Browsing by Author "Williams, Ellen D."
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Item A facet is not an island: step-step interactions and the fluctuations of the boundary of a crystal facet(Elsevier, 2005) Pimpinelli, Alberto; Degawa, M.; Einstein, Theodore L.; Williams, Ellen D.Item Accelerating Climate-Mitigating Technology Development and Deployment(2019-04) Edwards, Morgan R.; Surana, Kavita; Thomas, Zachary; Williams, Ellen D.Policymakers and investors alike covet better information about the risks and potential of early-stage technologies. The motivation for the workshop on accelerating climate-mitigating technology development and deployment was to explore how different perspectives from the policy, analysis, and investor communities involved in clean energy innovation may be combined for more effective decision making.Item Brownian motion of steps on Si(111)(American Physical Society, 1993) Bartelt, N. C.; Goldberg, J. L.; Einstein, Theodore L.; Williams, Ellen D.; Heyraud, J. C.; Metois, J. J.Step motion on surfaces can now be measured quantitatively. We present a formalism for analyzing equilibrium step fluctuations and apply it to real-time reflection electron microscope observations of step motion on Si(111). The time correlation functions of the step positions and of their Fourier components are compared with predictions from Langevin equations for two extreme mechanisms for step motion: edge diffusion and terrace exchange.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 Decay of Silicon Mounds: Scaling Laws and Description with Continuum Step Parameters(American Physical Society, 2000) Ichimiya, A.; Hayashi, K.; Williams, Ellen D.; Einstein, Theodore L.; Uwaha, M.; Watanabe, K.The decay of mounds about a dozen layers high on the Si(111)?(7x7) surface has been measured quantitatively by scanning tunneling microscopy and compared with analytic predictions for the power-law dependence on time predicted for a step-mediated decay mechanism. Conformably, we find an exponent 1/4 associated with the (3D) decay of the mound height and exponent 1/3 associated with the (2D) decay of top-layer islands. Using parameters from a continuum step model, we capture the essence of the kinetics. Qualitative features distinguish these mounds from multilayer islands found on metals.Item Disordering of the (3x1) reconstruction on Si(113) and the chiral three-state Potts model(American Physical Society, 1990) Yang, Y.-N.; Williams, Ellen D.; Park, R. L.; Bartelt, N. C.; Einstein, Theodore L.We have used high-resolution low-energy electron diffraction to study the disordering of the (3x1) reconstruction on Si(113). We find that the reconstruction disorders via a continuous transition at approximately 850 K. Above the transition temperature the positions of the superlattice diffraction beams shift away from their commensurate positions. The shift is proportional to the broadening of the beams, as expected from basic scaling arguments for a system in the chiral three-state Potts-model universality class.Item Distinctive Fluctuations in a Confined Geometry(American Physical Society, 2006) Degawa, M.; Stasevich, T. J.; Cullen, W. G.; Pimpinelli, Alberto; Einstein, Theodore L.; Williams, Ellen D.Spurred by recent theoretical predictions (Phys. Rev. E 69, 035102(R) (2004); Surf. Sci. Lett. 598, L355 (2005)), we find experimentally using STM line scans that the fluctuations of the step bounding a facet exhibit scaling properties distinct from those of isolated steps or steps on vicinal surfaces.Item Distinguishing step relaxation mechanisms via pair correlation functions(American Physical Society, 2004) Dougherty, D. B.; Lyubinetsky, I.; Einstein, Theodore L.; Williams, Ellen D.Item Dynamics of step fluctuations on a chemically heterogeneous surface of Al/Si(American Physical Society, 2002) Lyubinetsky, I; Dougherty, D. B.; Einstein, Theodore L.; Williams, Ellen D.Item Effect of impurities on pentacene island nucleation(American Physical Society, 2008) Conrad, B. R.; Gomar-Nadal, Elba; Cullen, W. G.; Pimpinelli, A.; Einstein, Theodore L.; Williams, Ellen D.Pentacenequinone (PnQ) impurities have been introduced into a pentacene source material in a controlled manner to quantify the relative effects of the impurity content on the grain boundary structure and thin film nucleation. Atomic force microscopy has been employed to directly characterize by weight films grown by using 0.0%–7.5% PnQ in the source material. Analysis of the distribution of capture zone areas of submonolayer islands as a function of impurity content shows that for a large PnQ content, the critical nucleus size for forming a Pn island is smaller than for a low PnQ content. This result indicates a favorable energy for the formation of Pn-PnQ complexes, which, in turn, suggests that the primary effect of PnQ on Pn mobility may arise from the homogeneous distribution of PnQ defects.Item Electron-induced extended-fine-structure measurements of thin-film growth and reaction(American Physical Society, 1987) Idzerda, Y. U.; Williams, Ellen D.; Einstein, Theodore L.; Park, R. L.The application of two electron-beam-induced extended-fine-structure (EFS) techniques (surface extended energy-loss fine structure (SEELFS) and extended appearance-potential fine structure (EAPFS)) to the study of thin films has been demonstrated by measurements on three well-characterized compositional phases of titanium deposited on Si(111).Item Impurity Decoration for Crystal Shape Control: C60 on Ag(111)(American Physical Society, 2009) Stasevich, T. J.; Tao, Chenggang; Cullen, William G.; Williams, Ellen D.; Einstein, Theodore L.The decoration of hexagonal Ag/Ag(111) monolayer islands by chains of C60, observed via STM at 300 K, dramatically changes the nanocrystalline shape and fluctuations of the islands. We tune coverage so that a single chain of C60 fully decorates each Ag island boundary, forming a closed circular “necklace.” We model the