I do research on nanotechnology at UNC-CH, specifically on materials called carbon nanotubes (CNT) and their properties. These are hexagonal graphitic lattices rolled up onto themselves to form a tube (right), which can be as little as a nanometer (.00000001 m) across. CNT are the strongest material on the planet for their size, are atomically ordered and can exhibit either semi-conductor or metallic transport properties, dependent on material properties such as diameter and the wrapping vector of carbon atoms around the tube axis.

I study a variety of CNT properties through the use of a new device first fabricated here at UNC, the nanotube-based torsional platform device (left). This incorporates a single nanotube as the torsional spring element in a “teeter-totter”-type device geometry. By measuring how much force is required to actuate the platform (and thus twist the nanotube), we are able to quantify intrinsic nanotube properties, such as the torsional spring constant and the shear modulus. It has been found that multi-shell CNT (many coaxial graphitic shells) exhibit a “work hardening”, or increase in torsional stiffness with repeated twisting. This work can be found here. Work is still being done on measurements similar to these.

 On a more practical level, these devices may be useful as an electrical component (variable resistor) or mechanical switch, because the transport properties may be changed during this twisting motion. This could lead to smaller, denser computer chips or to ultra-high accuracy chemical and biological sensor devices.

 Due to the atomic perfection of the CNT as a spring, we are also interested in using the torsional platform device as a nanometer scale resonator. This is done by electrostatically actuating the platform (below, scale bar 500 nm) at high frequency. We have had some success in this (which can be found here) and continue to work on these measurements. Such resonators could find use in clocks, scientific instrumentation and even as a mass sensor, effectively able to “weigh” a single virus.

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My previous work regarding CNT Atomic Force Microscope (AFM) tips using magnetic fields (right) can be found here.