A study on the preparation of aromatic polyimide Langmuir–Blodgett films

The PI Langmuir–Blodgett (LB) films were prepared by imidizing the PAAS LB films of PMDA and benzidine system with a thermal treatment at 250°C for 30 min, where the PAAS LB films were formed on substrates by using LB technique. The imidization of PAAS LB films with various thickness were identified with UV–VIS and FT-IR absorption spectroscopies. The PAAS and PI LB films have been characterized by electric capacitance measurement. The thicknesses of one layer of PAAS and PI LB film that deposited at the surface pressure of 27 mN/m were 20.9 and 4 Å, respectively. It was found that the PAAS and PI LB films formed well with molecular order was fabricated. SEM has been used to investigated the surface morphology of PAAS and PI LB films.     

Transient characteristics of light-emitting devices based on Langmuir–Blodgett films of a porphyrin derivative

Transient electroluminescence responses of light-emitting devices based on Langmuir–Blodgett films of a porphyrin derivative have been studied. A sequence of two rectangular voltage pulses separated by a delay has been applied. This has enabled us to study the effect of accumulated/trapped charges during the first pulse, while their relaxation dynamics have been studied during the second pulse. The separation time between the two pulses has been varied to study the relaxation of the accumulated charges in the device. The amplitude and polarity of the applied voltage pulse have been varied to study the barrier modification and space-charge limited electron injection in the device.     

Langmuir–Blodgett films of BEDT-TTF derivatives containing hydroxyl groups with long alkyl chains

BEDT-TTF (bis(ethylenedithio)tetrathiafulvalene) derivatives 1 and 2 containing hydroxyl groups with long alkyl chains were synthesized and characterized. Studies with Langmuir–Blodgett (LB) technique indicated that both compounds 1 and 2 were able to form stable monolayers at the air–water interface, but these monolayers were found difficult to be transferred onto solid substrates. Multilayer LB films based on the mixtures of 1 and 2 with arachidic acid (AA), however, could be prepared easily, and the ordered structures of these LB films were confirmed by small angle X-ray diffraction (SAXRD) analysis. The LB films of 1, 2, and their mixtures with AA were oxidized with iodide, and the conductivity of resulting thin films was measured. For comparison, the conductivity of these LB films was also measured before the oxidation with iodide.     

Photoelectrochemistry of Langmuir—Blodgett films of a C60 iminodiacetic acid ester derivative on ITO electrodes

The photoelectrochemical response of a C₆₀ iminodiacetic acid ester derivative (C₆₀IDA), deposited on ITO electrodes by means of the Langmuir—Blodgett technique, has been investigated. The anodic photocurrent observed on the modified electrode corresponds to an electron transfer from the electrolyte through the LB film to the electrode. The action spectrum of photocurrent indicates C₆₀IDA as the photoactive species in the photoinduced electron transfer process. Positive bias voltage, reducing agent and higher pH of the solution are beneficial factors for generating higher photocurrent. The quantum yield for photocurrent generation is 0.94% and can be raised to 3.40% under favorable conditions.     

Surface properties of Langmuir films of mono-, di-, and tetra-n-octyl adducts of C60 at the water–air interface

Relatively stable Langmuir films of mono-, di-, and tetra-n-octyl adducts of C₆₀ were prepared at the water–air interface. The adducts were obtained by selective bulk electrosynthesis at controlled potential. For the films, surface pressure (π) and a surface potential change (ΔV) were simultaneously measured as a function of surface area per molecule (A) during the film compression. The spreading properties of the adducts strongly depend on the number of n-octyl chains linked to the C₆₀ cage and nature of the spread solution. The determined zero-pressure limiting area per molecule (A₀) is larger the more n-octyl chains are attached to the C₆₀ cage. Aggregated multilayer films are formed for the toluene and tetrahydrofuran spread solutions while liquid monolayer films for the chloroform solutions. Remarkably, relatively stable liquid monolayer films of pristine C₆₀ are obtained also from the chloroform solutions. For relatively concentrated chloroform solutions, plateaus are developed in the π–A adduct isotherms. Isotherms for both concentrated and diluted chloroform solutions show reversible compression and expansion with virtually no hysteresis. Comparison of the estimated and determined A₀ values indicates that all adduct molecules are horizontally oriented in the monolayer films. Unexpectedly, large mean dipole moment components normal to the water–air interface, determined from inflection points of the ΔV–A isotherms, are presumably due to preferential orientation of water molecules adjacent to the interface of the water subphase and the floating adduct film.     

