Materiales de nanotecnologia

In touch with atoms
G. Binnig
¨ IBM Research Division, Zurich Research Laboratory, Saumerstrasse 4, ¨ 8803 Ruschilkon, Switzerland

H. Rohrer
8805 Richterswil, Switzerland
Scanning tunneling microscopy appeared as a new method to deal with atoms, molecules, and nanometer-scale structures. It was the first of a growing family of local probes for imaging and measuring, which can serve at thesame time as tools. Local probe methods have changed the way we perceive, think about, and treat atomic structures, and have brought about a new appreciation of mechanics. They play a central role for science and technology on the nanometer scale and will allow us to build systems of the same complexity as used by nature, which has built life on nanofunctionality. [S0034-6861(99)04402-5]

I. BACKTO THE FUTURE OF MECHANIICS

Quantum mechanics has dramatically changed our perception of atoms, molecules, and condensed matter and established the central role of electronic states for electronic, chemical, and mechanical properties. Electronics, understood broadly as the motion of electrons and the deformation of their arrangements, has become the basis of our high-tech world, including‘‘electronics,’’ computer science, and communications. Mechanics, on the other hand, understood as the motion of the mass of atomic cores and the deformation of their arrangements, played a lesser role, at best that of the guardian of the electron. Quantum mechanics has become, for many, synonymous with electronic states and electronics, whereas mechanics is considered the Stone Age. In this respect, the‘‘mechanical’’ scanning tunneling microscope (STM) came as a surprise. The STM is a mechanically positioned, electrically sensitive kind of nanofinger for sensing, addressing, and handling individually selected atoms, molecules, and other tiny objects and for modifying condensed matter on an atomic scale (Sarid, ¨ 1991; Guntherodt and Wiesendanger, 1992; Chen, 1993; Stroscio and Kaiser, 1993; Hamers,Weaver, Weimer, and Weiss, 1996). And like with finger tips, it is the ‘‘touch’’ that makes the difference (see Fig. 1). Back to the future of mechanics: Nanomechanics, a new era. The STM emerged as a response to an issue in technology. [For a historical reivew of STM see Binnig and Rohrer (1987a,1987b).] Inhomogeneities on the nanometer scale had become increasingly important as theminiaturization of electronic devices progressed. Condensed-matter physics, on the other hand, was occupied predominantly with periodic structures in solids and on surfaces and thus had developed very successfully momentum-space methods and concepts for the nanometer scale. Inspired by the specific problem of inhomogeneities in thin insulating layers — a central challenge to our colleagues working on thedevelopment of a computer based on Josephson tunnel junctions — and realizing the general scientific significance associated with it, we started to think in terms of local phenomena. Tunneling appeared a natural and promising
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Reviews of Modern Physics, Vol. 71, No. 2, Centenary 1999

solution. This was the beginning of a new approach to the nanometer scale, the local-probe methods. Local probesare small-sized objects, usually the very end of a sharp tip, whose interactions with a sample or a field can be sensed at selected positions. Proximity to or contact with the sample is required for good resolution. This is in principle an old concept, the medical doctor’s stethoscope being a well-known example. ‘‘Small sized’’ in this case means small compared to the wavelength of the sound to beheard and comparable to the distance from the sound source. The local-probe concept even appeared sporadically in the scientific literature in context with electromagnetic radiation (Synge, 1928,1932;

FIG. 1. Principle of a local probe: The gentle touch of a nanofinger. If the interaction between tip and sample decays sufficiently rapidly on the atomic scale, only the two atoms that are...