Approximate high-order dynamic theory of a fluid layer in between two thick solids

A thin layer of heavy fluid with bound faces is considered first. For the sake of simplicity, the effects of vortex and viscosity are neglected. Two cases of compressible and incompressible fluids are treated, assuming that a thickness-over-wavelength ratio is a small parameter. For the internal state of medium the relations between the quantities on the layer surfaces are deduced. In contrast to the standard approach, which expands the propagator matrix into power series of a small wave number, the asymptotic integration of 3D equations and boundary conditions of fluid dynamics is performed. Respective relations are represented in a recurrent form and permit one to obtain the high-order components of the displacements and pressure rather simply. When considering two thick solids with a fluid in between, this result is used to derive the so-called "impedance boundary conditions" (IBC) with a relative asymptotic error up to tenth order. Tests show their validity until the first quasiresonance frequency of a layer, so, the analysis is not just long wave but essentially low frequency. Thus, these IBC are applicable to reduce the dimension in the analysis of challenged multicomponent system of fluid-coupled solids in a reasonable frequency range.     

Modulated angle beam ultrasonic spectroscopy for evaluation of imperfect interfaces and adhesive bonds

An experimental method incorporating high frequency pulsed angle beam ultrasonic measurements modulated by low frequency vibrations of a bonded structure is described. This method uses parametric/nonlinear mixing between high and low frequencies to characterize adhesive degradation. It is demonstrated that good quality (undamaged) bonds exhibit little dependence of ultrasonic signature on the overlay of low frequency vibration loads; however, environmentally degraded or imperfect bonds exhibit strong modulation of the resonance frequency of the ultrasonic signal reflected from the bond. The results are interpreted using a model for normal and oblique wave interaction with two nonlinear interfaces separated by an adhesive layer under quasi-static stress modulation.     

The magnetic properties of a finite superlattice with two disordered interfaces

Within the framework of the effective field theory, based on a probability distribution technique, we examine the critical and compensation behaviors of a ferrimagnetic alternating superlattice on a simple cubic structure. The superlattice consists of k unit cells each of which consists of L layers of spin-1/2 A atoms, L layers of spin-1 B atoms and a disordered interface with two layers in between that is characterized by a random arrangement of A and B atoms A_pB_1−pA_1−pB_p with a negative coupling A − B. Considering a finite and infinite superlattices, the effect of the thickness of the film and the surface exchange coupling on the magnetic properties are studied. The obtained results show a number of characteristic phenomena.     

Thermodynamics and kinetics of shear-induced melting of a thin layer of lubricant confined between solids

Using Landau’s phenomenological theory of phase transitions, the shear-induced melting of a thin layer of substance confined between two crystalline surfaces is considered. The kinetics of melting and solidification is considered for static and alternating loads. The possibility of two consecutive “melting” (solid-to-liquid) transitions is discussed. As a result of the first transition, modulation of the microscopic density becomes zero only in the direction of shear (partial melting) and as a result of the second, it also disappears in the normal direction (complete melting).     

Reflection and transmission of phonons at a planar interface between two dissimilar solids

Two semi-infinite dissimilar crystals with, however, the same crystal structure and lattice parameter are in contact at a planar interface. Using a simple force constant model, restricted to near-neighbour interaction reflection and transmission coefficients for sound waves propagating along one solid are calculated. At low frequencies the reflection and transmission coefficients are determined solely by the force constants and the atomic masses in the two media. At high frequencies the transmission coefficient becomes small if the force constant at the interface between the two media is weak. Information of the local force constant in the interface region can be gained at least in principle, by measuring the reflection and transmission coefficients at high frequencies.     

Relation between the parameters of the elasticity theory and averaged bulk modulus of solids

A relation between the elastic moduli and Poisson’s ratio of crystalline and vitreous solids is considered. The feasibility of introducing the averaged bulk modulus, which has the same attributes as other elastic moduli, is substantiated. A relationship between the Grüneisen parameter and Poisson’s ratio is discussed.     

