Delivering liquid through the void spaces in porous metals is a daunting challenge for a variety of emerging interface technologies ranging from battery electrodes to evaporation surfaces. Hydraulic transport characteristics of well-ordered porous media are governed by the pore distribution, porosity, and morphology. Much like energy transport in polycrystalline solids, hydraulic transport in semi-ordered porous media is predominantly limited by defects and grain boundaries. Here, we report the wicking performances for porous copper inverse opals having pore diameters from 300 to 1000 nm by measuring the capillary-driven liquid rise. The capillary performance parameter within single crystal domain (Kij/Reff = 10−3 to 10−2 µm) is an order of magnitude greater than the collective polycrystal (Keff/Reff = ~10−5 to 10−3 µm) due to the hydraulic resistances (i.e. grain boundaries between individual grains). Inspired by the heterogeneity found in biological systems, we report that the capillary performance parameter of gradient porous copper (Keff/Reff = ~10−3 µm), comparable to that of single crystals, overcomes hydraulic resistances through providing additional hydraulic routes in three dimensions. The understanding of microscopic liquid transport physics through porous crystals and across grain boundaries will help to pave the way for the spatial design of next-generation heterogeneous porous media.

Light-induced off-diagonal thermoelectric effect via indirect optical heating of incline-oriented CaxCoO2 thin film Appl. Phys. Lett. 100, 181907 (2012) Thermal artifact on the spin Seebeck effect in metallic thin films deposited on MgO substrates J. Appl. Phys. 111, 07B106 (2012) Evolution of structural and thermoelectric properties of indium-ion-implanted epitaxial GaAs Appl. Phys. Lett. 100, 102101 (2012) Interplay of point defects, biaxial strain, and thermal conductivity in homoepitaxial SrTiO3 thin films Thermoelectric phenomena strongly influence the behavior of chalcogenide materials in nanoelectronic devices including phase-change memory cells. This work uses a novel silicon-oninsulator experimental structure to measure the phase and temperature-dependent Seebeck and Thomson coefficients of Ge 2 Sb 2 Te 5 films including the first data for films of thickness down to 25 nm. The Ge 2 Sb 2 Te 5 films annealed at different temperatures contain varying fractions of the amorphous and crystalline phases which strongly influence the thermoelectric properties. The Seebeck coefficient reduces from 371 lV/K to 206 lV/K as the crystalline fraction increases by a factor of four as quantified using x-ray diffraction. The data are consistent with modeling based on effective medium theory and suggest that careful consideration of phase purity is needed to account for thermoelectric transport in phase change memory. V C 2012 American Institute of Physics.

No abstract

Capillary wicking through homogeneous porous media remains challenging to simultaneously optimize due to the unique transport phenomena that occur at different length scales. This challenge may be overcome by introducing hierarchical porous media, which combine tailored morphologies across multiple length scales to design for the individual transport mechanisms. Here, we fabricate hierarchical nanowire arrays consisting of vertically aligned copper nanowires (∼100 to 1000 nm length scale) decorated with dense copper oxide nanostructures (∼10 to 100 nm length scale) to create unique property sets that include a large specific surface area, high rates of fluid delivery, and the structural flexibility of vertical arrays. These hierarchical nanowire arrays possess enhanced capillary wicking (K/R eff = 0.004–0.023 μm) by utilizing hemispreading and are advantageous as evaporation surfaces. With the advent and acceleration of flexible electronics technologies, we measure the capillary properties of our freestanding hierarchical nanowire arrays installed on curved surfaces and observe comparable fluid delivery to flat arrays, showing the difference of 10–20%. The degree of effective inter-nanowire pore and porosity is shown to govern the capillary performance parameters, thereby this study provides the design strategy for capillary wicking materials with unique and tailored combinations of thermofluidic properties.

Self‐assembly continuously gains attention as an excellent method to create novel nanoscale structures with a wide range of applications in photonics, optoelectronics, biomedical engineering, and heat transfer applications. However, self‐assembly is governed by a diversity of complex interparticle forces that cause fabricating defectless large scale (>1 cm) colloidal crystals, or opals, to be a daunting challenge. Despite numerous efforts to find an optimal method that offers the perfect colloidal crystal by minimizing defects, it has been difficult to provide physical interpretations that govern the development of defects such as grain boundaries. This study reports the control over grain domains and intentional defect characteristics that develop during evaporative vertical deposition. The degree of particle crystallinity and evaporation conditions is shown to govern the grain domain characteristics, such as shapes and sizes. In particular, the grains fabricated with 300 and 600 nm sphere diameters can be tuned into single‐column structures exceeding ≈1 mm by elevating heating temperature up to 93 °C. The understanding of self‐assembly physics presented in this work will enable the fabrication of novel self‐assembled structures with high periodicity and offer fundamental groundworks for developing large‐scale crack‐free structures.