The application of Langmuir–Blodgett films of a new asymmetrically substituted phthalocyanine,amino-tri-tert-butyl-phthalocyanine,in diodes and in all organic field-effect-transistors

Amino-tri-tert-butyl-phthalocyanine (AmBuPc) was used as the semiconductor thin layers in model Schottky diode and all organic field-effect transistor (OFET). The diode cell showed a rectifying effect with a rectification ratio of 60 at ±3.2 V. The ideality factors were 1.38 in the low voltage region and 3.09 in the high voltage region, respectively. The results of OFET proved that AmBuPc Langmuir–Blodgett (LB) films could be used as the semiconducting layer of OFET, and the OFET could function as a p-channel accumulation device. From the OFET electrical characteristics, the channel carrier mobility is calculated to be about 5.2×10⁻⁶ cm² V⁻¹ s⁻¹, which is higher than that of vacuum-deposited film OFET (7.8×10⁻⁷ cm² V⁻¹ s⁻¹) utilizing the same polymer. This phenomenon can be explained as the highly ordered structure of AmBuPc molecules in the LB films. This suggests that a wide conduction channel is able to form in this all organic device, which provides a new method to simplify the fabrication process of OFET and improve their properties.     

Coefficient of thermal expansion of stressed thin films

A new technique was proposed to determine the coefficient of thermal expansion （CTE） of thin films at low temperature. Different pre-stress could be applied and the elastic modulus of materials at different temperatures was measured with CTE simultaneously to eliminate the influence of mechanical deformation caused by the pre-stress. By using this technique, the CTEs of polyimide/silica nanocomposite films with different silica doping levels were experimentally studied at temperature from 77 K to 287 K, and some characteristics related to this new technique were discussed.     

Photoconductivity in Langmuir—Blodgett multilayer structures of phthalocyaninato-polysiloxane

The electrical and photoelectrical properties of planar photodiodes based on phthalocyaninato-polysiloxane (PcPS) are presented. Sandwich structures consisting of thin PcPS Langmuir—Blodgett films have been prepared between semi-transparent gold and aluminum electrodes. These structures possess pronounced rectifying behavior. The photocurrent spectra exhibit peaks at 550 and 700 nm. The wavelength dependence of the photoconductivity clearly differs from the linear optical properties.     

Electrodeposition of Pr-Fe ahoy films in urea-dimethylsulfoxide

Cyclic voltammetry and chronoamperometry were used to investigate the electrochemical behavior of Pr^3 ions in a system of 0.01 mol-dm-3 Pr(CH3SO3)3 0.01 mol-dm^-3 FeCl2 3.0 mol.dm^-3 urea DMSO on a Pt electrode. Some electrochemical parameters were measured. Potentiostatic depositions between -1.6 and -2.4 V were applied to deposit Pr-Fe films in urea-DMSO mixed solution. The Pr content in the alloy films was in the range of 34.89 wt.% to 37.15 wt.%.The Pr-Fe alloy films are proven to be amorphous by XRD (X-ray diffraction).     

Electrodeposition of Pr-Fe alloy films in urea-dimethylsulfoxide

Cyclic voltammetry and chronoamperometry were used to investigate the electrochemical behavior of Pr3 ions in a system of 0.01 mol·dm-3 Pr(CH3SO3)3 0.01 mol·dm-3 FeCl2 3.0 mol·dm-3 urea     

Critical misfit of epitaxial growth metallic thin films

The critical misfit of epitaxial growth metallic thin films fc was thermodynamically considered. It is found that there exists a competition between the energy of the misfit dislocation of film and non-coherent interface energy of film-substrate. Equilibrium between these energies was present at a critical atomic misfit ft. When the atomic misfit is larger than the critical value, epitaxial growth does not occur. The critical misfit of the epitaxial growth thin films can be predicted. The results show that fe is proportional to the non-coherent interface energy of the film-substrate, and inversely proportional to the elastic modulus and the thickness of the film.     

Fabrication and magnetic properties of NiFe-ZnO nano-granular films

Excellent soft magnetic and high frequency properties were obtained successfully in the (Ni75Fe25 )x(ZnO)1-x granular films fabricated on the glass substrate by RF magnetron oblique sputtering. The microstructure, mag- netic and high frequency properties were investigated systematically. High resolution transmission electron micrographs show that the film consists of fcc Ni75Fe25 particles uniformly embedded in an amorphous insulating matrix ZnO with particle size a few nanometers. The (Ni75Fe25 ) x(ZnO)1-x films exhibit excellent soft magnetic properties in a wide x range from 0.50 to 0.80 with coercivity not exceeding 5×10-4T, which is ascribed to the exchange coupling between magnetic particles. Especially for the sample with x = 0.64, coercivities in hard and easy axes are 5.0×10-5 and 3.6×10-4 T, respectively, and the electric resistivity ρ reaches 1,790 μΩ·cm. The dependence of complex permeability u = u’ - ju" on frequency f shows that the real part u’ is more than 130 below 500 MHz, and the ferromagnetic resonance frequency fr reaches 1.32 GHz, implying the promising for high frequency application.     

