Study on photoelectrochemical solar cells of nanocrystalline Cd0.7Zn0.3Se -water soluble conjugated polymer

Cadmium zinc selenide (Cd_0.7Zn_0.3Se) nanocrystalline thin films were chemically synthesized onto indium tin oxide (ITO)-coated glass substrate at relatively low temperature (<90 °C). The as-deposited films were annealed in air at 200, 300, and 400 °C for 60 min. The structure and surface morphology of the films were studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The water-soluble conjugated polymer, poly(2-ethynyl-N-carboxy-propyl-pyridinium bromide) (LM3), with quaternary pyridinium salts was layered by dipping the as-deposited and annealed Cd_0.7Zn_0.3Se films in the aqueous polymer solution. This hybrid photoanode system was subjected to photoelectrochemical (PEC) study under a light illumination intensity of 80 mW/cm².     

Growth and structural characteristics of perovskite-wurtzite oxide ceramics thin films

Wurtzite ZnO thin films were grown on single-crystal perovskite SrTiO₃(STO) (1 0 0) substrates at various temperatures. The ZnO/STO thin films thus formed exhibit a preferred (1 1 0)-orientation at a growth temperature of 600-700 °C. A high growth temperature enhances not only the (1 1 0)-texture of ZnO/STO thin films but also the crystalline quality of the film. (La_0.7Sr_0.3)MnO₃ (LSMO) thin films were subsequently grown on ZnO(1 1 0)/STO(1 0 0) substrates with various thicknesses, and were polycrystalline. A thicker LSMO film has a stronger (0 0 l)-preferred orientation than the thinner one. The lattice distortion of LSMO decreases as the LSMO thickness increases. Magnetization vs. temperature curves show that both crystalline quality and lattice distortion influence the magnetic properties of LSMO thin films. The physical properties of the manganite oxide can be modulated by forming a heterostructure with wurtzite ZnO.     

Tribological behaviors of single and dual sol–gel ceramic films on Ti–6Al–4V

TiO₂, SiO₂, hydroxyapatite (HA), TiO₂–HA and SiO₂–HA thin films with good biocompatibility were grown on Ti–6Al–4V (coded as TC4) substrate by sol–gel and dip-coating processes from specially formulated sols, followed by annealing at 500 °C. The chemical states of some typical elements in the target films were detected by means of X-ray photoelectron spectroscopy (XPS). High-resolution scanning electron microscopy (SEM) is applied to characterize the surface and cross-sectional morphologies of obtained films. Various phases of the films were characterized by XRD. The tribological properties of thin films sliding against an AISI52100 steel ball were evaluated on a reciprocating friction and wear tester. As a result, the target films were obtained. Compared with the TC4 substrate, all the sol–gel ceramic films are superior in resisting wear. Among all, HA film shows the best resistance while SiO₂ film shows the worst wear resistance both under higher (3 N) and lower load (1 N). TiO₂ shows a good wear resistance under lower load but higher load. Compared with TiO₂, the wear resistance of the dual film TiO₂–HA can be improved under 3 N but deteriorated under 1 N. Compared with SiO₂, the wear resistance of SiO₂–HA is improved both under 3 N and 1 N. Compared with HA, the wear resistances of dual films are deteriorated both under 3 N and 1 N. Under 0.5 N, a very long wear life for TiO₂–HA is also obtained, illustrating that the lower wear resistance of dual films is closely related to the applied load. SEM observation of the morphologies of worn surfaces indicates that the wear of TC4 is characterized by abrasive wear. Differently, abrasion, plastic deformation and micro-crack dominate the wear of ceramic films. The superior friction reduction and wear resistance of HA films are greatly attributed to the slight plastic deformation of the film. Sol–gel is a potential method being applied to implant materials for wear protection according to proper process designs. The single HA film and the dual TiO₂–HA film is suggested for biomedical application from the point of view of wear protection.     

Electrochromism in spray deposited iridium oxide thin films

Electrochromic iridium oxide thin films were deposited onto fluorine doped tin oxide coated glass substrates from an aqueous iridium chloride solution by pneumatic spray pyrolysis technique. The as-deposited samples were X-ray amorphous. The electrochromic properties of thin films were studied in an aqueous electrolyte (0.5N H₂SO₄) using cyclic voltammetry (CV), chronoamperometry (CA) and spectrophotometry. Iridium oxide films show pronounced anodic electrochromism owing to Ir⁺⁴ ↔ Ir⁺³ intervalency charge transition. The reversibility of cyclic process in Ir oxide films is found to be higher, which increases with increasing number of colour-bleach cycles.     

