Pyroelectric properties of PLT thin films

Pyroelectric properties of PLT thin films prepared by MOD method are characterized. Dynamic pyroelectric responses of the films measured with Chynoweth method are presented. Pyroelectric responses of point and quadruple pyroelectric detectors using PLT20 thin films are measured. One-dimensional heat conduction model is used to analyze the properties of the detectors. requirements to the PLT films used for pyroelectric detectors are proposed.     

Dielectric properties of amorphous cellulose acetate-butyrate polymer films

The dielectric constant, loss tangent and AC conductivity of solution grown cellulose acetate-butyrate films of 5μm thickness were studied as a function of temperature (300-450 K) in the frequency range 10 Hz-10 MHz. The decrease in dielectric constant was observed with the increase in frequency as well as with temperature. A loss peak was observed in the dielectric loss spectra and was identified as the β-relaxation peak. The frequency-dependent conductivity was also studied. The results were interpreted in terms of electronic conduction via hopping processes.     

Mechanical properties of PECVD thin ceramic films

Silicon dioxide (thickness 350 nm and 969 nm) and silicon nitride (thickness 218 nm) films deposited on silicon substrate using plasma enhanced chemical vapor deposition process were investigated using a Berkovich nanoindenter. The load-depth measurements revealed that the oxide films have lower modulus and hardness compared to the silicon substrate, where as the nitride film has a higher hardness and slightly lower modulus than the substrate. To delineate the substrate effect, a phenomenological model, that captures most of the ‘continuous stiffness measurement’ data, was proposed and then extended on both sides to determine the film and substrate properties. The modulus and hardness of the oxide film were around 53 GPa and 4–8 GPa where as those of the nitride film were around 150 GPa and 19 GPa, respectively. These values compare well with the measurements reported elsewhere in the literature.     

Optoelectronic properties of In-doped SnS thin films

Nanostructured un- and In-doped SnS thin films were deposited on fluorine-doped tin oxide (FTO) substrates via an electrochemical deposition technique. The deposited thin films were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), energy dispersive spectroscopy (EDS), atomic force microscopy (AFM), electrochemical impedance spectroscopy (EIS), photoluminescence (PL) spectroscopy and UV–visible spectroscopy. The XRD patterns demonstrated that all deposited thin films are made of polycrystalline SnS particles. The AFM images illustrated a distinct change in the surface topography of the SnS thin films due to In-doping. The PL spectra showed two blue emission peaks and a green emission peak for all samples. Also, they highlighted a PL peak for the In-doped thin films. The incorporation of In-dopant leads to enhance in the optical absorption of SnS lattice. The optical energy band gap (E_g) of the deposited thin films was estimated using UV–vis spectroscopy, which indicated that In-doping decreases the E_g value of SnS thin films by creating defect levels. The photocurrent results demonstrated a higher photocurrent response and photocurrent amplitude for the In-doped SnS samples relative to the un-doped SnS thin film. The Mott–Schottky analysis revealed p-type conductivity for all samples. In addition, the carrier concentration of SnS was increased after In doping. The EIS spectra declared that In-doping improves the rate of charge transfer for SnS thin films. The charge transfer resistance of In-doped SnS decreased compared to the undoped SnS thin film. Finally, according to the J-V characteristics, the conversion efficiency of the In-doped SnS thin films was higher than that of the un-doped SnS sample. Therefore, the optical and electrical performance of SnS thin films were improved due to In-doping.     

Thermal and dynamic mechanical properties of hydroxypropyl cellulose films

Differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA) were used to characterize the morphology of solvent cast hydroxypropyl cellulose (HPC) films. DSC results were indicative of a semicrystalline material with a melt at 220°C and a glass transition at 19°C (T₁), although an additional event was suggested by a baseline inflection at about 80°C (T₂). Corresponding relaxations were found by DMTA. A secondary relaxation at ?55°C was attributed to the interaction between hydroxyl groups of the polymer and residual diluent. The tan δ peak at T₂ was found to arise from an organized phase, presumably from a liquid-crystal mesophase formed while in solution. Crosslinking with a diisocyanate increased the peak temperature of the two primary relaxations, and resulted in a more clearly defined peak for the T₂ transition. From this behavior it was concluded that both T₁ and T₂ are similar to glass transitions (T_g's) associated with an amorphous component and a more highly ordered phase (due to a residual liquid crystal superstructure) in the HPC bulk.     

