What are the mechanisms leading to shape relaxation of three-dimensional crystallites? Kinetic Monte Carlo simulations fcc clusters show that usual theories equilibration, via atomic surface diffusion driven by curvature, verified only at high temperatures. Below roughening temperature, is much slower, kinetics being governed nucleation a critical germ on facet. We energy barrier for this step linearly increases with size crystallite, an exponential dependence time.

A detailed theoretical study of the elementary mechanisms occurring during shear-coupled grain boundary (GB) migration at low temperature is performed focusing on both energetic and structural characteristics. The a $\ensuremath{\Sigma}13(320)$ GB in copper bicrystal response to external shear displacements simulated using semiempirical potential. minimum energy path computed nudge elastic band method. occurs through nucleation motion steps identified as disconnections. Energy barriers for...

Abstract The present work reports dynamical observations of the grain boundary (GB)-mediated plasticity during in situ transmission electron microscopy straining experiments at moderate temperature (400C) both a 76.4 bicrystalline and polycrystalline Al sample. We show that GB migration occurs by lateral motion elementary dislocation steps. accumulation steps eventually form macro-steps. This observation agrees with idea generally operate high angle GBs similarly as twinning or martensitic...

The response of small-grained metals to mechanical stress is investigated by a theoretical study the elementary mechanisms occurring during shear-coupled migration grain boundaries (GB). Investigating model $\mathrm{\ensuremath{\Sigma}}17(410)$ GB in copper bicrystal, both $\ensuremath{\langle}110\ensuremath{\rangle}$ and $\ensuremath{\langle}100\ensuremath{\rangle}$ modes are studied focusing on structural energetic characteristics. minimum energy paths these migrations computed using nudge...

We present a detailed molecular-dynamics study of the diffusion and coalescence large (249-atom) gold clusters on graphite surfaces. The diffusivity monoclusters is found to be comparable that for single adatoms. Likewise, even more important, cluster dimers are also diffuse at rate which adatoms monoclusters. As consequence, islands formed by aggregation expected mobile. Using kinetic Monte Carlo simulations, assuming proper scaling law dependence size clusters, we find consisting as many...

Fe–Au core–shell nanoparticles displaying an original polyhedral morphology have been successfully synthesized through a physical route. Analyses using transmission electron microscopy show that the Au shell forms truncated pyramids epitaxially grown on (100) facets of iron cubic core. The evolution elastic energy and strain field in as function their geometry composition is calculated finite-element method. stability remarkable centered experimentally observed attributed to weak resulting...

Self-assemblies of gold nanocrystals (a) examined using an original spectrometry method and apparatus (b) to get a representation their vibrational density states (c).

The release of Ag+ ions into the environment through silica layers is a promising strategy for development anti-microbial surface coating devices. aim present study to provide some insight elementary mechanisms diffusion with objective proposing control strategies. Thanks interaction potentials based on neural networks, processes were studied via molecular dynamics simulations. Silver was found be anomalous and sub-diffusive, origin which could attributed deceleration temporal...

Surface optical modes in cylindrical ZnO nanoparticles have been studied theoretically using a dielectric continuum model and experimentally by Raman spectrometry. Theoretically, both wave vector dispersion outer medium constant effects investigated. Consequently, we attribute the intense peak at $490\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ experiment to surface mode related top basis of nanoparticles. We deduce that bonding long alkyl chain amines is likely lateral

Using Raman spectrometry, we obtained results showing the influence of organic ligands on vibrational properties small zinc oxide nanocrystals (2.1–6.8nm). It is shown that it possible to distinguish both mechanical and dielectric effects from E2 nonpolar phonon mode a surface mode, theoretically predicted but rarely observed. has been found not dependent nanocrystal size, its frequency decreases with increasing ligand length, characteristic tensile stress nanocrystal. We report also...

A density functional theory (DFT) investigation of the structural and electronic properties Au(001)/Fe(001) interface, as a function number Au layers deposited on Fe substrate (from 1 to 11 monolayers), is presented. The elastic effects interface due lattice mismatch between Au, calculated by DFT using generalized gradient approximation, are also evaluated. At interlayer distances in well slab expand. atoms exhibit an enhanced magnetic moment bear nonzero (but very low) moment. energy favors...

An investigation of the vibrational density states (VDOS) in silver nanocrystals is performed using Raman scattering. A specific sample architecture, setup configuration, and original elaboration process are used order to take simultaneously advantage spectrally spatially localized surface plasmon resonance, optical amplification, dark-field spectroscopy. Disentangling contributions atom vibrations electron-hole excitations (i.e., so-called ``background'' surface-enhanced scattering)...