The effect of thickness on the composition of passive films on a Ti-50Zr at% alloy

Anodic films were grown potentiodynamically in different electrolytes (pH = 1-14) on a Ti-50Zr at% cast alloy, obtained by fusion in a voltaic arc under argon atmosphere. The thickness of the films was varied by changing formation potential from the open circuit potential up to about 9 V; growth was followed by 30 min stabilization at the forming potential. Films having different thicknesses were characterized by photocurrent spectroscopy (PCS) and electrochemical impedance spectroscopy (EIS). Moreover, film composition was analyzed by X-ray photoelectron spectroscopy (XPS).Regardless of the anodizing conditions, passive films on the Ti-50Zr at% alloy consist of a single layer mixed oxide phase containing both TiO₂ and ZrO₂ groups. However, an enrichment of Ti within the passive film, increasing with the film thickness, is detected both by PCS and XPS. This leads to concentration profiles of Ti⁴⁺ and Zr⁴⁺ ions along the thickness, and to different electronic properties of very thin films (more insulating) with respect to thicker films (more semiconducting), as revealed by the photocurrent-potential curves.     

The ultraviolet emission mechanism of ZnO thin film fabricated by sol–gel technology

ZnO thin films were successfully deposited on SiO₂/Si substrate by sol–gel technology. The as-grown ZnO thin films were annealed under an ambient atmosphere from 600 to 900 °C by rapid thermal annealing (RTA) process. X-ray diffraction and scanning electron microscopy analyses reveal the physical structures of ZnO thin films. From PL measurement, two ultraviolet (UV) luminescence bands were obtained at 375 and 380 nm, and the intensity became stronger when the annealing temperature was increased. The strongest UV light emission appeared at annealing temperature of 900 °C. The chemical bonding state in ZnO films was investigated by using X-ray photoelectron spectrum. The mechanism of UV emission was also discussed.     

Simultaneous Laser‐Induced Reduction and Nitrogen Doping of Graphene Oxide in Titanium Oxide/Graphene Oxide Composites

Titanium oxide/graphene oxide nanocomposite thin films were grown by ultraviolet (UV) matrix‐assisted pulsed laser evaporation (MAPLE) technique in controlled oxygen or nitrogen atmospheres. The effect of graphene oxide addition and laser‐induced reduction as well as nitrogen doping on the wetting behavior and photoactive properties of titanium oxide thin films was investigated. Hydrophobic to hydrophilic conversion of titanium oxide films takes place progressively as the relative amount of graphene oxide in the MAPLE composite target increases. Nitrogen doping leads to further decrease of the static contact angle of the composite films. The photoactive properties of the synthesized materials were investigated through the evolution of contact angle under UV light irradiation. Wetting properties of both TiO₂ and TiO₂/GO nanocomposite thin films improved upon exposure to UV light.     

Evaluation on the optical properties of Ga2O3−x thin films co-doped with Tb and transition metals (Mn,Cr) prepared by a photochemical route

Gallium β-diketonate complexes were studied as precursors for the photochemical deposition of amorphous thin films of gallium oxide doped with terbium and co-doped with chromium or manganese. Solutions of the inorganic complexes were spin coated on Si(100) and quartz substrates and photolyzed at room temperature using 254 nm UV light. The photolysis of these films induces the fragmentation of the complexes and the partial reduction of the metal ion together with the release of volatile organic compounds as sub-products. When the metallic complexes are irradiated under air, the products of the reactions are metal oxide thin films. The photochemical reactivity of these films was monitored by UV–vis spectroscopy, followed by a post-annealing treatment. The obtained films were characterized by X-ray photoelectron spectroscopy and X-ray diffraction. The optical properties of the films showed that these are highly transparent in the visible spectrum but decrease significantly in doped and co-doped films. Under UV light excitation (254 nm) the doped films (Ga₂O_3−x/Tb) show the characteristic emissions at 486, 530, 542 and 610 nm associated to ⁵D₄→⁷F_J (J=6,5,4,3) transitions of Tb⁺³ ion. However, these emissions decrease and deteriorate in the co-doped films (Ga₂O_3−x/Tb/M, where M=Mn or Cr). A possible emission mechanism and energy transfer have been proposed.     

