Page 25 - Science at the nanoscale

RPS: PSP0007 - Science-at-Nanoscale
15:10
June 9, 2009
1.3. Examples of Interesting Nanoscience Applications
and spin-based quantum computer where the spin of a single
electron trapped in a quantum dot is used as a qubit.
(c) Molecular electronics The emerging field of molecular elec-
tronics is now becoming a popular alternative paradigm to current
silicon microelectronics. In 1974, Ari Aviram and Mark Ratner,
then at New York University, published a paper in Chemical
Physics Letters proposing that individual molecules might exhibit
9
the behaviour of basic electronic devices. Their hypothesis, for-
mulated long before anyone was able to test it, was so radical
that it was not pursued for another 15 years. The story continues
in December 1991, when James Tour and Mark Reed discovered
they had a common interest at a small gathering of “moletron-
ics” researchers in the Virgin Islands. The meeting was hosted by
Ari Aviram, who was then working at IBM’s Thomas J. Watson
Research Center in New York. They started collaborating, but
it was not until 1997 when they successfully used the so-called
“break-junction” technique to measure the conductance of a sin-
10
gle molecule.
In their work, benzene-1,4-dithiol molecules were
self-assembled onto two facing gold electrodes of a mechani-
cally controllable break junction to form a stable gold-sulphur-
This allowed the direct
aryl-sulphur-gold system (Fig. 1.8).
observation of charge transport through the molecules for the
first time. Their study provided a quantitative measure of the
conductance of a junction containing a single molecule, which
is a fundamental step towards the realization of the new field of
molecular electronics.
Many papers have since followed demonstrating conductance
measurements on single molecules and simple single molecule
devices. A useful review of the early days of the field has 15 ch01
been written by Carroll and Gorman. 11 Nanogaps were formed
using electromigration whereby a high electric field causes gold
atoms to move along the current direction, eventually causing
a nanogap. More recently, a research team at Hewlett-Packard
(HP) Laboratories has proposed the crossbar architecture as the
most likely path forward for molecular electronics. 12 A crossbar
9
A. Aviram and M. A. Ratner, Chem. Phys. Lett. 29, 277–283 (1974).
10 M. A. Reed, C. Zhou, C. J. Muller, T. P. Burgin and J. M. Tour, Science 278 (1997)
252.
11 R. L. Carroll and C. B. Gorman, Angew. Chem. Int. Ed. 41, 4378 (2002).
12 P. J. Kuekes, G. S. Snider and R. S. Williams, Scientific American, November 2005,
72.