Anomalous roughening of viscous fluid fronts in spontaneous imbibition

We report experiments on spontaneous imbibition of a viscous fluid by a model porous medium in the absence of gravity. The average position of the interface satisfies Washburn's law. Scaling of the interface fluctuations suggests a dynamic exponent z approximately 3, indicative of global dynamics driven by capillary forces. The complete set of exponents clearly shows that interfaces are not self-affine, exhibiting distinct local and global scaling, both for time (beta = 0.64 +/- 0.02, beta(*) = 0.33 +/- 0.03) and space (alpha = 1.94 +/- 0.20, alpha(loc) = 0.94 +/- 0.10). These values are compatible with an intrinsic anomalous scaling scenario.     

Electron mobility in a modulation doped AlGaN/GaN quantum well

We consider a two dimensional electron gas confined to a modulation doped AlGaN/GaN quantum well and study the dependence of low field mobility on various parameters such as composition, well width, remote impurity and interface roughness as a function of temperature. GaN is assumed to be in the zincblende structure. Acoustic and optical phonon, ionized remote impurity and interface roughness scatterings are taken into account in mobility calculations. The scattering rates are calculated using the self-consistently calculated wave functions obtained from the numerical solution of Poisson and Schr?dinger equations. Also found from the self-consistent solutions are the potential profile at the junction, the energy levels in the well and electron concentrations in each level. Ensemble Monte Carlo method is used to find the drift velocities of the two dimensional electrons along the interface under an applied field. The mobility of two dimensional electrons is obtained from the drift velocity of electrons. It is found that while remote impurity scattering is very effective for small values of spacer layer and doping concentrations, increasing Al concentration reduces the mobility of electrons. The effect of surface roughness, on the other hand, on mobility is almost independent of well width. The results of our simulations are compatible with the existing experimental data.     

Scattering of conduction electrons by interface roughness in semiconductor heterostructures

A fluctuation transport theory is applied to describe the mobility limiting effect of interface roughness scattering in semiconductor heterostructures. As an example we consider a high mobility transistor and compare electron scattering by interface roughness with Coulomb scattering processes by ions and dipole fluctuations. We show that the dynamical resistivity measurement provides detailed information about the autocorrelation of the interface morphology.     

Elastic properties of 2D colloidal crystals from video microscopy

Elastic constants of two-dimensional (2D) colloidal crystals are determined by measuring strain fluctuations induced by Brownian motion of particles. Paramagnetic colloids confined to an air-water interface of a pendant drop are crystallized under the action of a magnetic field, which is applied perpendicular to the 2D layer. Using video microscopy and digital image processing we measure fluctuations of the microscopic strain obtained from random displacements of the colloidal particles from their mean (reference) positions. From these we calculate system-size dependent elastic constants, which are extrapolated using finite-size scaling to obtain their values in the thermodynamic limit. The data are found to agree rather well with zero-temperature calculations.     

The field-theoretic description of dynamics of interfaces in disordered media

The time evolution of an interface in a disordered media is described by using the propagator method. The method enables one to represent the perturbation expansions of different quantities characterizing the interface by means of diagrams which are familiar from the field theory. By the analysis of the divergences in the vicinity of the critical dimension d_c = 4 we found that the regularization of the theory demands the renormalization of the mobility and all moments of the disorder correlator excepting the zero one. The renormalization group (RG) calculations of the average velocity of the interface, the roughness, and the functional RG equation of the disorder correlator are presented to order ? = 4 - d. The latter coincides with the result obtained by D. S. Fisher in the equilibrium case. The RG equations have a pole at the value of the driving force, which coincides with the value of the threshold below which the interface becomes pinned as predicted by Bruinsma and Aeppli. The behavior of the mobility in the vicinity of the pole is discussed.     

Atomistic study on the activation enthalpies for interface mobility and boundary diffusion in an interface-controlled phase transformation

A multi-lattice kinetic Monte Carlo atomistic simulation method has been used to simulate the austenite to ferrite interface-controlled transformation in pure iron. By performing simulations with different amounts of “free volume” at the interface, quantitative relations between the activation energies for interface mobility, boundary self diffusion and bulk self diffusion were investigated. The effect of different interface orientations on the distribution of free volume over the interface, as determined by interface crystallography, and its consequences for interface mobility activation energy was also evaluated. The essential role of thermal fluctuations in free volume distribution at the interface has been shown. The activation enthalpy for boundary diffusion is shown to be larger than the interface mobility activation enthalpy.     

