NIST researchers announced in the September 10, 1999, issue of Science magazine that they have developed the first working prototype of a new standard for capacitance based on a means of manipulating and counting electrons one at a time. The new standard is the latest to rely on a fundamental property of nature and not be determined by a constructed artifact, classical physics or a combination of both. Nature-based standards currently in use include length (the meter) and time (the second), both defined by precise measurements of the vibrations of the cesium atom.The work on the capacitance standard depends on two technologies developed at NIST. The first is an electron pump, based on ultra-small electrical devices called tunnel junctions. Operating at temperatures less than one-tenth of a degree above absolute zero, the pump passes and counts individual electrons with an uncertainty of 0.01 parts per million. In other words, the pump would miss tallying only one electron of every 100 million passing through.
展开▼
