Photoelectrical properties of ZnS thin films deposited from aqueous solution using pulsed electrochemical deposition

ZnS is an n-type semiconductor with a wide direct band gap (3.7 eV at room temperature), and it is very suitable as a window layer in heterojunction photovoltaic solar cells. We deposited ZnS thin films on Sn-doped In₂O₃-coated glass substrate using pulsed electrochemical deposition (ECD) from aqueous solutions containing Na₂S₂O₃ and ZnSO₄ with two different compositions, the first group grown from ZnSO₄-rich solution, and the second grown from Na₂S₂O₃-rich solution. We investigated electrical properties of the ZnS thin films and properties of contacts with different metals evaporated on the surfaces. We found that Au and In contacts have Ohmic-like characteristics to ZnS. Furthermore, we observed photoconductivity of the ZnS thin films by means of photoelectrochemical (PEC) measurements. We found that for both the groups of ZnS thin films, the as-deposited film shows weak photosensitivity and after annealing at 300 °C the photosensitivity improved.     

Characterization of electrical properties and photosensitivity of SnS thin films prepared by the electrochemical deposition method

Using the electrochemical deposition (ECD) method, we prepared tin sulfide thin films, which are suitable for the absorption layer in solar cells because of its bandgap energy (1 eV). We first optimized pulse-form biasing for ECD by characterizing deposited samples with scanning electron microscope, Auger electron spectroscopy and X-ray diffraction measurements. Then, we investigated the electrical properties of deposited SnS thin films and the properties of contacts with several different metals. Furthermore, we observed the photoconductivity of the films by means of photoelectrochemical measurements. From these results, we confirmed that the SnS thin films show p-type conduction.     

Electrodeposition of ZnO thin films by using molecular oxygen and hydrogen peroxide as oxygen precursors: Structural and optical properties

Zinc oxide thin films were potentiostatically electrodeposited from a ZnCl₂+LiCl bath using two different oxygen precursors: molecular oxygen and hydrogen peroxide. X-ray diffraction (XRD) studies confirmed the presence of the ZnO wurtzite structure with marked preferential orientation along the (0 0 2) axis. The optical transmittance shows a clear absorption edge in the ultraviolet (UV) region which corresponds to an energy band gap of 3.41±0.03 eV. As a general rule the higher band gap energies are related to the more transparent films.     

Optical and photoconductive properties of SnS thin films prepared by electron beam evaporation

Thin films of SnS have been prepared by electron beam evaporation. The films represent Herzbergite orthorhombic structure, established by their XRD patterns. The band gap energy and type of optical transitions were determined from transmission spectra and an optical band gap of E_g(tr)=1.23 eV for indirect transitions and E_g(tr)=1.38 eV for direct transitions were estimated. Using the dependence of photoconductivity from wavelength, a band gap of E_g(ph)=1.2 eV was determined as well. A thermal band gap of E_g(T)=1.29 eV was evaluated from the temperature dependence of the dark resistivity, and admixture level with activation energies (0.25 and 0.36 eV) were found. Roughness of the surface of SnS thin films was evaluated using atomic force microscopy.     

A study of the electrochemical performance of vanadium oxide thin films grown by atmospheric pressure chemical vapour deposition

Thin films of vanadium oxide were deposited on glass substrates at 450 ^oC by atmospheric pressure chemical vapour deposition. The effect of the vanadium tetrachloride to water precursor ratio on the structural and morphological properties of the films was investigated. The water concentration was observed to strongly affect the vanadium oxidation state and the morphological characteristics of the films. The importance of achieving single-phase of a particular oxidation state towards the improvement of the electrochemical performance of thin films grown by atmospheric pressure CVD is highlighted.     

A study on properties of yttrium-stabilized zirconia thin films fabricated by different deposition techniques

This paper investigates the micro-structural, chemical and crystalline properties of yttrium-stabilized zirconia (YSZ) thin films by using pulsed laser deposition (PLD), atomic layer deposition (ALD) and sputter. Atomic ratio of Y:Zr of YSZ thin films fabricated by three different deposition methods was adjustable. ALD YSZ with smaller grains has high density compared to PLD YSZ and sputter YSZ. On the other hand, the low crystallinity of ALD YSZ can be supplemented by annealing process. From these experimental results, ALD YSZ thin film has the characteristics that satisfy requirements for using an electrolyte of thin film solid oxide fuel cells.     

