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Full-Text Articles in Physics

Photoemission Study Of Ce-Catalyzed Oxidation Of W(110) And W(111), C. Gu, C. G. Olson, David W. Lynch Oct 1993

Photoemission Study Of Ce-Catalyzed Oxidation Of W(110) And W(111), C. Gu, C. G. Olson, David W. Lynch

Physics and Astronomy Publications

Different catalytic oxidation effects of Ce on W(110) and W(111) were observed with photo- emission spectroscopy. On Ce-covered W(110), the top W layer is quickly oxidized to a surface monoxide at room temperature. Oxidation is almost halted after the completion of one monolayer of WO. On Ce/W(111), instead of WO, WO3 grows on the surface under the same conditions. The monolayer suboxide formation found on Ce/W(110) and Ce/Ta(110) (as reported earlier) is a direct consequence of the most densely packed structure of the bcc (110) surfaces. The more effective oxidation promotion ...


Random And Cooperative Sequential Adsorption, James W. Evans Jan 1993

Random And Cooperative Sequential Adsorption, James W. Evans

Physics and Astronomy Publications

Irreversible random sequential adsorption (RSA) on lattices, and continuum "car parking" analogues, have long received attention as models for reactions on polymer chains, chemisorption on single-crystal surfaces, adsorption in colloidal systems, and solid state transformations. Cooperative generalizations of these models (CSA) are sometimes more appropriate, and can exhibit richer kinetics and spatial structure, e.g., autocatalysis and clustering. The distribution of filled or transformed sites in RSA and CSA is not described by an equilibrium Gibbs measure. This is the case even for the saturation "jammed" state of models where the lattice or space cannot fill completely. However exact analysis ...


Transitions In The Kinetics And Steady States Of Irreversible A+Bc Surface-Reaction Models, B. Weng, W. H. Weinberg, James W. Evans Jan 1993

Transitions In The Kinetics And Steady States Of Irreversible A+Bc Surface-Reaction Models, B. Weng, W. H. Weinberg, James W. Evans

Physics and Astronomy Publications

The three-component irreversible surface-reaction model A+BCAC+1/2B2 with infinite reaction rates between nearest-neighbor adspecies is studied by Monte Carlo simulations. For a square lattice the system evolves to a degenerate poisoned state exponentially in time, except for a narrow range of pressures in which a reactive quasi-steady-state exists. The latter poisons very slowly in time. For a hexagonal lattice a true reactive steady state occurs for a range of pressures bordered by continuous and discontinuous transitions to poisoned states. The latter behavior is observed by adding the reaction channel A+BAB on a square lattice. Some ...


Island-Size Scaling In Surface Deposition Processes, M. C. Bartelt, Michael C. Tringides, James W. Evans Jan 1993

Island-Size Scaling In Surface Deposition Processes, M. C. Bartelt, Michael C. Tringides, James W. Evans

Physics and Astronomy Publications

Diffusion-mediated nucleation and growth of islands during deposition occurs essentially irreversibly in a variety of systems. We provide a scaling theory for the full island-size distribution, both with the ratio of surface diffusion to deposition rates and with time. Scaling functions and exponents are determined by simulation and explained analytically by an unconventional rate-equation analysis. Experimental tests for theoretical predictions are discussed, including the scaling of superlattice beam profiles for diffraction studies of heteroepitaxial systems.


Zgb Surface Reaction Model With High Diffusion Rates, James W. Evans Jan 1993

Zgb Surface Reaction Model With High Diffusion Rates, James W. Evans

Physics and Astronomy Publications

The diffusionless ZGB (monomer–dimer) surface reaction model exhibits a discontinuous transition to a monomer‐poisoned state when the fraction of monomer adsorption attempts exceeds 0.525. It has been claimed that this transition shifts to 2/3 with introduction of rapid diffusion of the monomerspecies, or of both species. We show this is not the case, 2/3 representing the spinodal rather than the transition point. For equal diffusion rates of both species, we find that the transition only shifts to 0.5951±0.0002.


Kinetics Of The Monomer-Monomer Surface Reaction Model, James W. Evans, T. R. Ray Jan 1993

Kinetics Of The Monomer-Monomer Surface Reaction Model, James W. Evans, T. R. Ray

Physics and Astronomy Publications

The two-dimensional monomer-monomer (AB) surface reaction model without diffusion is considered for infinitesimal, finite, and infinite reaction rates k. For equal reactant adsorption rates, in all cases, simulations reveal the same form of slow poisoning, associated with clustering of reactants. This behavior is also the same as that found in simulations of the two-dimensional voter model studied in interacting-particle systems theory. The voter model can also be obtained from the dimer-dimer or monomer-dimer surface reaction models with infinitesimal reaction rate. We provide a detailed elucidation of the slow poisoning kinetics via an analytic treatment for the k=0+ AB reaction ...


The Car‐Parking Limit Of Random Sequential Adsorption: Expansions In One Dimension, M. C. Bartelt, James W. Evans, M. L. Glasser Jan 1993

The Car‐Parking Limit Of Random Sequential Adsorption: Expansions In One Dimension, M. C. Bartelt, James W. Evans, M. L. Glasser

Physics and Astronomy Publications

We consider the irreversible random sequential adsorption of particles taking ksites at a time, on a one‐dimensional lattice. We present an exact expansion for the coverage, θ(t,k)=A0(t)+A1(t)k−1+A2(t)k−2+..., for times, 0≤tO(k), and at saturation t=∞. The former is new and the latter extends Mackenzie’s results [J. Chem. Phys. 37, 723 (1962)]. For these expansions, we note that the coefficients Ai≥1(∞) are not obtained as large‐t limits of the Ai≥1(t). Finally, we comment on the ...