Bridging nanoscale devices with functional molecular wires

During my graduate work I have studied methods to create molecular electronic devices that depart significantly from the experiments involving dithiolated aromatic molecules between gold electrodes. In particular I have been interested in highly functional molecular bridges that are capable of molecular recognition and switching. For these studies, I have been integrated into a team of scientists in the Columbia University Nanocenter and Chemistry Department. I provide the reaction chemistry expertise on the projects described below to design and synthesize molecules for tailor made molecular scale junctions that we are fabricating. The projects I worked on were centered around two discoveries for junction fabrication.;The first project was based on some electrodes pioneered by a fellow graduate student, Jinyao Tang. Jinyao has developed a method to make large quantities of gaps in metals with an innovative method he calls self-aligned lithography. He can routinely make ∼3 nm gaps. I developed terpyridyl ligands with thiol endgroups suitable for the metals surfaces. The key result for this project is that we are able to add and remove cobalt ions to see changes in the conductance (Figure 1).*;The other project I worked on is performed in the precisely cut single-walled carbon naotubes. This method is pioneered by Xuefeng Guo, a joint Kim/Nuckolls post doctoral associate. Using oxygen plasma he precisely cut individual SWNTs while they are in devices (Shown in Figure 2). We do this through a lithographic mask to yield point contacts that are separated by molecular length scales. This turns out to be an extremely versatile platform for attaching molecules to make single molecule devices that are robust. The important point is that the ends of these nanotube contacts are functionalized with carboxylic acids.*;I synthesized the two candidate wires, shown in Figure 3. I was interested in the typyridyl based wires because I wanted to test if functionalization of the ends of the nanotubes would make them sensitive to metal ions such as cobalt. This would form the basis for a simple sensor that was based on current not light to detect metal ions. The oligoanilines were interesting because their conductivity should switch with pH (Figure 4).*;*Please refer to dissertation for diagrams.