We report on a single-state measurement of electrical conductivity of warm dense gold in the solid to plasma transition regime. This is achieved using the idealized slab plasma approach of isochoric heating of ultrathin samples by a femtosecond laser, coupled with femtosecond probe measurements of reflectivity and transmission. The experiment also reveals the time scale associated with the disassembly of laser heated solid.
Gold nanostructured materials exhibit important size- and shape-dependent properties that enable a wide variety of applications in photocatalysis, nanoelectronics and phototherapy. Here we show the use of superfast dynamic compression to synthesize extended gold nanostructures, such as nanorods, nanowires and nanosheets, with nanosecond coalescence times. Using a pulsed power generator, we ramp compress spherical gold nanoparticle arrays to pressures of tens of GPa, demonstrating pressure-driven assembly beyond the quasi-static regime of the diamond anvil cell. Our dynamic magnetic ramp compression approach produces smooth, shockless (that is, isentropic) one-dimensional loading with low-temperature states suitable for nanostructure synthesis. Transmission electron microscopy clearly establishes that various gold architectures are formed through compressive mesoscale coalescences of spherical gold nanoparticles, which is further confirmed by in-situ synchrotron X-ray studies and large-scale simulation. This nanofabrication approach applies magnetically driven uniaxial ramp compression to mimic established embossing and imprinting processes, but at ultra-short (nanosecond) timescales.
Pulsed power accelerators compress electrical energy in space and time to provide versatile experimental platforms for high energy density and inertial confinement fusion science. The 80-TW “Z” pulsed power facility at Sandia National Laboratories is the largest pulsed power device in the world today. Z discharges up to 22 MJ of energy stored in its capacitor banks into a current pulse that rises in 100 ns and peaks at a current as high as 30 MA in low-inductance cylindrical targets. Considerable progress has been made over the past 15 years in the use of pulsed power as a precision scientific tool. This paper reviews developments at Sandia in inertial confinement fusion, dynamic materials science, x-ray radiation science, and pulsed power engineering, with an emphasis on progress since a previous review of research on Z in Physics of Plasmas in 2005.
Effect of temperature, strain, and strain rate on the flow stress of aluminum under shock-wave compression J. Appl. Phys. 112, 073504 (2012); 10.1063/1.4755792Comparative studies of yield strength and elastic compressibility between nanocrystalline and bulk cobalt Modeling of the elastic precursor behavior and dynamic inelasticity of tantalum under ramp wave loading to 17 GPa A magnetic loading technique was used to study the strength of pure, annealed, and cold-rolled polycrystalline tantalum under planar ramp loading at strain rates of ϳ10 6 / s. Both the initial yield strength and the flow strength after compression to peak loading stresses of 18 GPa were determined. For sample thicknesses ranging from 0.5-6.0 mm, it was found that the elastic limit of ϳ3.2 GPa, corresponding to a yield strength of 1.6 GPa, for annealed Ta was sharply defined and essentially independent of sample thickness. After elastic yielding, relaxation of the longitudinal stress occurred for sample thicknesses greater than ϳ0.5 mm, approaching an asymptotic value of ϳ1.6 GPa. Two different purities of annealed Ta showed no difference in initial yield strength. Cold-rolling annealed Ta to 26% plastic strain resulted in a more dispersed elastic precursor with an amplitude of about 1.6 GPa and with no stress relaxation after yielding. Analysis of unloading wave profiles from the peak loading states allowed determination of the flow stress, which increased to about 0.9 GPa for annealed Ta and 1.3 GPa for cold-rolled Ta at peak stresses of 17-18 GPa.
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