Structural properties of zinc oxide nanoparticles are theoretically studied focusing on the effects induced by surfaces. In this aim, we compare two models: an atomistic and elastic model. Atomistic model uses a semiempirical potential: shell Effects surface relaxation stress taken into account in while they were not Studying with sizes varying from 1.5 to 4.5 nm, show that occurs typical length about 1 nm vicinity surfaces within This significant is due existence long-range interaction...

We report an observation by low-frequency Raman spectrometry of acoustic phonons in wurtzite prismatic zinc oxide nanoparticles sizes varying from 2.3 to 6.6 nm. Several confined the are exhibited, shifting toward higher frequencies with a decrease nanoparticle size. provide comparison between experimental and those given linear elasticity theory including both structural anisotropy specific shape nanoparticles. found that addition usual breathing fundamental extensional modes, spectra...

An extensive DFT search of (meta)stable structures the screw dislocation in hcp-Ti is presented. It reveals that stable core are never basal but always prismatic. This prismatic dissociates into two partial dislocations same or neighboring planes depending on initial position line, leading to either a symmetric an asymmetric core. alternative way defining region from electronic structure point view also proposed. evidences clearly character cores. We then introduce ansatz for straightforward...

The structure of ledges in otherwise symmetrical tilt boundaries built from atomistic simulations is investigated copper terms continuous dislocation and generalized disclination fields. A ″discrete-to-continuum" crossover method used to build the relevant kinematic defect density fields on basis discrete atomic displacements appropriately defined boundary area. resulting incompatibility compared with so-called disconnection model ledges. In addition their content, which characterizes...

Shear-coupled grain boundary (GB) migration has been evidenced as an efficient mechanism of plasticity in the absence dislocation activity. The GB occurs through nucleation and motion disconnections. Using molecular simulations, we report a detailed study elementary mechanisms occurring during heterogeneous disconnection nucleation. We effect preexisting sessile symmetric $\mathrm{\ensuremath{\Sigma}}17(410)\phantom{\rule{4pt}{0ex}}[001]$ tilt on mechanism. Shearing this imperfect induces...

The validity of the linear elasticity theory is examined at nanometer scale by investigating vibrational properties silver and gold nanoparticles whose diameters range from about 1.5--4 nm. Comparing vibration modes calculated atomistic simulation based on embedded-atom method, we first show that anisotropy stiffness tensor in elastic calculation essential to ensure a good agreement between models. Second, illustrate reduction number due diminution atoms when reducing size. Finally, exhibit...

The diffusion of an adatom on a substrate submitted to standing surface acoustic wave is theoretically studied. By performing large scale molecular dynamic simulations, we show that the dynamically structures by encouraging presence in vicinity maximum displacements substrate. Using analytical model, explain this feature introducing effective potential induced wave. Applied atomic deposition experiment, structuring process should govern nucleation sites distribution opening route accurately...

Spontaneously formed Al-As type interfaces of the InAs/AlSb system grown by molecular beam epitaxy for quantum cascade lasers were investigated atomic resolution scanning transmission electron microscopy. Experimental strain profiles compared to those coming from a model structure. High negative out-of-plane strains with same order magnitude as perfect observed. The effects geometrical phase analysis used determination evidenced and discussed in case abrupt huge variations both composition...

Thin films are usually obtained by depositing atoms with a continuous flux. We show that using chopped flux leads to different morphologies or growth regimes. For example, cannot be simply understood replacing the its average (or instantaneous) value and usual theories: regimes appear, in one of them diffusion constant has no effect on saturation island density, contrary what is observed all theories fluxes. present simple scaling analysis predict how densities change as function frequency...

The resonant inelastic light scattering by acoustic vibration modes in spherical germanium nanocrystals is studied theoretically. Raman-Brillouin efficiency calculated using quantum perturbation theory and assuming deformation-potential interaction between the confined electronic states nanocrystal modes. are described effective mass approximation. calculated, on one hand, an atomistic approach based Stillinger-Weber potential and, other elasticity (Lamb's model). Both models compared...

Core–shell nanoparticles made from iron embedded in gold have a strong potential interest nanomedicine, the Au shell providing an efficient biocompatible coating for magnetic Fe core. With aim of determining theoretically equilibrium morphologies Fe–Au broad size range and with different compositions, semiempirical many-body was designed combining well-established models pure metals introducing dedicated contributions interactions involving mixed elements. The parametrized against various...