Film Thickness Direction Research Articles

Proton Conductivity Measurement of Polymer Electrolyte Membrane in Film Thickness Direction Using Small-Size Electrodes

The proton conductivity of a polymer electrolyte membrane has been measured in the film thickness direction by employing an Au/polymer electrolyte membrane/Au sandwiched cell by varying the electrode area, pressure of the sandwiched cell, and applied voltage. As a result, the optimized electrode area, gauge pressure and applied voltage were found to be 0.015–0.070 cm2, 0.8–1.5×105 Pa, and 10–50 mV, respectively. By using Nafion 117 as a polymer electrolyte membrane, we measured the proton conductivity in the film thickness direction and compared it to that in the film surface direction evaluated by a conventional four-probe method, which resulted in the same magnitude of 0.090 S cm−1.

A Rapid Method of Numerical Calculation for Oil Film Temperature in Engine Bearings

In the design and analysis of engine bearings for automobiles, the elastic deformation of bearing surface due to high pressure and temperature of oil film affects significantly on the bearing characteristics. Thermo-elasto-hydrodynamic lubrication analysis (TEHL) is usually used to consider such effects, but a large amount of calculation time is needed to obtain the numerical solution of oil film temperature by solving the conventional type of 3-dimensional energy equation in TEHL. This paper describes a rapid method of numerical calculation of oil film temperature in engine bearings. In this modeling, it is assumed that the temperature distribution in the oil film thickness direction takes the parabolic form. Under such and assumption, averaging the 3-dimensional energy equation over the film thickness, the 2-dimensional energy equation is newly obtained. The numerical solutions of oil film temperature based on the 2-dimensional model are compared with the solutions based on the 3-dimensional model. It is confirmed that the calculation time is remarkably reduced to obtain the oil film temperature with an allowable accuracy. Moreover, the predicted oil film temperature by the 2-dimentional model is compared with measured data, and the good agreement is seen between them.

Modeling and experimental investigation of looped separate heat pipe as waste heat recovery facility

A looped separate heat pipe as waste heat recovery facility for the air-conditioning exhaust system has been developed in this work. A one-dimensional steady-state model is presented for determining the upper and lower operating boundaries of the initial filling ratio of the working fluid, as a function of the separate heat pipe geometry, vapor temperature of working fluid and power throughput, combined with two-phase heat exchange characteristics and distribution of the liquid film velocity along with the liquid film thickness direction. A parametric analysis is performed to investigate the effects of the length of the evaporator, vapor temperature, and power throughput on the critical values of the upper and lower boundaries. Simulation results show that the length of the evaporator makes almost no influence on the upper boundary, but great effect on the lower boundary. An increase of the vapor temperature leads to the easier arriving of the lower boundary. Moreover, operation ranges of the separate heat pipe vary with the working fluids. Water and methanol were used separately. An experiment was implemented to validate the simulated results. The numerical predictions compare favorably with experimental results.

Influence of temperature distributions in EHL film on its thickness under high slip ratio conditions

This paper describes the influence of temperature rise of oil film in Hertzian contact area on the film thickness or profile under high slip ratio conditions. Temperatures of both surfaces of a ball and a disk as well as average temperature across the oil film were measured by means of an improved infrared. Two kinds of optical band-pass filters were used to separate the radiations from the ball surface and the oil film through an infrared transparent disk made of sapphire glass. In case of temperature measurement of the disk surface, another sapphire glass disk was coated with 300 nm chromium layer on the contact surface to radiate the infrared from the disk surface and also to intercept the radiation from the ball surface and the oil film. Temperature profiles across the oil film were estimated by assuming a parabolic profile with the measured three kinds of temperatures. For case within 200% in slip ratio, both minimum and central film thickness decreased under constant entrainment velocity as slip ratio increased. Measured film shapes were not flat at central Hertzian contact region under high-slip condition and differed from the results by the conventional EHD theory assuming constant viscosity in the direction of film thickness. The profile of Couette flow varied due to the distribution of oil film temperature in thickness direction. The viscosity wedge action, that is the variation of the profile of Couette flow causes reduction of film thickness or deformation of film profile. For case over 200% in slip ratio, the relation between central film thickness and slip ratio under constant relative slide speed had a great difference from the results calculated from the formula presented by Chittenden et al.

Structural and dielectric properties of perovskite-type artificial superlattices

BaTiO 3/SrTiO 3, SrZrO 3/SrTiO 3 and BaTiO 3/BaZrO 3 artificial superlattices were fabricated by the molecular beam epitaxy process. X-ray diffraction (XRD) reciprocal space mapping measurement was performed using high-resolution XRD. In all artificial superlattices, the superlattices with the 10-periodic structure showed the clear satellite peaks in the XRD pattern and were mostly distorted in the direction of film thickness. Superlattices with the 10-periodic structure showed a high dielectric permittivity of ε r = 33,000 or artificially induced ferroelectricity. It was clarified that the anisotropic lattice distortion introduced by the strains due to the lattice mismatch was the origin of the unique dielectric characteristics of artificial superlattices.

