de Jeff Hosson

WETTING ON ROUGH SURFACES

This paper concentrates on effects of roughness on the wettability. Surface roughness is described by an rms amplitude Δ, a correlation length ξ, and a roughness exponent H (0 θtr. The transition angle θtr appears to be smaller than 90°, and decreases with increasing roughness exponent H.

Misfit dislocations : An atomistic and elastic continuum approach

This paper presents the results of an atomistic model in which the misfit and the bond strength between a metal and a substrate can be controlled. The model is applied to a simple case, i.e. an interface with misfit in one direction. Calculated energies are presented and the corresponding atomic structures for various misfits and interaction parameters are discussed. It turned out that the structure of the misfit dislocations depends both on misfit and bond strength. A trend from delocalized structures to localized structures that resemble bulk-like dislocations can be seen for decreasing misfit at constant interaction parameter, and increasing interaction parameter at constant misfit. This atomistic approach is compared with a description based on linear elasticity theory of interface dislocations. Although a fair correlation exists between these two different concepts, it is shown that the elastic continuum approach cannot account for the possible configurations at an interface, because it does not contain any information on the effects different bond strengths may have on the interface structure.

Reversible strain by physisorption in nanoporous gold

Reversible strain amplitudes up to 0.02% in response to a 15% change in relative humidity were detected in nanoporous gold. We show that the mechanism involved in dimensional changes during physisorption is associated with changes in the surface stress when molecules are adsorbed from the vapor phase onto the metal interface.

High-speed dislocations in high strain-rate deformations

Abstract In this paper, shear deformation at high strain rates is modelled within the framework of discrete dislocation plasticity. The question is addressed whether dislocation accelerations may be ignored at high strain rates. Furthermore, the usage of high-velocity stress and displacement fields are studied. The simulations take place in a computational cell representing Al and Cu that is sheared at a strain rate of 10 6 s −1 . The computations show that the inertial effects may not be neglected. Furthermore, although the high-velocity stress and displacement fields yield significant differences locally with respect to their quasi-static counterparts, their effect on the overall stress–strain curve is negligible.

High-resolution transmission electron microscopy imaging of misfit-dislocation networks at Cu-MgO and Cu-MnO interfaces

Abstract Misfit dislocation networks at Cu-MgO and Cu-MnO {111}metal//{111}oxide interfaces were studied with high-resolution transmission electron microscopy. Experimental results were compared with image simulations of tentative atomic structures of the interface region derived from lattice statics calculations. The calculations take into account the two-dimensional misfit at the interface, which is necessary given the high misfit and short repeat distances at the interfaces. The lattice statics calculations use simplified potentials across the interface which capture essential characteristics that have emerged from recent experimental results and ab-initio calculations. Trigonal networks of edge misfit locations with Burgers vectors ⅙〈112〉 and line direction 〈110〉 follow from these calculations. These misfit-dislocation networks have associated strain fields in the metal, stretching out from the interface with approximately the repeat distance along the interface. These strain fields show up in image s...

Atomic structure and orientation relations of interfaces between Ag and ZnO

This paper presents the results of investigations of Ag-ZnO interfaces, produced by internal oxidation of an Ag-Zn alloy. ZnO precipitates with the wurtzite structure were found exhibiting mainly one orientation relation with the Ag matrix. However, closely related ORs were found, rotated by small angles from that orientation relation. The atomic structures of several interfaces surrounding these precipitates were studied and compared using HRTEM. The paper concentrates on interfaces between low index facets of ZnO and vicinal planes of Ag. These interfaces clearly show relaxations. An interpretation of these relaxations in terms of dissociation of partial dislocations at the interface is put forward.

In situ compression study of taper-free metallic glass nanopillars

Because tapering leads to inevitable artifacts in the analyses of compression experiments on micrometer sized pillars, in this study taper-free nanosized pillars of Zr-based metallic glass of Zr61.8Cu18Ni10.2Al10 composition with diameter ranging from 600 to 90 nm were fabricated. These pillars were compressed in situ in a transmission electron microscope as a function of pillar diameter. Under compression each pillar of large diameter exhibits predominant inhomogeneous and intermittent plastic flow characterized by shear banding (SB) events. However, pillars around 150 nm in diameter and below show homogeneous deformation during compression without SB.

A two-dimensional computational methodology for high-speed dislocations in high strain-rate deformation

In this paper, shear deformation at high strain rates is modeled within the framework of discrete dislocation plasticity. The total stress and deformation state is split into the state due to the dislocations in an infinite medium and the complementary image field, which is enforced by a finite element solution. The stress and displacement fields for high-speed dislocations are used, as well as a velocity-dependent drag coefficient. Sources and obstacles are put into the material, and constitutive rules are implemented for the creation and annihilation of dislocations. A novel criterion is introduced according to which the properties are projected into the two-dimensional (2D) domain of simulation. The question is addressed whether it is allowed to neglect accelerations, as is done in simulations at lower deformation rates.

Nanoporous gold formation by dealloying: A Metropolis Monte Carlo study

a b s t r a c t A Metropolis Monte Carlo study of the dealloying mechanism leading to the formation of nanoporous gold is presented. A simple lattice-gas model for gold, silver and acid particles, vacancies and products of chemical reactions is adopted. The influence of temperature, concentration and lattice defects on the dealloying process is investigated and the morphological properties are characterized in terms of the Euler characteristic, volume, surface area and the specific surface area. It is shown that a minimal threeparameter model suffices to yield nanoporous gold structures which have morphological properties akin to those found in the experiment. The salient features of the structures found by simulation are that the ligament size of the dealloyed material is of the order of 2–3 nm, the structure is disordered, percolating and entirely connected.

Electrochromic artificial muscles based on nanoporous metal-polymer composites

This work shows that a nano-coating of electrochromic polymer grown onto the ligaments of nanoporous gold causes reversible dimensional and color changes during electrochemical actuation. This combination of electromechanical and optical properties opens additional avenues for the applications of artificial muscles, i.e., a metallic muscle exhibits its progress during work by changing color that can be detected by optical means.