Fabrication of ZnO thin films by the photochemical deposition method

ZnO thin films were fabricated by the photochemical deposition (PCD) method. The deposition solution contains ZnSO₄, Na₂SO₃, Na₂S₂O₃ and a small amount of NH₄OH for pH adjustment. We blew oxygen or oxygen + ozone (O₃) gas into the solution to increase the dissolved oxygen content and enhance the oxidation reaction. The films were characterized by Auger electron and optical spectroscopy, and a photoelectrochemical (PEC) measurement. On an indium-tin-oxide (ITO) substrate, the films showed high optical transmission in the visible range. In a current-voltage measurement for films on a p-Si substrate, the O₃ bubbling sample showed rectification properties and photovoltaic effects.     

Growth and characterization of nitrogen-doped TiO2 thin films prepared by reactive pulsed laser deposition

Nitrogen-doped titanium dioxide (TiO₂) thin films were grown on (001) SiO₂ substrates by reactive pulsed laser deposition. A KrF* excimer laser source (λ = 248 nm, τ_FWHM ≅ 10 ns, ν = 10 Hz) was used for the irradiations of pressed powder targets composed by both anatase and rutile phase TiO₂. The experiments were performed in a controlled reactive atmosphere consisting of oxygen or mixtures of oxygen and nitrogen gases. The obtained thin film crystal structure was investigated by X-ray diffraction, while their chemical composition as well as chemical bonding states between the elements were studied by X-ray photoelectron spectroscopy. An interrelation was found between nitrogen concentration, crystalline structure, bonding states between the elements, and the formation of titanium oxinitride compounds. Moreover, as a result of the nitrogen incorporation in the films a continuous red-shift of the optical absorption edge accompanied by absorption in the visible spectral range between 400 and 500 nm wavelength was observed.     

Photoelectrochemical performance of aluminum-doped AgIn5S8 electrodes created using chemical bath deposition

A solution growth method for the deposition of Al-doped silver-indium-sulfide film electrodes is presented. Structural, optical, and photoelectrochemical (PEC) properties of samples were studied as a function of Al content. An X-ray diffraction pattern of the cubic spinel AgIn₅S₈ phase was obtained for the undoped sample. No Al alloys or other binary compounds that included the Al element were present in Al-doped samples. Images from a scanning electron microscope and atomic ratios of elements in samples from the energy dispersion analysis of X-ray revealed a change of surface morphology and composition for Al-doped samples. The direct band gaps and thicknesses of samples prepared in this study varied from 1.78 to 1.90 eV and from 391 to 293 nm, respectively. The carrier concentration and mobility of samples determined from Hall measurements are in the ranges of 1.02 × 10¹³-1.97 × 10¹⁴ cm^− 3 and 16-75 cm²/Vs, respectively. The maximum photo-enhancement current density of samples reached 3.22 mA/cm² at an external potential of + 1.0 V vs. an Ag/AgCl reference electrode in an aqueous solution containing S²⁻ and SO₃²⁻ ions under illumination using a 300 W Xe lamp system. The experimental results show that Al doping improves the performance of AgIn₅S₈ photo-absorber for the PEC applications with an Al/(Al + In) molar ratio of 0.03 in samples.     

Visible light photoelectrocatalysis with salicylic acid-modified TiO2 nanotube array electrode for p-nitrophenol degradation

This research focused on immersion method synthesis of visible light active salicylic acid (SA)-modified TiO₂ nanotube array electrode and its photoelectrocatalytic (PEC) activity. The SA-modified TiO₂ nanotube array electrode was synthesized by immersing in SA solution with an anodized TiO₂ nanotube array electrode. Scanning electron microscope (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), infrared spectroscopy (IR), UV–vis diffuse reflectance spectrum (DRS), and Surface photovoltage (SPV) were used to characterize this electrode. It was found that SA-modified TiO₂ nanotube array electrode absorbed well into visible region and exhibited enhanced visible light PEC activity on the degradation of p-nitrophenol (PNP). The degradation efficiencies increased from 63 to 100% under UV light, and 79–100% under visible light (λ > 400 nm), compared with TiO₂ nanotube array electrode. The enhanced PEC activity of SA-modified TiO₂ nanotube array electrode was attributed to the amount of surface hydroxyl groups introduced by SA-modification and the extension of absorption wavelength range.     