Characterization and modeling of PPy bilayer microactuators: Part 1. Curvature

Bilayer actuators of gold and polypyrrole doped with dodecylbenzenesulfonate, PPy(DBS), were microfabricated with lengths and thicknesses that varied over two orders of magnitude. The actuators were connected to rigid plates. The curvature of the bilayers was examined as a function of PPy and Au layer thicknesses to enable a determination of the actuation strain and Young's modulus of the PPy(DBS). Four different Au thicknesses were tested, and maximum curvature was obtained in all cases at a PPy:Au thickness ratio of 5:1. The data could not be fit with a constant value for the actuation strain; in addition, the PPy film bent even in the absence of an Au layer. Therefore, a model was developed that included strain and modulus variations along the direction of film thickness. The experimental data were fit with an exponential variation in actuation strain, starting at 20% at the surface of the PPy and decreasing to 3% at the gold interface in thicker films. The Young's modulus was found to be constant between 0.08 and 0.20 GPa in the oxidized state. These values differ significantly from thick-film values. With this information, micro-actuators can now be designed to achieve a specified radius of curvature.

Effect of stretching on the structure and electrical conductivity of doped and undoped poly(phenylene vinylene) thin films

Impedance spectroscopy, X-ray diffraction, infrared dichroism and AFM imaging were used to investigate the effect of orientation and doping on the electrical properties of a series of stretched poly(phenylene vinylene) (PPV) films. The degree of orientation was determined by infrared dichroism. X-ray diffraction patterns clearly display a transition from random orientation to a high degree of orientation. Analysis of the AFM images indicates that a fibrillated structure was formed on the stretched films. Solid state impedance measurements of doped and undoped films were carried out parallel to and perpendicular to the stretch direction (i.e. in the through-plane direction) in an attempt to understand the effect of the fibrillar structure on the electrical properties. It was found that the bulk conductivity of undoped PPV in the through film thickness direction decreased with increasing orientation, while the conductivity of undoped PPV along the stretch direction is independent of orientation. Doping of the stretched PPV thin films with a 0.58 M FeCl 3 solution for 10 min increased the conductivity by over two orders of magnitude.

On the pressure projection in elasto-hydrostatic lubrication problems—Part 2: FE approximation to observe the pressure projection

We have argued in Part 1 that the conventional Reynolds equation including the deformation of elastic disc does not obtain the pressure spike. However, as the experimental results in some papers have found the pressure projection, it can be intuitively explained as being caused by something hard in the oil film; by the pressure sensor, namely, manganin; or by the solidified lubricant. In this paper, the first of these possible causes is analyzed, for the first time, by introducing the fluid velocity variable in the direction of the oil film thickness and using the solid–fluid coupled finite-element (FE) method. It is shown by the numerical results based on Hamilton's experimental data that the pressure projection can be obtained by introducing the thickness of the pressure sensor, and that the projection profile varies with the sensor location on the disc. However, to solve the non-linearity of lubricant viscosity accurately is left for future research because the above FE analysis does not converge with the experimental data.

Novel biodegradable poly(butylene succinate)/poly(ethylene oxide) blend film with compositional and spherulite‐size gradients

AbstractBiodegradable poly(butylene succinate) (PBS)/poly(ethylene oxide) (PEO) polymer blend film with compositional gradient in the film thickness direction was prepared using a method of interdiffusion across the interface between the PBS and PEO layers at a temperature above the melting points of both the component polymers. The miscibility between PBS and PEO was confirmed by observation of the glass transition temperature by differential scanning calorimetry. The compositional gradient structure of PBS/PEO was characterized by microscopic mapping measurement of Fourier transform infrared spectra and dynamic mechanical thermal analysis. Furthermore, a new method for confirming the crystalline/crystalline compositional gradient structure through observing the crystallization behavior by POM (polarized optical microscopy) was put forward. A continuous gradient of the spherulite size along the film thickness direction was succeessfully generated in the PBS/PEO blend film. The compositional gradient blend was found to have significantly improved physical properties that cannot be realized for pure PBS, pure PEO, and even their homogeneous miscible blend system. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 368–377, 2005

Advanced Resonant-Ultrasound Spectroscopy for Studying Anisotropic Elastic Constants of Thin Films

