SET FOR FUNDAMENTAL MEASUREMENTS IN ELECTRICITY EXPLAINED.Single-electron tunneling tunneling, quantum-mechanical effect by which a particle can penetrate a barrier into a region of space that would be forbidden by ordinary classical mechanics. , or SET, devices provide a means of manipulating individual electrons and detecting the motion of these electrons with extraordinary precision. The potential for these devices to impact the field of electrical measurement--specifically, capacitance capacitance, in electricity, capability of a body, system, circuit, or device for storing electric charge. Capacitance is expressed as the ratio of stored charge in coulombs to the impressed potential difference in volts. and current standards--was first recognized in the 1980s. More recently, the performance of these devices has been pushed to the levels needed for fundamental standards and high-precision measurements. A new paper from a NIST (National Institute of Standards & Technology, Washington, DC, www.nist.gov) The standards-defining agency of the U.S. government, formerly the National Bureau of Standards. It is one of three agencies that fall under the Technology Administration (www.technology. researcher describes the essential physics of SET devices, discusses various schemes for making capacitance and current standards based on SET devices, and covers the relevance of SET standards for fundamental constants and the International System of Units International System of Units, officially called the Système International d'Unités, or SI, system of units adopted by the 11th General Conference on Weights and Measures (1960). It is based on the metric system. . The development of a NIST prototype SET capacitance standard is described as proceeding along three pathways: (1) a transportable version of the prototype is being constructed for direct comparison with the calculable cal·cu·la·ble adj. 1. That can be calculated or estimated: calculable odds. 2. Readily relied on; dependable: a calculable assistant. capacitor capacitor or condenser, device for the storage of electric charge. Simple capacitors consist of two plates made of an electrically conducting material (e.g., a metal) and separated by a nonconducting material or dielectric (e.g. at NIST headquarters in Gaithersburg, MD; (2) a detailed uncertainty analysis of all aspects of the standard is being developed; and (3) an effort is under way to design an easy-to-use, robust and automated system with computer control of as many functions as possible. "There is still much room for improvement in our basic understanding of the limits on performance of these devices that attempt to transfer individual electrons as fast as possible and with as few mistakes as possible," the researcher writes. He adds that "given the relative immaturity of SET metrology, the progress reported here is impressive." Standards based on SET devices are being pursued in other areas as well. For example, an absolute thermometer thermometer, instrument for measuring temperature. Galileo and Sanctorius devised thermometers consisting essentially of a bulb with a tubular projection, the open end of which was immersed in a liquid. based on SET effects has been demonstrated and is available as a commercial product. In another case, regulated sources of single photons based on SET effects have been proposed in two types of semiconductor systems. The paper, No. 53-00, is available free of charge by contacting Sarabeth Harris, NIST, MC 104, Boulder, CO 80305-3328; (303) 497-3237; sarabeth@boulder.nist.gov. |
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