Generation of higher acoustic harmonics at a flat rough interface between two solids

The results of experimental studies of the influence of a static pressure applied to a flat rough interface between two solids on its nonlinear elastic properties are presented. The studies were performed by the spectral method on the basis of an analysis of the efficiency of generation of higher acoustic harmonics, which arise upon the reflection of a longitudinal elastic wave of finite amplitude from the boundary and the passage through it. A nonmonotonic dependence of the amplitudes of acoustic harmonics on the value of the external reversible static pressure applied to the interface was revealed: pronounced amplitude maxima for the amplitudes of the second and third harmonics were observed with a decrease in the external static pressure. It was also found that the amplitudes of the second, third, and fourth acoustic harmonics increase with a decrease in the external static pressure (in comparison with their values at the same pressure values during its increase). The experimentally determined power dependence of the higher acoustic harmonics on the amplitude of the first acoustic harmonic significantly differed from the classical indices for these harmonics. The influence of the external pressure on the values of the nonlinear second- and third-order elastic parameters was analyzed. The experimental results were analyzed on the basis of nonclassical acoustic nonlinearity.     

Inverse relation between photocurrent and absorption layer thickness in polymer solar cells

Organic solar cells based on polymer–fullerene bulk heterojunctions were optimised with respect to the short circuit photocurrent by means of optical modelling. Due to interference effects present in the thin film multilayer device, an inverse relation between active layer thickness and photocurrent was predicted and experimentally verified. Optimised photovoltaic devices yield power conversion efficiencies of 4%. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Formation and stability of ultrasonic generated bulk nanobubbles

Although various and unique properties of bulk nanobubbles have drawn researchers' attention over the last few years,their formation and stabilization mechanism has remained unsolved. In this paper, we use ultrasonic methods to produce bulk nanobubbles in the pure water and give a comprehensive study on the bulk nanobubbles properties and generation. The ultrasonic wave gives rise to constant oscillation in water where positive and negative pressure appears alternately. With the induced cavitation and presence of dissolved air, the bulk nanobubbles formed. Nanosight(which is a special instrument that combines dynamic light scattering with nanoparticle tracking analysis) was used to analyze the track and concentration of nanobubbles. Our results show that in our experiment, sufficient bulk nanobubbles were generated and we have proven they are not contaminations. We also found nanobubbles in the ultrasonic water change in both size and concentration with ultrasonic time.     

Photothermal methods for determination of thermal properties of bulk materials and thin films

Information on the thermal properties of materials is very important both in fundamental physical research and in engineering applications. The development of materials with desirable heat transport properties requires methods for their experimental determination. In this paper basic concepts of the measurement of parameters describing the heat transport in solids are discussed. Attention is paid to methods utilizing nonstationary temperature fields, especially to photothermal methods in which the temperature disturbance in the investigated sample is generated through light absorption. Exemplary photothermal measuring techniques, which can be realized using common experimental equipment, are described in detail. It is shown that using these techniques it is possible to determine the thermal diffusivity of bulk transparent samples, opaque and semi-transparent plate-form samples, and the thermal conductivity of thin films deposited on thick substrates. Results of the investigation of thermal diffusivity of the ground in the polar region, which is based on the analysis of the propagation of the thermal wave generated by sun-light, are also presented. Based on chosen examples one can state that photothermal techniques can be used for determination of the thermal properties of very different materials.     

A simple relation between bulk and surface properties of nuclear matter

Starting from a previously derived relation between the derivatives of the bulk nucleon energy e(n_c) and the surface tension σ(n_c) with respect to the central density n_c we obtain a simple model-independent relation between the values of n_c, σ(n_c), the surface parameter t and the bulk modulus K_∞ at saturation. This relation is checked for values obtained in ETF calculations. K_∞=230 MeV is calculated from the well-known experimental values of n₀, σ₀ and t₀.     

Pressure derivatives of bulk and shear modulus of rare gas solids

Expressions for the isothermal bulk and shear modulus and also their first and second order pressure derivatives for rare gas solids are derived by a simple method considering the different interactions i.e. modified variable induce dipoles, short range overlap repulsion and the vibrational contribution. The derived relations for dK_T/dP, dC_S/dP, dC′₄₄/dP, d²K_T/dP², d²C_S/dP² and d²C′₄₄/dP² are used to compute the numerical values of these constants at P=0 for Ne, Ar, Kr and Xe.     

