Isotropic Films Research Articles

Prediction and Measurement of Thermal Transport Across Interfaces Between Isotropic Solids and Graphitic Materials

Due to the high intrinsic thermal conductivity of carbon allotropes, there have been many attempts to incorporate such structures into existing thermal abatement technologies. In particular, carbon nanotubes (CNTs) and graphitic materials (i.e., graphite and graphene flakes or stacks) have garnered much interest due to the combination of both their thermal and mechanical properties. However, the introduction of these carbon-based nanostructures into thermal abatement technologies greatly increases the number of interfaces per unit length within the resulting composite systems. Consequently, thermal transport in these systems is governed as much by the interfaces between the constituent materials as it is by the materials themselves. This paper reports the behavior of phononic thermal transport across interfaces between isotropic thin films and graphite substrates. Elastic and inelastic diffusive transport models are formulated to aid in the prediction of conductance at a metal-graphite interface. The temperature dependence of the thermal conductance at Au-graphite interfaces is measured via transient thermoreflectance from 78 to 400 K. It is found that different substrate surface preparations prior to thin film deposition have a significant effect on the conductance of the interface between film and substrate.

Atomic layer deposition of Pt growth template for orienting PbZrxTi1−xO3 thin films

Atomic layer deposition (ALD) offers a method for sidewall growth due to its ability to deposit isotropic thin films. As a first step to provide underlying growth templates on sidewalls, proof-of-principal depositions were made on flat wafer surfaces using ALD Pt thin films deposited on: ALD HfO2, ALD Al2O3, and oxidized sputtered-Ti films. X-ray diffraction rocking curve full-width half maxima for 25 nm Pt films obtained after a rapid thermal anneal at 700 °C were 2.06°, 5.45°, and 7.84° on the TiO2, Al2O3, and HfO2 coatings, respectively. Sheet resistance decreased with Pt thickness (deposited onto TiO2/SiO2/Si): from 5 Ω/□ at 25 nm to 0.63 Ω/□ at 100 nm. A 500 ± 25 nm PbZr0.52Ti0.48O3 film was deposited by a chemical solution deposition process onto 100 nm ALD Pt films deposited on the TiO2/SiO2/Si substrates. The 001 Lotgering factor derived from x-ray diffraction data was 0.56 for 001/100 oriented PbZr0.52Ti0.48O3.

Wing Flexibility Effects in Clap-and-Fling

The work explores the use of time-resolved tomographic PIV measurements to study a flapping-wing model, the related vortex generation mechanisms and the effect of wing flexibility on the clap-and-fling movement in particular. An experimental setup is designed and realized in a water tank by use of a single wing model and a mirror plate to simulate the wing interaction that is involved in clap-and-fling motion. The wing model used in the experiments has the same planform with the DelFly II wings and consists of a rigid leading edge and an isotropic polyester film. The thickness of the polyester film was changed in order to investigate the influence of flexibility. A similarity analysis based on the two-dimensional dynamic beam equation was performed to compare aeroelastic characteristics of flapping-wing motion in-air and in-water conditions. Based on the experimental results, the evolution of vortical structures during the clap-and-peel motion is explained. The general effects of flexibility on vortex formations and interactions are discussed. It was observed that the flexibility affects the behavior and orientation of the vortices in relation to the deformation of the wing and interaction with the mirror plate.

Precise Acid Copolymer Exhibits a Face-Centered Cubic Structure.

A linear polyethylene precisely functionalized with geminal phosphonic acid pendants on every 21st carbon atom exhibits face-centered cubic (FCC) packing of acid aggregates. X-ray scattering from isotropic films result in higher-order scattering peaks used to determine the lattice parameter at room temperature (aFCC = 4.19 nm) and above the melting temperature of the polyethylene matrix (aFCC = 4.06 nm). Upon stretching the precise acid copolymer, an anisotropic scattering pattern featuring two coexisting crystalline orientations results, both having the ⟨110⟩ direction of the FCC lattice along the stretching direction. This is the first report of cubic ordering of aggregates in an acid copolymer and it is the direct consequence of the molecular precision of the polymer.

