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.     

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.     

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.     

Spin coated versus dip coated electrochromic tungsten oxide films: Structure, morphology, optical and electrochemical properties

A sol-gel derived acetylated peroxotungstic acid sol encompassing 4 wt.% of oxalic acid dihydrate (OAD) has been employed for the deposition of tungsten oxide (WO₃) films by spin coating and dip coating techniques, in view of smart window applications. The morphological and structural evolution of the as-deposited spin and dip coated films as a function of annealing temperature (250 and 500 °C) has been examined and compared by Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM) and X-ray diffraction (XRD). A conspicuous feature of the dip coated film (annealed at 250 °C) is that its electrochromic and electrochemical properties ameliorate with cycling without degradation in contrast to the spin coated film for which these properties deteriorate under repetitive cycling. A comparative study of spin and dip coated nanostructured thin films (annealed at 250 °C) revealed a superior performance for the cycled dip coated film in terms of higher transmission modulation and coloration efficiency in solar and photopic regions, faster switching speed, higher electrochemical activity as well as charge storage capacity. While the dip coated film could endure 2500 color-bleach cycles, the spin coated film could sustain only a 1000 cycles. The better cycling stability of the dip coated film which is a repercussion of a balance between optimal water content, porosity and grain size hints at its potential for electrochromic window applications.     

Structure and properties of PbO2-CeO2 anodes on stainless steel

The lack of ideal anodes with excellent activity and stability is one of the critical problems in electrochemical oxidation for organic wastewater treatment. It is reported in this paper that the PbO₂-CeO₂ films electrodeposited on stainless steel were used as catalytic electrodes for treating antibiotic wastewater. The PbO₂-CeO₂ films on stainless steel were proved to be high stability, good activity and relatively low cost. Because of these properties, the films are more attractive than any other electrocatalytic materials among conventional dimensionally stable anodes (DSA). Experimental results showed that the PbO₂-CeO₂ electrode has a service life of 1100 h in 3 M H₂SO₄ solution under a current density of 1 A cm⁻² at 35 °C, compared with 300 h for PbO₂ under the same conditions. The X-ray diffraction (XRD) patterns and SEM images indicated that the PbO₂-CeO₂ films on stainless steel have a dense structure and the preferred crystalline orientation on the substrate surface was changed. Color and chemical oxygen demand (COD) of antibiotics wastewater were studied by electrolysis by using these electrodes as anode and stainless steel as cathode. The results indicated that the anodes have excellent activity in antibiotic wastewater treatment. The PbO₂-CeO₂ electrodes have high chemical stability which contributed by the superstable nature of the electrode, dense microstructure, good conductivity and the improvement of bonding with the stainless steel during electrodeposition.     

Electrochromic Nb-doped WO3 films: Effects of post annealing

The Nb-doped WO₃ films were deposited by e-beam co-evaporation method using ceramic WO₃ targets and metal Nb slugs. The films were analyzed by glancing incident angle X-ray diffraction (GIAXRD), UV/visible spectrophotometer, electrochemical cyclic voltammetry, X-ray photoelectron spectroscopy (XPS). The as-prepared film is brown and amorphous in structure. The film has low transmission in optical visible region. The XPS results indicate that the as-deposited film is non-stoichiometric. By applying a negative potential, the as-deposited film does not show obvious electrochromic effect. However, the electrochromic properties of Nb-doped WO₃ films are improved by post annealing treatment at 350, 400, and 450 °C in oxygen atmosphere. The Nb-doped WO₃ films transform into crystalline structure and become transparent after post annealing treatment. The energy band gap, optical modulation, and color efficiency increase with annealing temperature.     

Direct anodic growth of thick WO3 mesosponge layers and characterization of their photoelectrochemical response

Thick mesoporous tungsten oxide (WO₃) layers can be formed by anodization of tungsten in a 10 wt% K₂HPO₄/glycerol electrolyte, if the electrolyte temperature is around 80-100 °C. At 90 °C, a regular mesoporous WO₃ layer was grown up to a thickness of approximately 9 μm. This WO₃ mesosponge layer consists of typical feature sizes of 20-30 nm and pore widths of 10-30 nm. The photoresponse of different layer thicknesses and different annealing treatments was characterized in a photoelectrochemical cell. The highest photocurrents were observed with a 2.5 μm thick WO₃ layer annealed at 550 °C consisting of a mixture of orthorhombic, triclinic and monoclinic phases. Incident photon to current efficiencies (IPCEs) of the samples were 73.4% in a 1 M HClO₄ electrolyte and 167.5% for methanol photo-oxidation in 0.1 M CH₃OH/1 M HClO₄ electrolyte, at 1 V vs. Ag/AgCl under illumination at a wavelength of 420 nm.     