Influence of adhesive layer properties on laser-generated ultrasonic waves in thin bonded plates

This paper studies quantitatively the generation of Lamb waves in thin bonded plates subjected to laser illumination, after considering the viscoelasticity of the adhesive layer. The displacements of such plates have been calculated in the frequency domain by using the finite element method, and the time domain response has been reconstructed by applying an inverse fast Fourier transform. Numerical results are presented showing the normal surface displacement for several configurations: a single aluminum plate, a three-layer bonded plate, and a two-layer plate. The characteristics of the laser-generated Lamb waves for each particular case have been investigated. In addition, the sensitivity of the transient responses to variations of material properties (elastic modulus, viscoelastic modulus, and thickness) of the adhesive layer has been studied in detail.     

Thermodynamics of stressed solids: Slow deformation and roughening of material interfaces

At every turn in nature we are confronted with complex patterns. Patterns often formed in multiphase systems by an intricate dynamics of mass transport, e.g. diffusion and/or advection, and mass exchange between individual phases. Here we consider instabilities of phase boundaries in idealized stressed multiphase systems. Specifically, we study the growth of small perturbations of surfaces by considering mass transport from regions, where the stress and chemical potential is high, to surrounding regions where the stress and chemical potential is low. We present a linear stability analysis for various stress configurations and their corresponding stability diagrams.     

Ultrasonic wave propagation across a thin nonlinear anisotropic layer between two half-spaces

Boundary conditions and perturbation theory are combined to create a set of equations which, when solved, yield the reflected and transmitted wave forms in the case of a thin layer of material that is perfectly bonded between two isotropic half-spaces. The set of perturbed boundary conditions is created by first using the fully bonded boundary conditions at each of the two interfaces between the thin layer and the half-spaces. Then, by restricting the layer's thickness to be much smaller than an acoustic wavelength, perturbation theory can be used on these two sets of boundary equations, producing a set of equations which effectively treat the thin layer as a single interface via a perturbation term. With this set of equations, the full range of incident and polar angles can be considered, with results general enough to use with a layer that is anisotropic, nonlinear, or both anisotropic and nonlinear. Finally the validity of these equations is discussed, comparing the computer simulation results of this theory to results from standard methods, and looking at cases where the results (or various properties of the results) are known or can be predicted.     

Interface and bulk properties of Cu(In,Ga)Se2 solar cell with a cracker-ZnS buffer layer

Cu(In,Ga)Se₂ (CIGS) solar cells were fabricated by varying the film thickness of the cracker-ZnS (c-ZnS) buffer layer from 0 nm to 20 nm, and performance was found to depend on c-ZnS film thickness. The best cell efficiency of approximately 8% was obtained from the CIGS solar cell with an 8 nm thick-c-ZnS buffer layer. To investigate the primary factor to determine the cell performance, we utilized the impedance spectroscopy (IS) reflecting interface qualities, and capacitance-voltage (CV) profiling sensitive to bulk properties. In IS results, an equivalent circuit model including the resistance and capacitance was proposed to interpret cell performance, and carrier lifetime was obtained in connection with recombination probability at p-n junction. In CV profiling, the carrier concentration in the CIGS bulk, the depletion width, and the charge distribution related to the defect states along the depth direction were evaluated. The formation mechanism of c-ZnS buffer layer is suggested by measuring the chemical states, which is closely associated with the IS and CV results. The depletion width substantially increased at c-ZnS film thickness more than 15 nm due to the diffusion of Zn atoms toward CIGS layer, resulting in negative influence on cell performance. From this study, we demonstrated that IS and CV profiling are complementary analysis tools for interpretation of the solar cell operation concerning the interface and bulk properties.     

Ab initio determination of the optical properties of bulk Au and free surfaces of Au

The optical properties of bulk Au and a (100) free surface of Au are determined by solving the Helmholtz–Fresnel equations for a geometry reflecting layered systems. This approach is based on the use of the microscopical conductivity tensor evaluated fully relativistically and, for later purposes, does include the option of choosing an arbitrary uniform direction of a possibly present magnetization. It will be shown that, while so-called experimental bulk data agree reasonably well with their theoretically obtained counterparts, in the case of free surfaces of Au (semi-infinite systems) they not only disagree substantially in size between different experiments but also with the theoretical values. The shapes of the curves for the real and the imaginary parts of the diagonal permittivity tensor elements ? _xx and ? _zz , however, are rather similar.