Morphological study by TEM on uniaxially oriented thin films of PBT

We prepared uniaxially oriented thin films of poly(butylene terephthalate) (PBT) by applying shear strain to the melt and studied their resulting morphology by transmission electron microscopy (TEM), and could show visually that stacked-lamellar structures are formed in aromatic polyesters. On the basis of crystallographic consideration, we assigned each of the recognized stacked-lamellar structures to a shish-kebab structure or a part of it. In addition, we successfully demonstrated that in one shish-kebab structure all or almost all kebabs (namely, lamellae) have a same crystallographic orientation.     

Physical properties of novel free-standing polymer-nanotube thin films

Novel polymer-nanotube composites have been fabricated by the introduction of polymeric material into the free volume contained in carbon nanotube (CNT) mats grown by chemical vapour deposition. The resulting composite material can then be peeled from the substrate to give a free-standing film, the properties of which are controlled by the nanotubes. The nanotube mat acts as a percolative network resulting in increases in surface and bulk conductivities by factors of 10⁷ and 10⁸, respectively. The presence of CNTs also causes the Young’s Modulus of the polymer film to double. It is shown that the presence of CNTs has no effect on the morphology of the polymer itself.     

Preparation and properties of films and fibers of disordered cellulose

The preparation and properties of films and fibers of highly disordered cellulose are described; the basis of the preparation is the regeneration of cellulose from cellulose derivatives in non-aqueous media. These cellulose are at least 97% hydrogen-bond disordered (as measured by the infrared-deuteration technique), give x-ray diagrams showing poor three-dimensional order, and are practically completely accessible to swelling agents such as water and formic acid. The crystallization of these disordered celluloses is described. The effects on native cellulose of ball milling, mercerization, amine treatment, swelling in acid and salt solutions, and swelling in solutions of potassium hydroxide in non-aqueous solvents are described with reference to changes in fine structure as measured by the infrared-deuteration technique.     

Influence of electrolyte on electrical properties of thin cellulose acetate membranes

The electrical behavior of thin cellulose-2.5-acetate membranes for chemical semiconductor sensor applications was investigated. The influence of electrolyte on the electrical membrane properties was studied by means of electrochemical impedance spectroscopy. The polymeric membranes can be described using the electrical model of Cole and Cole. The membrane electrolyte distribution equilibria were investigated by means of an absorption–desorption method using conductivity measurements. The desorption kinetics for thin cellulose acetate membranes differ significantly from those of thicker cellulose acetate reverse osmosis membranes because here the rate of the ionic exchange at the membrane interface cannot be neglected. The experimentally determined distribution coefficients were used for the discussion of the electrolyte influence on the electrical membrane parameters. A functional dependence was found between the specific membrane resistance of cellulose acetate membranes and the ionic hydration enthalpy. The effect of electrolyte on the relative permittivity can be explained by a theoretical model. © 1994 John Wiley & Sons, Inc.     

Tribological properties of perfluoralkylethyl methacrylate-polymethyl methacrylate copolymer thin films

Perfluoroalkylethyl methacrylate and polymethyl methacrylate copolymers (FMA/MMA) were synthesized by the atom transfer radical polymerization at various FMA/MMA mole ratios. 5 wt% copolymer solutions were spun cast onto PMMA sheet substrates. The effects of monomer ratio on tribological properties were investigated in terms of the surface energy calculated from contact angles, the dynamic friction, and the wear obtained from multiple scratchings. There is a range of optimum FMA/MMA ratios between (1–5)×10⁻³ in which we attain a minimum dynamic friction. The results obtained are discussed in terms of connections between friction, surface tension, and wear mechanisms.     

Electronic properties of thermally formed thin iron oxide films

The oxide layer, present between an organic coating and the substrate, guarantees adhesion of the coating and plays a determinating role in the delamination rate of the organic coating. The purpose of this study is to compare the resistive and semiconducting properties of thermal oxides formed on steel in two different atmospheres at 250 °C: an oxygen rich atmosphere, air, and an oxygen deficient atmosphere, N₂. In N₂, a magnetite layer grows while in air a duplex oxide film forms composed by an inner magnetite layer and a thin outer hematite scale. The heat treatment for different amounts of time at high temperature was used as method to sample the thickness variation and change in electronic and semiconducting properties of the thermal oxide layers. Firstly, linear voltammetric measurements were performed to have a first insight in the electrochemical behavior of the thermal oxides in a borate buffer solution. Electrochemical impedance spectroscopy in the same buffer combined with the Mott-Schottky analysis were used to determine the semiconducting properties of the thermal oxides. By spectroscopic ellipsometry (SE) and atomic force microscopy (AFM), respectively, the thickness and roughness of the oxide layers were determined supporting the physical interpretation of the voltammetric and EIS data. These measurements clearly showed that oxide layers with different constitution, oxide resistance, flatband potential and doping concentration can be grown by changing the atmosphere.     

