Polarizing their interface creates space-charge regions, indicated on the right, which store energy or allow the behavior of the interface to be tuned. Adding an aqueous electrolyte in the pore space as a second component creates a hybrid nanomaterial in which the constituent metal and water phases are intermixed at the nanoscale. Dealloying can produce macroscopic samples, such as the millimeter-sized cylinder of nanoporous gold (NPG) on the left, exhibiting a uniform network structure with characteristic strut or “ligament” size in the nanometer range, as can be seen in the scanning electron micrograph of NPG in the background. Nanoporous metal network structures with interface-controlled behavior. Reference Weissmüller, Viswanath, Kramer, Zimmer, Würschum and Gleiter4įigure 1. Nanoporous metals afford an implementation of this strategy-their pore space can be filled with electrolyte, and the capacitive coupling between the ionic and electronic conduction paths in the electrolyte and the metal, respectively, provide for control of interfacial electric charge ( Figure 1).
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Reference Gleiter, Weissmüller, Wollersheim and Würschum3 This requires control of the space-charge region at interfaces by external stimuli. Subsequently, it was recognized that a materials design strategy based on maximizing the number of operando tunable interfaces by manipulating electronic structure could yield additional new behavior. Reference Gleiter1, Reference Gleiter2 Owing to their modified atomic short-range order, grain boundaries were the defects of choice in early studies of “nanocrystalline” materials, and this class of solids remains the subject of active research.
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New material behaviors were expected through mixing local properties of matter in the core of the defects into the more conventional behavior of crystalline matter. The interest in nanomaterials, one of the current trends in materials science, started out from the thought that pushing the characteristic scale of the microstructure down to the 2–5 nm range might maximize the number of defects in a material. The current interest in interface-controlled phenomena displayed by dealloyed nanoporous metals and their potential applications reflects the relative ease of manufacturing nanoporous materials using a simple ambient-temperature corrosion process, as well as the general interest of the materials community in nanomaterials. Dealloying is the selective dissolution of less noble elements from an alloy, leaving behind a porous structure.
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Approaches to new functional materials include electrochemical potential switching of strength, stiffness, fracture resistance, fluid sorption, actuation, and quasi-piezoelectric strain sensing.ĭealloying has emerged as a convenient and versatile method for making nanoporous metal with high structural definition. New experimental approaches unraveling surface effects involving small-scale plasticity and elasticity have been demonstrated. These materials present new opportunities for exploring the impact of surfaces on material behaviors and for exploiting surface effects in novel materials design strategies. Their surface-to-volume ratio is extremely large and their bicontinuous structure provides transport pathways to tune the surface state under control of an electric or chemical potential. These porous solids can be made with macroscale dimensions, and, prior to dealloying, can be shaped to form engineered components. Dealloying, the selective dissolution of less noble elements from an alloy, enables the preparation of monolithic macroscale bodies, which at the nanostructure level exhibit a network of “ligaments” with a well-defined characteristic size that can be tuned to between a few nanometers and several microns.