Photoanodic properties of ZnO thin films prepared from zinc acetate solutions containing cobalt acetate and polyvinylpyrrolidone

ZnO thin films were deposited on nesa silica glass substrates via sol-gel method using Zn(CH₃COO)₂·2H₂O—Co(CH₃COO)₂ ·4H₂O—polyvinylpyrrolidone (PVP)—diethanolamine—2-methoxyethanol solutions. The effects of the Co²⁺ ions and PVP in coating solutions on the photoanodic properties of the resultant films were studied by measuring photocurrent—potential curves and action spectra in a three-electrode cell with a supporting electrolyte of pH = 9.18. The photoanodic current under xenon lamp light decreased with increasing amount of Co²⁺ ions due to the decreased quantum efficiency in the UV regions. The photoresponse was extended to wavelengths of ca. 450 nm when the Co/Zn mole ratios were 0.05 and 0.15, while the response to the visible light diminished at Co/Zn > 0.3. The UV photoresponse of Co²⁺-free ZnO films increased when PVP was added in the coating solutions, where the maximum quantum yield of 0.62 was obtained at a wavelength of 364 nm. On the other hand, the UV photoresponse rather decreased when PVP was added in Co²⁺-containing solutions.     

Ferroelectric properties of PLZT films prepared by the sol-gel process using chemically modified metal-alkoxides

Homogeneous PLZT films of the composition (Pb_0.91La_0.09) (Zr_0.65Ti_0.35)_0.98O₃ were prepared via the sol-gel process using lead and lanthanum salts, and zirconium and titanium alkoxides chemically modified with acetylacetone. The hydrated lead acetate was dissolved in an ethanol solvent in the presence of monoethanolamine, the whole preparation procedure was carried out in an ambient atmosphere, without dehydration of the metal salts. The heat-treatment of the coating films on a Pt substrate at 700 C produced PLZT films of perovskite single phase. The ferroelectric properties, such as remanent polarization and coercive field, of the films were dependent on the film thickness.     

Estimation of nonlinear interfacial capacitance from domain switching current of ferroelectric thin films

We introduce a methodology to estimate the nonlinear capacitance of interfacial “passive” layers of ferroelectric thin films from domain switching currents directly. The methodology has the advantage over the traditional extrapolation technique of a linear plot of the inversed capacitance against the film thickness which neglects the size effect on the ferroelectricity. Expectedly, this technique remains suitable in ultrathin films with the thickness scaling down into a few nanometers, where the size effect is important. From our measurements, we found that the interfacial capacitance increases nonlinearly with the reduction of the applied voltage in a tendency similar to the capacitance-voltage curve of ferroelectric thin films above the coercive voltage. Nevertheless, the capacitance at a high field drops down closely to a value derived from the traditional extrapolation technique. The pertinent physics is discussed in this work. Finally, we observed the reduction of the interfacial capacitance with the rising temperature, which suggests the thickening of interfacial layers at high temperatures.     

Structural properties of Cu(In,Ga)Se2 thin films prepared from chemically processed precursor layers

We have developed a chemical process for incorporating copper into indium gallium selenide layers with the goal of creating a precursor structure for the formation of copper indium gallium diselenide (CIGS) photovoltaic absorbers. Stylus profilometry, EDX, Raman spectroscopy, XRD and SIMS measurements show that when indium gallium selenide layers are immersed in a hot copper chloride solution, copper is incorporated as copper selenide with no increase in the thickness of the layers. Further measurements show that annealing this precursor structure in the presence of selenium results in the formation of CIGS and that the supply of selenium during the annealing process has a strong effect on the morphology and preferred orientation of these layers. When the supply of Se during annealing begins only once the substrate temperature reaches ≈ 400 °C, the resulting CIGS layers are smoother and have more pronounced preferred orientation than when Se is supplied throughout the entire annealing process.     

