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.     

Solution-processed semiconducting aluminum-zinc-tin-oxide thin films and their thin-film transistor applications

We prepared aluminum-zinc-tin-oxide (AZTO) thin films by the solution spin-coating method and investigated their physical and electrical properties according to different incorporated amounts of Al. AZTO films annealed at 400 °C were amorphous. Though SnO₂ crystallites were detected in films annealed at temperatures higher than 500 °C, the number of crystallites decreased as the Al content increased. Thin films had a smooth and uniform surface morphology with an optical transmittance value higher than 92% in the visible range. Electrical conductivity and its temperature dependence varied markedly according to the amount of Al incorporated in the film. We therefore systematically investigated activation energies for carrier transport for each film composition. Thin-film transistors (TFTs) were fabricated using solution-processed AZTO as an active channel layer. The effects of the amount of Al incorporated in the thin film on TFT characteristics were also evaluated. The best device performance was observed for a TFT with a 5 mol%-Al-incorporated AZTO channel. Field effect mobility, subthreshold swing, and on/off ratio were approximately 0.24 cm² V⁻¹ s⁻¹, 0.69 V/dec, and 1.03×10⁶, respectively.     

Thermal treatment effect on nanostructured TiO2 films deposited using diethanolamine stabilized precursor sol

A clear ethanol based precursor sol obtained using diethanolamine has been utilized for the deposition of TiO₂ films annealed at different temperatures. The influence of annealing temperature on the structural, optical and electrochemical properties of TiO₂ thin films has been examined. Diethanolamine stabilizes the precursor sol due to its chelate forming ability with the alkoxides. It reacts as a tridentate ligand with the titanium isopropoxide. The threshold for the onset of crystallization in the films is identified at a temperature of 300 °C. The SEM study on the films elucidates segregation of irregularly shaped features into finer round clusters as a function of annealing temperature. As determined from the AFM study, the roughness parameter in the films has shown an increase with the annealing temperature. Photoluminescence measurements have given an indirect evidence for the presence of stoichiometric titanium oxide in the films. An optimum crystallite size and high ion storage capacity in the 300 °C annealed film has led to its superior electrochromic activity with the transmission modulation and coloration efficiency of the same film being 42% and 8.1 cm² C⁻¹, respectively at 550 nm. The highest degree of porosity in the 300 °C annealed film as established from the SEM study is also the reason behind its best electrochromic performance. In addition, the 300 °C annealed film also exhibits the fastest coloration switching kinetics.     

Characterization of indium tin oxide (ITO) thin films prepared by a sol-gel spin coating process

Indium tin oxide (ITO) thin films were prepared by a sol-gel spin coating method, fired, and then annealed in the temperature range of 450-600°. The XRD patterns of the thin films indicated the main peak of the (2 2 2) plane and showed a higher degree of crystallinity with an increase in the annealing temperature. Upon annealing the films at 500 and 600°, two binding energy levels of Sn⁴⁺ ion of 486.9 eV and 486.6 eV, respectively, were measured in the XPS spectra. The ITO film that was annealed at 600° contained two oxidation states of Sn, Sn²⁺ and Sn⁴⁺, and it had a higher sheet resistance based on a rather low doping concentration of Sn⁴⁺. The film that was annealed at 500° and subsequently treated with 0.1 N HCl solution for 40 s showed a sheet resistance of 225 Ω/square. The surface treatment by the acidic solution diminished the RMS (root mean square) roughness value and the residual carbon content (XPS peak intensity of carbon) of the ITO films. It seems that the acid-cleaning of the ITO thin films led to a decrease of the surface roughness and sheet resistance.     

Characterization of electrodeposited WO3 films and its application to electrochemical wastewater treatment

WO₃ films have been prepared on to IrO₂-coated Ti substrate by cathodic deposition, and as-deposited and annealed films have been characterized using XRD, TEM, Raman and FT-IR spectroscopy. The as-deposited film consists of nanocrystalline, orthorhombic WO₃·H₂O and this phase transforms to amorphous WO₃ by annealing at 250 °C and to monoclinic WO₃ by annealing at and above 350 °C. The as-deposited and annealed films have been used as anodes for electrochemical decomposition of phenol in aqueous solutions with and without chloride ions. The monoclinic WO₃ anodes prepared by annealing at 350 and 400 °C show relatively high electrochemical activity in the chloride-containing solution. In addition, the anodes possess high chemical and physical stabilities: very low dissolution rate of WO₃ during the electrolysis and good adhesion to the substrate. Thus, WO₃ anodes may be promising materials for anodic oxidation of bio-refractory organics in wastewater, although further improvement of electrochemical activity is needed for more effective decrease in total organic carbons in wastewater.     