Li-intercalation behaviour of vanadium oxide thin film prepared by thermal oxidation of vanadium metal

In order to produce thin films of crystalline V₂O₅, vanadium metal was thermally oxidised at 500 °C under oxygen pressures between 250 and 1000 mbar for 1-5 min. The oxide films were characterised by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), X-ray diffraction (XRD) and Rutherford backscattering spectrometry (RBS). The lithium intercalation performance of the oxide films was investigated by cyclic voltammetry (CV), chronopotentiometry and electrochemical impedance spectroscopy (EIS). It was shown that the composition, the crystallinity and the related lithium intercalation properties of the thin oxide films were critically dependent on the oxidation conditions. The formation of crystalline V₂O₅ films was stimulated by higher oxygen pressure and longer oxidation time. Exposure for 5 min at 750 mbar O₂ at 500 °C resulted in a surface oxide film composed of V₂O_5, and consisting of crystallites up to 200 nm in lateral size. The thickness of the layer was about 100 nm. This V₂O₅ oxide film was found to have good cycling performance in a potential window between 3.8 and 2.8 V, with a stable capacity of 117 ± 10 mAh/g at an applied current density of 3.4 μA/cm². The diffusion coefficients corresponding to the two plateaus at 3.4 and 3.2 V were determined from the impedance measurements to (5.2 and 3.0) × 10⁻¹³ cm² s⁻¹, respectively. Beneath the V₂O₅ layer, lower oxides (mainly VO₂) were found close to the metal. At lower oxygen pressure and shorter exposure times, the oxide films were less crystalline and the amount of V⁴⁺ increased in the surface oxide film, as revealed by XPS. At intermediate oxygen pressures and exposure times a mixture of crystalline V₂O₅ and V₆O₁₃ was found in the oxide film.     

Effect of annealing on the properties of nanostructured CuO thin films for enhanced ethanol sensitivity

Copper oxide (CuO) thin films were grown on glass substrates by low cost spray pyrolysis technique for three different molar concentrations (0.05 M, 0.10 M and 0.15 M), at a substrate temperature of 350 °C, and subsequently annealed at 400 °C for 2 h. The effects of precursor concentration and annealing on the structural, electrical and morphological properties of the crystallized films were investigated. X-ray diffractograms of the films showed the formation of single phase CuO with tenorite structure. The electrical properties of the films like carrier concentration, Hall co-efficient (R_H), mobility and conductivity were studied from Hall effect measurements. The positive values of R_H confirmed the p-type conductivity of the films. Resistivity decreased drastically by two orders of magnitude for the annealed films. The microstructures characterized by a scanning electron microscope for 0.15 M concentration of the precursor revealed that the morphology of the films was substantially affected by annealing. The film surface revealed uniformly distributed cluster of peanut shaped grains after annealing. The response of the as deposited and annealed CuO sensor to low concentration of ethanol (10 ppm) was compared. The annealed CuO film showed higher sensor response than the as-deposited CuO film did. The result suggested that annealing causes significant effect on the sensing performance of CuO to ethanol.     

Improved performance of dense TiO2/CdSe coupled thin films by low temperature process

Dense TiO₂ and TiO₂/CdSe coupled nanocrystalline thin films were synthesized onto ITO coated glass substrate by chemical route at relatively low temperature (≤100 °C). TiO₂ films were nanocrystalline and crystallinity disappears after CdSe deposition as evidenced by X-ray powder diffraction. Surface morphology and physical appearance of films were studied from SEM and actual photo-images, reveals dense nature of TiO₂ (10-12 nm spherical grains, faint violet) and CdSe (80-90 nm spherical grains, deep brown), respectively. Presence of two absorption edges in UV spectra implies existence of separate phases rather than composite formation. TiO₂ film was found to have higher water contact angle (71°) than TiO₂/CdSe (61°) and CdSe (56°). I-V and stability tests of photo-electrochemical cells were performed with TiO₂ and TiO₂/CdSe film electrodes (under light of illumination intensity 80 mW/cm²) in lithium iodide as an electrolyte using two-electrode system.     

