1,721,467 research outputs found
Surface molecular dynamics simulation with two orthogonal surface steps: how to beat the particle conservation problem
No full textMicroscopic interaction between a gold tip and a Pb(110) surface
No full textWe have studied the interaction in the contact regime between a pyramidal gold tip and a Pb(110) surface using molecular dynamics simulation. Runs have been done at room temperature and in the surface melting regime of the substrate. We present results on the force acting on the tip as a function of distance, and on the formation of adhesion necks, their nature and their effect on the structural and diffusive properties of the substrate. The adhesion neck between the tip and a melted surface has also a liquid-like nature, explaining recent STM observations
Explanation of the Force Constant Softening in Noble Metals: the Case of Au(111)
No full textA new mechanism for the well known in-plane force softening on the noble metal surfaces is presented. The mechanism is discussed in terms of a many-body force scheme and is shown to amount to an effective decrease of the lateral atomic ‘size’ of the surface atom. Its strong sensitivity to surface relaxation and reconstruction is emphasized. As a non-trivial illustration we calculate the phonon density of states of Au(111) and show that the large softening leading to the observed anomalous longitudinal resonance is directly related to our proposed mechanism. We also discuss the importance of the surface stress on the statics and dynamics of these surfaces
Realistic simulations of Au(100): Grand canonical Monte Carlo and molecular dynamics
No full textThe large surface density changes associated with the (100) noble metals surface hex-reconstruction suggest the use of nonparticle-conserving simulation methods. We present an example of a surface Grand Canonical Monte Carlo applied to the transformation of a square nonreconstructed surface to the hexagonally covered low temperature stable Au(100). On the other hand, classical Molecular Dynamics allows one to investigate microscopic details of the reconstruction dynamics, and we show, as an example, retraction of a step and its interplay with the surface reconstruction/deconstruction mechanism
The Origin of Force Constant Softening on the Close Packed Noble Metal Surfaces
No full textA qualitatively new mechanism is proposed for the well-known in-plane force softening found on many noble-metal surfaces. The mechanism is discussed in terms of one of the recently developed many-body force schemes and is shown to amount to an effective decrease of the lateral atomic .sizes of the surface atom. Its strong sensitivity to the strength of the manybodyforce terms, as well as to surface relaxation and reconstruction, is emphasized. -As a nontrivial illustration, we calculate the phonons of Au(lll), and show that the exceedingly large softening leading to the recently observed anomalous longitudinal resonance is directly related to our proposed mechanism
Islands, craters, and a moving surface step on a hexagonally reconstructed (100) noble metal surface
No full textDeposition/removal of metal atoms on the hex reconstructed (100) surface of Au, Pt and Ir should present intriguing aspects, since a new island implies hex-->square deconstruction of the substrate, and a new crater implies the square-->hex reconstruction of the uncovered layer. To obtain a microscopic understanding of how islands/craters form in these conditions, we have conducted simulations of island and crater growth on Au(100), whose atomistic behavior, including the hex reconstruction on top of the square substrate, is well described by means of classical many-body forces. By increasing/decreasing the Au coverage on Au(100), we find that island/craters will not grow unless they exceed a critical size of about eight to 10 atoms. This value is close to that which explains the non-linear coverage of dependence observed in molecular adsorption on the closely related surface Pt (100). This threshold size is rationalized in terms of a transverse step correlation length, measuring the spatial extent where reconstruction of a given plane is disturbed by the nearby step. (C) 2000 Elsevier Science B.V. All rights reserved
Bending strain-driven modification of surface reconstructions
No full textStrain can affect the morphology of a crystal surface, and cause modifications of its reconstruction even when weak, as in the case of mechanical bending. We carried out calculations of strain-dependent surface free energy and direct bending simulations demonstrating the change of incommensurate reconstruction in Au(111) under strain, in good agreement with recent data. Time-dependent strain should cause a sliding of the topmost layer over the second, suggesting an interesting case of nanofriction. Bending strain could also be used to fine tune the spacing of selectively absorbed nanoclusters
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Reentrant layering in rare gas adsorption: preroughening or premelting?
No full textAccepted for publication in Phys. Rev. LettersConsiglio Nazionale delle Ricerche - Biblioteca Centrale - P.le Aldo Moro, 7 Rome / CNR - Consiglio Nazionale delle RichercheSIGLEITItal
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