Effect of Annealing on the Electrical Properties of CuxS Thin Films

Copper sulphide CuS was deposited on three substrates; glass, Indium Tin Oxide (ITO) and Ti by using spray pyrolysis deposition (SPD). After depositing CuS thin films on the substrates at 200 °C, they were annealed at 50, 100, 150, and 200 °C for 1 hour. Structural measurements revealed covellite CuS and chalcocite Cu₂S phases for thin films before and after annealing at 200 °C with changes in intensities, and only covellite CuS phase for thin films after annealing at 50, 100, and 150 °C. Morphological characteristics show hexagonal-cubic crystals for the CuS thin film deposited on glass substrate and plates structures for films deposited on ITO and Ti substrates before annealing, these crystals became bigger in size and there were be oxidation and some agglomerations in some regions with formation of plates for CuS on glass substrate after annealing at 200 °C. For Hall Effect measurements, thin films sheet resistivity and mobility increased after annealing while the carrier concentration decreased. Generally, the thin film deposited on ITO substrate had the lowest resistivity and the highest carrier concentration before and after annealing. The thin film deposited on Ti substrate had the highest mobility before and after annealing, which makes it the best thin film for device performance. The objective of this research is to show the improvement of thin films electrical properties especially the mobility after annealing those thin films.     

Synthesis of nickel selenide thin films for high performance all-solid-state asymmetric supercapacitors

As a significant semiconductor, nickel selenide shows enormous potential and extensive application prospects in the field of sensor, photocatalysis and supercapacitor. In this paper, nickel selenide (Ni₃Se₂, NiSe) thin films were successfully fabricated on stainless-steel sheet using a facile, effective electrodeposition technique. The morphologies, microstructures and chemical compositions of the thin films are characterized systematically. Electrochemical tests exhibit that the Ni₃Se₂ and NiSe possess high specific capacitance of 581.1 F/g and 1644.7 F/g, respectively. A flexible, all-solid-state asymmetric supercapacitor is assembled by utilizing NiSe film as positive electrode and activated carbon as negative electrode. The solid device delivers a high areal capacitance of 27.0 mF/cm² at the current density of 0.7 mA/cm². The maximum volumetric energy density and power density of the NiSe//AC asymmetric SCs can achieve 0.26 mWh/cm³ and 33.35 mW/cm³, respectively. The device shows robust cycling stability with 84.6% capacitance retention after 10,000 cycles, outstanding flexibility and satisfactory mechanical stability. Moreover, two devices in series can light up a red light-emitting diode, which displayed great potential applications for energy storage.     

Effect of Hg2+doping and of the annealing temperature on the nanostructural properties of TiO2 thin films obtained by sol–gel method

This work is a study of Hg²⁺-doped TiO₂ thin films deposited on silicon substrates prepared by sol–gel method and treated at temperatures ranging between 600 to 1000 °C for 2 h. The structural and optical properties of thin films have been studied using different techniques. We analyzed the vibrations of the chemical bands by Fourier transform infrared (FTIR) spectroscopy and the optical properties by UV–Visible spectrophotometry (reflection mode) and photoluminescence (PL). The X-ray diffraction and Raman spectra of TiO₂ thin films confirmed the crystallization of the structure under the form of anatase, rutile, mercury titanate (HgTiO₃) as a function of the annealing temperature. The observation by scanning electron microscopy (SEM) showed the changing morphology, with respect to nanostructures, nanosheets, nanotubes, with the annealing temperature. The diameters of nanotubes ranged from 50 nm to 400 nm. The photoluminescence and reflectance spectra indicated that these structures should enhance photocatalytic activity.     

Synthesis and characterization of CaBi4Ti4O15 thin films annealed by microwave and conventional furnaces

CaBi₄Ti₄O₁₅ thin films were deposited by the polymeric precursor method and crystallized in a domestic microwave oven and conventional furnace. The films obtained for microwave energy are well-adhered, homogeneous and with good specularity when treated at 700 ^°C for 10 min. The microstructure and the structure of the films can be tuned by adjusting the crystallization conditions. When microwave oven is employed, the films presented bigger grains with mean grain size around 80 nm. For comparison, films were also prepared by the conventional furnace at 700 °C for 2 h.     