Electrical and structural properties of polyaniline/cellulose triacetate blend films

Polyaniline (PANI) has been blended with cellulose triacetate (CTA) to obtain both good mechanical properties and good electrical properties. The effects of PANI weight percentage on the optical, structural, morphological and electrical properties in the blend films of polyaniline and cellulose triacetate (PANI/CTA) have been investigated. The phenomenon of percolation was observed in these blend films. It is found that the electrical conductivity of the blend films increases with the increase of polyaniline content up to a value of 10⁻⁴ S cm⁻¹ at 84 weight percentage of PANI. The experimental percolation threshold of the dried blend films is obtained at 9.5 wt% of polyaniline. The values of Mott’s temperature, density of states at the Fermi level [N (E _f)], hopping distance (R _hop), and barrier height (W _hop) for PANI/CTA blend films are calculated. By applying Mott’s theory, it is found that the PANI/CTA blend films obey the three dimensional variable range hopping mechanism.     

Substrate temperature-dependent physical properties of nanocrystalline zirconium titanate thin films

Nanocrystalline zirconium titanate thin films were deposited by direct current magnetron reactive sputtering on to glass substrates at room temperature and at different substrate temperatures of 423, 473, 523, and 573 K under high vacuum conditions. The deposited films have been characterized to study the physical properties of the films as a function of substrate temperature. Though the film exhibited amorphous characteristics at room temperature the higher temperatures resulted in the evolution of crystallites in the films. The crystallinity increased with temperature from 423 K onwards and the film deposited at 523 K exhibited a high crystallite size of 22 nm. The SEM images of the films revealed the improvement in the crystallinity from 423 to 523 K with dense columnar structure normal to the substrate. Further higher treatment deteriorated the film properties. The films showed a good transmittance of above 80%. A high optical transmittance of 91% and a high packing density of 96% have been observed for the film deposited at 523 K. The thickness of the films remained consistent at ~230 nm (±6 nm). It is noticed that an increase in the substrate temperature enhanced the structural, optical, and electrical properties of the films up to 523 K.     

化学镀CoWP薄膜的制备及磁性研究

利用化学镀的方法制备了CoWP磁性薄膜。研究了施镀时间对化学镀CoWP薄膜矫顽力和饱和磁化强度的影响,并利用场发射扫描电子显微镜(FSEM)、X射线衍射(XRD)和振动样品磁强计(VSM)研究了CoWP磁性薄膜的表面形貌、成分、微结构及磁学性能。结果表明,化学镀CoWP薄膜主要为hcp结构Co相,晶粒大小为2~3μm;随着施镀时间的增加,CoWP薄膜的饱和磁化强度也随之增大,最高达到122emu/g;CoWP薄膜的矫顽力都在250Oe以下。通过计算Kelly-Hankel(δM)曲线,证实了CoWP磁性薄膜中存在交换耦合作用,产生了剩磁增强效应。     

Magnetic properties of electrodeposited CoFeB thin films and nanowire arrays

A pulse electrodeposition method for preparing stress-free CoFeB thin films is described. The method was optimized to produce amorphous films with soft magnetic properties and the best composition was found to be Co₉₄Fe₅B₁. The optimized conditions were used to obtain arrays of ordered nanowires, using nanoporous alumina membranes as templates. While magnetization measurements demonstrate that the microstructure of the array influences the detailed characteristics of the hysteresis loops, the general pattern of the magnetization curves, characterized by high saturation fields and low squareness, is the same as for crystalline Co arrays obtained in similar conditions. This observation, as well as data obtained from variable temperature measurements, shows that the overall magnetic behavior is determined mainly by the competition of the shape anisotropy and magnetostatic interactions. Whether the wire axis is easy or hard for the array depends upon the array geometry: wire diameter, length and the packing density of the wires. In order to explain these effects, a micromagnetic model was used to calculate the saturation fields for in-plane and out-of-plane magnetized array, as a function of the geometrical parameters. These agree well with the experimental results.     

Morphological considerations on the mechanical properties of blown high-density polyethylene films

Blown films having a broad range of morphologies were prepared from high-density polyethylenes (HDPE) with unimodal and bimodal molecular weight distribution under several processing conditions, and the effect of their morphological features on the dart drop impact resistance, Elmendorf tear strength, and tensile properties of the films has been studied. The organization of lamellar stacks seems to play a critical role on the mechanical properties of the blown HDPE films. The dart drop impact resistance of the blown HDPE films is highly dependent on the presence of the network structure of lamellar stacks and the level of the intraconnectivity and interconnectivity of lamellar stacks. The coherent orientation of lamellar stacks leads to significant anisotropy of tear and tensile properties. © 1997 John Wiley & Sons, Inc.     