Characterization of ferroelectric and superconducting ceramics prepared from precursor carbonates

The advantages of a new semi-wet method for the synthesis of (Ba, Ca)TiO₃ and YBa₂Cu₃O_{7 − y} powders from precursor carbonates are described. The precursor carbonates are prepared using chemical coprecipitation technique under controlled pH conditions to ensure uniform distribution of Ba⁺²/Ca⁺² and Y⁺³/Ba⁺² ions. It is shown that the powders synthesized by this route possess better chemical homogeneity as compared to those obtained by the conventional ceramic technique involving calcination of a mixture of BaCO₃, CaCO₃, TiO₂ and Y₂O₃, BaCO₃, CuO powders. The behaviour of the ferroelectric (Ba, Ca)TiO₃ and the superconducting YBa₂Cu₃O_{7 − y} ceramics prepared from powders obtained by our method are found to be markedly different from those known for the conventionally prepared ceramics.     

Optical and structural properties of sol-gel prepared MgZnO alloy thin films

Mg_xZn_1−xO (x = 0-0.5) alloy thin films were prepared by a sol-gel dip-coating method. Mg_0.1Zn_0.9O and Mg_0.5Zn_0.5O films prepared were annealed in the range of 400-900 °C to investigate their thermal stability and temperature-dependent optical properties. The Mg_0.1Zn_0.9O films were thermally stable in the investigated annealing temperature range and exhibited the maximum ultraviolet emission at 800 °C. The segregation of MgO occurred in the Mg_0.5Zn_0.5O films, and the near-band-edge ultraviolet emission of this alloy was enhanced with increasing annealing temperature. The Mg saturation content in the sol-gel prepared MgZnO alloys was found to be about 0.23 where the band gap extended to 3.48 eV.     

The influence of the precursor concentration on CuSbS2 thin films deposited from aqueous solutions

The paper discusses the influence of precursor concentration on the morphology and the structure of CuSbS₂ thin films obtained from aqueous solutions and used as absorber for three-dimensional (3D) solar cells. CuSbS₂ films are obtained by Spray Pyrolysis Deposition, varying the precursor weight ratio (CuCl₂·2H₂O: H₂NCSNH₂: (CH₃COO)₃Sb) between 2.57: 1: 5.71-6.86: 1: 5.71, at 240 °C. The films were analyzed by XRD, I-V dark measurements and SEM. Enriching the films in antimony proved to be a control method of the films morphology and structure.     

On the structural and electrical characteristics of zinc oxide thin films

ZnO thin films with thickness d = 100 nm were deposited by radio frequency magnetron sputtering onto glass substrate from different targets. The structural analyses of the films indicate they are polycrystalline and have a wurtzite (hexagonal) structure. Crystallites are preferentially oriented with (002) plane parallel to the substrate surface and the samples have low values for surface roughness, between 1.7 nm and 2.7 nm. The mechanism of electrical conduction in the studied films is strongly influenced by this polycrystalline structure and we used Van der Pauw method to analyze these properties. Electrical studies indicate that the ZnO thin films are n-type. For the cooling process, thermal activation energy of electrical conduction of the samples can vary from 1.22 eV to 1.07 eV (for the ZnO layer obtained from for metallic Zn target) and from 0.90 eV to 0.63 eV (for the ZnO layer obtained from ZnO target), respectively. The influence of deposition arrangement and oxidation conditions on the structural and electrical properties of the ZnO films was investigated in detail.     

金属有机物分解法制备SrBi2Ta2O9铁电薄膜的开关特性

用金属有机物分解（MOD）以及sol-gel方法制备了SiBi2Ta2O9（STB）铁电薄膜。经测量在750℃晶化的SBT薄膜具有很好的铁电性能。通过对SBT样品极化反转过程进行测试,得出了外加电压（0．5－5V）与SBT薄膜的开关时间（100－600ms）及极化反转电荷的关系。并研究了不同气氛不退火对SBT铁电薄膜形状特性的影响。     

Optical and structural properties of chemically deposited CdS thin films on polyethylene naphthalate substrates

