Presentation Speech by Professor Sven
Johansson of the Royal
Academy of Sciences
Translation from the Swedish text
Your Majesties, Your Royal Highnesses,
Ladies and Gentlemen,
The problem of the basic structure of matter has long interested man but it was not until the time of the Greek philosophers that the problem took on a scientific character. These ideas reached their culmination in Democritos' theory which postulated that atoms were the building blocks of matter. All this was, however, mere speculation, and it was first the early science and technology of Western Europe which made it possible to tackle the problem experimentally.
The first major breakthrough came with the invention of the microscope. The significance of the microscope in the fields of, for example, biology and medicine is well known, but it did not provide a means of studying the basic nature of matter. The reason is that there is a limit to the amount of detail one can see in a microscope. This is connected with the wave nature of light. In the same way as ocean waves are not affected, to any great degree, by small objects, but only by larger ones, for example a breakwater, light will not produce a picture of an object that is too small. The limit is set by the wavelength of light which is about 0.0005 mm. We know that an atom is 1000 times smaller. It is clear, therefore, that something radically new was needed in order to be able to see an atom.
This new development was the electron microscope. The electron microscope is based on the principle that a short coil of a suitable construction, carrying an electric current, can deflect electrons in the same way that a lens deflects light. A coil can therefore give an enlarged image of an object that is irradiated with electrons. The image can be registered on a fluorescent screen or a photographic film. In the same way that lenses can be combined to form a microscope, it was found that an electron microscope could be constructed of coils. As the electrons used in an electron microscope have a much shorter wavelength than light, it is thus possible to reach down to much finer details. Several scientists, among them Hans Busch, Max Knoll, and Bodo von Borries, contributed to the development of the instrument, but Ernst Ruska deserves to be placed foremost. He built in 1933 the first electron microscope with a performance significantly better than that of an ordinary light microscope. Developments since then have led to better and better instruments. The importance, in many areas of research, of the invention of the electron microscope should, by now, be well known.
The microscope can be regarded as an extension of the human eye. But sight is not the only sense we use to orientate us in our surroundings, another is feeling. With modern technology it is possible to construct equipment that is based on the principle of feeling, using, for example, a sort of mechanical linger. The "finger" may be a very fine needle which is moved across the surface of the structure to be investigated. By registering the needle's movements in the vertical direction as it traverses the surface, a sort of topographical map is obtained, which, in principle, is equivalent to the image obtained in a electron microscope. It is clear that this is a rather coarse method of microscopical investigation and no one had expected any revolutionary developments in this field. However, two basic improvements led to a breakthrough. The most important of these was that a method for keeping the tip of the needle at a very small and exact constant distance from the surface was developed, thus eliminating the mechanical contact between the needle and the surface, which was a limiting factor. This was achieved using the so-called tunnelling effect. This involves applying a potential between the needle tip and the surface so that an electric current flows between the needle and the surface without actually touching them, provided that the tip of the needle and the surface are close enough together. The magnitude of the current is strongly dependent on the distance, and can therefore be used to keep the needle a certain distance above the surface with the aid of a servo mechanism, typically 2-3 atomic diameters. It was also decisive that it turned out to be possible to produce extremely fine needles so that the tip consists of only a few atoms. It is clear that if such a fine tip is moved across a surface at a height of a few atomic diameters the finest atomic details in the surface structure can be registered. It is as if one were feeling the surface with an infinitely fine finger. A crystal surface which appears completely flat in a microscope is seen with this instrument to be a plain on which atoms rise like hills in a regular pattern.
Attempts by Russell Young and co-workers to realize these ideas revealed enormous experimental difficulties. The scientists who finally mastered these difficulties were Gerd Binnig and Heinrich Rohrer. Here it was a question of moving the needle over the surface of the sample and registering its vertical position, with great precision and without disturbing vibrations. The data obtained are then printed out, in the form of a topographic map of the surface, by a computer. The investigation may be concerned with a crystal surface, whose structure is of interest in microelectronic applications. Another example is the investigation of the adsorption of atoms on a surface. It has also been found to be possible to study organic structures, for example, DNA molecules and viruses. This is just the beginning of an extremely promising and fascinating development. The old dream from antiquity of a visible image of the atomic structure of matter is beginning to look like a realistic possibility, thanks to progress in modern microscopy.
Professor Ruska, Dr Binnig, Dr
In Ihrer bahnbrechenden Arbeit haben Sie den Grund fir die entscheidenden Entwicklungen moderner Mikroskopie gelegt. Es ist jetzt möglich, die kleinsten Einzelheiten der Struktur von Materie zu erkennen. Dies ist von grösster Bedeutung - nicht nur in der Physik, sondern such in vielen anderen Bereichen der Wissenschaft.
Es gereicht mir zur Ehre und Freude, Ihnen die herzlichsten Glöckwünsche der Königlich Schwedischen Akademie der Wissenschaften zu iibermitteln. Darf ich Sic nun bitten vorzutreten, urn Ihren Preis aus der Hand Seiner Majestät des Königs entgegenzunehmen.Nobel Lectures,
From Nobel Lectures, Physics 1981-1990, Editor-in-Charge Tore Frängsmyr, Editor Gösta Ekspång, World Scientific Publishing Co., Singapore, 1993
Copyright © The Nobel Foundation 1986