Characterization of sputter—deposited TiPdNi thin films

TiPdNi thin films were prepared by magnetron sputtering onto unheated glass and silicon substrate.Atomic force microscope,energy-dispersive X-ray microsanalyzer,X-ray diffractometer,differential scanning calorimeter and optican microsope were used to characterize the films.It is found that the surface morphology of the films change during the sputtering process and a shift of about 3%Ti(mole fraction(content from the center to the edge of the substrate occurs.The freestanding as-deposited films undergo crystallization followed by three kinds of cooling conditions.For all these heattreated films,B2→B19→B19‘ two-stage phase transformation takes place.Many Ti2Ni and Ti2Pd type of precipitates are detected in the films.The constraint films on silicon substrate are crystallized at high temperature.After crystallization,the films show a two-way shape memory effect.     

Synthesis of GaN films on porous silicon substrates

A novel and simple method was employed to synthesize GaN films on porous silicon (PS) substrates. GaN films were obtained through the reaction between NH3 and Ga2O3 films deposited on the substrates with magnetron sputtering. Since GaN and PS are all good materials for luminescence, it is expected to obtain some new properties from GaN on PS. The samples were analyzed with X-ray diffraction (XRD) to identify crystalline structure. Fourier transmit infrared (FTIR) spectrum was used to analyze the chemical state of the samples. The films were observed with scanning electron microscopy (SEM) and were found to consist of many big crystal grains. Photoluminescence (PL) spectrum was used to illuminate the optical property of the GaN films.     

Physical properties of CVD-grown Se—carbon films

A novel chemical vapor deposition (CVD) approach based on the thermal decomposition of an aromatic hydrocarbon in the presence of Se vapor is used to grow films of layered Se—carbon compounds. In principle, this technique can produce a wide variety of new carbon-based materials, for example, graphite intercalation compounds (GICs) which, for kinetic reasons, cannot be made if the intercalant vapor has to diffuse large distances into a pre-existing graphitic host. In particular, homogeneous oriented submicron films of either pure stage-3 (Se₂₄C) or mixed-stage Se—carbon layer compounds have been successfully grown on Ni substrates in evacuated sealed quartz tubes. X-ray diffraction, X-ray photoelectron spectroscopy, Raman scattering and the c-axis electrical transport measurements are discussed in terms of both covalent Se—carbon bonding and an ionic model assuming the formation of an acceptor-type Se—GIC with electron transfer from carbon to Se. Our CVD-grown Se—carbon films exhibit the largest thermoelectric power reported in the open literature among carbon-based compounds. However, the value is at least a factor of 10 less than reported for these materials in patents by Sharp Corp.     

Influence of intermittently etching on quality of CVD diamond thin films

A new method, called growing-etching repetitional process based on hot filament chemical vapor deposition, was proposed to improve the quality of diamond film. During the deposition carbon source was intermittently closed letting hydrogen etch the surface of the diamond film fi＇om time to time. In order to find whether it is helpful to the films＇ quality, a series of experiments were done. The results show that the new method can enhance the orientation of the chemical vapor deposition diamond films, reduce the graphite phase and increase the film＇s surface resistivity.     

Effect of annealing treatment onoptical and electrical properties of ZnO films

The ZnO-Al films were prepared by R. F. magnetron sputtering system using a Zn-Al target (with purity of 99.99 %). The obtained films were characterized by X-ray diffraction, SEM and optical and electrical measurements. The experimental results show that the properties of ZnO films can be further improved by annealing treatment. The crystallinity of ZnO films becomes better, and the optical gap energy is decreased, but thermoelectric power is enhanced after heat treatment. The optical gap energy decreases from 3.75 eV to 3.68 eV when the annealing temperature increases from 25℃ to 400℃. This can be ascribed to the decrease of carrier concentration, resulting in Burstein shift.     

Microstructures and transformation characteristics of thin films of TiNiCu shape memory alloy

Both sputtering conditions and crystallizing temperatures have great influence on the microstructures and phase transformation characteristics for TislNi44Cus. By means of the resistance-temperature measurement, X-ray diffraction and atomic fore microscopic study, the results indicate that the transformation temperatures of the thin films increase and the “rock candy“ martensitic relief is more easily obtained with promoting the sputtering Ar pressure, sputtering power, orcrystallizing temperature. However, when sputtering Ar pressure, sputtering power, or crystallizing temperature are lower, a kind of “chrysanthemum“ relief, which is related with Ti-rich GP zones, is much easier to be observed. The reason is that during crystallization process, both of the inherent compressive stresses introduced under the condition of higher sputteringpressure or higher crystallizing temperature are helpful to the transition from GP zones to Ti2(NiCu) precipitates and the increase of the transformation temperatures. The addition of copper to substitute for 5 96 nickel in mole fraction can reduce the transformation hvsteresis width to about 10 - 15 ℃.     

Layer-by-layer assembly of nanocomposite films with thickness up to hundreds of nanometers

1 Introduction In 1991, DECHER and his co-worker extended ILER’s pioneering work on fabrication of inorganic colloidal particle-based layer-by-layer assembled films to the preparation of polyelectrolyte-based layer-by-layer assembled films[1?3]. Now the…