As circuit miniaturization occurs, the need for smaller and more efficient component parts has increased. Metallic single-walled carbon nanotubes (SWNTs) are the ideal nanometer-scale wire, as they can conduct current densities from 2 to 3 orders of magnitude higher than copper wires currently used in electronic chips. These conductive nanotubes can be utilized as "nano-electrodes" to electrically contact another nanoscale object, such as a single quantum dot (QD). Whereas most of the Krauss group conducts fundamental studies on SWNTs and QDs, building integrated applied systems between these two specialized materials is new to our group and is in itself a fascinating and challenging problem. Although QDs have been attached to NTs in an unmediated fashion, direct and controlled attachment of QDs to SWNTs remains elusive. My research project has two major components: the fabrication of a novel QD-SWNT circuit and the subsequent photophysical study of the completed device. I have fabricated SWNT-QD devices by growing NTs across patterned Fe/Mo/Al2O3 catalyst islands on a silicon wafer using a chemical vapor deposition (CVD) method. After NT synthesis, Cr/Au electrodes were deposited ~2 m apart using photolithography techniques. NTs were cut by applying voltage pulses to a metal-coated atomic force microscope (AFM) tip in very close proximity to a grounded nanotube. The resulting carboxylic group moieties found at the cut NT edges will be used to covalently attach CdSe QDs with amine-terminated surface ligands using a bioconjugation reaction. The finished device will be used to study charge-transfer effects between the QD and the SWNT, with possible applications in solar cell technology.
