NIRT: Nanoscale Molecular Opto-Electronics

Arizona State University, Scottsdale AZ

Investigators

Abstract

0103175 Lindsay This proposal was submitted in response to the solicitation "Nanoscale Science and Engineering" (NSF 00-119). It brings together experts in organic photochemistry, experimental and theoretical physicists and engineers in a University (Arizona State)-Industry (Motorola)collaboration aimed at developing nanoscale molecular optoelectronic devices based on paradigms from photosynthetic electron transfer. The first phase of the project builds on the PIs' current work on the basic building blocks of molecular electronic devices. They will use bifunctionalized molecules covalently bonded at one end to a gold-coated conducting AFM tip and at the other end to a gold substrate. In this way they will measure the electrical properties of simple molecular insulators (n-alkanes) and molecular wires (carotenoids) at the single molecule level. These measurements will be compared to first-principles simulations, with the goal of developing both theory and experiment until they have a reasonably accurate description of transport in both the molecules and their contacts to the metal electrodes. Armed with this information, they will insert the molecules into nano-scale gaps in gold electrodes on oxidized silicon wafers.These devices will be made at Motorola. Final gap fabrication uses active-feedback control of electrochemical deposition, a technique developed by a consultant to the group.The goals of this step are to (1)make two electrode devices on wafers that can be characterized in terms of the single-molecule AFM data and (2) explore the current-voltage characteristics of these devices with greater flexibility than possible in the AFM (for example, making temperature-dependent measurements). The second phase will focus on the electronic properties of optically excited molecules, and molecules in high-energy charge-separated states. The use of light to provide additional inputs to molecular-scale electronic devices offers several advantages, and may lead the way to the design and fabrication of technologically useful constructs. They will use much the same approach as outlined above, but with the addition of controlled optical excitation of chromophores. They will start with the carotenoids, as the simplest system, but will go on to study molecules containing porphyrins and fullerenes that are built to make transitions into long-lived triplet states, or into long-live charge-separated states. These systems present theoretical as well as experimental challenges, and they propose computational approaches for dealing with nuclear-relaxation on excitation or charging and for dealing with highly correlated molecular electronic states. They propose a single-molecule opto-electronic switch as a candidate device on which to focus the long-range efforts of the group. The device might prove useful as an optoelectronic molecular-scale building block. But developing the science and technology that would go into building the device and understanding it are the main motivation for this project. This group provides an extraordinary opportunity for training minority students in multidisciplinary approaches to nanoscience in both academic and industrial research environments.