Including Surface Effects Research Articles

Pre-equilibrium–Emission Surface Effects in Activation Reactions

Description of the high-energy side of activation excitation functions, most sensitive to pre-equilibrium processes modeling, is reported in this work within the geometry–dependent hybrid (GDH) model. Improved cross-section calculations are reported for fast-neutron induced reactions on 51V and 92, 94–98, 100Mo based on partial level density including surface effects as well as energy–dependent single–particle level densities.

Lattice model for ferroelectric thin film materials including surface effects: Investigation on the “depolarizing” field properties

Ferroelectric properties of thin film materials like lead zirconate titanate differ from those observed for bulk material. It is well known that the surface can strongly influence phase transition phenomena. By the use of a thermodynamical approach, very similar to those generally used to describe phase transitions, we have proposed for studying ferroelectric states a two dimensional lattice model which allowed us to account for surface effects. These surface effects described by an inhomogeneous Landau–Devonshire theory were suggested to produce a finite size effect even if the surface charge is compensated at the metallic electrodes. The manifestations of the field induced by the bound charges in the polarization switching is discussed and is shown to depend strongly on the bulk correlation length and on the extrapolation length. Finally we have applied our model to investigate the influence of the surface effect and of the related bound charges on the thickness dependence of ferroelectric properties.

2-D MOSFET modeling including surface effects and impact ionization by self-consistent solution of the Boltzmann, Poisson, and hole-continuity equations

We present a new two-dimensional (2-D) MOSFET simulation method achieved by directly solving the Boltzmann transport equation for electrons, the hole-current continuity equation, and the Poisson equation self-consistently. The spherical harmonic method is used for the solution of the Boltzmann equation. The solution directly gives the electron distribution function, electrostatic potential, and the hole concentration for the entire 2-D MOSFET. Average quantities such as electron concentration and electron temperature are obtained directly from the integration of the distribution function. The collision integral is formulated to arbitrarily high spherical harmonic order, and new collision terms are included that incorporate effects of surface scattering and electron-hole pair recombination/generation. I-V characteristics, which agree with experiment, are calculated directly from the distribution function for an LDD submicron MOSFET. Electron-hole pair generation due to impact ionization is also included by direct application of the collision integral. The calculations are efficient enough for day-to-day engineering design on workstation-type computers.

Dynamical effects in electron tunnelling: Nonlocal image potentials

We generalize Jonson's nonlocal theory of dynamical exchange-correlation potential in tunnelling to the metal-insulator-metal (M-I-M) case, for zero and nonzero tunnelling currents, and solve in the second order exactly including surface effects. The correct treatment removes unphysical features near interfaces. The nonlocal calculation gives dynamical image potentials reduced in comparison to the classical image potential, but this reduction is less drastic than in the local approximation.

Raman scattering from microcrystals

Abstract This review discusses the size effects on Raman scattering from microcrystals. For ionic microcrystals, the existence of surface phonon modes is predicted from electromagnetic theories. It is shown that Raman spectroscopy is very effective to detect the surface phonon modes. The size effects on nonpolar phonons in covalent microcrystals can also be studied by Raman spectroscopy. However, the relaxation of the wave-vector selection rule or the phonon confinement explains only some of the experimental data. Development of lattice dynamical theories of Raman scattering from microcrystals including surface effects is highly required. Enhancement of Raman intensities arising from the excitation of electromagnetic normal modes of microcrystals is also discussed.

A Detailed and Simplified Solution to Hydrodynamic Forces on a Submerged Tank Subject to Lateral Ground Excitation

The domain where a submerged vertical cylindrical tank exists is divided into two regions. Assuming irrational motion and an ideal fluid the Laplace s equations in both regions are solved by the method of separation of variables. The integral equation resulting from matching the potentials at the interface is solved numerically by the Galerkin method. It is shown that the mathematical labor is greatly reduced by dropping the surface effects and the results are in good agreement with those obtained by including surface effects albeit at higher values of excitation frequencies. The case of protruding cylinder is presented to further illustrate the simplicity of the solution.