CdS thin films were deposited on polyethylene naphthalate substrates by means of the chemical bath deposition technique in an ammonia-free cadmium-sodium citrate system. Three sets of CdS films were grown in precursor solutions with different contents of Cd and thiourea maintaining constant the concentration ratios [Cd]/[thiourea] and [Cd]/[sodium citrate] at 0.2 and 0.1 M/M, respectively. The concentrations of cadmium in the reaction solutions were 0.01, 7.5 × 10⁻³ and 6.8 × 10⁻³ M, respectively. The three sets of CdS films were homogeneous, hard, specularly reflecting, yellowish and adhered very well to the plastic substrates, quite similar to those deposited on glass substrates. The structural and optical properties of the CdS films were determined from X-ray diffraction, optical transmission and reflection spectroscopy and atomic force microscopy measurements. We found that the properties of the films depend on both the amount of Cd in the growth solutions and on the deposition time. The increasing of Cd concentration in the reaction solution yield to thicker CdS films with smaller grain size, shorter lattice constant, and higher energy band gap. The energy band gap of the CdS films varied in the range 2.42-2.54 eV depending on the precursor solution. The properties of the films were analyzed in terms of the growth mechanisms during the chemical deposition of CdS layers.     

Investigation of structural properties of amorphous carbon nitride thin films prepared by xenon cloride pulsed laser deposition of camphoric carbon precursor

Raman scattering analysis revealed that the structure of carbon (C) films prepared by pulsed laser deposition at room temperature is predominantly amorphous and the structure of amorphous C nitride (a-CN_x) films can be changed with varying substrate temperatures (ST) from 20 to 500 °C. The deposited a-CN_x films are composed of C-N, C-N and C-O bonded materials and the C-N and C=N bonds are increased with ST. We have found no other obvious peaks can be distinguished in the range 900 to 2300 cm⁻¹ in which several peaks always appear in a-CN_x films. The spectra were deconvoluted into Raman D and G peaks and the structural parameters are determined. The upward shifts of Raman G peak towards 1592 cm⁻¹ shows the evidence of a progressive formation of crystallites in a-CN_x films upon increase of ST. While, the upward shifts of Raman D peak towards 1397 cm⁻¹ have been related to the decreased of bond-angle disorder and sp³ tetrahedral bonding in its structure. Raman FWHM and I_DI_G also indicate that N incorporation with increased of ST caused an increase in the number and/or size of graphitic domains in the a-CN_x films.     

Growth and characterization of thin films prepared from perfluoro-isopropyl-substituted perfluorophthalocyanines

Vapor deposition of perfluorinated phthalocyanines with bulky perfluorpropyl groups (F₆₄Pc) yielded intensely colored thin films (20-100 nm) despite the large molecular weight. In situ electrical conduction and optical transmission measurements revealed an almost negligible extent of intermolecular electronic coupling. Such quasi-independent character of molecules in solids was confirmed by detailed spectroscopic ellipsometry. The influence of the bulky peripheral groups on the packing in the films and on the electronic and optical properties of the films as well as potential applications of this class of strong electron acceptors are discussed.     

Growth and structural properties of Mg:C thin films prepared by magnetron sputtering

We investigate the growth and structure properties of Mg:C thin films. The films are prepared using a dc magnetron sputtering discharge where the electrical resistance over the films is monitored during growth in-situ with a four point probe setup. The structural properties of the films are investigated using X-ray diffraction measurements and the elemental composition and binding in the films is determined using elastic recoil detection analysis and X-ray photoelectron spectroscopy. The results show that during co-sputtering the carbon flux influences the initial stages of the film growth. The films are made of polycrystalline magnesium grains embedded in a carbon network, the size of which depends on the carbon content, but amorphous phases cannot be excluded. The XPS measurements show the presence of carbidic carbon whereas X-ray measurements find no Mg:C phases. The overall stability of the films is found to depend on the carbon content, where stable films capped with a 14 nm Pd layer cannot be obtained with carbon content above 18%.     

The role of drying-control chemical additives on the preparation of sol-gel derived PLZT thin films

Films of Pb _x/100La _x/100(Zr _y/100Ti _z/100)_1–x/400O₃ with x=8, y=65 and z=35 (PLZT(8/65/35)) with a single perovskite structural phase were successfully prepared by using drying-control chemical additives in sol-gel processing followed by rapid thermal annealing at 600 °C for only 1 min on Si(Pt) substrates. The roles of the drying-control chemical additives ethylene glycol and formamide in the gel preparation were studied. The hysteresis loop of PLZT(8/65/35) thin film was measured. The remanent polarization and coercive field were found to be about 1.3 C cm^–2 and 15 kVcm^–1, respectively.     

