### Browsing by Author "Szalma, F."

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Item Correlations in nanoscale step fluctuations: Comparison of simulation and experiments(American Physical Society, 2006) Szalma, F.; Dougherty, D. B.; Degawa, M.; Williams, Ellen D.; Haftel, Michael I. Haftel; Einstein, Theodore L.We analyze correlations in step-edge fluctuations using the Bortz-Kalos-Lebowitz kinetic Monte Carlo (MC) algorithm, with a two-parameter expression for energy barriers, and compare with our variable-temperature scanning tunneling microscopy line-scan experiments on spiral steps on Pb(111). The scaling of the correlation times gives a dynamic exponent confirming the expected step-edge-diffusion rate-limiting kinetics both in the MC simulations and in the experiments. We both calculate and measure the temperature dependence of (mass) transport properties via the characteristic hopping times and deduce therefrom the notoriously elusive effective energy barrier for the edge fluctuations. With a careful analysis we point out the necessity of a more complex model to mimic the kinetics of a Pb(111) surface for certain parameter ranges.Item Effects of next-nearest-neighbor interactions on the orientation dependence of step stiffness: Reconciling theory with experiment for Cu(001)(American Physical Society, 2004) Stasevich, T. J.; Einstein, Theodore L.; Zia, R. K. P.; Giesen, Margret; Ibach, Harald; Szalma, F.Within the solid-on-solid (SOS) approximation, we carry out a calculation of the orientational dependence of the step stiffness on a square lattice with nearest- and next-nearest-neighbor interactions. At low temperature our result reduces to a simple, transparent expression. The effect of the strongest trio (three-site, nonpairwise) interaction can easily be incorporated by modifying the interpretation of the two pairwise energies. The work is motivated by a calculation based on nearest neighbors that underestimates the stiffness by a factor of 4 in directions away from close-packed directions, and a subsequent estimate of the stiffness in the two high-symmetry directions alone that suggested that inclusion of next-nearest-neighbor attractions could fully explain the discrepancy. As in these earlier papers, the discussion focuses on Cu(001).Item Fluctuations, line tensions, and correlation times of nanoscale islands on surfaces(American Physical Society, 2005) Szalma, F.; Gebremariam, Hailu; Einstein, Theodore L.We analyze in detail the fluctuations and correlations of the (spatial) Fourier modes of nanoscale single-layer islands on (111) fcc crystal surfaces. We analytically show that the Fourier modes of the fluctuations couple due to the anisotropy of the crystal, changing the power spectrum of the fluctuations, and that the actual eigenmodes of the fluctuations are the appropriate linear combinations of the Fourier modes. Using kinetic Monte Carlo simulations with bond-counting parameters that best match realistic energy barriers for hopping rates, we deduce absolute line tensions as a function of azimuthal orientation from the analyses of the fluctuation of each individual mode. The autocorrelation functions of these modes give the scaling of the correlation times with wavelength, providing us with the rate-limiting kinetics driving the fluctuations, here step-edge diffusion. The results for the energetic parameters are in reasonable agreement with available experimental data for Pb(111) surfaces, and we compare the correlation times of island-edge fluctuations to relaxation times of quenched Pb crystallites.Item Step line tension and step morphological evolution on the Si(111) (1x1) surface(American Physical Society, 2008) Pang, A. B.; Man, K. L.; Altman, M. S.; Stasevich, T. J.; Szalma, F.; Einstein, T. L.The temperature dependence of the step line tension on the Si(111) (1×1) surface is determined from a capillary wave analysis of two-dimensional island edge fluctuations and straight step fluctuations that are observed with low energy electron microscopy. The line tension decreases by nearly 20% with a linear temperature coefficient of ?0.14meV/ÅK between 1145 and 1233K. Temporal correlations of step fluctuations exhibit the distinctive signature in the wavelength dependence of the relaxation time of a terrace diffusion-limited mechanism for step motion. We also find that the role of desorption in island decay increases dramatically in the temperature range (1145–1380K) that island decay is studied. Consequently, we generalize the current quasistatic model of island decay to take account of desorption. The evaluation of the island decay time with this model referenced to the temperature-dependent line tension accurately determines activation energies that are relevant to mass transport and sublimation.