Highly transparent and conducting fluorine-doped ZnO thin films prepared by pulsed laser deposition

Highly transparent and conducting fluorine-doped ZnO (FZO) thin films were deposited on glass substrates by pulsed laser deposition. Structural, electrical, and optical properties of the films were investigated as a function of oxygen pressure ranging from 0.01 to 0.5 Pa. All the films had a highly preferential c-axis orientation. The films obtained were dense and very smooth with a typical columnar structure. A minimum resistivity of 4.83×10⁻⁴ Ω cm, with a carrier concentration of 5.43×10²⁰ cm⁻³ and a Hall mobility of 23.8 cm² V⁻¹ s⁻¹, was obtained for FZO film prepared at the optimal oxygen pressure of 0.1 Pa. The average optical transmittance in the entire visible wavelength region was higher than 90%.     

Pd/Mg/Pd thin films prepared by pulsed laser deposition under different helium pressures: Structure and electrochemical hydriding properties

Three-layered Pd/Mg/Pd thin films were prepared by pulsed laser deposition in the presence of helium gas. For Pd layer deposition, the He pressure was fixed at 200 mTorr whereas different pressures of He were used for Mg layer deposition (50, 200 and 600 mTorr). The degree of crystallinity and of (001) texture in the Mg layer increase with increasing He pressure. In addition, the increase in He pressure upon Mg deposition greatly accentuates the roughness of the Mg layer, which induces an extension of the outer Pd/Mg interface region. In contrast, the inner Pd/Mg interface is sharp for all the Pd/Mg/Pd films. The electrochemical hydrogen sorption properties of the Pd/Mg/Pd films are improved by increasing the He pressure for Mg layer deposition. However, the maximum H-solubility in the Mg layer remains low (H/Mg ∼0.26) and is not significantly increased by the presence of the inner Pd layer, indicating that Mg hydride phase is confined in the outer Pd/Mg interface region.     

Fabrication of nickel boride-coated carbon nanotube films by electrophoresis and electroless deposition for electrochemical hydrogen storage

Network-like carbon nanotube (CNT) films free of polymer binder were deposited directly onto a stainless steel substrate by electrophoresis. Results of experiments indicated that a CNT film with duplex surface treatment (nitric acid etching and nickel boride coating) provides satisfactory electrochemical hydrogen storage. Nitric acid treatment increased the hydrogen storage capacity of the CNT film due to the opening of CNTs, the formation of micropores in the CNT surface, and the improvement of surface wettability. Coating the CNT film with nickel boride (Ni₂B) greatly improved the electrochemical activity of the film and consequently increased the hydrogen storage capacity. The optimal amount of nickel boride coating on the CNT film was found to be about 45 wt%. Smaller amounts of nickel boride cannot provide enough electrochemical activity. Excessive nickel boride, on the other hand, leads to a decrease in the number of active sites on CNTs that are available for hydrogen storage.     

Pulsed laser deposition of manganese oxide thin films for supercapacitor applications

Thin films of manganese oxides have been grown by the pulsed laser deposition (PLD) process on silicon wafer and stainless steel substrates at different substrate temperatures and oxygen gas pressures. By proper selection of processing parameters such as temperature and oxygen pressure during the PLD process, pure crystalline phases of Mn₂O₃, Mn₃O₄ as well as amorphous phase of MnO_x were successfully fabricated as identified by X-ray diffraction. The pseudo-capacitance behaviours of these different phases of manganese oxides have also been evaluated by the electrochemical cyclic voltammetry measured in 0.1 M Na₂SO₄ aqueous electrolyte at different scan rates. Their specific current and capacitance determined by electrochemical measurements were compared and the results show that crystalline Mn₂O₃ phase has the highest specific current and capacitance, while the values for crystalline Mn₃O₄ films are the lowest. The specific current and capacitance values of the amorphous MnO_x films are lower than Mn₂O₃ but higher than Mn₃O₄. The specific capacitance of Mn₂O₃ films of 120 nm thick reaches 210 F g⁻¹ at 1 mV s⁻¹ scan rate with excellent stability and cyclic durability. This work has demonstrated that PLD is a very promising technique for screening high performance active materials for supercapacitor applications due to its excellent flexibility and capability of easily controlling chemical composition, microstructures and phases of materials.     