Cadmium sulfide nanotubes thin films: Characterization and photoelectrochemical behavior

Monodisperse cadmium sulfide nanotubes (CdS NTs) with a diameter of 100 nm were synthesized on indium-doped tin oxide glass substrates using chemical bath deposition and self-sacrificial template technique. This CdS thin film was characterized by transmission electron microscope, scanning electron microscope, X-ray diffraction, X-ray photoelectron spectroscopy and UV-vis spectrophotometer. This film gave a short circuit photocurrent of 4.4 mA/cm², an open circuit photovoltage of 0.75 V, a fill factor of 0.49, and an overall conversion efficiency of 1.29% under a simulated solar illumination of 100 mW/cm². All these photoelectrochemical properties of the films were dependent on the microstructure of the nanotubes and the thickness of the film. A facile and efficient way to prepare CdS-based photoelectrodes for photoelectrochemical cells was provided in this report.     

Effect of aluminum doping on the properties of PEC cells formed with CdS:Al films

Aluminum doped and undoped CdS films were prepared by chemical bath deposition technique and the photoelectrochemical (PEC) properties have been studied by forming doped CdS/NaOHNa₂SS/C junction. Better results are obtained with 0.1 wt% Al doped CdS films. These results are discussed with the help of the optical and transport properties of the Al doped CdS films.     

Sub-2 nm SnO2 nanocrystals: A reduction/oxidation chemical reaction synthesis and optical properties

A simple reduction/oxidation chemical solution approach at room temperature has been developed to synthesize ultrafine SnO₂ nanocrystals, in which NaBH₄ is used as a reducing agent instead of mineralizers such as sodium hydroxide, ammonia, and alcohol. The morphology, structure, and optical property of the ultrafine SnO₂ nanocrystals have been characterized by high-resolution transmission electron microscopy (HRTEM), X-ray powder diffraction (XRD), differential scanning calorimetry and thermogravimetric analysis (DSC-TGA), X-ray photoelectron spectroscopy (XPS) and UV-vis absorption spectroscopy. It is indicated that the uniform tetragonal ultrafine SnO₂ nanocrystals with the size below 2 nm have been fabricated at room temperature. The band gap of the ultrafine SnO₂ nanocrystals is about 4.1 eV, exhibiting 0.5 eV blue shift from that of the bulk SnO₂ (3.6 eV). Furthermore, the mechanism for the reduction/oxidation chemical reaction synthesis of the ultrafine SnO₂ nanocrystals has been preliminary presented.     

Structural, optical and photoelectrochemical properties of electrodeposited CdSe thin films

Cadmium Selenide thin films have been electrodeposited from an acidic bath using CdSO₄ as a cadmium source and SeO₂ as a selenium source at pH=3 on to stainless steel and fluorine-tin oxide coated glass substrates. The CdSe films have been characterized by X-ray diffraction, scanning electron microscopy and optical absorption. X-ray diffraction spectra showed that CdSe is polycrystalline with single hexagonal phase. The intensity of the (0 0 2) peak increases remarkably by annealing in nitrogen atmosphere. A microstructural study revealed that the films were uniform and well covered the substrate. Optical absorption studies showed that the bandgap of the CdSe is 1.70 eV. It is observed that the conductivity of the CdSe films increases by annealing in nitrogen atmosphere. The photoelectrochemical activities of CdSe films deposited on stainless steel and fluorine-tin oxide coated glass have been studied by using CdSe/ 1 M NaOH-1 M Na₂S-1 MS / C cell configuration and it is found that films deposited on stainless steel give better performance, photoelectrochemical (PEC) studies also reveal that the CdSe has n-type conductivity.     

