thermoelectric power of the films were studied and results are reported.     

TiOx/Ag/TiOx multilayer for application as a transparent conductive electrode and heat mirror

Amorphous TiO_x films and Ag layer were deposited by electron-beam evaporation on soda-lime glass at room temperature. The details regarding the structure, surface morphology, and optical properties of the as-prepared TiO_x films were examined by X-ray diffraction, scanning electron microscopy, and ultra-violet (UV) -visible-near-infrared (NIR) spectrometry. The TiO_x films exhibit amorphous phase with an optical band gap of 3.35 eV. The polygrains oriented along the (111) and (200) directions in the Ag films were adopted to supply carriers into the TiO_x film and lower the sheet resistance of the stacked layer. The multilayer exhibited a sufficiently large Ag thickness (>15 nm), low resistance, high UV transmittance, visible transmittance, and high NIR reflection. Dependence of Ag thickness, TiO_x bottom-layer, and TiO_x overlayer on the optical and electrical properties of TiO_x/Ag/TiO_x were explored. A figure of merit (FOM) was used to find an optimal structure for a multilayer with superior conductivity and visible transparency. An FOM of 9.8 × 10^?2 (Ω^?1) at the visible wavelength of 550 nm for a TiO_x/Ag/TiO_x stacked layer with an 18-nm-thick Ag and a 20-nm-thick TiO_x was achieved. The TiO_x/Ag/TiO_x sample annealed at 500 °C 10 min also shows a good thermal stability.     

Some optical properties of Se-Ge-As amorphous chalcogenide glasses

The effects of composition, film thickness, substrate temperature, and annealing of amorphous thin films of Se₇₅Ge_25−x As _x (5⩽x⩽20) on their optical properties have been investigated. X-ray diffraction revealed the formation of amorphous films. The absorbance and transmission of vacuum-evaporated thin films were used to determine the band gap and refractive index. Optical absorption measurements showed that the fundamental absorption edge is a function of glass composition and the optical absorption is due to indirect transition. The energy gap increases linearly with increasing arsenic content. The optical band gap,E _opt, was found to be almost thickness independent. The shapes of the absorption edge of annealed samples displayed roughly the same characteristic as those of the unannealed films, but were shifted towards shorter wavelengths; as a result,E _opt increased andE _e, the width of the band tails, decreases. The increase inE _opt is believed to be associated with void removal and microstructural re-arrangement during annealing. The influence of substrate temperature on the optical parameters is discussed.     

Effect of excess Pb in PbTiO<Subscript>3</Subscript> precursors on ferroelectric and fatigue property of sol–gel derived PbTiO<Subscript>3</Subscript>/PbZr<Subscript>0.3</Subscript>Ti<Subscript>0.7</Subscript>O<Subscript>3</Subscript>/PbTiO<Subscript>3</Subscript> thin films

A series of Pb_(1+x)TiO₃/PbZr_0.3Ti_0.7O₃/Pb_(1+x)TiO₃ (PTO/PZT/PTO) and PbZr_0.3Ti_0.7O₃ (PZT) thin films were prepared by a sol–gel method. Different excess Pb content (x) (x = 0, 0.05, 0.10, 0.15, 0.20) were added to the PbTiO₃ (PTO) precursors to investigate their effect on ferroelectric and fatigue properties of the PTO/PZT/PTO thin films. X-ray diffraction results show that the crystallization behavior of the PTO/PZT/PTO thin films is greatly affected by the excess Pb content (x) in PTO precursors. Topographic images show that the PTO/PZT/PTO thin films with excess Pb content x = 0.10 appears the densest and the most uniform grain size surface morphology. The ferroelectric and fatigue properties of the films correlate straightforwardly to the crystallization behaviors and excess Pb content (x) in the PTO precursors. The excess Pb content (x) in the PTO layers which acts as a nucleation site or seeding layer for PZT films affects the crystallization of the PTO layer and ultimately affects the perovskite phase formation of the PZT films. With the proper excess Pb content (x = 0.10–0.15) in the PTO precursors, the pure perovskite structure PTO/PZT/PTO thin films, with dense, void-free, and uniform fine grain size are obtained, and a well-saturated hysteresis loop with higher remnant polarization is achieved. Using an appropriate Pb content, the fatigue has been avoided by controlling the inter-diffusion and surface volatilization.     