AbstractThis paper presents two advanced acoustic methods for the determination of anisotropic elastic constants of deposited thin films. They are resonant-ultrasound spectroscopy with laser-Doppler interferometry (RUS/Laser method) and picosecond-laser ultrasound method. Deposited thin films usually exhibit elastic anisotropy between the film-growth direction and an in-plane direction, and they show five independent elastic constants denoted by C11,C33,C44,C66 and C13 when the x3 axis is set along the film-thickness direction. The former method determines four moduli except C44, the out-of-plane shear modulus, through free-vibration resonance frequencies of the film/substrate specimen. This method is applicable to thin films thicker than about 200 nm. The latter determines C33, the out-of-plane modulus, accurately bymeasuring the round-trip time of the longitudinal wave traveling along the film-thickness direction. This method is applicable to thin films thicker than about 20 nm. Thus, combination of these two methods allows us to discuss the elastic anisotropy of thin films. The results for Co/Pt superlattice thin film and copper thin film are presented.

Fully-biodegradable poly(3-hydroxybutyrate)/poly(vinyl alcohol) blend films with compositional gradient.

Fully-biodegradable bacterial poly(3-hydroxybutyrate) (PHB)/chemosynthetic poly(vinyl alcohol) (PVA) blend films with compositional gradient from one surface to the other surface of the films were prepared by a dissolution-diffusion technique. Three kinds of PVA samples, high- and low-molecular weight atactic PVA and highly syndiotactic PVA (s-PVA), were used in order to investigate the effects of molecular weight and tactic structure on the generation of compositional gradient. The solution of PHB in 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP), which is also a good solvent for PVA, was cast on the PVA film and then the solvent HFIP was evaporated. By selecting the optimum volume of solvent and the evaporation rate, the PHB/PVA blend film with compositional gradient was obtained. The formation of compositional gradient was confirmed by FT-IR microscopy and ATR-FT-IR analysis. The 50%/50% PHB/s-PVA blend film with a nearly ideal compositional gradient, that is, the composition of PHB (or PVA) in the film changing gradually from 100% at one surface to 0% at the other surface of the film was obtained by casting PHB/HFIP solution on to the s-PVA film. Positional dependence of the absorbance of C==O and OH stretching bands along the film thickness direction for the PHB/S-PVA cast films.

Fabrication of nano-structured materials from aqueous solution by liquid phase deposition

Ti x Sn 1− x O 2 films with gradient composition profiles have been prepared by the liquid phase deposition method. The crystal structure and composition of these Ti x Sn 1− x O 2 films were investigated by means of high-resolution transmission electron microscopy (HRTEM) and energy dispersive X-ray (EDX) analysis with a nano-probe. The gradient profile of the films in the direction of film thickness could be controlled by varying the flow rate. The existence of microcrystalline rutile-SnO 2 and anatase-TiO 2 was observed near the substrate and the top-surface, respectively. The photocatalytic activity of Ti x Sn 1− x O 2 films with gradient composition profiles was markedly higher than that of the SnO 2/TiO 2 multilayer.

Structural Nonuniformity and Internal Stress in Chromium Films Deposited by Magnetron Sputtering

Using high-resolution transmission electron microscopy, selected area electron diffraction and X-ray diffraction methods, the microstructures and lattice parameters of different parts of Cr films deposited by magnetron sputtering under different deposition conditions have been studied. It was revealed that the microstructure and lattice parameter of the films deposited onto nonheated substrates vary in the film thickness direction. Lattice parameter a has a maximal value in the film-substrate interface region and gradually decreases towards the conventional value in the middle and upper film parts. In accordance with this, the internal tensile stress decreases, while the grain size increases in the direction from the substrate to the film surface. Elevation of the substrate temperature results in smoothing of nonuniformity of the film microstructure and stress distribution along the thickness. At a certain combination of a substrate temperature and bias voltage, unstressed large-grained films with uniform microstructure have been deposited. The model proposed for explanation of the obtained results is based on the supposition of dynamic elevation of condensation surface temperature during film growth that promotes the formation of the film with structure and stress nonuniformly distributed in the thickness direction.

Structure and electrical properties of undoped oriented poly(phenylene vinylene) films

AbstractThe influence of anisotropic structure on the electrical properties of undoped oriented poly(phenylene vinylene) (PPV) films was investigated with impedance spectroscopy and structural characterization. The oriented structure of the stretched PPV films was studied with wave‐guide coupling and infrared dichroism. It was found that the unstretched PPV film had a highly planar structure, and one‐way stretching converted the planar structure into a uniaxial structure. The impedance of undoped PPV thin films was measured along three different directions: through the film thickness direction, parallel to the stretch direction in the film plane, and perpendicular to the stretch direction in the film plane. Two relaxations were observed, one corresponding to the bulk behavior in the high‐frequency range and the other to an interfacial contact polarization in the low‐frequency range. From equivalent circuit modeling, it was found that the bulk conductivity through the film thickness direction decreased with increasing orientation, whereas the high‐frequency dielectric constant through the film direction remained constant. In addition, the conductivities measured in the film plane were at least two orders of magnitude higher than the conductivity in the direction normal to the film surface. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 98–116, 2004

