Search results for "Surface diffusion"
showing 10 items of 30 documents
Memory effects and coverage dependence of surface diffusion in a model adsorption system
1999
We study the coverage dependence of surface diffusion coefficients for a strongly interacting adsorption system O/W(110) via Monte Carlo simulations of a lattice-gas model. In particular, we consider the nature and emergence of memory effects as contained in the corresponding correlation factors in tracer and collective diffusion. We show that memory effects can be very pronounced deep inside the ordered phases and in regions close to first and second order phase transition boundaries. Particular attention is paid to the details of the time dependence of memory effects. The memory effect in tracer diffusion is found to decay following a power law after an initial transient period. This beha…
Au nanowire junction breakup through surface atom diffusion.
2018
Metallic nanowires are known to break into shorter fragments due to the Rayleigh instability mechanism. This process is strongly accelerated at elevated temperatures and can completely hinder the functioning of nanowire-based devices like e.g. transparent conductive and flexible coatings. At the same time, arranged gold nanodots have important applications in electrochemical sensors. In this paper we perform a series of annealing experiments of gold and silver nanowires and nanowire junctions at fixed temperatures 473, 673, 873 and 973 K (200 degrees C, 400 degrees C, 600 degrees C and 700 degrees C) during a time period of 10 min. We show that nanowires are especially prone to fragmentatio…
A dynamical mean field theory for the study of surface diffusion constants
1997
We present a combined analytical and numerical approach based on the Mori projection operator formalism and Monte Carlo simulations to study surface diffusion within the lattice-gas model. In the present theory, the average jump rate and the susceptibility factor appearing are evaluated through Monte Carlo simulations, while the memory functions are approximated by the known results for a Langmuir gas model. This leads to a dynamical mean field theory (DMF) for collective diffusion, while approximate correlation effects beyond DMF are included for tracer diffusion. We apply our formalism to three very different strongly interacting systems and compare the results of the new approach with th…
Dynamical mean field theory: an efficient method to study surface diffusion coefficients
1998
Abstract We test the accuracy of the dynamical mean field theory (DMF) developed recently for the collective and tracer diffusion coefficients D C and D T , respectively, by Monte Carlo simulations of two very strongly interacting model systems. The deviation of the DMF results from the true hydrodynamic diffusion coefficients is a measure of memory effects, which are not fully accounted for in DMF. In the cases studied here, DMF predicts the behavior of both D C and D T accurately, while the memory effects are found to be most pronounced at low temperatures, and at high coverages and stronger interactions. Nevertheless, the computational cost of DMF is just a fraction of what is needed for…
Kinetic model for surface reconstruction
2002
Institut fu ¨r Physikalische und Theoretische Chemie, Technische Universitat Braunschweig, Hans-Sommer-Strase 10,38106 Braunschweig, Germany~Received 7 December 2001; published 25 July 2002!A microscopic kinetic model for the ab @e.g., hex131 for Pt~100! and 132131 for Pt~110!#surface reconstruction is investigated by means of the mean field approximation and Monte Carlo simulations.It considers homogeneous phase nucleation that induces small surface phase defects. These defects can grow ordecline via phase border propagation in dependence on the chemical coverage by an adsorbate A ~CO!.Anasymmetry in the adsorbate surface diffusion from one surface phase to the other gives rise to two criti…
Epitaxial growth of molybdenum on TiO2(110)
2003
Abstract Molybdenum was deposited on blue (i.e. non-stoichiometric) TiO2(1 1 0) surface using a very low deposition rate (less than 0.05 eqML min−1). The resulting deposit was investigated by means of X-ray photoelectron diffraction (XPD), LEED and XPS. Just after deposition, the film is mainly constituted of metallic molybdenum, contains oxygen homogeneously dispersed through the whole deposit and the broad features detected in XPD scans are interpreted as a coarse epitaxy between TiO2(1 1 0) surface and the (0 0 1) face of bcc molybdenum. The orientation relationship is: Mo(1 0 0)[0 0 1]//TiO2(1 1 0)[0 0 1]. After annealing the deposit at 673 K, XPD scans become sharper and epitaxy is ach…
On dewetting dynamics of solid films of hydrogen isotopes and its influence on tritium [Beta] spectroscopy
2000
The dewetting dynamics of solid films of hydrogen isotopes, quench-condensed on a graphite substrate, was measured at various temperatures below desorption by observing the stray light from the film. A schematic model describing the dewetting process by surface diffusion is presented, which agrees qualitatively with our data. The activation energies of different hydrogen isotopes for surface diffusion were determined. The time constant for dewetting of a quench-condensed T2 film at the working temperature of 1.86 K of the mainz neutrino mass experiment was extrapolated.
Effect of kinks and concerted diffusion mechanisms on mass transport and growth on stepped metal surfaces
1997
Abstract We study the effect of kinks and concerted atomic mechanisms on diffusion processes relevant to metal-on-metal homoepitaxy on fcc metal surfaces vicinal to the fcc (100) direction. First, we carry out extensive finite-temperature molecular dynamics simulations based on the effective medium theory to search for diffusion mechanisms that dominate the mass transport perpendicular and parallel to step edges. Then, the energetics of these processes are studied by ground state calculations. Our results show that kinks play an important role for diffusion both across and along step edges. In particular, the combined effect of kinks and concerted exchange is found to be able to remove loca…
The non-equilibrium charge screening effects in diffusion-driven systems with pattern formation.
2011
The effects of non-equilibrium charge screening in mixtures of oppositely charged interacting molecules on surfaces are analyzed in a closed system. The dynamics of charge screening and the strong deviation from the standard Debye-Huckel theory are demonstrated via a new formalism based on computing radial distribution functions suited for analyzing both short-range and long-range spacial ordering effects. At long distances the inhomogeneous molecular distribution is limited by diffusion, whereas at short distances (of the order of several coordination spheres) by a balance of short-range (Lennard-Jones) and long-range (Coulomb) interactions. The non-equilibrium charge screening effects in …
Dynamics of multilayer adsorption: a Monte Carlo simulation
1992
Abstract The growth of an adsorbed film at an initially empty surface which is exposed at time t = 0 to a gas is studied within the framework of a kinetic lattice gas model by Monte Carlo simulation. The model includes an attractive potential V ( z ) between adsorbed particles at distance z from the surface, V(z) = −A z 3 and a nearest-neighbor attractive interaction between the gas atoms. Several choices of the surface potential depth A , corresponding to different sequence of layering transitions, are considered. The Monte Carlo process assumes random evaporation/condensation events of gas atoms in adsorbed layers close to the surface, while surface diffusion is disregarded. For temperatu…