Luciano Colombo
University of Cagliari
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Publication
Featured researches published by Luciano Colombo.
Physical Review B | 2010
Giulio Cocco; Emiliano Cadelano; Luciano Colombo
We exploit the concept of strain-induced band-structure engineering in graphene through the calculation of its electronic properties under uniaxial, shear, and combined uniaxial-shear deformations. We show that by combining shear deformations to uniaxial strains it is possible modulate the graphene energy-gap value from zero up to 0.9 eV. Interestingly enough, the use of a shear component allows for a gap opening at moderate absolute deformation, safely smaller than the graphene failure strain.
Physical Review B | 2010
Emiliano Cadelano; Pier Luca Palla; Stefano Giordano; Luciano Colombo
There exist three conformers of hydrogenated graphene, referred to as chair-, boat-, or washboard-graphane. These systems have a perfect two-dimensional periodicity mapped onto the graphene scaffold but they are characterized by a sp 3 orbital hybridization, have different crystal symmetry, and otherwise behave upon loading. By first-principles calculations we determine their structural and phonon properties, as well as we establish their relative stability. Through continuum elasticity we define a simulation protocol addressed to measure by a computer experiment their linear and nonlinear elastic moduli and we actually compute them by first principles. We argue that all graphane conformers respond to any arbitrarily oriented extension with a much smaller lateral contraction than the one calculated for graphene. Furthermore, we provide evidence that boat-graphane has a small and negative Poisson ratio along the armchair and zigzag principal directions of the carbon honeycomb lattice axially auxetic elastic behavior. Moreover, we show that chair-graphane admits both softening and hardening hyperelasticity, depending on the direction of applied load.
European Physical Journal B | 2009
Federico Bonelli; Nicola Manini; Emiliano Cadelano; Luciano Colombo
AbstractUsing a tight-binding atomistic simulation, we simulate the recent atomic-force microscopy experiments probing the slipperiness of graphene flakes made slide against a graphite surface. Compared to previous theoretical models, where the flake was assumed to be geometrically perfect and rigid, while the substrate is represented by a static periodic potential, our fully-atomistic model includes quantum mechanics with the chemistry of bond breaking and bond formation, and the flexibility of the flake. These realistic features, include in particular the crucial role of the flake rotation in determining the static friction, in qualitative agreement with experimental observations.
Journal of Physics: Condensed Matter | 2012
Riccardo Dettori; Emiliano Cadelano; Luciano Colombo
By means of tight-binding atomistic simulations we study a family of native defects in graphene which have recently been detected experimentally. Their formation energy is found to be as large as several electronvolts, consistent with the empirical evidence of high crystalline quality in most graphene samples. Defects, especially if associated with bond reconstructions, induce sizable deformation and stress fields with a spatial distribution closely related to their actual symmetry. The description of such fields proposed here is believed to be useful for the unambiguous characterization of images obtained by electron microscopy. We also argue that they define the basin of mutual interaction between two nearby defects. Finally, we provide evidence that defects differently affect the linear elastic moduli of monolayer graphene. In general, both the Young modulus and the Poisson ratio are decreased, but their dependence upon the defect surface density is remarkably more pronounced for vacancy-like than for number-like defects.
Nano Letters | 2012
Luca Ortolani; Emiliano Cadelano; Giulio Paolo Veronese; Cristian Degli Esposti Boschi; E. Snoeck; Luciano Colombo; Vittorio Morandi
While the unique elastic properties of monolayer graphene have been extensively investigated, less knowledge has been developed so far on folded graphene. Nevertheless, it has been recently suggested that fold-induced curvature (without in-plane strain) could possibly affect the local chemical and electron transport properties of graphene, envisaging a material-by-design approach where tailored membranes are used in enhanced nanoresonators or nanoelectromechanical devices. In this work we propose a novel method combining apparent strain analysis from high-resolution transmission electron microscopy (HREM) images and theoretical modeling based on continuum elasticity theory and tight-binding atomistic simulations to map and measure the nanoscale curvature of graphene folds and wrinkles. If enough contrast and resolution in HREM images are obtained, this method can be successfully applied to provide a complete nanoscale geometrical and physical picture of 3D structure of various wrinkle and fold configurations.