Computer simulation of coercive force and thermal viscosity in perpendicular recording media

The micromagnetic simulations for perpendicular recording media with incoherent magnetization rotation was performed by dividing a grain into subgrains in the direction of film thickness. When intra-grain exchange coupling was smaller, incoherent magnetization rotation occurred, leading to a stronger thermal fluctuation effect and lower coercive force H/sub c/. It was found that the critical thickness /spl delta//sub c/ exists, beyond which the incoherent magnetization rotation occurs. /spl delta//sub c/ is approximately proportional to 2.5/sup */(A/K/sub u/)/sup 1/2/, where A is the intra-grain exchange stiffness constant and K/sub u/ is the uniaxial perpendicular anisotropy energy. In the incoherent magnetization rotation, the decreasing rate of H/sub c/ by logarithmic time (in thermal viscosity slopes) was larger than that for coherent rotation. The calculations were in good agreement with the experimental coercive forces and thermal viscosity slopes.

Dependence of threshold thickness of crystallization and film morphology on film processing conditions in poly(vinylidene fluoride–trifluoroethylene) copolymer thin films

In spin-cast films of poly(vinylidene fluoride–trifluoroethylene) on metalized silicon substrate, there exists a threshold thickness of crystallization dth, below which the crystallinity drops precipitously. Due to the direct link between the crystallinity and functional properties in the polymer, there is a corresponding large change in the film ferroelectric properties, including the dielectric constant, the polarization level, and polarization switching speed, as the thickness is reduced to below dth. Detail microstructure studies show that this threshold thickness is controlled by the stable crystal lamellar size along the film thickness direction. By varying the film processing condition to reduce the crystal lamellar size in the thickness direction, dth can be reduced markedly. As a result, better ferroelectric responses were obtained in ultrathin films.

Study of polarization switching in PZT films with RuO 2 electrodes by conducting atomic force microscopy

Sol–gel derived lead zirconate titanate (PbZr 0.4Ti 0.6O 3, PZT) films, 2 μm thick, were deposited on ruthenium dioxide (RuO 2)/SiO 2/Si substrates. The domain structure and polarization switching of the PZT films were studied by conducting atomic force microscopy (AFM). Large self-polarization along the film thickness direction and asymmetric piezoresponse hysteresis loop were observed in the as-deposited RuO 2/PZT/RuO 2 films. The room-temperature pyroelectric coefficient of the as-deposited films was about 230 μC/m 2 K. The internal field associated with charged defects was believed to be responsible for the self-polarization and asymmetric piezoelectric response in the as-deposited RuO 2/PZT/RuO 2 films.

Antireflection microstructures fabricated upon fluorine-doped SiO_2 films

Two-dimensional periodic structures were fabricated upon a fluorine-doped SiO(2) film in which the fluorine content changed gradually in the direction of film thickness. The films were deposited by plasma-enhanced chemical-vapor deposition. The film was periodically patterned into a 1-mum period and an ~1-mum -groove depth by inductive coupled plasma reactive-ion etching followed by chemical etching in a diluted HF solution. A surface reflectance of 0.7% was attained at 1.85-mum wavelength, a value that is one fifth as large as the 3.5% Fresnel reflection of a SiO(2) substrate with a flat surface.

Synthesis of Vertically Aligned Helical Polyacetylene Films in Homeotropic Chiral Nematic Liquid Crystals

Vertically aligned helical polyacetylene thin films were synthesized by adding a chiral dopant into homeotropic nematic LC solvent to induce chiral nematic phase with homeotropic orientation. A scanning electron microscope (SEM) measurements showed that twisted polyacetylene fibrils are grown along the direction of film thickness, giving vertically aligned helical fibrillar morphology.

ウェットプロセスの新展開 無電解析出法による傾斜機能磁性薄膜の作製

Attempts made on the gradient control of functional properties for electroless deposited magnetic thin films were overviewed to introduce the methodology for the preparation of functionally graded thin films by means of electrochemical processes. By use of appropriate ultra-thin underlayers, the coercivity, Hc, of electroless CoNiP films was controlled toward the film thickness direction. Sequential control of the rotating speed of substrates during the deposition enabled the programmed control of the gradient of Hc. These procedures could be useful tools for optimizing graded magnetic properties of the films used in various magnetic devices. The tools are expected to be widely applied to fabricate various kinds of films with functionally-graded properties.