Deposition of rod-shaped antimony sulfide thin films from single-source antimony thiosemicarbazone precursors

Antimony sulfide thin films were deposited on glass substrates by aerosol assisted chemical vapour deposition technique using single source precursors, namely, antimony(III) thiosemicarbazones, SbCl₃(L) (L = thiosemicarbazones of thiophene-2-carboxaldehyde (1) and cinnamaldehyde (2)). The deposited films were characterized by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis and UV-visible spectroscopy in order to identify their phases, morphologies, compositions and optical properties respectively. These characterizations revealed that the films were comprised of rod-shaped particles of orthorhombic stibnite (Sb₂S₃) with a Sb:S stoichiometry of ∼ 1:1.3. The calculated optical band gap from UV-vis absorption spectrum is found to be 3.48 eV.     

Fabrication of novel SnO2 nanofibers bundle and their optical properties

Here we report on the synthesis of novel SnO₂ nanofibers bundle (NFB) by using ball milled Fe powders via chemical vapor deposition (CVD). The reaction was carried out in a horizontal tube furnace (HTF) at 1100 °C under Ar flow. The as prepared product was characterized by X-ray diffraction (XRD), scanning electron microscopy, energy dispersive X-ray spectroscopy, transmission electron microscopy, high resolution transmission electron microscopy and selected area electron diffraction (SAED). The microscopy analysis reveals the existence of tubular structure that might be formed by the accumulation of nanofibers. The Raman spectrum reveals that the product is rutile SnO₂ with additional peaks ascribed to defects or oxygen vacancies. Room temperature Photoluminescence (PL) spectrum exhibits three emission bands at 369, 450 and 466.6 nm. Using optical absorbance data, a direct optical bandgap of 3.68 eV was calculated.     

Room temperature metathetic synthesis and characterization of α-hopeite, Zn3(PO4)2·4H2O

The synthesis of crystalline zinc phosphates (α-hopeite phase) through the metathetic pathway has been investigated. The reaction has been carried out by room-temperature grinding. High lattice energy of the by-product NaCl has driven the reaction in the forward direction, and as a result, stable phosphate phases have been synthesized. Reaction of a different phosphorus source (like Na₃PO₄, Na₂HPO₄, NaH₂PO₄, and K₂HPO₄) with ZnCl₂ has been attempted. The structural, vibrational, thermal, optical, and chemical properties of synthesized powders are determined by powder X-ray diffraction (XRD), scanning electron microscope (SEM), thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR) and diffused reflectance spectra (DR) in the UV-vis range. The direct band gap of the title compound was determined to be 3.6 ± 0.2 eV.     

Composition dependence of structural and optical properties of Ba(Zrx,Ti1-x)O3 thin films grown on MgO substrates by pulsed laser deposition

Ba(Zr_x,Ti_1-x)O₃ (BZT) films with Zr concentration ranging from 0 to 40% were grown on MgO single crystal substrates by pulsed laser deposition, and their optical properties in the visible range were systematically characterized. A linear increase in the out-of-plane lattice constant of BZT unit cell with increasing Zr content was detected by X-ray diffraction. The surface morphology was observed by atomic force microscopy and the grain size was shown to increase with Zr concentration. Prism coupling and UV-visible transmission spectroscopy techniques were used to analyze the optical properties of the films. Refractive index between 2.15 and 2.3 was observed at 633 and 1547 nm respectively, which decreased with rising Zr content. The BZT films also possessed large optical band gap energy up to 3.92 eV, which increased with rising Zr content. Quadratic electro-optic effect was observed with electro-optic coefficients between 0.11 and 0.81 × 10^− 18 m²/V², which decreased with Zr concentration. Optical loss was estimated from scattering and absorption, and the absorption coefficient dropped with increasing Zr content at near band gap. The obtained results provide information for the design of BZT thin film-based optical devices.     