Structure and phase composition of thin TiO<Subscript>2</Subscript> films grown on the surface of metallized track-etched polyethylene terephthalate membranes by reactive magnetron sputtering

We have studied TiO₂, Ag, Ag/TiO₂, and Cu/TiO₂ coatings grown on track-etched polyethylene terephthalate membranes. The metals and oxides were deposited by reactive vacuum sputtering using a planar magnetron. The microstructure of the samples were examined by scanning and transmission electron microscopy techniques. The elemental composition of the coatings were determined by energy dispersive X-ray microanalysis, and their phase composition was determined by X-ray diffraction at different temperatures and by transmission electron diffraction. Titanium dioxide can be present on the surface of track-etched membranes (TMs) in three forms: nanocrystals of tetragonal anatase with orthorhombic brookite and amorphous TiO₂ impurities. The copper-metallized TM has been shown to contain cubic Cu₂O. The optical properties of the composite membranes and films have been studied by absorption spectroscopy. The energies of direct and indirect allowed optical transitions have been evaluated from measured absorption spectra of the TiO₂, Ag/TiO₂, and Cu/TiO₂ coatings.     

Investigation of structural,optical and micro-mechanical properties of (NdyTi1 − y)Ox thin films deposited by magnetron sputtering

TiO₂ and (Nd_yTi_1 − y)O_x thin films were deposited by reactive magnetron sputtering process from mosaic Ti–Nd targets and characterised by X-ray diffraction (XRD), Raman optical spectroscopy and nanoindentation technique. XRD measurements revealed that as-prepared titanium dioxide and TiO₂ thin films with 4 and 7 at.% of Nd had nanocrystalline rutile structure, while coatings with larger amount of Nd were amorphous. Raman spectroscopy investigations showed that the increase of the neodymium concentration caused amorphisation of the coatings and hindered their crystal growth. All as-prepared coatings were transparent in the visible wavelength range with a transmittance of approximately 80%. The refractive index and extinction coefficient of the thin films gradually decreased with the increase of the neodymium concentration. Micro-mechanical properties, i.e. hardness and elastic modulus, were determined using traditional load-controlled nanoindentation testing and continuous stiffness measurements. The highest hardness and elastic modulus values were obtained for thin films with 7 at.% of Nd and were approximately 14.8 GPa and 166.3 GPa, respectively.     

Nanocrystalline sol–gel TiO2–SnO2 coatings: Preparation,characterization and photo-catalytic performance

In this study, preparation of SnO₂ (0–30 mol% SnO₂)–TiO₂ dip-coated thin films on glazed porcelain substrates via sol–gel process has been investigated. The effects of SnO₂ on the structural, optical, and photo-catalytic properties of applied thin films have been studied by X-ray diffraction, Raman spectroscopy, and scanning electron microscopy. Surface topography and surface chemical state of thin films were examined by atomic force microscopy and X-ray photoelectron spectroscopy. XRD patterns showed an increase in peak intensities of the rutile crystalline phase by increasing the SnO₂ content. The prepared Sn doped TiO₂ photo-catalyst films showed optical absorption in the visible light area exhibited excellent photo-catalytic ability for the degradation of methylene blue under visible light irradiation. Best photo-catalytic activity of Sn doped TiO₂ thin films was measured in the TiO₂–15 mol% SnO₂ sample by the Sn⁴⁺ dopants presented substitution Ti⁴⁺ into the lattice of TiO₂ increasing the surface oxygen vacancies and the surface hydroxyl groups.     

Photoinduced superhydrophilicity of TiO2 thin film with hierarchical Cu doping

Abstract

Hydrophilic Cu–TiO₂ thin films with a gradient in the Cu concentration were prepared on glass by layer-by-layer dip-coating from TiO₂ precursors. The effects of the Cu doping on the structure and properties of TiO₂ self-cleaning thin films are discussed. The Cu gradient markedly affects the hydrophilicity of the films, with the water contact angle significantly reduced compared with those of the pure or uniformly doped TiO₂ thin films. This enhanced hydrophilicity is explained by the more efficient absorption of the solar light and by the reduced recombination of photoexcited electrons and holes in the TiO₂ films containing a gradient of Cu dopants.     