ZnSe thin films by chemical bath deposition method

The ZnSe thin films have been deposited onto glass substrates by the simple chemical bath deposition method using selenourea as a selenide ion source from an aqueous alkaline medium. The effect of Zn ion concentration, bath temperature and deposition time period on the quality and thickness of ZnSe films has been studied. The ZnSe films have been characterized by XRD, TEM, EDAX, TRMC (time-resolved microwave conductivity), optical absorbance and RBS techniques for their structural, compositional, electronic and optical properties. The as-deposited ZnSe films are found to be amorphous, Zn rich with optical band gap, Eg, equal to 2.9 eV.     

Low-temperature deposition of polycrystalline silicon thin films by hot-wire CVD

Polycrystalline silicon films have been prepared by hot-wire chemical vapor deposition (HWCVD) at a relatively low substrate temperature of 430°C. The material properties have been optimized for photovoltaic applications by varying the hydrogen dilution of the silane feedstock gas, the gas pressure and the wire temperature. The optimized material has 95% crystalline volume fraction and an average grain size of 70 nm. The grains have a preferential orientation along the (2 2 0) direction. The optical band gap calculated from optical absorption by photothermal deflection spectroscopy (PDS) showed a value of 1.1 eV, equal to crystalline silicon. An activation energy of 0.54 eV for the electrical transport confirmed the intrinsic nature of the films. The material has a low dangling bond-defect density of 10¹⁷ cm³. A photo conductivity of 1.9 × 10⁻⁵ Ω⁻¹cm⁻¹ and a photoresponse (σ_ph/σ_d) of 1.4 × 10² were achieved. A high minority-carrier diffusion length of 334 nm as measured by the steady-state photocarrier grating technique (SSPG) and a large majority-carrier mobility-lifetime (μτ) product of 7.1 × 10⁻⁷cm²V⁻¹ from steady-state photoconductivity measurement ensure that the poly-Si : H films possess device quality. A single junction n---i---p cell made in the configuration n⁺-c-Si/i-poly-Si: H/p-μc-Si : H/ITO yielded 3.15% efficiency under 100 mW/cm² AM 1.5 illumination.     

The electrochemical properties of LSM-based cathodes fabricated by electrostatic spray assisted vapour deposition

La_0.8Sr_0.2MnO_3−δ (LSM) and LSM–8 mol% yttria-stabilized zirconia (YSZ) composite cathodes were fabricated using electrostatic spray assisted vapour deposition (ESAVD) method. The porous cathode layers of LSM and LSM–YSZ with high specific surface areas were obtained by optimizing the deposition parameters. It was found that the introduction of YSZ into LSM decreased the electrochemical impedance significantly. The activation effect of passing current on the electrochemical activity of the LSM–YSZ composite cathodes was much lower than that of the LSM cathodes. For the LSM–YSZ composite cathodes, there was a saturation of current with increasing applied potential at higher temperatures (from 900 to 1000 °C). The LSM–YSZ composite cathode fabricated by ESAVD exhibited high electrochemical activity at high and intermediate temperatures (from 800 to 1000 °C). This suggests that ESAVD is a promising technique for the fabrication of solid oxide fuel cell (SOFC) cathodes.     

An electrochemical and analytical characterization of surface films on AISI 316 as electrode material for pulse electrolysis of water

Pulse electrolysis of water is a highly efficient method of production of hydrogen and hydrogen/oxygen gas mixtures, sometimes called hydroxygen. In conditions of pulse electrolysis, the process rate is reported to increase in comparison to the dc regime, which poses more stringent requirements to the corrosion resistance of the electrode materials. The processes of their corrosion and degradation are expected to depend on the electrical characteristics of the pulse (nominal current/voltage, frequency, duty cycle). The aim of the present paper is to investigate the effect of pulse characteristics on the electrochemical properties of surface films formed on AISI 316 stainless steel using voltammetry and electrochemical impedance spectroscopy. An attempt to correlate these properties with the surface state obtained from microscopic observations and X-ray photoelectron spectroscopic estimations of the surface film composition is also made.     