Effects of tungsten thickness and annealing temperature on the electrical properties of W-TiO2 thin films

TiO₂ thin films were prepared by RF magnetron sputtering onto glass substrates and tungsten was deposited onto these thin films (deposition time 15-60 s) to form W-TiO₂ bi-layer thin films. The crystal structure, morphology, and transmittance of these TiO₂ and W-TiO₂ bi-layer thin films were investigated. Amorphous, rutile, and anatase TiO₂ phases were observed in the TiO₂ and W-TiO₂ bi-layer thin films. Tungsten thickness and annealing temperature had large effects on the transmittance of the W-TiO₂ thin films. The W-TiO₂ bi-layer thin films with a tungsten deposition time of 60 s were annealed at 200 °C-400 °C. The band gap energies of the TiO₂ and the non-annealed and annealed W-TiO₂ bi-layer thin films were evaluated using (αhν)^1/2 versus energy plots, showing that tungsten thickness and annealing temperature had major effects on the transmittance and band gap energy of W-TiO₂ bi-layer thin films.     

Effect of rapid thermal annealing on the properties of zinc tin oxide films prepared by plasma-enhanced atomic layer deposition

The effect of rapid thermal annealing treatments on the microstructure, surface morphology, and optical characteristics of zinc tin oxide (ZTO) films produced by plasma-enhanced atomic layer deposition was investigated. The ZTO films were annealed in oxygen atmosphere for 2 min at four selected temperatures from 500 to 800 °C. The X-ray diffraction showed that the annealing temperature has a great influence on the crystalline characteristics of ZTO films. The film shows complete amorphous structure for as-deposited ZTO film. Meanwhile, the spinel zinc stannate Zn₂SnO₄ was obtained for the samples annealed from 500 to 800 °C, which shows polycrystalline nature. The X-ray photoelectron spectroscopy proved that the annealing process in oxygen gas can effectively can reduce the oxygen vacancy defects in the films. In addition, the photoluminescence spectroscopy manifests an ultraviolet emission with a broad peak range from 345 to 385 nm. Moreover, the ultraviolet luminescence intensity increases continuously with the increase of annealing temperature. Spectroscopic ellipsometry analyses demonstrate that the refractive index of annealed films increases as the increase of annealing temperature, while the extinction coefficient decreases gradually with the increase of annealing temperature in the visible light range.     

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.     

Understanding the thermal evolution of defects in carbon-implanted ZnO single crystal

Defects and impurities play a major role in controlling the electrical and optical properties of semiconductor materials. Herein, hydrothermally grown ZnO single crystals have been implanted with carbon (C) dopants at room temperature and then annealed in argon atmosphere at various temperatures between 400 and 800 °C. The thermal evolution of C-related defects and their effects on the structural, optical and electrical properties of ZnO single crystals were systematically characterized and discussed. The results show ion implantation induces serious lattice disorder, and post-implantation annealing could promote the lattice renormalization, accompanied by an increase in crystal quality and average visible transmittance. Furthermore, it is found that the diffusion of octahedral carbon interstitial (C_i) along parallel to c-axis facilitates the growth of carbon sp² clusters due to its low migration barrier during annealing, which energetically contribute to the decrease of the resistivity. Meanwhile, abundant C_i will be able to enter into V_Zn to form C_Zn or combine with lattice O to form (C_O)_O donor defects upon annealing, dominating the increase of electron carrier concentration and enhancing the anomalous Raman mode at 510-525 cm⁻¹. These findings strengthen the fundamental understanding of the donor behavior of C impurities in ZnO.     

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.     

Low-temperature solution combustion synthesis of high performance LiNi0.5Mn1.5O4

High-voltage LiNi_0.5Mn_1.5O₄ spinels were synthesized by a low temperature solution combustion method at 400 °C, 600 °C and 800 °C for 3 h. The phase composition, structural disordering, micro-morphologies and electrochemical properties of the products were investigated by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM) and constant current charge–discharge test. XRD analysis indicated that single phase LiNi_0.5Mn_1.5O₄ powders with disordered Fd-3m structures were obtained by the method at 400 °C, 600 °C and 800 °C. The crystallinity increased with increasing preparation temperatures. XRD and FTIR data indicated that the degree of structural disordering in the product prepared at 800 °C was the largest and in the product prepared at 600 °C was the least. SEM investigation demonstrated that the particle size and the crystal perfection of the products were increased with increasing temperatures. The particles of the product prepared at 600 °C with ~200 nm in size are well developed and homogeneously distributed. Charge/discharge curves and cycling performance tests at different current density indicated that the product prepared at 600 °C had the largest specific capacity and the best cycling performance, due to its high purity, high crystallinity, small particle size as well as moderate amount of Mn³⁺ ions.     

