How Does the Scanning Tunneling Microscope (STM) Work?
The STM doesnt work the way a conventional microscope does – it doesnt magnify a sample until it is big enough to see with an unaided eye. Instead, a fine needlelike tip that is electrically conductive is scanned just above the surface of an electrically conductive sample. The distance between the tip and the sample is only a few Angstroms (a nanometer is 10 times bigger than an Angstrom). When a tiny voltage is applied, the rules of quantum mechanics allow electrons to jump – or tunnel – across the space between tip and sample. Though very small, the flow of electrons can be detected easily. As the tip moves along the surface of the sample, the tips position is constantly adjusted to make sure the distance (and hence, the electrical current) remains constant. These adjustments trace the surface features of the sample. When the features are graphically displayed on a computer screen, it is possible to see the individual atoms and molecules that make up the sample.