Growth and characterization of epitaxial (La2/3Sr1/3)MnO3 films by pulsed laser deposition

High quality epitaxial (La_2/3Sr_1/3)MnO₃ (0 0 1) thin films were grown by pulsed laser deposition on SrTiO₃ (0 0 1) substrate at optimized growth parameters. The films quality was confirmed by both structural and physical properties characterization. Channeling Rutherford Backscattering Spectrometry characterization showed the minimal channeling coefficient as low as 4%. The LSMO thin films growth on SrTiO₃ substrate follows the island growth model. The Curie temperature of LSMO films is around 360 K, which is the one of the highest reported in literature. The resistivity of LSMO films showed the metal-insulate transition temperature coincides with the Curie temperature. This high quality LSMO is suitable for room temperature magnetic devices application.     

Nanocrystalline-diamond thin films with high pH and penicillin sensitivity prepared on a capacitive Si-SiO2 structure

A capacitive field-effect EDIS (electrolyte-diamond-insulator-semiconductor) sensor with improved pH and penicillin sensitivity has been realised using a nanocrystalline-diamond (NCD) film as sensitive gate material. The NCD growth process on SiO₂ as well as an additional surface treatment in oxidising medium have been optimised to provide high pH-sensitive, non-porous O-terminated films without damage of the underlying SiO₂ layer. The surface morphology of O-terminated NCD thin films and the layer structure of EDIS sensors have been studied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) methods. To establish the relative coverage of the surface functional groups generated by the oxidation of NCD surfaces, X-ray photoelectron spectroscopy analysis was carried out. The hydrophilicity of NCD thin films has been studied by water contact-angle measurements. A nearly Nernstian pH sensitivity of 54-57 mV/pH has been observed for O-terminated NCD films treated in an oxidising boiling mixture for 80 min and in oxygen plasma. The high pH-sensitive properties of O-terminated NCD have been used to develop an EDIS-based penicillin biosensor. A freshly prepared penicillin biosensor possesses a high sensitivity of 85 mV/decade in the concentration range of 0.1-2.5 mM penicillin G. The lower detection limit is 5 μM.     

Annealing temperature and environment effects on ZnO nanocrystals embedded in SiO2: a photoluminescence and TEM study

We report on efficient ZnO nanocrystal (ZnO-NC) emission in the near-UV region. We show that luminescence from ZnO nanocrystals embedded in a SiO₂ matrix can vary significantly as a function of the annealing temperature from 450°C to 700°C. We manage to correlate the emission of the ZnO nanocrystals embedded in SiO₂ thin films with transmission electron microscopy images in order to optimize the fabrication process. Emission can be explained using two main contributions, near-band-edge emission (UV range) and defect-related emissions (visible). Both contributions over 500°C are found to be size dependent in intensity due to a decrease of the absorption cross section. For the smallest-size nanocrystals, UV emission can only be accounted for using a blueshifted UV contribution as compared to the ZnO band gap. In order to further optimize the emission properties, we have studied different annealing atmospheres under oxygen and under argon gas. We conclude that a softer annealing temperature at 450°C but with longer annealing time under oxygen is the most preferable scenario in order to improve near-UV emission of the ZnO nanocrystals embedded in an SiO₂ matrix.     

UV photodetection properties of pulsed laser deposited Cu-doped ZnO thin film

Nanocrystalline undoped and 2 at% copper (Cu) doped zinc oxide (ZnO) thin films were successfully grown onto SiO₂/n-Si substrates at 600 °C by using pulsed laser deposition (PLD) technique. The influence of Cu incorporation on structural, surface morphological, elemental composition and UV detection properties of ZnO film was investigated. X-ray diffraction studies of thin films show that they are polycrystalline and have a hexagonal wurtzite structure; however, Cu doping improves the preferential orientation along c-axis. The chemical state of constituent elements was analysed by X-ray photoelectron spectroscopy (XPS). It indicates the presence of Cu ions in the doped film that exist in a mixed univalent and bivalent state. FE-SEM observations support the crystallographic results. The effective incorporation of Cu ions into the lattice of the ZnO nanostructure without changing its wurtzite structure was confirmed by an energy dispersive X-ray spectroscopic analysis (EDX). The UV photodetection characteristics of both films were further studied in metal-semiconductor-metal (MSM) planar configurations at room temperature and are found to be greatly influenced by Cu doping. The incorporation of Cu into ZnO lattice increases the resistivity of thin film; which leads to lower dark current. As a result, the Cu-doped ZnO film based UV PD demonstrates improved UV sensitivity of about 66.92 upon 2 mW/cm² UV illumination at 365 nm peak wavelengths and 5 V applied bias. The reproducible UV detection performance of MSM devices was also ensured by periodically switching UV light on and off at fixed time intervals.     

