November 14, 2001
FRONTIERS IN MATERIALS SCIENCE
VINSE COLLOQUIUM SERIES
Dr. Michael Simpson
Molecular-scale Engineering and Nanoscale Technologies Group
Oak Ridge National Laboratory
"Controlled Synthesis and Directed Assembly for the Realization of Functional Molecular-scale Devices"
Abstract. The main goal of nanotechnology is the realization of functional molecular-scale devices that can be manufactured in an economically feasible way. Such devices would have a significant positive impact on human health, scientific investigation, and the world economy as they find applications in areas such as computing and data storage; sensors, biosensors, and biomedical devices; and scientific instrumentation, to name a few. The challenge for nanoscale science, engineering, and technology is the controlled synthesis of nanoscale elements with the desired attributes, followed by the directed assembly of these elements into functional materials, devices or systems.
Toward this goal, we have developed a method for catalytically controlled growth of vertically aligned (i.e. perpendicular to the substrate surface) carbon nanofibers (CNFs). The process utilizes plasma-enhanced chemical vapor deposition (PE-CVD) in conjunction with micro and nanofabrication techniques to construct deterministically placed nanostructures with controllable diameter, length, orientation, and shape. Consequently, with scalability to the wafer-scale, this catalytically controlled CNF-growth technique is a powerful controlled synthesis/directed assembly method that allows for the precise placement and then directed growth of arrays of functional elements with nanoscale diameters and lengths that can reach several microns. At present we are growing nanofibers with tip diameters on the order of 40 nm (~ 20 nm at the tip, somewhat larger at the base), and with center-to-center spacing on the order of 50 nm.
Since the method described above allows for the controlled synthesis of nanoscale components whose assembly into microscale or nanoscale structures can be directed, we envision many applications of this nanotechnology. At present we are focusing on the realization of field emission (FE) devices, biomimetic devices, and devices with CNF arrays interfaced to intact whole cells. This presentation will describe the synthesis process and show examples of how the structure of the CNFs can be precisely controlled on the nanoscale. The directed assembly of CNFs into microstructured substrates and the functionality of these elements within these structures will be shown for the applications described above.