Electrodeposition of CuInSe2 films by an alternating double-potentiostatic method using nearly neutral electrolytes

One step electrodeposition with an alternating double-potentiostatic(DPSED) program was used to prepare CuInSe₂ thin films in nearly neutral aqueous electrolytes with sodium citrate complex. Linear sweep voltammetry(LSV) was measured to probe voltammetric properties of electrolytes with respect to Cu, In and Se individual precursor and their mixed solutions. Compositional and structural characteristics of the as-deposited and annealed films at 400 °C in Ar atmosphere for 0.5 h were analyzed by XRD and XPS. The results showed that reduction of Cu²⁺ to Cu⁺ at one potential point of ?800 mV and subsequently formation of CuIn alloy as well as metal In and amorphous Se at the other potential point of ?1400 mV were responsible for synthesis of CISe chalcopyrite. Composition self-regulation made DPSED films have three elements co-deposition and more uniform element distribution, which promoted chalcopyrite CISe formation.     

Thickness dependent physical properties of close space evaporated In2S3 films

In recent years, In₂S₃ is considered as a promising buffer layer in the fabrication of heterojunction solar cells. Film thickness is one of the important parameters that alters the physical characteristics of the grown layers significantly. The effect of film thickness on the structural, morphological, optical and electrical properties of close space evaporated In₂S₃ layers has been studied. In₂S₃ thin films with different thicknesses in the range, 100–700 nm were deposited on Corning glass substrates at a constant substrate temperature of 300 °C. The films were polycrystalline exhibiting strong crystallographic orientation along the (103) plane. The deposited films showed mixed phases of both cubic and tetragonal structures up to a thickness of 300 nm. On further increasing the film thickness, the layers showed only tetragonal phase. With increase of film thickness, both the crystallite size and surface roughness in the films were found to be increased. The optical constants such as refractive index and extinction coefficient of the as-grown layers have been calculated from the optical transmittance data in the wavelength range, 300–2500 nm. The optical transmittance of the films was decreased from 82% to 64% and the band gap varied in the range, 2.65–2.31 eV with increase of film thickness. The electrical resistivity as well as the activation energy was evaluated and found to decrease with film thickness. The detailed study of these results was presented and discussed.     

Effects of electron beam irradiation on the photoelectrochemical properties of TiO2 film for DSSCs

TiO₂ has been widely utilized for various industrial applications such as photochemical cells, photocatalysts, and electrochromic devices. The crystallinity and morphology of TiO₂ films play a significant role in determining the overall efficiency of dye-sensitized solar cells (DSSCs). In this study, the preparation of nanostructured TiO₂ films by electron beam irradiation and their characterization were investigated for the application of DSSCs. TiO₂ films were exposed to 20–100 kGy of electron beam irradiation using 1.14 MeV energy acceleration with a 7.46 mA beam current and 10 kGy/pass dose rates. These samples were characterized using X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), and X-ray photoelectron spectroscopy (XPS) analysis. After irradiation, each TiO₂ film was tested as a DSSC. At low doses of electron beam irradiation (20 kGy), the energy conversion efficiency of the film was approximately 4.0% under illumination of simulated sunlight with AM 1.5 G (100 mW/cm²). We found that electron beam irradiation resulted in surface modification of the TiO₂ films, which could explain the observed increase in the conversion efficiency in irradiated versus non-irradiated films.     

Exploration of spray pyrolysis technique in preparation of absorber material CFATS: Unprecedented hydrophilic surface and antibacterial properties

In this study, we achieve the production of nontoxic Cu₂Fe_1-xAl_xSnS₄ films (x = 0, 0.25, 0.50, 0.75 and 1) by substituting Fe with Al atoms. Physical properties of the investigated films were studied using: Energy dispersive X-ray spectrometry (EDX), scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, spectrophotometer and drop shape analysis system (DSA). The formation of new quaternary Cu₃Al_0.6Sn₁S₆ (CATS) chalcogenide for x = 1 was proven from EDX study. Notably, the major diffraction peaks were located at 2θ = 28.34°, 47.43° and 55.93° which are respectively tagged as (1 1 2), (2 0 4), and (3 1 2) plans, confirming the stannite crystal structure of Cu₃Al_0.6Sn₁S₆ film. The morphological states show a nanofiber structure accompanied with voids and cavities for CATS films. Tauc-relation plot reveals direct energy bandgap, close to 1.52 eV, which proves the absorber film type of Cu₃Al_0.6Sn₁S₆. The effluent toxicity of the obtained thin films has been assessed using the inhibition of Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) bacteria and indicated good antibacterial activity of the CATS/SnO₂:F heterojunction. The viability rates against S. aureus achieved 40 %, 31 % and 15% for SnO₂:F, Cu₃Al_0.6Sn₁S₆ films and CATS/SnO₂:F heterojunction. These results highlight the great antibacterial activity of coupled CATS/SnO₂:F. Therefore this research underscores the effectiveness of CATS/SnO₂:F surface which demonstrates self-disinfecting and self-cleaning with hydrophilicity and high antibacterial activity.     

