Applications of Nanotubes in Electronic and Nanomechanical Devices

Research funded by the Office of Naval Research

Richard J. ENBODY
Department of Computer Science and Engineering
Michigan State University
David TOMANEK
Department of Physics and Astronomy
Michigan State University
Rodney S. RUOFF
Director, Laboratory for the Study of Novel Carbon Materials
Department of Physics
Washington University

Project Summary

Combining the expertise of a Theoretical and an Experimental Physicist, both specializing in carbon nanostructures, with that of a Computer Scientist specialized in computer architectures, we will study the usefulness of nanotubes in electronic and nanomechanical devices. These recently discovered structures, consisting of carbon or other elements, offer an unusual combination of molecular nature, chemical inertness, and unusual electronic properties with high mechanical and thermal stability. Our research will focus on modeling, synthesis, and interfacing of a novel nanometer-sized memory device, based on self-assembling carbon nanotubes. The ``bucky-shuttle'', described in an upcoming Nature article by one of the P.I.'s, offers an order-of-magnitude increase in memory density, nonvolatility, and Terahertz switching speed.

The Theory and Computer Science components will study the properties of the nanotube memory device and problems associated with its integration into current (silicon-based) microelectronic memory circuitry. The Experimental component will study ways to synthesize this or related nanotube-based structures for use in electronic and nanomechanical devices.


Background

One of the highest priority projects in nanotechnology is scale reduction of electronic and mechanical devices to atomic dimensions. Owing to their nanometer dimensions, combined with a high chemical and thermal stability, carbon nanotubes [Iijima91] and fullerenes [Dresselhaus96] appear to be ideal candidates for such devices [Yakobson].

Carbon nanotubes [Iijima91], consisting of seamless and atomically perfect graphitic cylinders a few nanometers in diameter have been synthesized in bulk quantities [Thess96],[bulk-nanotubes]. The unusual combination of their molecular nature and micrometer-size length [Dekker98],[Lieber98] gives rise to uncommon electronic properties of these systems. Electrical transport measurements for individual nanotubes indicate that these systems may behave as genuine quantum wires [Dekker97], nonlinear electronic elements [Zettl97], or transistors [Dekker-Nature98]. Nanotubes are rapidly gaining recognition as serious candidates for future electronic and mechanical nano-scale devices. Their potential use for permanent data storage, discussed in an upcoming Nature article by one of the P.I.'s [NATxNTM], would significantly extend their range of application. The current method of manufacturing submicron-scale memory devices relies on assisted assembly, e.g. using X-ray lithography. This approach, which requires tools that are smaller than the products, has fundamental limitations and cannot be applied at the nanometer scale. Carbon nanotubes, on the other hand, with diameters as small as a nanometer, are known to self-assemble under specific conditions. An integral part of research in Nanotechnology must therefore consider not only the functionality and integration of individual device components, but also the self-assembly mechanism of these components, and the final self-assembly of the integrated circuitry.

To achieve this, we will use the expertise of a Theoretical and an Experimental Physicists, who have been pioneering the field of fullerenes and nanotubes, with that of a Computer Scientist specializing in modern computer architectures. Tomanek has considerable experience in developing and applying the techniques of quantum many-body theory to investigate the functionality of nanotube devices. The computer codes for the relevant techniques have been developed to a large degree and are locally available. Enbody has been actively involved in computer architecture and parallel processing. Ruoff is one of the pioneers in the synthesis of fullerenes, nanotubes, and devices based on these structures. We expect our research to benefit also from the close ties of the P.I.s with industrial companies and groups performing fundamental research in this field.


Proposed Research

The proposed research will investigate the synthesis, functionality, and systems integration of nanotube-based electronic and nanomechanical devices. The primary focus will be the realization of a nanometer-sized, nanotube-based electronic memory element.

An upcoming article in Nature by one of the P.I.s investigates the dynamics of the ``bucky-shuttle'', a two-level system consisting of a C-60 molecule moving freely inside a carbon capsule, and its possible use as a memory device. This nanometer-sized device would offer

The proposed research initiates an investigation into some of the feasibility questions such a novel device presents. The primary questions to be investigated are:

It is important to note that even though the particular design envisaged here may not lead to an optimum memory device, most of our studies will have a much broader impact, describing the functionality of switchable two-level/two-isomer systems for uses as memory devices. Also, this device is sufficiently novel that fabrication of a working Carbon NanoMemory is beyond the capabilities of a three-P.I. team in three years. However, we expect to make significant progress on nanotube-based systems that will be of great benefit to future designers of electronic and nanomechanical devices based on nanotubes.