Investigation of grain-boundary diffusion of nickel in molybdenum by auger electron spectroscopy

The dependence of the grain-boundary diffusion coefficient of nickel in molybdenum on annealing temperature was investigated. Possible causes are analyzed for differences in the values of the grain-boundary diffusion coefficients and the activation energies for this process from those obtained by earlier researchers.Institute of the Physics of Strength and Materials Science, Siberian Branch, Russian Academy of Sciences (SO RAN). Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 28–31, July, 1992.     

Roughness of boundary interfaces in polycrystals and its influence on the yield strength of nanocrystalline materials

The distribution in roughness of grain-boundary interfaces in polycrystals is measured metallographically. The result shows that there are high populations of localized interface areas with roughness much lower than the average in polycrystals. Effects of the roughness on the boundary sliding in nanocrystalline materials are discussed, suggesting that the sliding in the localized interface areas produces stress concentrations to cause a reduction in the yield strength of nanocrystalline materials.     

Hysteresis mediated by a domain wall motion

The position of an interface (domain wall) in a medium with random pinning defects is not determined unambiguously by the instantaneous value of the driving force, even on average. Employing the general theory of the interface motion in a random medium, we study this hysteresis, different possible shapes of the hysteresis loop, and the dynamical phase transitions between them. Several principal characteristics of the hysteresis, including the coercive force and the curves of dynamical phase transitions obey scaling laws and display a critical behavior in the vicinity of the mobility threshold. At finite temperature the threshold is smeared and a new range of thermally activated hysteresis appears. At a finite frequency of the driving force there exists a range of the non-adiabatic regime in which not only the position, but also the average velocity of the domain wall, displays hysteresis.     

Dynamics at the liquid-vapor interface of a supercooled organic glass former

We investigated the dynamics near the liquid-vapor interface of the supercooled model organic glass former dibutyl phthalate by using surface-sensitive x-ray scattering techniques. Our results reveal significant enhancement of the relaxation rate over a wide length-scales range. The analysis of the dispersion relation of long-wavelength surface fluctuations yields a nonzero value of the share modulus near the free surface. At the molecular level, the dynamics in the near surface region (10-15 nm) is inhomogeneous. The mobility is decreasing with increasing distance from the free surface. Below the bulk glass transition, two distinct relaxation times were observed differing by 1 order of magnitude. The observed fast relaxation proves the existence of a high mobility liquidlike surface layer of 10 nm thickness on top of a frozen in bulk system.     

Constitutive modeling of the densification of PZT ceramics

In the present work, sintering constitutive models were employed to investigate the high-temperature densification behavior of undoped stoichiometric lead zirconate titanate (PZT) ceramics with perovskite structure. The constitutive models used were based on classical grain-boundary diffusion and interface reaction, and also the coupled mechanism of the two processes. PZT ceramics were fabricated and the calcination and sintering of the materials were discussed. Using the constitutive models employed and the experimental results obtained, the activation energy for densification of the PZT ceramics investigated was determined as 390±30 KJ/mol. It was noted that the coupled mechanism of grain-boundary diffusion and interface reaction was the controlling process during the densification of the materials investigated.     

有机二极管基于通用迁移率模型的解析电流电压关系

提出一种有机半导体二极管电流电压关系的解析表达式。该表达式是基于Pasveer 等人[Phys. Rev. Lett. 94, 206601 (2005)]的迁移率模型建立的,其中考虑了影响有机半导体载流子输运最重要的因素,包括温度、载流子浓度和电场强度。将Pasveer等人迁移率公式中的载流子浓度和电场强度用常数迁移率下严格解计算的平均值代入,然后将得到的迁移率取代Mott-Gurney电流电压关系中的常数迁移率从而得到解析电流电压表达式。将新解析表达式应用于三种材料制作的有机二极管,计算结果与实验数据符合很好,表明解析表达式是合理的。     

有机二极管基于通用迁移率模型的解析电流电压关系

提出一种有机半导体二极管电流电压关系的解析表达式.该表达式是基于Pasveer等人[Phys.Rev.Lett.94,206601 (2005)]的迁移率模型建立的,其中考虑了影响有机半导体载流子输运最重要的因素,包括温度、载流子浓度和电场强度.将Pasveer等人迁移率公式中的载流子浓度和电场强度用常数迁移率下严格解...     

