How the doors to the nanoworld were opened.


I n March 1981 a new type of microscope made its debut. Unlike traditional microscopes, however, the scanning tunnelling microscope (STM) did not use lenses. Instead, a sharp tip was moved close enough to a conductive surface for the electron wavefunctions of the atoms in the tip to overlap with the wavefunctions of the surface atoms. When a voltage was applied, electrons started to ‘tunnel’ through the vacuum gap, causing a current to fl ow from the foremost atom of the tip into the surface. Quantum tunnelling had been studied theoretically before, but had never been demonstrated so elegantly as in these experiments at the IBM Zurich Research Laboratory in Switzerland. Moreover, the tunnelling current depended exponentially on the distance between the tip and the surface: changing this distance by just an atomic diameter changed the current by a factor of a thousand. Th erefore, by scanning the tip over a sample in two dimensions and keeping the tunnelling current constant, it was possible to image surfaces on the atomic scale. Th e initial results were written up in a manuscript entitled “Tunnelling through a controllable vacuum gap”, which was submitted to a leading physics journal in June 1981. However, the paper was declined by the editors based on the following referee reports: one referee said that the exponential dependence of the tunnelling current on distance was well accepted, so the experiment would not give any new insight; the other report described the work as “extraordinary” and a “technical jewel”, but this referee said that whether such technological work should be published in this particular physics journal was an editorial decision. Eventually the results were published in another leading journal, Applied Physics Letters, in January 19821. In terms of science, the real breakthrough for the STM came in 1983 with the experimental observation of one of the most intriguing phenomena in surface science at that time: atom-by-atom imaging of the 7×7 surface reconstruction in Si(111) (ref. 2). Th e STM images allowed the now widely accepted model of the reconstruction to be worked out from the models of the time3. For the fi rst time it was possible to get up close and personal with individual atoms on surfaces in a threedimensional representation. It took the small but steadily growing community another two years to verify the initial results obtained in Zurich, and it was only at a workshop at Oberlech in the Austrian Alps in 1985 that researchers started to realize the potential of the new method. Devices such as the atomic force microscope (AFM) have their roots in this meeting, and during the last night of the workshop the Alps were buzzing with Figure 1 Keep it clean. Molybdenum disulphide nanocrystals are used as catalysts to remove sulphur impurities at oil refi neries. Reducing harmful sulphur emissions from the combustion of transport fuel is a major environmental challenge. Recent STM studies of MoS2 nanocrystals6 — which are triangular — on gold surfaces have clarifi ed how these catalysts work and lead to improvements in their performance. F. BE SE NB AC HE R, IN AN O, A AR HU S

DOI: 10.1038/nnano.2006.70

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@article{Gerber2006HowTD, title={How the doors to the nanoworld were opened.}, author={Christoph Gerber and Hans Peter Lang}, journal={Nature nanotechnology}, year={2006}, volume={1 1}, pages={3-5} }