Measurement of the extinction of sputtered TiO2 films

In this paper a method for separate measurement of the extinction of optical thin films is presented. The method combines a laser calorimetric technique and a light-scattering goniophotometer. As an example, the spectral extinction properties of r.f. reactively sputtered TiO₂ films were measured. Under certain conditions absorption indices of 10^-5 or less can be achieved. Thus light scattering, rather than absorption, is the dominant optical loss mechanism in sputtered TiO₂ films.     

On the optical properties of Mn/SiO and SiO thin films

The ultraviolet, visible and infrared properties of unannealed and annealed amorphous Mn/SiO cermet thin films (300 to 1000 nm thick) prepared by vacuum evaporation at 5.0×10^–4 Pa are investigated. The ultraviolet and visible results are analysed assuming optical absorption by indirect transitions. A systematic reduction of the optical energy gap and an increase in the width of the band-tail region is observed with increasing metallic content. The effects of the ratio deposition rate/residual pressure and substrate temperature on the optical properties of SiO _x (1<x<2) thin films are also investigated.     

Preparation and properties of ferroelectric Pb1 − xCaxTiO3 thin films produced by the polymeric precursor method

Pb_{1 – x} Ca _x TiO₃ thin films with x = 0.24 composition were prepared by the polymeric precursor method on Pt/Ti/SiO₂/Si substrates. The surface morphology and crystal structure, and the ferroelectric and dielectric properties of the films were investigated. X-ray diffraction patterns of the films revealed their polycrystalline nature. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) analyses showed the surface of these thin films to be smooth, dense and crack-free with low surface roughness. The multilayer Pb_{1 – x} Ca _x TO₃ thin films were granular in structure with a grain size of approximately 60–70 nm. The dielectric constant and dissipation factor were, respectively, 174 and 0.04 at a 1 kHz frequency. The 600-nm thick film showed a current density leakage in the order of 10^–7 A/cm² in an electric field of about 51 kV/cm. The C-V characteristics of perovskite thin films showed normal ferroelectric behavior. The remanent polarization and coercive field for the deposited films were 15 C/cm² and 150 kV/cm, respectively.     

Optical band gap and optical constants in a-Se100–xSbx thin films

Abstract

The optical properties of a-Se_100-xSb_x thin films (where x = 0, 0.5, 2.5, 5 and 10) have been studied in the wavelength range 540–900 nm. It was found that the optical band gap increases with increasing Sb concentration in the a-Se_100-x Sb _x system. The refractive index n decreases, while the extinction coefficient k increases with increasing photon energy. DC conductivity measurements of a-Se_100-x Sb _x thin films have been reported in the temperature range 349–375 K. It has been observed that the conductivity increases while the activation energy decreases with increasing Sb concentration. We correlated the optical band gap with the electronegativity of the sample. The band gap increases with the decrease in electronegativity of each sample of a-Se_100-x Sb _x .     

Synthesis and characterization of sol-gel derived TiO<Subscript>2</Subscript> thin films: Effect of different pretreatment process

Titanium dioxide (TiO₂) thin films have been successfully synthesized deposited on glass substrates by the sol-gel dip-coating method through different pretreating processes, including heated at 100, 500°C, via freeze drying, microwave heating for 10 min and subsequently annealed at 500°C for 2 h. The as-synthesized TiO₂ films were characterized using X-ray diffraction (XRD), atomic force microscopy (AFM) and ultravioletvisible (UV-vis) absorption spectra analysis technology. The preparation of the precursor sols and TiO₂ films were described in detail. Effects of 100, 500°C, freeze drying and microwave heating pretreatment on crystalline structure, surface morphology, roughness, particle size, optical property and electronic transition of TiO₂ thin films have been primarily investigated. The XRD results demonstrate that the TiO₂ films were well-crystallized and consisted of anatase TiO₂ phase only with (101) plane. The average crystalline size is only about 15 nm at 100°C pretreatment and the absorption edge shifts to shorter wavelength comparing with that at 500°C, freeze drying and microwave heating pretreatment. Pretreatment process is important during the preparation of thin films and has obviously effect on the structure and optical property of TiO₂ films due to the different heating mechanisms.