Growth and optical properties of uniform tungsten oxide nanowire bundles via a two-step heating process by thermal evaporation

Tungsten oxide (WO₃) nanowires with diameters of 15-40 nm and lengths of hundreds of nanometers were synthesized by thermal chemical vapor deposition (CVD) without using any catalyst in a low-temperature zone (200-300 °C) of a tube furnace via a two-step heating process. The morphology, composition, and crystal structure were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDS), Raman, ultraviolet UV-visible, and cathodoluminescence (CL) spectroscopy. XRD and TEM confirmed that the nanowires were triclinic WO₃ with growth direction along [001]. Blue emission was observed in both the UV-visible and CL spectrum, indicating that the WO₃ nanowires exhibited a red-shift at an optical absorption wavelength due to oxygen deficiencies. The crystallinity and size distribution of the nanowires influenced the bandgap. In the CL spectrum, the blue emission was at shorter wavelengths than reported previously, which can be attributed to the nanoscale size effect.     

Synthesis and photoluminescence of ultra-pure germanium nanoparticles

We have used aerosol deposition to synthesize defect and micro-strain free, ultra-pure germanium nanoparticles. Transmission electron microscopy images show a core-shell configuration with highly crystalline core material. Powder X-ray diffraction measurements verify the presence of highly pure, nano-scale germanium with average crystallite size of 30 nm and micro-strain of 0.058%. X-ray photoelectron spectroscopy demonstrates that GeO_x (x ? 2) shells cover the surfaces of the nanoparticles. Under optical excitation, these nanoparticles exhibit two separate emission bands at room temperature: a visible emission at 500 nm with 0.5-1 ns decay times and an intense near-infrared emission at 1575 nm with up to ∼20 μs lifetime.     

Nonlinear optical properties of laser deposited CuO thin films

In this work we investigate the third-order optical nonlinearities in CuO films by Z-scan method using a femtosecond laser (800 nm, 50 fs, 200 Hz). Single-phase CuO thin films have been obtained using pulsed laser deposition technique. The structure properties, surface image, optical transmittance and reflectance of the films were characterized by X-ray diffraction, Raman spectroscopy, scanning electron microscopy and UV-vis spectroscopy. The Z-scan results show that laser-deposited CuO films exhibit large nonlinear refractive coefficient, n₂ = − 3.96 × 10^− 17 m²/W, and nonlinear absorption coefficient, β = − 1.69 × 10^− 10 m/W, respectively.     

The effect of heating time on growth of NaxWO3 nanowhiskers

A simple method for synthesis of Na_xWO₃ nanowhiskers on tungsten thin films with 40 nm thickness sputtered on soda lime substrate as a source of sodium atoms has been reported for the first time. After heat treatment of the W thin films at 650 °C in N₂ ambient for different times (15, 80 and 180 min), crystalline Na_xWO₃ nanowhiskers with [0 0 1] direction were obtained. scanning electron microscopy (SEM), X-ray diffractometry (XRD), X-ray photoelectron spectroscopy (XPS) and optical transmission/reflection measurements were employed to determine various properties of the grown nanowhiskers. Experimental results revealed that size and density of nanowhiskers were dependent on the annealing time and found that the 80-min heat treatment was a proper time for the growth of sodium-doped tungsten oxide nanowhiskers, in our experimental conditions. According to SEM observations, the synthesized nanowhiskers have 70-300 nm in width and 1-10 μm in length. It was also observed that by increasing the heating time to 180 min resulted in diffusion of the nanowhiskers into the substrate.     

