Riccardo Dettori

Elastic fields and moduli in defected graphene

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.

Thermal transport in porous Si nanowires from approach-to-equilibrium molecular dynamics calculations

We study thermal transport in porous Si nanowires (SiNWs) by means of approach-to-equilibrium molecular dynamics simulations. We show that the presence of pores greatly reduces the thermal conductivity, κ, of the SiNWs as long mean free path phonons are suppressed. We address explicitly the dependence of κ on different features of the pore topology—such as the porosity and the pore diameter—and on the nanowire (NW) geometry—diameter and length. We use the results of the molecular dynamics calculations to tune an effective model, which is capable of capturing the dependence of κ on porosity and NW diameter. The model illustrates the failure of Matthiessens rule to describe the coupling between boundary and pore scattering, which we account for by the inclusion of an additional empirical term.

Thermal rectification in silicon by a graded distribution of defects

We discuss about computer experiments based on nonequilibrium molecular dynamics simulations providing evidence that thermal rectification can be obtained in bulk Si by a non-uniform distribution of defects. We consider a graded population of both Ge substitutional defects and nanovoids, distributed along the direction of an applied thermal bias, and predict a rectification factor comparable to what is observed in other low–dimensional Si–based nanostructures. By considering several defect distribution profiles, thermal bias conditions, and sample sizes, the present results suggest that a possible way for tuning the thermal rectification is by defect engineering.

Thermal boundary resistance in semiconductors by non-equilibrium thermodynamics

We critically address the problem of predicting the thermal boundary resistance at the interface between two semiconductors by atomistic simulations. After reviewing the available models, lattice dynamics calculations and molecular dynamics simulation protocols, we reformulate this problem in the language of non-equilibrium thermodynamics, providing an elegant, robust and valuable theoretical framework for the direct calculation of the thermal boundary resistance through molecular dynamics simulations. The foundation of the method, as well as its subtleties and the details of its actual implementation are presented. Finally, the Si/Ge interface showcase is discussed as the prototypical example of semiconductor heterojunction whose thermal properties are paramount in many front-edge nanotechnologies. Graphical Abstract

Phonon Scattering in Silicon by Multiple Morphological Defects: A Multiscale Analysis

Ideal thermoelectric materials should possess low thermal conductivity

Model for thermal conductivity in nanoporous silicon from atomistic simulations

\kappa

SixGe1-x alloy as efficient phonon barrier in Ge/Si superlattices for thermoelectric applications

κ along with high electrical conductivity