Characterization of a liquid crystal microlens array using multiwalled carbon nanotube electrodes.

Reconfigurable liquid crystal microlenses employing arrays of multiwalled carbon nanotubes (MWNTs) have been designed and fabricated. The cells consist of arrays of 2 microm high MWNTs grown by plasma-enhanced chemical vapor deposition on silicon with a top electrode of indium tin oxide coated glass positioned 20 microm above the silicon and the gap filled with the nematic liquid crystal BLO48. Simulations have found that, while its nematic liquid crystal aligns with MWNTs within a distance of 10nm, this distance is greatly enhanced by the application of an external electric field. Polarized light experiments show that light is focused with focal lengths ranging from approximately 7 microm to 12 microm.

Transformation of unipolar single-walled carbon nanotube field effect transistors to ambipolar induced by polystyrene nanosphere assembly.

We have fabricated single-walled carbon nanotube (SWNT) field effect transistors (FETs) with molybdenum source and drain contacts. Normally, these devices operate only as p-channel transistors, however, after polystyrene latex nanospheres were attached to the nanotubes close to the contacts, they changed to ambipolar operation. This strategy provides a simple method to modify the electrical behavior of unipolar SWNT-FETs by influencing the gate-channel electric field distribution and offset charge, so enabling complementary circuits to be fabricated.

On the suitability of carbon nanotube forests as non-stick surfaces for nanomanipulation.

A carbon nanotube forest provides a unique non-stick surface for nanomanipulation, as the nanostructuring of the surface allows micro- and nanoscale objects to be easily removed after first being deposited via a liquid dispersion. A common problem for smooth surfaces is the strong initial stiction caused by adhesion forces after deposition onto the surface. In this work, carbon nanotube forests fabricated by plasma-enhanced chemical vapour deposition are compared to structures with a similar morphology, silicon nanograss, defined by anisotropic reactive ion-etching. While manipulation experiments with latex microbeads on structured as well as smooth surfaces (gold, silicon, silicon dioxide, Teflon, diamond-like carbon) showed a very low initial stiction for both carbon nanotube forests and silicon nanograss, a homogeneous distribution of particles was significantly easier to achieve on the carbon nanotube forests. Contact-angle measurements during gradual evaporation revealed that the silicon nanograss was superhydrophic with no contact-line pinning, while carbon nanotube forests in contrast showed strong contact-line pinning, as confirmed by environmental scanning electron microscopy of microdroplets. As a consequence, latex microbeads dispersed on the surface from an aqueous solution distributed evenly on carbon nanotube forests, but formed large agglomerates after evaporation on silicon nanograss. Lateral manipulation of latex microbeads with a microcantilever was found to be easier on carbon nanotube forests and silicon nanograss compared to smooth diamond-like carbon, due to a substantially lower initial stiction force on surfaces with nanoscale roughness. Nanomanipulation of bismuth nanowires, carbon nanotubes and organic nanofibres was demonstrated on carbon nanotube forests using a sharp tungsten tip. We find that the reason for the remarkable suitability of carbon nanotube forests as a non-stick surface for nanomanipulation is indeed the strong contact-line pinning in combination with the nanostructured surface, which allows homogeneous dispersion and easy manipulation of individual particles.