Anodic formation of low-aspect-ratio porous alumina films for metal-oxide sensor application

Thin nanoporous anodic alumina films, of low aspect ratio (1:1), with two distinctive pore sizes and morphologies were prepared by two-step constant-current anodising of aluminium layers on SiO₂/Si substrates in 0.4 mol dm⁻³ tartaric (TA) and malonic acid (MA) electrolytes and then modified by open-circuit dissolution. The anodic films were employed as a support material for sputtering-deposition of thin WO₃ layers in view of exploiting their gas sensing properties. The films and deposits were characterized by scanning electron microscopy, X-ray diffraction and electric resistance measurements at fixed temperatures in the range of 100-300 °C upon NH₃ and CO gas exposures. Test sensors prepared from the annealed and stabilized alumina-supported WO₃ active layers were insensitive to CO but showed considerably enhanced responses to NH₃ at 300 °C, the sensitivity depending upon the anodic film nature, the pore size and the surface morphology. The increased sensor sensitivity is due to the substantially enlarged film surface area of the TA-supported WO₃ films and the nanostructured, camomile-like morphology of the MA-supported WO₃ films. Sensing mechanisms in the alumina-supported WO₃ active layers are discussed.     

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.     

Improved pseudo-capacitive performance of manganese oxide films synthesized by the facile sol–gel method with iron acetate addition

Manganese oxide electrodes possessing pseudo-capacitance behaviors were successfully made with a simple sol–gel method. The experimental results showed that the specific capacitance was 101.2 F/g for pure manganese oxide films after annealing at 300 °C. However, the specific capacitance increased to 232.3 F/g with iron acetate (1.0 mol% Fe) addition and after annealing at 350 °C. The surface morphology observations revealed that the annealing temperature of 350 °C produced a higher surface area film with smaller pores. X-ray diffraction results showed that the manganese-iron oxide was composed of Mn₃O₄ and Mn₂O₃ phases, without iron oxide diffraction peaks. The manganese-iron oxide electrode with Mn₃O₄ and Mn₂O₃ phases exhibited good electrochemical performance and capacitance efficiency.     

Preparation of Li–Mn–O thin films by r.f.-sputtering method and its application to rechargeable batteries

Spinel-LiMn₂O₄ thin films were fabricated on stainless steel substrate by the r.f.-sputtering method. They were annealed within the range 400–700 °C for 1 h in O₂ and their electrochemical performance was compared to that of as-deposited film. The thin films were characterized by X-ray diffractometry and electron spectroscopy for chemical analysis (ESCA). Charge–discharge tests were carried out in an LiClO₄/propylene carbonate solution. The films heat-treated at 400–700 °C exhibited excellent cyclability over a wide potential region from 2.0 to 4.3 V vs Li/Li⁺.     

Visible light photoelectrochemical responsiveness of self-organized nanoporous WO3 films

Visible light-responsive WO₃ nanoporous films with preferential orientation of the (0 0 2) planes were prepared by anodization in neutral F⁻-containing strong electrolytes. The pore diameter of the self-organized structure was estimated to be in the region of 70-90 nm. Voltages were applied by stepping, which positively influenced passivity breakdown and played a significant role in the formation of self-organized nanoporous films. Under visible light irradiation, the photocurrent density (at 1.6 V vs. Ag/AgCl) and maximum photoconversion efficiency generated by the annealed nanoporous film were 3.45 mA/cm² and 0.91%, respectively. The annealed nanoporous WO₃ films show maximum incident photon-to-current conversion efficiency of 92% at 340 nm at 1.2 V vs. Ag/AgCl. These values are higher than that of annealed compact WO₃ film due to the large interfacial heterojunction area. The photoelectrochemical activities and electronic conductivities were also enhanced by annealing crystallization, which removed the recombination centers.     