Optical rectification on a surface of isotropic chiral thin film

In this study, the optical rectification (OR) effect on a surface of the isotropic thin film which consists of chiral molecules that base on a one-electron-on-helix model and a two-coupled-oscillator (Kuhn) model have been investigated by us separately. The expressions of dc electric polarization on the isotropic chiral thin film surface and the relations between the OR and microscopic parameters of chiral molecular configuration have been obtained by theoretical derivation. Furthermore, the relations of dc electric polarization with the wavelength of incident light and microscopic parameters of chiral molecular configuration have been simulated numerically. We find the fact that the OR on the isotropic chiral thin film surface is influenced by microscopic parameters of chiral molecular configuration. As well, compared with chiral molecules based on a two-coupled-oscillator Kuhn model, which are based on a one-electron-on-helix model are more suitable for the OR from the point of the influences of molecular microscopic parameters on the OR. The influences of molecular microscopic parameters on the OR might aid in providing some insights into designing and synthesizing new better nonlinear chiral material.

Highly Oriented J-Aggregates of Bisazomethine Dye on Aligned Poly(tetrafluoroethylene) Surfaces

Highly oriented J-aggregates have been obtained in solid, thin films of a bisazomethine dye on aligned poly(tetrafluoroethylene) (PTFE) surfaces. The aggregates show remarkable optical anisotropy resulting from their high orientational order: the dichroic ratios at their J peaks in polarized absorption spectra reach 25. Moreover, this orientation also brings about a remarkable increase in the third-order nonlinear optical susceptibility [χ(3)] of the films of over 10 times that of their isotropic films. Major molecules do not form the aggregates, but rather, form crystalline domains where the aggregates should be dispersed. Polarized absorption spectra (visible and IR) and X-ray diffraction measurements reveal that the molecules are oriented with their long axis parallel to the PTFE chains both in the aggregates and in the crystalline domains ([2 0 −1] axis ∥ PTFE chains, (010) plane ∥ substrate surface). The growth mechanism of the aggregates is discussed on the basis of both the morphology observed by atomic force microscopy and the structural affinity between the crystal and the aggregate.

Nanosize-Induced Optically Isotropic Nematic Phase

We fabricated, in a polymer matrix, liquid crystal (LC) nanosized droplets with a correlation length ξ of about 140 nm, which appear as an optically isotropic film. Differential scanning calorimetry (DSC) and light scattering measurements gave unambiguous evidences of an existence of nematic LC (NLC) order and fluctuation over a wide temperature range. The correlation length obtained by light scattering was consistent to the droplet size determined by a scanning electron microscope (SEM). The dynamic electro-optic (EO) response in such an isotropic NLC (IsoN) phase was found to be very fast, tens of µs, in a confined geometry because of the local short-range nematic order in the IsoN phase. This type of EO effect is very attractive for next-generation LC displays and light waveguides because of (1) very dark view in the absence of a field, (2) very fast response being independent of temperature and applied electric field, (3) gray-scale display capability with a constant response time, and (4) unnecessity of any surface treatment.

Nd–Fe–B thick film magnets with Nb additive prepared by vacuum arc deposition method

Isotropic Nd–Fe–B thick film magnets were prepared by a vacuum arc deposition method with the deposition rate of approximately 10 μm/h followed by pulse-annealing process. It was found that an optimum amount of Nb additive is effective to enhance the coercivity without the deterioration of remanence and (BH)max values of the isotropic thick films.

Kinetics of a retracting solid film edge: The case of high surface anisotropy

A model describing the retraction kinetics of a fully faceted edge of a single crystalline thin film deposited on a non-wetting substrate is proposed. The kinetics of retraction is very similar to that of a fully isotropic film. The calculated topography profile of the edge exhibits a single maximum and no local minima (depressions). The implications for the solid-state dewetting mechanisms are discussed.

Multi-polarly micro rotor prepared from isotropic nano-crystalline films with self-bonding layer

A magnetized micro rotor such as 1.6 mm in outer diameter was prepared from a laminated isotropic nanocrystalline film with an optimized self-bonding layer. A relative density(RD) higher than 85 % in perpendicular direction of the above film could be obtained, and an estimated permeance coefficient, B/μoH, exceeded 20 by 3-D finite element method. Furthermore, an enhancement of magnetic torque and relative torque constant, dT/dH-gradient, of the above-mentioned sample with the single pole pair could be achieved. Consequently, it was found that use of laminated isotropic film with optimized self-bonding layer is effective in obtaining a multi-polarly magnetized micro rotor with highly dense torque compared with those of a bonded magnet prepared from consolidated flake with the same materials.