Electrodeposition and characterization of ZnSe semiconductor thin films

In this work, results on the preparation and characterization of ZnSe thin films obtained by electrodeposition are presented. Voltammetric curves were recorded in order to characterize the electrochemical behavior of the Zn⁺²/SeO₂ system on different substrates. Thin films were deposited potentiostatically from an unstirred, deareated aqueous solution onto titanium, glass substrates coated with fluorine doped tin oxide and ITO glass substrates. The effect of main parameters such as the deposition potential, SeO₂ concentration and annealing on film composition and structure were analyzed. The as-grown and treated layers were characterized by X-ray energy dispersive analysis, X-ray diffraction, scanning electron microscopy and photoelectrochemical studies. Optical measurements were done on these samples which gave a clear band edge near 2.6 eV quite close to the accepted room temperature value of 2.7 eV for ZnSe.     

Electrophoretic deposition of graphene nanosheets on nickel foams for electrochemical capacitors

Graphene nanosheets are deposited on nickel foams with 3D porous structure by an electrophoretic deposition method using the colloids of graphene monolayers in ethanol as electrolytes. The high specific capacitance of 164 F g⁻¹ is obtained from cyclic voltammetry measurement at a scan rate of 10 mV s⁻¹. When the current densities are set as 3 and 6 A g⁻¹, the specific capacitance values still reach 139 and 100 F g⁻¹, respectively. The high capacitance is attributed to nitrogen atoms in oxidation product of p-phenylene diamine (OPPD) adsorbed on the surface of the graphene nanosheets. The comparable results suggest potential application to electrochemical capacitors based on the graphene nanosheets.     

Copper oxide thin films prepared by chemical vapor deposition from copper dipivaloylmethanate

Polycrystalline copper oxide thin films are prepared at a reaction temperature above 280°C by an atmospheric-pressure chemical vapor deposition method. The source materials were copper dipivaloylmethanate and oxygen. It has been shown from the experiment that two kinds of films, i.e., Cu₂O and CuO are grown by controlling oxygen partial pressure. A series of characterizations on the film quality by scanning electron microscope, X-ray photoelectron spectroscopy, X-ray diffraction and Fourier transform infrared spectrometer has been made, and the performance of solar thermal conversion are also identified on the produced films. Results show that the well-crystallized CuO film has lower infrared transmittances due to the scatterings of light through the optically anisotropic monoclinic structure.     

Cathodic deposition and characterization of tin oxide coatings on graphite for electrochemical supercapacitors

Amorphous tin oxide (SnO_x) was cathodically deposited onto graphite electrode in a bath containing 0.1 M stannous chloride (SnCl₂), 0.5 M sodium nitrate (NaNO₃), and 0.4 M nitric acid (HNO₃) in an aqueous solution of 50% (v/v) ethanol. The SnO_x coatings grown on graphite were characterized as typical capacitive behaviors by cyclic voltammetry (CV), chronopotentiometric (CP) in 0.5 M KCl. Specific capacitance (in milli-farad per square centimeter, C_a) changes linearly with the deposition charge up to 4.5 C cm⁻², and a maximum of as high as 355 mF cm⁻² was obtained with the SnO_x coating grown at around 5 C cm⁻². For the SnO_x coating deposited at 0.2 C cm⁻², a maximum specific capacitance (in farad per gram, C_m) of 298 and 125 F g⁻¹ was achieved from CVs at a scan rate of 10, and 200 mV s⁻¹, respectively. The value of C_m significantly gets lower from 265 to around 95 F g⁻¹ when the deposition charge increases from 0.2 to around 6.0 C cm⁻². The long cycle-life and stability of the SnO_x coatings on graphite via the presented cathodic deposition were also demonstrated.