1、A look into the futureWith a little imagination, it is not difficult to conjure up visions of future developments in high technology, in whatever direction one cares to look. The following two examples illustrate how advances may take place both by novel applications and refinements of old technolog
2、ies and by development of new ones.(1) Molecular electronicsLithography and thin-film technology are the key technologies that have made possible the continuing and relentless reduction in the size of integrated circuits, to increase both packing density and operational speed. Miniaturization has be
3、en achieved by engineering downwards from the macro to the micro scale. By simple extrapolation it will take approximately two decades for electronic switches to be reduced to molecular dimensions. The impact of molecular biology and genetic engineering has thus provided a stimulus to attempt to eng
4、ineer upwards, starting with the concept that single molecules, each acting as an electronic device in their own right, might be assembled using biotechnology, to form molecular electronic devices or even biochip computers.Advances in molecular electronics by downward engineering from the macro to t
5、he micro scale are taking place over a wide front. One fruitful approach is by way of the Langmure-Biodgett(LB) film using a method first described by Blodgett(1935). A multi-layer LB structure consists of a sequence of organic monolayers made by repeatedly dipping a substrate into a trough containi
6、ng the monolayer floating on a liquid (usually water), one layer being added at a time. The classical film forming materials were the fatty acids such as stearic acid and their salts. The late 1950s saw the first widespread and commercially important application of LB films in the field of X-ray spe
7、ctroscopy (e.g,Henke 1964,1965). The important properties of the films that were exploited in this application were the uniform thickness of each film, i.e. one molecule thick, and the range of thickness, say from 5to 15nm, which were available by changing the composition of the film material. Stack
8、s of fifty or more films were formed on plane of curved substrates to form two-dimensional diffraction gratings for measuring the characteristic X-ray wavelengths of the elements of low atomic number for analytical purposes in instruments such as the electron probe of X-ray micro-analyzer.(2) Scanni
9、ng tunneling engineeringIt was stated that observational techniques such as microscopy do mot, at least for the purposes of this article, fall within the domain of nanotechnology. However,it is now becoming apparent that scanning tunneling microscopy(STM) may provide the basis of a new technology, w
10、hich we shall call scanning tunneling engineering.In the STM, a sharp stylus is positioned within a nanometre of the surface of the sample under investigation. A small voltage applied between the sample and the stylus will cause a current to foow through the thin intervening insulating medium(e.g.ai
11、r,vacum, oxide layer). This is the tunneling electron current which is exponentially dependent on the sample-tip gap. If the sample is scanned in a planr parallel to ies surface and if the tunneling current is kept cnstant by adjusting the height of the stylus to maintain a constant gap, then the di
12、splacement of the stylus provides an accurate representation of the surface topographyu of the sample. It is relevant to the applications that will be discussed that individual atoms are easily resolved by the STM,that the stylus tip may be as small as a single atom and that the tip can be positione
13、d with sub-atomic dimensional accuracy with the aid of a piezoelectric transducer.The STM tip has demonstrated its ability to draw fine lines, which exhibit nanometre-sized struture, and hence may provide a new tool for nanometre lithography.The mode of action was not properly understood,but it was
14、suspected that under the influence of the tip a conducting carbon line had been drawn as the result of polymerizing a hydrocarbon film, the process being assisted by the catalytic activity of the tungsten tip. By extrapolating their results the authors believed that it would be possible to deposit f
15、ine conducting lines on an insulating film. The tip would operate in a gaseous environment that contained the metal atoms in such a form that they could either be pre-adsorbed on the film and then be liberated from their ligands or they would form free radicals at the location of the tip and be tran
16、sferred to the film by appropriate adjustment of the tip voltage.Feynman proposed that machine tools be used to make smaller machine tools which in turn would make still smaller ones, and so on all the way down to the atomic level. These machine tools would then operate via computer control in the nanometre domain, using high resolution electron microscopy for observation and control. STM technology has short-cricuired this rather cumbrous concept,but the potential appli
