Prospects for Molecular-Scale Electronics
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This effect was first seen a number of years ago, when groups at Delft University of Technology and Cambridge University demonstrated the use of a quantum point contact in a two-dimensional electron gas.2,3 To be able to achieve conductance quantization, they realized that they had to cool the sample down to a very low temperature because of the relative length scales involved. Those length scales are determined by the Fermi wavelength. Imagine being able to examine a very small metallic system, where we might be able to actually see that effect. The length scales involved turn out to be atomic in length, since the Fermi energies are so high. We should easily be able to see those effects at room temperature.
Prospects for
Molecular-Scale Electronics Mark A. Reed
The following article is an edited transcript of the Symposium X: Frontiers of Materials Research address by Mark A. Reed, the Harold Hodgkinson Professor of Engineering and Applied Science and Chair of Electrical Engineering at Yale University, presented at the MRS Fall Meeting on December 1, 1999.
Introduction Scientific consideration of how to scale electronics down to the molecular level started in the mid-1970s. Unfortunately, at the time, researchers did not have the adequate analytical tools to perform the experiments. That has changed drastically, and therefore interest in this field has been renewed, especially over the last few years. I will be presenting a collection of results from a number of different studies, all of which were made possible by the availability of new analytical tools. The work presented here comes from the collaboration of a number of laboratories. My team is composed of researchers involved in the electrical-measurement aspect of this work. Others involved in this work are chemists.
Characterizing Nanoscale Materials Researchers have been trying to scale systems down to the nanoscale level in various ways. They have explored semiconductors and metallic quantum dots and found various types of nanoscale phenomena. They have reported roomtemperature, single-electron transistors and have observed some interesting quantization phenomena. The field of nanotubes and carbon systems, and the electronic properties of them, have been investigated. Researchers have also made tiny structures that look like abacuses and have developed molecular-scale organic systems. While many interesting developments are taking place in all of these various areas,
MRS BULLETIN/FEBRUARY 2001
the one in which actual products are being made is in charge transport in bulk organic systems.
Quantizing Conductance in Single-Atom Systems Let us go back to basics for a moment and talk about Ohm’s law. About three decades ago, Rolf Landauer1 at IBM proposed that the conductance of very small systems is, in fact, relatively well defined and that the conductance is quantized in units of the fundamental constant 2e 2/h, where e is the electronic charge and h is Planck’s constant (in this case, the inverse of approximately 12.9 k) times the transmission coef
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