Microscope

Scanning-tunneling microscopes do not look like conventional microscopes at all. These are used to resolve individual atoms, identifying details down to one-tenth of an angstrom in height and less than two angstroms in width. Instead of lenses or mirrors, this microscope sports a tungsten rod with a tip is made up of a pyramid of atoms and three pieces of piezoelectric crystal, which compress and stretch in response to changes in the voltage of an electric charge. Electrons "tunnel" or flow through the vacuum or water from the tungsten tip to the atoms on an object's surface, creating a current that reacts with the crystal. Its inventors, Gerd Binnig of West Germany, and Heinrich Rohrer of Switzerland, won the Nobel Prize in 1986 for this development. They shared the prize with Ernst Ruska.

In 1986, the atomic force microscope (AFM) debuted. The AFM produces three-dimensional images of surfaces both in air and under liquids at a resolution of nanometers, or billionths of a meter. In its contact mode, the AFM lightly touches a tip at the end of a 50–300 micrometer long leaf spring (the cantilever) to the sample. As the tip is scanned over the sample, a detector measures the vertical deflection of the cantilever, yielding the precise height of the sample at local points. The deflections of the cantilever are monitored by a laser beam that is reflected off the cantilever and into a position-sensitive detector. If the tip and sample are coated with two types of molecules, an AFM can measure force of attraction or repulsion between them, potentially at the level of a single hydrogen bond. Since its invention, the atomic force microscope has permitted high-resolution imaging at the subnanometer level. More recently, scientists introduced the microscope to a liquid environment and the resolution improved to the atomic level.