Gamma irradiation effect on the enzymatic activities of horseradish and apple peroxidases

The behavior at low-dose exposure (0.033–0.4 kGy) of horseradish peroxidase (HRP) and of two different purified fractions of apple (Jonathan cultivar) peroxidases (named APR_1S and APR_2S) was studied. The HRP solutions were added with either 0.32 M fructose or glucose in order to study their effect on enzymes activity response under γ (¹³⁷Cs, dose rate 0.4 kGy/h) irradiation. The obtained results showed similar behavior between HRP-sugar-added solution and apple fraction with higher oligosaccharides content (APR_2S) undergoing low-dose treatment. The same pattern was observed between unglycosylated HRP and APR_1S with lower oligosaccharides content. These similarities gave us the possibility to conclude that the presence of oligosaccharides, in more or less quantities, influences in the same way the peroxidases activity, from different plant species, exposed to γ irradiation.     

Preparation and photocatalytic activity of Cu-deposited TiO2 film with high transparency

Cu-deposited TiO₂ films were prepared by photoreduction of Cu(II) in the presence of sodium formate. With the initial Cu(II) concentrations more than 100 mg L^?1, induction periods were observed before the transmittance decreased. Scanning electron microscopy indicated that Cu particles of 2.6 ± 0.5 μm were deposited isolatedly with much open space in the induction periods. The films prepared by changing the irradiation time within the induction periods showed a higher photocatalytic activity than a pure TiO₂ for the degradation of methylene blue under the reaction condition without purging air.     

Spontaneous formation of an electroactive co-polymeric film derived from nordihydroguaiaretic acid and 4,4′-diaminobibenzyl

Binary solution of nordihydroguaiaretic acid (NDGA) and 4,4′-diaminobibenzyl (DABB) undergoes rapid oxidation by ambient oxygen to form a thin film of poly-NDGA-co-DABB on the surface of the reaction chamber and on immersed substrates. Electrochemistry of thus formed films was studied in 0.1 M sulfuric acid and in phosphate buffer (pH 7.4). Electrochemical behavior of the co-polymeric film is characterized by two redox couples, the predominant one being observed at more negative potentials comparing to parent NDGA i.e. 0.28 vs. 0.49 V (vs. Ag/AgCl) in 0.5 M H₂SO₄. The peak potentials were shifted toward lower values with solution pH at the rate of 59 mV/pH unit indicating a 2e/2H⁺ transition as expected for quinone-containing films. The poly-NDGA-co-DABB film exhibits catalytic activity toward electroreduction of nitrite to nitric oxide in acidic electrolytes. This reaction can be used to quantify nitrite in a broad concentration range with low detection limit (0.3 μM, S/N = 3).     

Effect of γ-irradiation exposure on optical properties of chalcogenide glasses Se70S30−xSbx thin films

We investigate in the present paper the effect of the γ-irradiation exposure by 100–500 kGy doses on the optical properties and single oscillator parameters for chalcogenide glasses Se₇₀S_30?xSb_x (x=0, 12, 18 and 30 at%) thin films. These parameters were modeled from transmission spectra data measured by spectrophotometry in the wavelength range 200–2500 nm. It was found that the refractive index of the investigated films increases with increasing the doses of γ-radiation. This post-irradiation increase in the refractive index was interpreted in terms of the increase of the density of the investigated films with irradiation due to ionization or atomic displacements. Besides, the refractive index dispersions data of both the as-deposited and γ-irradiated Se₇₀S_30?xSb_x films obeyed the single oscillator model. The calculated single oscillator parameters; oscillator strength E_d, static refractive index n_o, zero frequency dielectric constant ε_o increased after irradiation while the oscillator energy E_o, reduced after irradiation. The absorption coefficient was found to increase with the increase of the doses of γ-radiation. Furthermore, the obtained optical energy gap of chalcogenide glasses Se₇₀S_30?xSb_x films was found to decrease with increasing the doses of γ-radiation which is attributed to increase of the defects after irradiation. This is confirmed by the decrease in the Urbach energy E_e after radiation. The γ-irradiation stimulated increase in the absorption coefficient and change in the optical parameters which can be utilized for industrial dosimetric purposes.     