Kosterlitz's recursion relations for dirty quasi-2D superconductors and the anisotropic XY model

Abstract The theory of quasi-2D superconductors including surface effects is shown to be equivalent to the anisotropic XY model when a 3D parameter space is introduced. Fixed-point equations for 2D and 3D systems are readily recovered together with the finite cut-off characterizing the quasi-2D approach.

Surface effects and vortex-induced flux-flow resistance in dirty quasi-2D superconductors

Flux-flow resistance in dirty superconductors including surface effects is calculated below the vortex depairing temperature within a renormalization procedure for quasi-2D systems. Although the theory predicts a non-universal jump in the superfluid density, the result favours a universal vortex current when the dependence of the GL parameter on the temperature is neglected.

Melting of dilute alloys including surface effects

The two phase equilibrium for the melting transition is calculated for dilute alloys, using a thermodynamic description. Different atomic diameters as well as interchange energies are taken into account. In addition the role of a possible interface contribution is examined.

Surface and size effects on the electronic states of small metallic clusters: a model calculation

The authors compute exactly the eigenvalues of atomic clusters of arbitrary size with a simple cubic structure in the tight-binding approach (LCAO), including surface effects. To represent the electronic structure of the hypothetical metallic clusters they consider well separated and p states. They find strong deviations from the corresponding states of the bulk cubium where the number of particles is of the order of 104 or less (R<or approximately=50 AA): new states appear near the top of the bands and states disappear near the bottom of the bands. This produces an upward shift of the Fermi level and of the mean energy with decreasing size and an asymmetric and deformed shape of the density of states. Effects of the geometrical shape of the cluster and of the environment are also considered. They discuss the relevance of their results on the interpretation of recent photoemission experiments on small metallic clusters.

A Monte-Carlo calculation of the secondary electron emission of normal metals: I. The model

A model is proposed to describe the secondary electron emission (SEE) of pure normal metals. The various types of collisions suffered by an electron travelling in the solid are analyzed. The dielectric theory is used to account for the collisions with the jellium, including surface effects in an approximate way. The different damping mechanisms for plasmons are reviewed and their influence on SEE is emphasized. The elastic and ionizing collisions with the ionic cores are described by a randium model. The relative importance of each of the above processes for the SEE of normal metals is discussed.

On the origin of long‐period features in low‐angle sea backscatter

When viewed at extremely shallow grazing angles with a microwave radar, sea backscatter displays a variety of spatio‐temporal features with time scales of the order of several minutes or more. A modest body of experimental evidence accumulated from several radars looking at different oceans shows components with a period of 3–4 min sometimes imposed on a much stronger periodicity of 10–15 min, and sharply defined moving striations with speeds of the order of 15 kts and lifetimes of several minutes. The origin of these features may be sought among a wide assortment of physical phenomena, including surface effects (such as wave packets or interference patterns, illumination thresholding at extreme grazing angles, internal waves in the thermocline, shelf waves, fluctuations in the surface wind field), or propagation effects resulting from refractivity perturbations due to traveling disturbances in the atmospheric boundary layer or to water vapor perturbations in the evaporative layer. None of these hypotheses can account for all of the features observed in the data, but the more likely candidates are discussed in detail, using available data for the relevant oceanographic and atmospheric parameters. It is concluded that the behavior shown in this paper is most probably due to group effects among surface waves emphasized by illumination thresholding at low grazing angles.

Generalized Theory of Acoustic Propagation in Porous Dissipative Media

The theory of acoustic propagation in porous media is extended to include anisotropy, viscoelasticity, and solid dissipation. A more refined analysis of the relative motion of the fluid in the pores is also developed by introducing the concept of viscodynamic operational tensor. The nature of this operator is analyzed by applying variational and Lagrangian methods. Viscoelasticity and solid dissipation are introduced by applying the correspondence principle as derived from thermodynamics in earlier work by the author. Various dissipative models are discussed and the corresponding operators and relaxation spectra are derived. The physical chemistry of the multiphase porous medium including surface effects lies within the scope of the thermodynamic theory. The nature of thermoelastic dissipation and electrokinetic effects in relation to the thermodynamic theory is also brought out.