M. El-Batanouny

Dynamics of the clean and hydrogen covered Pd(111) surface

Abstract We report a study of the dynamics of the clean and hydrogen-covered Pd(111) surface using elastic and inelastic scattering of a monoenergetic thermal He beam. We present surface phonon dispersion curves along the direction measured at 140K for saturated H(1 × 1) coverage, and at 320K for ⋍ 10% coverage. We discuss these results in the light of recent evidence that H behaves like a correlated quantum fluid on this surface of Pd and completely delocalizes at medium and low coverages. We present possible explanations and suggest further experiments.

Molecular dynamics study of the surface vibration of the rconstructed Au(111) surface

Abstract The surface dynamics of the dislocation-mediated reconstruction of the Au(111) surface is investigated using three dimensional Molecular Dynamics. At low temperatures the surface phonon dispersions are calculated along the direction. The computational results reproduce the experimentally observed anomalies in the surface phonon curves and provide detailed interpretation of their origin, and of the polarization of the different phonon branches. The anomaly in the vertical-shear branch is found to be due to a cross-over to localization when the phonon wavelength becomes shorter than the size of the dislocations. The high temperature dynamics is followed by trajectory diagrams.

Collective Coordinates and Linear Modes of the Double-Sine-Gordon Kink

We present a complete Hamiltonian treatment of a kink with an internal degree of freedom, namely the double-sine-Gordon (DSG) kink. In this formalism we assign two canonical coordinates and their associated momenta to describe the motion of the center of mass of the DSG kink and the relative motion of its two sub-kinks. We show that the canonical coordinate representing the separation of the two sub-kinks describes a nonlinear oscillatory degree of freedom. We have also used the method of supersymmetry to obtain, for the first time,the complete set of eigenfunctions of small oscillations about the 4π DSG kink. This analysis was motivated by the need for an accurate expression of the shape mode in the Hamiltonian formalism.

Dynamics of Mismatched Overlayers

The interest in the dynamics of surfaces and overlayers on surfaces has recently intensified. This is largely due to the development of new, more detail-yielding, experimental techniques [1] and the investigation of new materials. The complexities inherent in these systems have hindered the development of a clear theoretical understanding of their dynamic behavior. The simultaneous occurrence of nonlinear interaction laws, incommensurabilities, disorder due to pinning effects and the resulting complexity of the excitation spectra did not favor a simple analytical approach [2]. We present here the results of a molecular dynamics study. This numerical method, coupled with a simple, but very effective, Fourier transformation allowed us to investigate this complicated problem without further approximations.

Molecular Dynamics Investigation of Dislocation-Depinning Transitions in Mismatched Overlayers

In recent years great strides have been made towards understanding the structural properties of incommensurate systems [55.1]. This is largely due to the advent of novel experimental methods and the discovery of systems amenable to these methods [55.1, 2]. In an effort to explain the experimental results, theoretical investigations have concentrated mainly on determining the phase diagrams and the order of the structural phase transitions involved [55.1,3–5]. Although understanding the dynamical behavior of these systems is an essential ingredient for interpreting the experimental results, we find very little work done towards that end [55.6,7]. This stems from the inherent complexities involved: nonlinearity, discreteness, and incommensurability.