Optical properties of a-Se90In10−x Snx chalcogenide thin films before and after gamma irradiation

Amorphous Se₉₀In_10?xSn_x (x=2, 4, 6, and 8) thin films of thickness 1000 Å were prepared on glass substrates by the thermal evaporation technique. Optical parameters of the films were investigated, in the wavelength range 400–700 nm, before and after irradiation by 4, 8, and 12 kGy doses of γ-ray. The optical absorption coefficient α for as-deposited and gamma irradiated films was calculated from the reflectance R and transmittance T measurements, which were recorded at room temperature. From the knowledge of α, at different wavelengths, the optical band gap E_g was calculated for all compositions of Se–In–Sn thin films before and after gamma irradiation. Results indicate that allowed indirect optical transition is predominated in as-deposited and irradiated films. Besides, it is found that the band gap decreases with increasing Sn concentration and this is attributed to the corresponding decrease in the average single bond energy of the films. The band gap, after irradiation at different doses of γ-ray, was found to decrease for all compositions of the studied films. This post-irradiation decrease in the band gap was interpreted in terms of a bond distribution model.     

Towards sustainable materials for solar energy conversion: Preparation and photoelectrochemical characterization of Cu2ZnSnS4

The feasibility of a new fabrication route for films of the attractive solar absorber Cu₂ZnSnS₄ (CZTS) has been studied, consisting of electrodeposition of metallic precursors followed by annealing in sulfur vapour. Photoelectrochemical measurements using a Eu³⁺ contact have been used to establish that the polycrystalline CZTS films are p-type with doping densities in the range (0.5–5) × 10¹⁶ cm⁻³ and band gaps of 1.49 ± 0.01 eV, making them suitable for terrestrial solar energy conversion. It has been shown that a somewhat Cu-poor composition favours good optoelectronic properties.     

Enhancement of lithium ion conduction in the cubic rare earth oxide

A new type of lithium ion conducting solid electrolyte based on a cubic rare earth oxide was developed by co-doping LiNO₃ and KNO₃ into a (Gd_1−xNd_x)₂O₃ solid, which possesses large interstitial open spaces within the structure. Among the samples prepared, 0.6(Gd_0.4Nd_0.6)₂O₃–0.16LiNO₃–0.24KNO₃ exhibits the highest lithium ion conductivity of 8.05 × 10⁻² and 1.35 × 10⁻³ S cm⁻¹ at 400 and 100 °C, respectively, which is comparable to that of the LISICON materials. Pure Li⁺ ion conduction was successfully demonstrated by the dc electrolysis method.     

Photoelectrochemical water splitting using a Cu(In,Ga)Se2 thin film

The effects of surface modification and reaction conditions on the photoelectrochemical properties of polycrystalline Cu(In,Ga)Se₂ (CIGS) thin films for water splitting were studied. CIGS modified with platinum particles (Pt/CIGS) generated a cathodic photocurrent at potentials up to + 0.4 V vs. RHE at pH = 9.5. The photocurrent was stable for 16 h, which resulted in a turnover number of over 500. A CdS-inserted film (Pt/CdS/CIGS) had significantly improved properties compared to Pt/CIGS: a 0.3 V higher onset potential of cathodic photocurrent and a three-fold increase in the quantum efficiency. Our results suggest the feasibility of CIGS as a photocathode for biphotoelectrochemical water splitting.     