Synthesis and luminescent properties of ZnNb2O6 nanocrystals for solar cell

The phase formation, morphology and luminescent properties of ZnNb₂O₆ nanocrystals by the sol-gel method were investigated at a lower temperature than that of the traditional solid-state reaction method. The products were characterized by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), photoluminescence spectroscopy (PL) and absorption spectra. The activation energy of ZnNb₂O₆ grain growth is obtained about 18.4 kJ/mol. The diameters of the nanocrystals are in the range of 20-40 nm. The PL spectra excited at 276 nm have a broad and strong blue emission band maximum at 450 nm, corresponding to the self-activated luminescence of the niobate octahedra group [NbO₆]⁷⁻. The optical absorption spectrum of the sample at a calcination temperature of 800 °C has a band gap energy of 3.68 eV.     

Impedance spectroscopy and relaxation phenomena of (Na,K) excess Na0.5K0.5NbO3 thin films grown by chemical solution deposition

Na_0.5K_0.5NbO₃ (NKN) and 10 mol% (Na,K) excess Na_0.5K_0.5NbO₃ (NKN10) thin films on Pt/Ti/SiO₂/Si substrate were prepared by chemical solution deposition. Crystallization of NKN10 thin films was confirmed by X-ray diffraction. The (Na,K) excess Na_0.5K_0.5NbO₃ thin film shows a ferroelectric P-E hysteresis loop. Dielectric properties and impedance spectroscopy of thin films were investigated in the frequency range from 0.1 Hz to 100 kHz and the temperature range of 25 ~ 500 °C. By analyzing the complex impedance relaxation with Cole-Cole plots, we found impedance relaxations for the thin film. The contribution of electrical conduction is discussed in relation to grain, grain boundary, and interface effects.     

Hydrothermal growth of double-layer TiO2 nanostructure film for quantum dot sensitized solar cells

A double-layer (DL) film with a TiO₂ nanosheet-layer on a layer of TiO₂ nanorod-array, was synthesized on a transparent conductive fluorine-doped tin oxide substrate by a two-step hydrothermal method. Starting from the precursors of NaSeSO₃, CdSO₄ and the complex of N(CH₂COOK)₃, CdSe quantum dots (QDs) were grown on the DL-TiO₂ substrate by chemical bath deposition method. The samples were characterized by X-ray diffraction, Scanning electron microscopy, Energy dispersion spectroscopy, and their optical scattering property was measured by light reflection spectrometry. Some CdSe QDs sensitized DL-TiO₂ films serve as the photoanodes, were assembled into solar cell devices and their photovoltaic performance were also characterized. The short circuit current and open-circuit voltage of the solar cells range from 0.75 to 4.05 mA/cm² and 0.20 − 0.42 V under the illumination of one sun (AM1.5, 100 mW/cm²), respectively. The photocurrent density of the DL-TiO₂ film is five times higher than that of a bare TiO₂ nanorod array photoelectrode cell.     

A photoelectrochemical study of CdS modified TiO2 nanotube arrays as photoanodes for cathodic protection of stainless steel

An electrodeposited CdS nanoparticles-modified highly-ordered TiO₂ nanotube arrays (CdS-TNs) photoelectrode and its performance of photocathodic protection are reported. The self-organized TiO₂ nanotube arrays are fabricated by electrochemical anodization in an organic-inorganic mixed electrolyte and sensitized with CdS nanoparticles by electrodeposition via a single-step direct current. The morphology, crystalline phase, and composition of the CdS-TNs films were characterized systematically by scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and ultraviolet-visible (UV-Vis) spectroscopy, respectively. The photoelectrochemical performances of the CdS-TNs film under illumination and dark conditions in 0.5 M NaCl solution were evaluated through the electrochemical measurements. It is indicated that the TNs incorporated by CdS effectively harvest solar light in the UV as well as the visible light (up to 480 nm) region. It is supposed that the high photoelectro-response activity of the CdS-TNs is attributed to the increased efficiency of charge separation and transport of electrons. The electrode potentials of 304 stainless steel coupled with the CdS-TNs is found to be negatively shifted for about 246 mV and 215 mV under UV and white light irradiation, respectively, which can be remained for 24 h even in darkness. It is implied that the CdS-TNs are able to effectively function a photogenerated cathodic protection for metals both under the UV and visible light illumination.