Effects of annealing temperature on the photocatalytic activity of N-doped TiO2 thin films

The effects of annealing temperature on the photocatalytic activity of nitrogen-doped (N-doped) titanium oxide (TiO₂) thin films deposited on soda-lime-silica slide glass by radio frequency (RF) magnetron sputtering have been studied. Glancing incident X-ray diffraction (GIAXRD), Raman spectrum, scanning electron microscopy (SEM), atomic force microscopy (AFM) and UV-vis spectra were utilized to characterize the N-doped TiO₂ thin films with and without annealing treatment. GIAXRD and Raman results show as-deposited N-doped TiO₂ thin films to be nearly amorphous and that the rutile and anatase phases coexisted when the N-doped TiO₂ thin films were annealed at 623 and 823 K for 1 h, respectively. SEM microstructure shows uniformly close packed and nearly round particles with a size of about 10 nm which are on the slide glass surface for TiO₂ thin films annealed at 623 K for 1 h. AFM image shows the lowest surface roughness for the N-doped TiO₂ thin films annealed at 623 K for 1 h. The N-doped TiO₂ thin films annealed at 623 K for 1 h exhibit the best photocatalytic activity, with a rate constant (k_a) of about 0.0034 h⁻¹.     

Microstructure and electrochemical properties of electron-beam deposited Sn-Cu thin film anodes for thin film lithium ion batteries

Thin film Sn-Cu anodes with high Cu content were prepared by electron-beam evaporation deposition using Cu substrate as current collector. Annealing, with the condition being determined by DSC, was used to improve the performance of these electrodes. X-ray diffraction (XRD), scanning probe microscopy (SPM), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) were used to characterize the structure and composition of the Sn-Cu thin film electrodes. Cyclic voltammetry and galvanostatical charge-discharge measurement were carried out to characterize the electrochemical properties of the as-deposited and annealed electrodes. ?-Cu₃Sn intermetallic phase was formed and interface strength between deposited active materials layer and current collector was enhanced by annealing the as-deposited film under suitable condition. The annealed thin film electrode showed good cycleability and had no phase change during cycling. Although large initial capacity loss was found associated with SEI formation due to increase of surface roughness of annealed electrode, a stable discharge capacity near 300 mAh/g with Coulomb efficiency of about 96% was obtained at voltage window of 0.1-2.0 V and a discharge capacity of about 200 mAh/g and Coulomb efficiency of 97% were kept stable up to 30th cycle at a narrower voltage window of 0.2-1.5 V versus Li/Li⁺.     

Mechanosynthesis,crystal structure and magnetic characterization of M-type SrFe12O19

M-type strontium hexaferrite was prepared by mechanosynthesis using high-energy ball milling. The influence of milling parameters, hematite excess and annealing temperature on magnetic properties of SrFe₁₂O₁₉ were investigated. Commercial iron and strontium oxides were used as starting materials. It was found that mechanical milling followed by an annealing treatment at low temperature (700 °C) promotes the complete structural transformation to Sr-hexaferrite phase. For samples annealed at temperatures from 700 to 1000 °C, saturation magnetization values (M_s) are more sensitive to annealing temperature than coercivity values (H_c). The maximum M_s of 60 emu/g and H_c of 5.2 kOe were obtained in mixtures of powders milled for 5 h and subsequently annealed at 700 °C. An increase in the annealing temperature produces negligible changes in magnetic saturation and coercivity. An excess of hematite as a second phase produces a slight decrease in the saturation magnetization but leads to a significant increase in coercive field, reaching 6.6 kOe.     

Soft template synthesis of mesoporous Co3O4/RuO2·xH2O composites for electrochemical capacitors

Co₃O₄/RuO₂·xH₂O composites with various Ru content (molar content of Ru = 5%, 10%, 20%, 50%) were synthesized by one-step co-precipitation method. The precursors were prepared via adjusting pH of the mixed aqueous solutions of Co(NO₃)₂·6H₂O and RuCl₃·0.5H₂O by using Pluronic123 as a soft template. For the composite with molar ratio of Co:Ru = 1:1 annealed at 200 °C, Brunauer-Emmet-Teller (BET) results indicated that the composite showed mesoporous structure, and the specific surface area of the composite was as high as 107 m² g⁻¹. The electrochemical performances of these composites were measured in 1 M KOH electrolyte. Compared with the composite prepared without template, the composite with P123 exhibited a higher specific capacitance. When the molar content of Ru was rising, the specific capacitance of the composites increased significantly. It was also observed that the crystalline structures as well as the electrochemical activities were strongly dependent on the annealing temperature. A capacitance of 642 F/g was obtained for the composite (Co:Ru = 1:1) annealed at 150 °C. Meanwhile, the composites also exhibited good cycle stability. Besides, the morphologies and textural characteristic of the samples were also investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM).     