Electrodeposited Prussian blue films: Annealing effect

The correlation between the temperature-dependent electrochromic (EC) activity and other properties of galvanostatically deposited Prussian Blue (PB) films is presented here. Films subjected to annealing treatment in air at temperatures up to 500 °C were characterized by a variety of techniques which include TGA, XRD, FTIR, UV-vis spectrophotometry, SEM, XPS, cyclic voltammetry etc. The as-deposited X-ray amorphous hydrated PB films were blue in color and had Fe in both Fe^II and Fe^III valence states and were electrochromically active. Consequent to changes in the valence state, degree of hydration and coordination environment of the iron ions upon annealing, EC activity and morphology of the films exhibited dramatic changes. Annealing at moderate temperatures retained the blue color of the films and decreased the EC activity consistent with dehydration and decreased the Fe^II content. Lack of EC activity at higher temperatures was consistent with dehydration and quenching of Fe^II states accompanied with change of color from blue to rust (Fe^III) typical of Fe₂O₃. Independent of the annealing temperature, the films retained their amorphicity, however, prolonged annealing at 500 °C yielded hexagonal Fe₂O₃.     

Microstructure and through-film electrical characteristics of vertically aligned amorphous carbon films

The microstructure and electrical properties of in-situ annealed carbon films is studied in this paper. In-situ annealing (150 °C to 600 °C) was done during the deposition of carbon films with −300 V substrate bias. Transmission electron microscopy and two points electrical probing studies were performed and the deduced transition for vertical orientated graphitic planes occurs at temperatures above 400 °C. The microstructure of the films strongly depends on the deposition temperature of the films (room temperature, 400 °C and 600 °C). Electrical conductivity of the film strongly depends on texturing due to the formation of preferred orientation in the vertical direction. The vertically orientated carbon (VOC) sheet provides effective nanochannels for electron transport, thus significantly improves the electrical properties of the annealed film.     

Sol–gel synthesis of red-emitting LiEuW2O8 powder as a near-ultraviolet convertible phosphor

LiEuW₂O₈ phosphor with the optical function of color conversion from near-UV to red wavelength was prepared by sol–gel method using inorganic salts as a starting material. Viscous mixing sol was prefired at 300 °C for 120 min in air and then white precursor was finally annealed at 800 °C for 240 min in Ar. Structural and photoluminescent properties of the sample were analyzed by an X-ray diffraction analysis, field emission-scanning electron microscope and a fluorescent spectrophotometer. The main emission peak is ⁵D₀ → ⁷F₂ transitions of Eu³⁺ at 615 nm, other transitions from the ⁵D₀ → ⁷F₁, ⁵D₀ → ⁷F₃ and ⁵D₀ → ⁷F₄ located at 570–700 nm range are weak. The characteristic emission of WO₄²⁻ in LiEuW₂O₈ is quenched absolutely and only red-light emission of Eu³⁺ appears.     

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.     

Orientation of graphitic planes during annealing of “dip deposited” amorphous carbon film: A carbon K-edge X-ray absorption near-edge study

Annealing effect of amorphous carbon thin films on Si(1 0 0) substrates is studied by normal incidence and angle dependent carbon K-edge X-ray absorption near-edge structure (XANES) spectroscopy. The angle dependence of the XANES signal shows that the graphitic basal planes are oriented perpendicular to the surface when the film is annealed at 1000 °C. Micro-Raman spectroscopy reveals two well-separated bands the D band at 1355 cm⁻¹ and G band at ∼1600 cm⁻¹, and their I_D/I_G intensity ratio indicates the formation of more graphitic film at higher annealing temperatures. X-ray diffraction pattern of 1000 °C temperature annealed film confirms the formation of graphite structure.     