Physical properties of spray deposited Ni-doped zinc oxide thin films

Transparent thin films of nickel doped zinc oxide were deposited on to corning glass substrates via chemical spray pyrolysis using zinc acetate and nickel nitrate as precursors. Structural, morphological, optical, electrical, dielectrical and impedance properties of the films as a function of nickel doping concentration as well as inter-particle interactions by complex impedance spectroscopy were investigated. The deposited films are polycrystalline with a hexagonal (wurtzite) crystal structure along (002) preferential orientation. The films are highly transparent in the visible region with a transmittance higher than 86%, and have an optical band gap ranging from 3.23 to 3.19 eV depending on the nickel doping concentration. The high electrical conductivity of doped films is explained on the basis of the presence of oxygen vacancies. Decrease of electrical conductivity due to nickel doping is explained on the basis of compensation of oxygen vacancies. The dielectric constant and loss tangent as a function of frequency are reported. Interparticle interactions in the deposited films are studied by complex impendence spectroscopy.     

不同温度下退火的二氧化钛纳米薄膜的光催化性能

采用磁控直流溅射的方法,使用TiO2靶材直接制备二氧化钛纳米薄膜,并在不同温度(500、550或600°C)下进行退火处理.利用扫描电子显微镜(SEM)、X射线衍射仪(XRD)和紫外可见光分光光度计(UV-VIS)研究了热处理温度对TiO2纳米薄膜性能的影响.结果表明,热处理温度为550°C时TiO2纳米薄膜的光催化性...     

Compostability of cellulose acetate films

Composting is an accelerated biological decay process viewed by many to be a potential solution to the solid-waste management crisis existing in many parts of the world. As part of a program to develop environmentally nonpersistent polymers that are compatible with a composting environment, we have developed a bench-scale compost methodology that emulates a high efficiency municipal windrow composting operation. A series of cellulose acetate films, differing in degree of substitution, were evaluated in this bench-scale system. In addition, commercially available biodegradable polymers such as poly(hydroxybutyrate-co-valerate) (PHBV) and polycaprolactone (PCL) were included as points of reference. Based on film disintegration and on film weight loss, cellulose acetates, having degrees of substitution less than approximately 2.20, compost at rates comparable to that of PHBV. NMR and GPC analyses of composted films indicate that low molecular weight fractions are removed preferentially from the more highly substituted and slower degrading cellulose acetates. © 1994 John Wiley & Sons, Inc.     

Effect of heterojunction on photocatalytic properties of multilayered ZnO-based thin films

In the present study, the effects of the heterojunctions on the optical and structural characteristics and the resulting photocatalytic properties of multilayered ZnO-based thin films were investigated. The junctions were composed of semiconducting ZnO nano-porous films coated on the In₂O₃ and SnO₂ counterpart layers. The multilayered ZnO films based on the triple-layered Ag-doped indium oxide (AIO)/tin oxide (TO)/zinc oxide (ZnO), indium oxide (IO)/Ag-doped tin oxide (ATO)/zinc oxide (ZnO), indium oxide (IO)/tin oxide (TO)/zinc oxide (ZnO) and tin oxide (TO)/indium oxide (IO)/zinc oxide (ZnO) have been fabricated by subsequent sol–gel dip coating. Their structural and optical properties combined with photocatalytic characteristics were examined toward degradation of Solantine Brown BRL (C.I. Direct Brown), an azo dye using in Iran textile industries as organic model under UV light irradiation. Effects of operational parameters such as initial concentration of azo dye, irradiation time, solution pH, absence and presence of Ag doping and consequent of sublayers on the photodegradation efficiencies of ZnO nultilayered thin films were also investigated and optimum conditions were established. It was found that the photocatalytic degradation of azo dye on the composite films followed pseudo-first order kinetics. Photocatalytic activity of AIO/TO/ZnO interface composite film was higher compared with other films and the following order was observed for films activities: AIO/TO/ZnO > IO/TO/ZnO > ATO/IO/ZnO > TO/IO/ZnO. Differences in the film efficiencies can be attributed to differences in crystallinity, interfacial lattice mismatch, and surface morphology. Besides, the presence of Ag doping between layers that may act as trap for electrons generated in the ZnO over layer thus preventing electron–hole recombination.