Influence of particle size on the photoactivity of Ti/TiO2 thin film electrodes,and enhanced photoelectrocatalytic degradation of indigo carmine dye

Photoanodes based on Ti/TiO₂ thin films were prepared by the sol–gel method, using either tetraisopropoxide (Ti(OPri)₄) or modified tetraisopropoxide, producing electrodes with different sized nanoparticle coatings, termed nanoporous (20 nm) or nanoparticulated (10 nm) electrodes. The anatase form dominated the composition of the nanoparticulated electrode, which presented a higher surface area, a flat band potential shift of ?160 mV and a 50% improvement in photoactivity, compared to the nanoporous electrode. 100% color removal, and 75% mineralization, of indigo carmine dye were achieved after 15 min of photoelectrocatalytic treatment using a nanoparticulated Ti/TiO₂ electrode operated at a current density of 0.4 mA cm^?2. Our findings indicate that the use of nanoparticulated electrodes, under UV irradiation and with controlled current density, is an efficient alternative for the removal of food dye contaminants during wastewater treatment.     

Chemically stable anode-supported solid oxide fuel cells based on Y-doped barium zirconate thin films having improved performance

Anode-supported solid oxide fuel cells (SOFCs) based on thin BaZr_0.8Y_0.2O_3 ? δ (BZY) electrolyte films were fabricated by pulsed laser deposition (PLD) on sintered NiO–BZY composite anodes. After in situ reduction of NiO to Ni, the anode substrates became porous, while retaining good adhesion with the electrolyte. A slurry-coated composite cathode made of La_0.6Sr_0.4Co_0.2Fe_0.8O_3 ? δ (LSCF) and BaCe_0.9Yb_0.1O_3 ? δ (BCYb), specifically developed for proton conducting electrolytes, was used to assemble fuel cell prototypes. Depositing by PLD 100 nm thick LSCF porous films onto the BZY thin films was essential to improve the cathode/electrolyte adhesion. A power density output of 110 mW/cm² at 600 °C, the largest reported value for an anode-supported fuel cell based on BZY at this temperature, was achieved. Electrochemical impedance spectroscopy (EIS) measurements were used to investigate the different contributions to the total polarization losses.     

Visible light active hydrogen modified (HM)-n-TiO2 thin films for photoelectrochemical splitting of water

Visible light active hydrogen modified n-type titanium oxide (HM-n-TiO₂) thin films were synthesized by thermal oxidation of Ti metal sheet (Alfa Co. 0.25 mm thick) in an electric oven followed by incorporation of hydrogen electrochemically under cathodic polarization at ?1.6 V vs Pt. The photoresponse of the HM-n-TiO₂ was evaluated by measuring the rate of water splitting reaction to hydrogen and oxygen in terms of photocurrent density, J_p. The optimized electric oven-made n-TiO₂ and HM-n-TiO₂ photoelectrodes showed photocurrent densities of 0.2 mA cm^?2 and 1.60 mA cm^?2, respectively, at a measured potential of ?0.4 V vs Pt at illumination intensity of 100 mW cm^?2 from a 150 W xenon lamp. This indicated an eightfold increase in photocurrent density for HM-n-TiO₂ compared to oven-made n-TiO₂ at the same measured electrode potential. The band-gap energy of HM-n-TiO₂ was found to be 2.7 eV compared to 2.82 eV for electric oven-made n-TiO₂ and a mid-gap band at 1.67 eV above the valence band was also observed. The HM-n-TiO₂ thin film photoelectrodes were characterized using photocurrent density under monochromatic light illumination and UV–Vis spectral measurements.     

Preparation of conducting silver paste with Ag nanoparticles prepared by e-beam irradiation

Conducting silver paste was prepared by using Ag nanoparticles which were synthesized by e-beam irradiation method (from KAERI); its conductivity was comparatively determined with Ag nanoparticles which were prepared by thermolysis method (commercial). The silver nanoparticles with the diameter of approximately 150 nm size prepared by e-beam irradiation were mixed with glass frit and sintered for 1 h at 500 °C. It is presumably concluded that the wt% of silver nanoparticle, size distribution and homogenous dispersibility of Ag nanoparticles in the pastes are the critical factors for the high conductivity of the paste. Among the various wt% of silver nanoparticle in the conducting silver pastes, silver paste with 90 wt% of silver nanoparticle has the highest conductivity as 1.6×10⁴ S cm^?1. This conductivity value is 1.6 times higher than the Ag pastes which were prepared with silver nanoparticles obtained by thermolysis method.