C60-induced rounding in terms of competing energetic and entropic effects. We thereby characterize the decorated-step fluctuations and estimate the C60-Ag and C60?C60 attractions to be ?0.13 and ?0.03??eV, respectively. Generalizations of our model show that decorating molecules of both circular and rectangular surface-projected symmetry will similarly lower the energy of fully kinked boundaries, leading to corner rounding and reorientations by 30° on (111) surfaces and 45° on (100) surfaces.Item Reaction and structure of Ti on Si probed by surface extended energy?loss fine structure and extended appearance potential fine structure(AIP, 1987) Idzerda, Y. U.; Williams, Ellen D.; Einstein, Theodore L.; Park, R. L.Item Regional Clean Energy Innovation(2020-02-20) Surana, Kavita; Williams, Ellen D.; Krawczyk, Wojciech; Montgomery, Michael; O'Neill, Jon; Thomas, Zachary; Zhang, YingThis report provides data-driven approaches and insights for federal and state planning to accelerate clean energy innovation by aligning programs with regional resources and economic development goals.Item Si(111) step fluctuations at high temperature: Anomalous step-step repulsion(American Physical Society, 2002) Cohen, Saul D.; Schroll, Robert D.; Einstein, Theodore L.; Metois, J.-J.; Gebremariam, Hailu; Richards, Howard L.; Williams, Ellen D.Using reflection electron microscopy we examine the step fluctuations of Si(111) at 1100°C. Evaporation is compensated by a replenishing flux. The step fluctuation behavior is qualitatively similar to that at 900°C (where sublimation is negligible), with unexplained quantitative differences. We focus on the three parameters of the step continuum model of vicinals. The step stiffness scales with an increase in T from 900°C as predicted by an appropriate lattice model. The kinetic coefficient is larger than scaling of the parameters from 900°C would predict. The step-step correlations are assessed in traditional and novel ways; step repulsions are at least 6 times as strong as predicted from lower temperatures, suggesting nonequilibrium effects probably due to electromigration.Item Step doubling and related transitions on vicinal surfaces(AIP, 1992) Einstein, Theodore L.; Jung, T. M.; Bartelt, N. C.; Williams, Ellen D.; Rottman, CraigWe discuss two types of step?height doubling transitions on vicinal surfaces. In one type, exemplified by Ge(111)(121), a phase transition can occur since the symmetry between alternate terraces is broken at low temperatures. There is evidence in both experiment and in Monte Carlo simulations that this transition can have Ising character. In the second type, exemplified by Si(001)(110), one subset of terraces is always favored, so that no symmetry is broken. If an actual phase transition occurs (rather than a smooth crossover), it is expected to be first order, implying a coexistence region in a temperature?misorientation phase diagram. Finally, the coalescence of steps into steps of height more than two atomic layers is briefly considered.Item Step Fluctuations on Ag(111) Surfaces with C60(American Physical Society, 2006) Tao, C.; Stasevich, T. J.; Einstein, Theodore L.; Williams, Ellen D.STM has been used to characterize fluctuation properties of segments of step edges partly covered by C60 on Ag(111) at room temperature. The distribution of C60 at step edges exhibits a step orientation dependence: Low-symmetry step edges are more favorable for C60 binding. The temporal correlation functions of step segments between C60-covered step regions scale as a power law, with an average exponent of 0.23+-0.02, indicating that fluctuations of these “confined” steps are consistent with step-edge diffusion limited fluctuations. Parameters extracted from temporal correlation and autocorrelation analysis consistently indicate that close-packed steps have smaller fluctuation magnitude and higher step mobility than low-symmetry steps. The measured effective system sizes of step segments with different lengths show at most a weak step-length dependence. Fluctuation features thus yield the surprising conclusion that C60 molecules are not acting as pinning points that constrain mass transport along the step edges.Item Summary Abstract: Relationship between many-parameter lattice gas systems and simpler models: Easy approximations for Tc(AIP, 1984) Bartelt, N. C.; Einstein, Theodore L.; Williams, Ellen D.Item Terrace-width distributions on vicinal Si(111)(American Physical Society, 1991) Wang, X.-S.; Goldberg, J. L.; Bartelt, N. C.; Einstein, Theodore L.; Williams, Ellen D.Using scanning tunneling microscopy, we have quantitatively characterized the configurations of steps on vicinal Si(111) surfaces misoriented by 1.2 degrees and 2.3 degrees towards the (1- 1- 2) direction. The measured terrace-width distributions are strongly peaked, consistent with predictions for thermally wandering steps. However, the distributions are much narrower than predicted for the simple terrace-step-kink model, indicating that the steps interact with energetic short-range repulsions. The magnitude of this energetic repulsion is gauged from a Gaussian fit to the data. The width of the distribution scales with step density as expected for repulsions which decay as the inverse square of step separation.Item Two-dimensional ordering of chlorine on Ag(100)(American Physical Society, 1985) Taylor, David E.; Williams, Ellen D.; Park, Robert L.; Bartelt, N. C.; Einstein, Theodore L.Chlorine adsorption on Ag(100) saturates at (1/2) monolayer (ML) in a c(2x2) structure. Desorption occurs above 650 K without disordering. The sticking coefficient remains constant to within 0.05 ML of saturation, consistent with the existence of a highly mobile precursor to adsorption. The c(2x2) structure forms at a critical coverage of 0.394+-0.007 ML at room temperature. This is slightly higher than the critical coverage of the hard-square model (0.368 ML), suggesting the influence of further-neighbor interactions.