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Molecular dynamics simulations of an embedded atom copper system in the isobaric-isenthalpic ensemble are used to study the effective solid-liquid interfacial free energy of quasi-spherical solid crystals within a liquid. This is within the larger context of molecular dynamics simulations of this system undergoing solidification, where single individually prepared crystallites of different sizes grow until they reach a thermodynamically stable final state. The resulting equilibrium shapes possess the full structural details expected for solids with weakly anisotropic surface free energies (in these cases, ~5% radial flattening and rounded [111] octahedral faces). The simplifying assumption of sphericity and perfect isotropy leads to an effective interfacial free energy as appearing in the Gibbs-Thomson equation, which we determine to be ~177 erg/cm², roughly independent of crystal size for radii in the 50-250 Å range. This quantity may be used in atomistically informed models of solidification kinetics for this system. [ABSTRACT FROM AUTHOR]

We have performed a computational study to determine how the wetting of liquid deuterium to the walls of the material influences nucleation. We present the development of a pair-wise interatomic potential that includes zero-point motion of molecular deuterium. Deuterium is used in this study because of its importance to inertial confinement fusion and the potential to generate a superfluid state if the solidification can be suppressed. Our simulations show that wetting dominates undercooling compared to the pore geometries. We observe a transition from heterogeneous nucleation at the confining wall to homogeneous nucleation at the bulk of the liquid (and intermediate cases) as the interaction with the confining wall changes from perfect wetting to non-wetting. When nucleation is heterogeneous, the temperature needed for solidification changes by 4 K with decreasing deuterium-wall interaction, but it remains independent (and equal to the one from bulk samples) when homogeneous nucleation dominates. We find that growth and quality of the resulting microstructure also depends on the magnitude of liquid deuterium–wall interaction strength. [ABSTRACT FROM AUTHOR]

We report on an experimental and simulation campaign aimed at exploring the radiation response of nanoporous Au (np-Au) foams. We find different defect accumulation behavior by varying radiation dose-rate in ion-irradiated np-Au foams. Stacking fault tetrahedra are formed when np-Au foams are irradiated at high dose-rate, but they do not seem to be formed in np-Au at low dose-rate irradiation. A model is proposed to explain the dose-rate dependent defect accumulation based on these results. [ABSTRACT FROM AUTHOR]

Although actuation in biological systems is exclusively powered by chemical energy, this concept has not been realized in man-made actuator technologies, as these rely on generating heat or electricity first. Here, we demonstrate that surface-chemistry-driven actuation can be realized in high-surface-area materials such as nanoporous gold. For example, we achieve reversible strain amplitudes of the order of a few tenths of a per cent by alternating exposure of nanoporous Au to ozone and carbon monoxide. The effect can be explained by adsorbate-induced changes of the surface stress, and can be used to convert chemical energy directly into a mechanical response, thus opening the door to surface-chemistry-driven actuator and sensor technologies. [ABSTRACT FROM AUTHOR]

It was recently proposed that within a particular window in the parameter space of temperature, ion energy, dose rate, and filament diameter, nanoscale metallic foams could show radiation tolerance [Bringa et al., Nano Lett. 12, 3351 (2012)]. Outside this window, damage appears in the form of vacancy-related stacking fault tetrahedra (SFT), with no effects due to interstitials [Fu et al., Appl. Phys. Lett. 101, 191607 (2012)]. These SFT could be natural sources of dislocations within the ligaments composing the foam and determine their mechanical response. We employ molecular dynamics simulations of cylindrical ligaments containing an SFT to obtain an atomic-level picture of their deformation behavior under compression. We find that plastic deformation originates at the edges of the SFT, at lower stress than needed to create dislocations at the surface. Our results predict that nanoscale foams soften under irradiation, a prediction not yet tested experimentally. [ABSTRACT FROM AUTHOR]