Synthesis of titania/carbon nanotube heterojunction arrays for photoinactivation of E. coli in visible light irradiation

TiO₂/multi-wall carbon nanotube (MWNT) heterojunction arrays were synthesized and immobilized on Si(0 0 1) substrate as photocatalysts for inactivation of Escherichia coli bacteria. The vertically aligned MWNT arrays were grown on ∼5 nm Ni thin film deposited on the Si by using plasma enhanced chemical vapor deposition at 650 °C. Then, the MWNTs were coated by TiO₂ using dip-coating sol-gel method. Post annealing of the TiO₂/MWNTs at 400 °C resulted in crystallization of the TiO₂ coating and formation of Ti-C and Ti-O-C carbonaceous bonds at the heterojunction. The visible light-induced photoinactivation of the bacteria increased from MWNTs to TiO₂ to TiO₂/MWNTs, in which the bacteria could even slightly breed on the MWNTs. In addition, the TiO₂/MWNTs annealed at 400 °C showed a highly improved antibacterial activity than the TiO₂/MWNTs annealed at 100 °C. The excellent visible light-induced photocatalytic efficiency of the TiO₂/MWNTs/Si film annealed at 400 °C was attributed to formation of the carbonaceous bonds at the heterojunction, in contrast to the 100 °C annealed TiO₂/MWNTs/Si sample which had no such effective bonds.     

Growth and optical properties of large-scale MoS2 films with different thickness

The synthesis of large-scale molybdenum disulfide (MoS₂) with high quality is highly desirable for the promising applications in flexible optoelectronic devices. Here, we report a feasible one-step chemical vapor deposition (CVD) synthesis of continuous MoS₂ films with different layer-number via adjusting the growth temperature in the range of 740–800 °C. Influences of the annealing treatments at diverse temperature ranging from 300 to 500 °C on Raman and PL spectra of the monolayer MoS₂ film grown at 780 °C are reported. PL characterization shows that the PL emission of film annealed at 400 °C exhibits highest intensity with a blue-shift in comparison to that of the pristine film grown at 780 °C. The PL fluctuation of the MoS₂ film annealed at 400 °C is mainly originated from the high crystalline quality and strain-release. This study sheds a light on growth and performance optimization of the large-area two-dimensional transition metal dichalcogenides films.     

Influence of post-annealing atmosphere on microstructure,optical and electrical properties of zinc cadmium oxide films deposited by DC and RF magnetron co-sputtering

Zinc cadmium oxide (Zn_1−xCd_xO) films were deposited on quartz substrates by direct current (DC) and radio frequency (RF) reactive magnetron co-sputtering and the influence of post-annealing atmosphere on their microstructure, optical and electrical properties were investigated by X-ray diffraction (XRD), optical absorbance, photoluminescence (PL) and Hall measurements. Results indicate that the band gap (E_g) of all Zn_1−xCd_xO films annealed in different atmospheres are smaller than that of the undoped ZnO, the observed shifts in E_g being 0.43, 0.37 and 0.32 eV for the Zn_1−xCd_xO films annealed in argon, oxygen and vacuum, respectively. Hall measurement results indicate that all Zn_1−xCd_xO films annealed in different atmospheres show the n-type conduction, but the Zn_1−xCd_xO film annealed in vacuum has low resistivity and high concentration, which has room-temperature resistivity of 1.59 Ω cm and carrier concentration of 2.07×10¹⁷ cm⁻³. Compared with Zn_1−xCd_xO films annealed in oxygen and argon, Zn_1−xCd_xO film annealed in vacuum has the best crystal quality, luminescence and electrical properties. The influencing mechanism of the post-annealing atmosphere on the electrical and optical properties of the Zn_1−xCd_xO film is discussed.     

Sol-gel derived 6CaO·6SrO·7Al2O3 thin films using metal alkoxides

The novel 6CaO·6SrO·7Al₂O₃ (C6S6A7) thin films were deposited onto soda lime glass substrate using calcium, strontium, aluminium isopropoxide and 2-methoxy ethanol as starting materials via sol-gel dip coating technique. The electrical and optical properties of C6S6A7 films were investigated for films sample annealed at 450 °C for 2 h in air and hydrogen (H₂) atmosphere, respectively. X-ray diffraction pattern and Fourier transformed infrared spectroscopy analysis confirms cubic structure to the C6S6A7 material. The optical transmission spectra of C6S6A7 films showed the high transparency in wide visible range of ∼ 88 and 80% for air and H₂ annealed samples, respectively. The C6S6A7 films sheet resistance of 528 and 0.65 k Ohm/square has been observed for films annealed in air and H₂ atmosphere at 450 °C, respectively.