Thermal stress analysis of thin films in the context of generalised thermoelasticity

This study deals with the three-dimensional generalised thermoelasticity based on Lord and Shulman's theory and Green and Lindsay's theory. The fundamental equations which include both theories, are used. The thermoelastic problems for a homogeneous and isotropic film whose surfaces are traction free and subjected to a partial heating are analysed by means of the Laplace and Fourier transforms. The state space approach is used in the transformed domains. The inversion are carried out numerically. The numerical calculations for temperature and stresses are carried out. The influence of the finite velocity of the thermal wave grows as the film thins.

A New Realization on Electro-Elastic Love Waves In Piezoelectric Layered Solids

In this paper, we study the propagation of electro-elastic Love waves in a piezoelectric layered solid consisting of a transversely isotropic piezoelectric ceramic film deposited on an isotropic metal substrate. Dispersion relations are obtained in a very concise mathematical form for both electrically open and shorted circuits. Numerical example is given for a PZT-4/steel system. An interesting phenomenon on the fundamental mode of the Love waves in the case of electrically shorted circuit is realized and validated through the discussion on the limit values of phase velocity using the obtained dispersion relations. This validation appears new and is significant to understand the Love wave modes themselves and to the design of acoustic wave devices.

Color-temperature tunable white reflector using bichiral liquid crystal films

We have demonstrated multicolored reflections showing various whitish colors from a bichiral liquid crystal (LC) film. The bichiral LC film was fabricated by using left-handed and right-handed polymeric cholesteric liquid crystal (CLC) films with two different helical pitches and an isotropic polymer film in between. Color temperatures of the multiple reflections are controlled from ~4000 K to ~10000 K by changing linear polarization directions of normally incident and reflected lights. This characteristic can extend practical applications of CLCs to illuminant devices.

Plane-strain discrete dislocation plasticity incorporating anisotropic elasticity

The increasing application of plane-strain testing at the (sub-) micron length scale of materials that comprise elastically anisotropic cubic crystals has motivated the development of an anisotropic two-dimensional discrete dislocation plasticity (2D DDP) method. The method relies on the observation that plane-strain plastic deformation of cubic crystals is possible in specific orientations when described in terms of edge dislocations on three effective slip systems. The displacement and stress fields of such dislocations in an unbounded anisotropic crystal are recapitulated, and we propose modified constitutive rules for the discrete dislocation dynamics of anisotropic single crystals. Subsequently, to handle polycrystalline problems, we follow an idea of O’Day and Curtin (J. Appl. Mech. 71 (2004) 805–815) and treat each grain as a plastic domain, and adopt superposition to determine the overall response. This method allows for a computationally efficient analysis of micro-scale size effects. As an application, we study freestanding thin copper films under plane-strain tension. First, the computational framework is validated for the special case of isotropic thin films modeled by means of a standard 2D DDP method. Next, predictions of size dependent plastic behavior in anisotropic columnar-grained thin films with varying thickness/grain size are presented and compared with the isotropic results.

Influence of surface energy anisotropy on the dynamics of quantum dot growth

We investigate the influence of surface energy anisotropy on the dynamics of quantum dot growth by looking at the long-time dynamics of the morphological (Asaro-Tiller-Grinfeld) instability of a strained thin film driven by surface diffusion during growth and annealing. We derive a continuum model accounting for anisotropic surface energy, wetting, and elastic energies. We obtain a nonlinear nonlocal evolution equation for the film height in the small-slope approximation which we solve numerically given a gamma plot of the surface energy based on experimental properties of silicon-germanium films. A small anisotropy induces a complete change in the coarsening dynamics. The noninterrupted coarsening (Ostwald ripening) at stake for isotropic strained films is destroyed by anisotropy and the system is glued in metastable states. We characterize the statistical properties of the resulting pyramids and show that both their density and mean volume can increase with the total amount of matter. We find an optimal mean film height at which the island size distribution is peaked. These results indicate that different island density or volume may be obtained by varying solely the quantity of matter. Finally, we present an energetic model which describes energetic pathways along which ripening can indeed be suppressed.