Effects of thermal annealing on the optical properties of Ar ion irradiated ZnS films

Ar-ion-implantation to a dose of 1×10¹⁷ ions/cm² was performed on cubic ZnS thin films with (111) preferred orientation deposited on fused silica glass substrates by vacuum evaporation. After ion implantation, ZnS films were annealed in flowing argon at different temperatures from 400 to 800 °C. The effects of ion implantation and post-thermal annealing on the structural and optical properties of ZnS films were investigated by X-ray diffraction (XRD), photoluminescence (PL) and optical transmittance measurements. XRD reveals that the diffraction peaks recover at ∼500 °C. The optical transmittances show that the bandgap of ZnS films blueshifts when annealed below 500 °C, and redshifts when annealed above 500 °C. PL results show that the intrinsic defect related emissions decrease with increasing annealing temperature from 400 to 500 °C, and increase with increasing annealing temperature from 500 to 800 °C. The observed PL emissions at 414 and 439 nm are attributed to the transitions of Zn_i→V_Zn and V_S→VBM, respectively.     

Preparation and magnetic properties of iron titanium oxide nanotube arrays

FeTi alloy was prepared by a vacuum smelting method, iron titanium oxide nanotube arrays have been made directly by anodization of the FeTi alloy. Morphologies and microstructures of the samples were characterized by scanning electron microscope, transmission electron microscope, and X-ray diffractometer. Influences of temperature and H₂O concentration on the morphologies of the nanotube arrays have been discussed in detail. Magnetic properties of the samples have also been investigated. The as-prepared samples were amorphous. When annealed at 500 °C and 550 °C, pesudobrookite Fe₂TiO₅ was obtained. At 600 °C, there were mixed Fe₂TiO₅, rutile TiO₂, and α-Fe₂O₃. Magnetic performance of the nanotube arrays exhibited high sensitivity to temperature and changed interestingly upon annealing. The values of the coercivity and remanence were 340 Oe and 0.061 emu/g respectively for the sample annealed at 550 °C.     

Electrochemical characterization of amorphous LiFe(WO4)2 thin films as positive electrodes for rechargeable lithium batteries

Amorphous LiFe(WO₄)₂ thin films have been fabricated by radio-frequency (R.F.) sputtering deposition at room temperature. The as-deposited and electrochemically cycled thin films are, respectively, characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, selected area electron diffraction, and X-ray photoelectron spectra techniques. An initial discharge capacity of 198 mAh/g in Li/LiFe(WO₄)₂ cells is obtained, and the electrochemical behavior is mostly preserved in the following cycling. These results identified the electrochemical reactivity of two redox couples, Fe³⁺/Fe²⁺ and W⁶⁺/W^x+ (x = 4 or 5). The kinetic parameters and chemical diffusion coefficients of Li intercalation/deintercalation are estimated by cyclic voltammetry and alternate-current (AC) impedance measurements. All-solid-state thin film lithium batteries with Li/LiPON/LiFe(WO₄)₂ layers are fabricated and show high capacity of 104 μAh/cm² μm in the first discharge. As-deposited LiFe(WO₄)₂ thin film is expected to be a promising positive electrode material for future rechargeable thin film batteries due to its large volumetric rate capacity, low-temperature fabrication and good electrode/electrolyte interface.     

The vacuum-annealed undoped polycrystalline CVD diamond electrodes: the impedance-spectroscopy and photoelectrochemical studies

The electrochemical impedance, photocurrent, and photopotential are measured in the supporting electrolyte solution (2.5 M H₂SO₄) for electrodes made of the undoped polycrystalline CVD diamond films annealed in vacuum at 1500-1640 °C. Analysis of the impedance spectra allowed concluding that both the amount of a nondiamond conducting phase in the electrode bulk and its conductivity increased upon annealing. With increasing annealing temperature, the photopotential passed through a maximum at ∼1570 °C. The photosensitivity of “metal-like” samples (annealed at temperatures ≥1630 °C) is negligibly small. Judging from the sign of the photopotential (positive) and photocurrent (cathodic), the studied material formally behaves as a p-type semiconductor. It is suggested that the photoeffects are caused by the structure defects, in particular, dislocations in diamond crystallites, formed close to intercrystalline boundaries during the high-temperature annealing.