Surface of a 3He crystal: crossover from quantum to classical behavior

3He crystals start to show facets on their surface only at about 100 mK, well below the roughening transition temperature. To understand the reason for that, we have performed the first quantitative investigation on the growth dynamics of the basic (110) facet at 60-110 mK. The obtained values of the step free energy suggest an extremely weak coupling of the solid-liquid interface to the crystal lattice which we show to be the result of quantum fluctuations of the interface. The renormalization group approach by Nozières and Gallet, modified to incorporate quantum fluctuations, explains well the temperature dependence of the step energy measured in this work and at ultralow temperatures by Tsepelin et al., where the coupling is known to be strong. We have thus shown that, paradoxically, the role of quantum fluctuations is at higher temperatures much larger than at low temperature.     

Well-width dependence of interface roughness scattering in GaAs/Ga1 − xAlxAs quantum wells

Well-width dependence of quantum and transport mobilities of electrons in GaAs/GaAlAs multiple quantum wells is studied for wells with widths ranging between 50 Å and 145 Å Experimental results are obtained from the amplitude analysis of the Shubnikov–de Haas (SdH) oscillations and from conventional Hall measurements at temperatures betweenT = 15 K and 4.2 K. A novel technique is employed to estimate, theoretically, the interface roughness parameters from electron quantum and transport lifetimes. The modelling is carried out for a range of layer fluctuations, width (Δ) and lateral size (Λ), as to obtain the best fit to the experimental results for individual samples. Our results indicate that the interface roughness scattering limits equal both quantum and transport mobilities at low temperatures, and that the nature of scattering by interface roughness (small or large angle) depends not only on the size and the width of the fluctuations but also on the distribution of these fluctuations within the samples. Therefore, unlike the predictions of the existing theoretical models, which assume constant values of Δ and Λ for all well widths, the well-width dependence of interface roughness scattering cannot be verified experimentally.     

Fluctuations of the fringe pattern generated by a partially developed speckle

The fluctuations of fringe pattern intensity are studied experimentally by means of Young's interference experiment. It is shown that the average contrast of the fringe intensity changes with the position in the fringe pattern. The characteristic values of the contrast are measured as a function of the separation of the pinholes. The experimental results are discussed qualitatively.     

Tagged particle fluctuations in uniform shear flow

The nonlinear Boltzmann and Boltzmann-Lorentz equations are used to describe the dynamics of a tagged particle in a nonequilibrium gas. For the special case of Maxwell molecules with uniform shear flow, an exact set of equations for the average position and velocity, and their fluctuations, is obtained. The results apply for arbitrary magnitude of the shear rate and include the effects of viscous heating. A generalization of Onsager's assumption of the regression of fluctuations is found to apply for the relationship between the equations for the average dynamics and those for the time correlation functions. The connection between fluctuations and dissipation is described by the equations for the equal-time correlation function. The source term in these equations indicates that the “noise” in this nonequilibrium state is qualitatively different from that in equilibrium, or even local equilibrium. These equations are solved to determine the velocity autocorrelation function as a function of the shear rate.     

Kinetic properties of a first-order boundary ridge in Zn

The motion of a grain-boundary half-loop system with a first-order ridge is investigated and a theory of the steady-state motion of such a system is presented. The pattern of variation in the shape and properties of a moving boundary that contains various structural elements (curved segments, facets, first-order ridges) is presented. Important kinetic parameters (the mobility and the migration activation enthalpy) of a first-order grain-boundary ridge with curved segments are measured.     

Effect of Laser Beam Dimensions on Electrophoretic Mobility Measurements

The effect of the finite dimension of the measuring probe, i. e. the laser beam width, on the electrophoretic mobility distribution as determined by electrophoretic light scattering in closed capillary cells is presented on a quantitative basis. The experimental mobility broadening as a function of the probe position in the capillary is in agreement with the broadening expected from the laser beam waist. A strategy for the accurate determination of average mobility and mobility distributions is proposed.     

光散射法同时测量气液二元体系的黏度、界面张力和热、质扩散系数的研究

当气液二元体系处于宏观热力学平衡状态时,表面与体相的波动弛豫时间具有不同量级,通过调节散射体积和改变采样时间,利用表面光散射实验系统可以同时探测到来自界面处表面波及体相中温度和浓度的波动信息。本文在已有的表面光散射实验系统上,以正庚烷与二氧化碳二元系统为例,同时实现了该体系黏度、界面张力和热、质扩散系数的测量,其扩展不确定度分布为3.0%,3.7%,20%,4.3%(k=2)。实验所得到的数据与文献进行了对比,其偏差在不确定度范围内,证明了本文提出的测量方法可以实现气液二元体系四种性质的同时测量,且测量精度可以满足一般工程应用。