Fatigue,retention and switching properties of PLZT(x/30/70) thin films with various La concentrations

We investigated the fatigue, retention and switching properties of PLZT(x/30/70) thin films with various La concentrations. By applying 10⁹ square pulse switching cycles with a voltage of ±5 V to study the fatigue properties of the film, we found that the decrease of the initial polarization is improved from 64% to 40% as the La concentration is increased from 0 mol% to 10 mol%. The retention properties are also greatly improved as the decrease of the initial polarization decrease is reduced from 47% to 9% after 10⁵ s. The switching time is decreased from 0.8 μs to 0.55 μs as the La concentration is increased. While the dielectric constant of the PLZT thin films increases from 450 to 600 as the La concentration is increased, the dielectric loss and leakage current density measured at 100 kV/cm decrease from 0.075 to 0.025 and from 5.83 × 10⁻⁷ to 1.38 × 10⁻⁷ A/cm², respectively. By analyzing the hysteresis loops of the PLZT thin film measured at 175 kV/cm, we found that the remnant polarization and coercive electric field decrease from 20.8 μC/cm² to 10.5 μC/cm² and from 54.48 kV/cm to 32.12 kV/cm, respectively, as the La concentration is increased.     

Optical and structural characteristics of silicon nanoparticles thin film prepared by laser ablation

In this paper thin film of silicon nanoparticles on glass substrates have been prepared by dip-coating method using colloidal silicon nanoparticles generated by nanosecond laser ablation of silicon wafer in ethanol. The resulting nanoparticles and structural properties and morphology of thin film were characterized by UV-Visible absorption spectrometry, transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction pattern and atomic force microscopy image. Nanoparticles with diameters ~ 9 nm were observed to be formed in the colloidal solution. The atomic force microscopy image of Si nanoparticles thin film shows that the overall average width is about 80 nm.     

Magnetic and structural characteristics of ion beam sputter deposited Co-Cr thin films

-The magnetic and structural characteristics of ion beam sputter deposited Co82Cr18films were investigated. Films of between 1000A and 10,000A thickness were deposited on glass, titanium, chromium and amorphous Ta-W-Ni. The average angle of incidence of the sputtered species was normal to the substrate surface. Film orientation was determined by x-ray pole figure analysis. In films deposited on glass with thicknesses below 10,000A, the     

Determination of structural and optical parameters of CuO thin films prepared by double dip technique

Cupric oxide (CuO) thin films are deposited on glass substrates by double dip method at various molar concentrations of copper sulphate salt. Growth mechanism is derived using oxolation process. The structural studies revealed the deposited films exhibited polycrystalline nature with monoclinic structure. The change in the molar concentration of copper sulphate salt has pronounced effect on the microstructural properties of deposited thin films. XPS and EDS spectra confirm the presence of Cu and O. Micro Raman spectra shows two A_g and B_g active Raman mode peaks corresponding to CuO phase. Deposited films showed a high absorbance in the visible range with the bandgap value of 1.3 eV making it a suitable material as semiconductor tandem absorber for solar cells. Optical constants such as refractive index (n), extinction coefficient (k), optical conductivity (σ) and dielectric constants (ε) were evaluated using an approximation protocol developed from well recognized procedures using the data obtained from UV spectroscopic technique. The prepared CuO thin films are identified as suitable candidates for optoelectronic devices and solar cell fabrication.     

Electrical and optical characteristics of SnO2 thin films prepared by dip coating from aqueous colloidal suspensions

Starting from aqueous colloidal suspensions, undoped and Nb⁵⁺ doped SnO₂ thin films have been prepared by using the dip-coating sol-gel process. X-ray diffraction results show that films are polycrystalline with crystallites of average size 1–4 nm. Decreasing the thickness of the films and increasing the Nb⁵⁺ concentration limits the crystallite size growth during firing. Complex impedance measurements reveal capacitive and resistive effects between adjacent crystallites or grains, characteristic of electrical potential barriers. The transfer of charge throughout these barriers determines the macroscopic electrical resistance of the layer. The analysis of the optical absorption spectra shows that the samples present more than 80% of their transmittance in the visible region and the value of the band gap energy increases with decreasing crystallite size. This revised version was published online in July 2006 with corrections to the Cover Date.