Scanned-probe microscopes

Objects smaller than the wavelengths of visible light are a staple of contemporary science and technology. Biologists study single molecules of protein or DNA; materials scientists examine atomic-scale flaws in crystals; microelectronics engineers lay out circuit patterns only a few tens of atoms thick. Until recently this minute world could be seen only by cumbersome, often destructive methods such as electron microscopy and X-ray diffraction. It lay beyond the reach of any instrument as simple and direct as the familiar light microscope. A family of new microscopes opens this realm to direct observation. The devices can map atomic and molecular shapes, electrical, magnetic and mechanical properties and even temperature variations at a higher resolution than ever before, without the need to modify the specimen or expose it to damaging, high-energy radiation. These new microscoped are typified by the scanning tunneling microscoped. In 1956 J.A. O'Keefe, then of the U.S. Army Mapping Service, proposed a microscope in which light would shine through a tiny hole in an opaque screen, illuminating an object directly in front of the screen. Light transmitted through the specimen or reflect back through the hole would be recorded as the sample was scanned back and forth. O'Keefemore » pointed out that the resolution of such a scanning near-field microscope would be limited only by the size of the hole and not by the wavelength of the light. In principle the device could make superresolving images-images showing details smaller than half a wavelength.« less