Elastic waves interacting with a thin, prestressed, fiber-reinforced surface film

Elastic surface waves propagating at the interface between an isotropic substrate and a thin, transversely isotropic film are analyzed. The transverse isotropy is conferred by fibers lying parallel to the interface. A rigorous leading-order model of the thin-film/substrate interface is derived from the equations of three-dimensional elasticity for prestressed, transversely isotropic films having non- uniform properties. This is used to study Love waves.

Identification of elastic parameters of transversely isotropic thin films by combining nanoindentation and FEM analysis

We develop the nanoindentation method to identify the elastic parameters of transversely isotropic thin films by combining nanoindentation test with finite element method (FEM) simulation. In the forward analysis, CAX4R and CAX4E element types of ABAQUS are used to simulate the purely mechanical indentation and the piezoelectric indentation. With assistance of the substrate effect, the numerical results give indentation responses at the moderate ratio of penetration depth to film thickness, and the dimensionless equations between the maximum indentation load, loading curve exponent and the elastic parameters of film/substrate system are established by extensive FEM simulations. In the reverse analysis, the nanoindentation test is performed on ZnO thin film as transversely isotropic material, and the experimental indentation curves can be fitted as the power function. The maximum indentation load and the loading curve exponent can be obtained from the experimental indentation curves and substituted into the dimensionless equations to obtain the elastic parameters of ZnO thin film. The results show the transverse Young’s modulus, the longitudinal Young’s modulus, and the longitudinal shear modulus under the piezoelectric indentation mode are closer to the experimental values measured by the acoustic method than those under the purely mechanical indentation mode. This study develops the nanoindentation method to extract the elastic parameters of transversely isotropic thin films, and it may be helpful to the measurement of thin film mechanical properties by means of nanoindentation.

Investigation on Magnetic Torque of Multi-Polarly Micro Rotor Using Shape-Magnetic-Anisotropy

A double pole pair milli-size rotor with 1 mm in outer diameter and 0.3 mm in inner diameter was fabricated from an isotropic laminated film magnet with a non-magnetic material. Permeance coefficient distribution together with static magnetic field of the film were also estimated by using 3-D and 2-D finite element model, and the average permeance coefficient, B/¿oH, could be estimated as 18.7. A torque of the isotropic film magnet with the remanence value of approximately 1 T was measured under the different field strength, and a relative torque and relative torque constant, dT/dH-gradient, of the above-mentioned magnet with the double pole pair increased by 172% and 152%, respectively, compared with those of an anisotropic bulk magnet with a single pole pair whose remanence value was approximately 1.3 T. It was found that use of isotropic laminated film magnet is effective in obtaining a micro multi-polarly magnetized rotor with highly dense torque.

Small-angle neutron spin-flip scattering in ferromagnetic films

This paper reports on the results of reflectometric measurements of anisotropic (Co67Fe31V2) and almost isotropic (Fe) films prepared by magnetron sputtering. Nonspecular reflections and the corresponding peaks of the intensities of refracted neutrons have been observed for the alloy samples in magnetic fields H ≤ 7 Oe applied in the film plane along the easy magnetization axis. For iron films, angular splitting of the reflected neutron beam becomes observable only at H > 100 Oe and increases with an increase in the magnetic field. A general scheme has been proposed for this small-angle scattering with allowance made for different variants of changes in the Zeeman energy of neutrons. This scheme has allowed us to identify the magnetic structures of Co-Fe films. The magnetization of 0.15-μm-thick films with uniaxial and unidirectional textures leads to the formation of unidirectional textures characterized by different intensity distributions, for which the qualitative differences are retained with an increase in the magnetic field from 7 to 800 Oe. It has been revealed that, for 2.5-μm-thick films with the initial unidirectional texture, the oppositely magnetized states are nonequivalent.

34.3: Drawing‐Induced Biaxiality Change from a Positive C to a Negative A Plate and Its Application in Wide Viewing Angle IPS LCDs

AbstractMechanical drawing is widely used to induce the optical birefringence (positive A or negative C plates) in optically isotropic polymer films. We propose a method to make the optical films having the optical biaxiality lying in between that of the positive C and the negative A plates (nx < ny < nz) utilizing the solvent evaporation and the mechanical drawing processes. A theoretical model is proposed to calculate the birefringence induced by the processes. Numerical calculation shows that the biaxial film drawn properly can widen the viewing angle of IPS mode LCDs.