Reports on Progress in Physics | 2011
Luciano Colombo; Stefano Giordano
We elaborate on a blended continuum/atomistic theoretical picture of the nonlinear elastic properties of nanostructured materials, looking at diverse aspects such as dispersions of inhomogeneities within a matrix, random or graded nanograined materials, two-dimensional atomic sheets. In particular, we discuss the possible onset of length-scale effects and we establish the limits and merits of continuum versus atomistics. While most situations here discussed correspond to model systems, the main conclusions have a paradigmatic relevance and indeed apply to most nanomaterials of current interest.
Journal of Chemical Physics | 2007
Simone Meloni; Mario Rosati; Luciano Colombo
The authors develop an efficient particle labeling procedure based on a linked cell algorithm which is shown to reduce the computing time for a molecular dynamics simulation by a factor of 3. They prove that the improvement of performance is due to the efficient fulfillment of both spatial and temporal locality principles, as implemented by the contiguity of labels corresponding to interacting atoms. Finally, they show that the present label reordering procedure can be used to devise an efficient parallel one-dimensional domain decomposition molecular dynamics scheme.
Journal of Chemical Physics | 2012
Fabio Manca; Stefano Giordano; Pier Luca Palla; Fabrizio Cleri; Luciano Colombo
Recent developments of microscopic mechanical experiments allow the manipulation of individual polymer molecules in two main ways: uniform stretching by external forces and non-uniform stretching by external fields. Many results can be thereby obtained for specific kinds of polymers and specific geometries. In this work, we describe the non-uniform stretching of a single, non-branched polymer molecule by an external field (e.g., fluid in uniform motion, or uniform electric field) by a universal physical framework, which leads to general conclusions on different types of polymers. We derive analytical results both for the freely-jointed chain and the worm-like chain models based on classical statistical mechanics. Moreover, we provide a Monte Carlo numerical analysis of the mechanical properties of flexible and semiflexible polymers anchored at one end. The simulations confirm the analytical achievements, and moreover allow to study the situations where the theory cannot provide explicit and useful results. In all cases, we evaluate the average conformation of the polymer and its fluctuation statistics as a function of the chain length, bending rigidity, and field strength.
Physical Review B | 2012
Emiliano Cadelano; Luciano Colombo
We blend together continuum elasticity and first principles calculations to measure by a computer experiment the Young modulus of hydrogenated graphene. We provide evidence that hydrogenation generally leads to a much smaller longitudinal extension upon loading than in pristine graphene. Furthermore, the Young modulus is found to depend upon the loading direction for some specific conformers, characterized by an anisotropic linear elastic behavior.
Nano Letters | 2015
Xavier Cartoixà; Luciano Colombo; Riccardo Rurali
We show that thermal rectification by design is possible by joining/growing Si nanowires (SiNWs) with sections of appropriately selected diameters (i.e., telescopic nanowires). This is done, first, by showing that the heat equation can be applied at the nanoscale (NW diameters down to 5 nm). We (a) obtain thermal conductivity versus temperature, κ(T), curves from molecular dynamics (MD) simulations for SiNWs of three different diameters, then (b) we conduct MD simulations of a telescopic NW built as the junction of two segments with different diameters, and afterward (c) we verify that the MD results for thermal rectification in telescopic NWs are very well reproduced by the heat equation with κ(T) of the segments from MD. Second, we apply the heat equation to predict the amount of thermal rectification in a variety of telescopic SiNWs with segments made from SiNWs where κ(T) has been experimentally measured, obtaining r values up to 50%. This methodology can be applied to predict the thermal rectification of arbitrary heterojunctions as long as the κ(T) data of the constituents are available.