Molecular-electronics theorist proposes mechanism for molecular switches. (General Developments).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 has proposed a mechanism for the negative-differential resistance (an electrical off-on switching behavior) that has been observed in devices made from conjugated conjugated adj. Conjugate. estrogens, conjugated Warning - Hazardous drug! C.E.S. organic compounds. The model is based on first-principles, quantum mechanical calculations that follow the changes in the electron clouds surrounding the molecular backbone when a voltage is applied across a molecule. The calculations indicated that the application of the bias voltage See bias. caused a substantial charge density rearrangement re·ar·range tr.v. re·ar·ranged, re·ar·rang·ing, re·ar·rang·es To change the arrangement of. re . This behavior was only observed in compounds that had been chemically modified by attaching an electron-withdrawing group somewhere in the middle of the molecule. This functional group acted as an electron basin, which makes the system act like a quantum well A quantum well is a potential well that confines particles, which were originally free to move in three dimensions, to two dimensions, forcing them to occupy a planar region. , trapping electron density Electron density is the measure of the probability of an electron being present at a specific location. In molecules, regions of electron density are usually found around the atom, and its bonds. between two barriers (in the case of a device, a molecule between two electrodes). A conductance model that used these calculations as input predicted switching at the voltage at which it had been observed. The value of an idea, it has been noted, lies more in what it can predict than in what it can explain. With this principle in mind, the approach outlined above was used to find other compounds that exhibited the type of voltage-dependant charge rearrangement that had been found in compounds exhibiting negative-differential resistance. A compound, with the not-so-easy to remember name of 2-fluoro-4-phenylethynyl-1[(4-thiol)-phenylethynyl]-benzene, has been predicted to possess the desired switching behavior. Collaborators have synthesized this new compound, and NIST researchers will soon be testing its electrical properties in silicon-oxide device prototypes. CONTACT: Carlos Gonzalez, (301) 975-4063; carlos. gonzalez@nist.gov. |
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