Nano Lett. 13, 6281–6286 (2013)

Semiconductor nanowires have electronic and optical properties that are intrinsically linked to the one-dimensional motion of electrons. Therefore, the ability to control the diameter of nanowires during growth could lead to both complex nanostructures and tailored devices. James Cahoon and colleagues at the University of North Carolina at Chapell Hill have now developed a fabrication technique that can modulate the diameter of silicon nanowires and create features as small as 10 nm.

The phosphorus-doped silicon nanowires were grown using the vapour–liquid–solid (VLS) mechanism. Previous work has shown that the level of phosphorus-doping affects the growth rate of the nanowire and the etch rate in a KOH solution. Cahoon and colleagues calibrated these phosphorus-doping dependences and then used the calibration to predict the exact phosphorus content that would allow the design of very precise and complex structures. With the approach they were able to fabricate a range of structures including bowties, nanogaps, and nanowires with periodically modulated cross-sections (see the scanning electron microscopy image).

The technique, which is termed ENGRAVE (encoded nanowire growth and appearance through VLS and etching) by the authors, was also used to create two proof-of-principle devices. In the first, a nanowire with a gap was used as a template to fabricate metal nanostructures with precise surface plasmon resonances. In the second, nanowires with constrictions were used to demonstrate resistive memory elements. The next step will be to extend the technique beyond silicon, and to demonstrate devices on a larger scale.