Skilful manipulation

nanotechnology, or the ability to manipulate matter on an atomic scale is one of the most revolutionary developments in material science in recent years. What was in the realm of conjecture is now a laboratory reality.

With the development of tools like the scanning tunnelling microscope (stm), the field has really grown in importance. Significantly, it is not just that the discipline is important from the point of view of development of better machines and gadgets but there is a whole new range of phenomena which occur when matter is explored on the atomic level. New quantum effects are now seen because it has become possible to confine the motion of electrons in materials to one or two dimensions.

Recently, Ali Yazdani and his colleagues at the ibm research division have measured the electric resistance of wires with a single xenon atom and two xenon atoms in series.They used a stm to perform atomically controlled measurements of the transport of electrons through wires with the xenon atom. The stm was a low temperature one (operating at about 5 K) in an ultra-high vacuum. The xenon wires were constructed between two electrodes, one the tungsten tip of the stm and another a very clean nickel tip. The resistance is measured by recording the current through the stm junction.

The results obtained by Yazdani and his group show that the resistance for single atom systems is far greater than that expected for an ideal one dimensional conduction channel. This calls for a revision of some of our ideas about how the electron conduction takes place in such systems. Microfabricated silicon sensors, better and smaller measuring devices and control systems are only some of the applications that are being explored in nanotechnology. The whole field is still in its infancy and one can look forward to many exciting developments.

Of course, all this would not have been possible without the semiconductor growth techniques developed in the preceding decade, which allows for very sharp (on the atomic level) contacts between different semiconductors. One area of intense research is the conduction and transport of electrons through nanometre-scale structures, which is supposed to be of great importance for the development of devices which use such structures (Science , Vol. 272, No 5270).