Nature Materials - Arrays of indefinitely long uniform nanowires and nanotubes A new nanofabrication technique based on iterative size reduction is able to produce ordered, indefinitely long nanowire and nanotube arrays. Nanowires that are more than 1000 meters long have been made.
Nanowires are arguably the most studied nanomaterial model to make functional devices and arrays. Although there is remarkable maturity in the chemical synthesis of complex nanowire structures their integration and interfacing to macro systems with high yields and repeatability still require elaborate aligning, positioning and interfacing and post-synthesis techniques. Top-down fabrication methods for nanowire production, such as lithography and electrospinning, have not enjoyed comparable growth. Here we report a new thermal size-reduction process to produce well-ordered, globally oriented, indefinitely long nanowire and nanotube arrays with different materials. The new technique involves iterative co-drawing of hermetically sealed multimaterials in compatible polymer matrices similar to fibre drawing. Globally oriented, endlessly parallel, axially and radially uniform semiconducting and piezoelectric nanowire and nanotube arrays hundreds of metres long, with nanowire diameters less than 15 nm, are obtained. The resulting nanostructures are sealed inside a flexible substrate, facilitating the handling of and electrical contacting to the nanowires. Inexpensive, high-throughput, multimaterial nanowire arrays pave the way for applications including nanowire-based large-area flexible sensor platforms, phase-changememory, nanostructure-enhanced photovoltaics, semiconductor nanophotonics, dielectric metamaterials,linear and nonlinear photonics and nanowire-enabled high-performance composites.
Ordered selenium nanowire arrays obtained by three step iterative size reduction. Selenium is a glass making chalcogenide element with a crystallization temperature of 110 °C and melting temperature of 230 °C. Therefore it is molten at the drawing temperature of 270 °C. XRD diffraction studies indicate that Se is amourphous after each thermal drawing/size reduction. a-b, In the first step a 10 mm Selenium rod is reduced to 250-50 μm single wire (reduction factor 40-200x). Extracted microwires retain their global alignment . c-d, For the second step, ~100 selenium wires are cut and tighly packed and redrawn to 7 μm (reduction factor 34×) to obtain hundreds of meters long ordered selenium microwires. e-f, In the final step, previously obtained selenium microwire arrays are cut, packed and redrawn to 250 nm hierarchically ordered nanowire arrays (reduction factor 28×, total reduction factor is 40,000×).
Within this pencil-wound, 10-meter stretch of nanowire are hundreds of even smaller wires (shown in cross section). Such wires-within-wires might have broad uses in electronics, sensors and other devices.
Credit: M. Yaman et al/Nature Materials 2011
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