Spontaneously ordered TiO2 nanostructures

Titanium dioxide thin films were deposited on quartz substrates kept at different O₂ pressures using pulsed laser deposition technique. The effects of reactive atmosphere and annealing temperature on the structural, morphological, electrical and optical properties of the films are discussed. Growth of films with morphology consisting of spontaneously ordered nanostructures is reported. The films growth under an oxygen partial pressure of 3 × 10⁻⁴ Pa consist in nanoislands with voids in between them whereas the film growth under an oxygen partial pressure of 1 × 10⁻⁴ Pa, after having being subjected to annealing at 500 °C, consists in nanosized elongated grains uniformly distributed all over the surface. The growth of nanocrystallites with the increase in annealing temperature is explained on the basis of the critical nuclei-size model.     

Investigation of thin sputtered Mn films for electrochemical capacitors

Pseudocapacitive manganese oxide films have been synthesized by anodic oxidation of metallic films deposited by sputtering. Results are presented from an electrochemical investigation into properties of these thin sputtered manganese films. Mn films with thickness ranging from 20 to 200 nm have been sputtered onto Pt coated Si wafers in an Argon atmosphere. Electrochemical oxidation converts the metal film into a porous, dendritic structure which displays significant pseudocapacitance. We have observed a specific capacitance (C_s) of 700 F/g when cycled very slowly at a constant current density of 160 μA/cm². The same films probed by cyclic voltammetry (CV) at a rate of 5 mV/s yielded a lower specific capacitance of 400-450 F/g. Post-oxidation material loading was measured to be in the range of 25-75 μg/cm².     

Dry densification of carbon nanotube bundles

A dry method for densifying vertically aligned carbon nanotube bundles is proposed and experimentally validated. The process uses the deposition of thin SiO₂ films to seal the porous CNT bundles at low pressure. When the CNT bundles are transferred back to ambient pressure they are densified by the pressure difference obtained between the inner and outer sides of the thin film. The effects of the densification have been studied for different thicknesses of SiO₂ films deposited by two different deposition techniques. The diameters of the narrowest densified sections are 26 ± 3% of their original sizes after dry densification by 50 nm thick SiO₂. The proposed dry densification method is also compared to existing liquid-based methods and its limitations are discussed.     

Investigation of the corrosion protection of SiOx-like oxide films deposited by plasma-enhanced chemical vapor deposition onto carbon steel

The paper reports on the corrosion behavior of carbon steel coated with thin SiO_x-like oxide films. The SiO_x-like coatings were deposited by plasma-enhanced chemical vapor deposition (PECVD) and their thickness was varied between 20 and 200 nm. The coated carbon steel interfaces were investigated for their corrosion protection efficiency when immersed in an aqueous saline solution of 3% NaCl. FTIR measurements and electrochemical impedance spectroscopy (EIS) experiments revealed that thin SiO_x-like coating layers (20 nm thick) do not prevent the carbon steel from corrosion, while thicker silica layers (d ≥ 100 nm) protect efficiently carbon steel interfaces in highly saline media with a protection efficiency of about 96% for a 200 nm thick coating.     

Dielectric properties of sol–gel derived CaCu3Ti4O12 thin films onto Pt/TiO2/Si(1 0 0) substrates

The ultrahigh relative dielectric constant (K′) values reported for the CaCu₃Ti₄O₁₂ bulk ceramics (10⁴ at RT) joined to their low thermal dependence, no phase transitions are expected between −173 and 330 °C, make this material very promising for capacitor applications and certainly for microelectronics. The interest in the preparation of this material in thin film form is twofold, the understanding of its physical properties and the integration of this high K′ oxide with the Si technology. In this work, the preparation of CCTO thin films onto Pt/TiO₂/SiO₂/Si(1 0 0) substrates is attempted using sol–gel processing and rapid thermal processing (RTP) at 650 °C. Structural, microstructural and dielectric characterization of the films is performed. The results are commented and discussed on the light of the grain boundary effect on the dielectric constant and the possibility of application of these thin films in microelectronic devices.