Capped Nanoparticles as Potential Electronic Components with Nanoscale Dimensions
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covering various aspects of the field have been published in recent years.2–6 The use of DNA as a template has been left out from this article for reasons of space.
Capped
Nanoparticles as Potential Electronic Components with Nanoscale Dimensions David J. Schiffrin
Introduction Nanotechnology, a much abused term, refers to the fabrication and assembly of functional objects of nanometer dimensions. In this article, we will refer only to specific aspects of chemical nanotechnology, meaning by this the production of structures of nanometer dimensions by chemical means. In particular, we will center the discussion on the use of metal nanoparticles as chemical building blocks. Nanoparticles were first studied by Faraday in a series of seminal experiments in 1856. He was the first to observe the remarkable changes in the properties of metals as the size of the phase was reduced. He noted that on transmission, the color (optical properties) of nanoparticles deposited by evaporating Au wires with an electrical discharge close to a glass surface changed from that of colloidal gold to the green of gold leaf. On March 11, 1856, he wrote in his diary, referring to the properties of gold deposited on a coated slide: . . . and then put on the gold above the convex surface of a rock crystal planoconvex lens and pressed it by hand steadily, rocking it a little. This pressure converted the violet or dark tint of the place of contact to a beautiful green— far more beautiful than any I have seen in gold leaf beaten—the effect was perfect. Has the pressure converted the layer of atoms into a continuous layer
MRS BULLETIN/DECEMBER 2001
by expansion and welding, and is that all the difference? I rather think it is.1 Faraday had discovered that the plasmon band exhibited by gold nanoparticles disappears when particles are coalesced into a continuous film (see the article by Mulvaney in this issue). Considering that the electron had not been discovered and the structure of metals was not understood at the time, he showed a remarkable insight into the physical phenomena that he was investigating. This article is further divided into three sections. The section on “Nanoparticle Preparations” presents some recent advances in the synthesis, characterization, and separation of nanoparticles. The section titled “Electronic Components” discusses electronic devices of nanometer dimensions and how supramolecular structures and nanoparticles can be employed for the construction of switching components. Finally, the “Prospects” section gives some thoughts to the way in which this field is developing. In any review of a rapidly growing multidisciplinary field, the amount of information discussed has to be restricted. In this case, reference will be made exclusively to metal nanoparticles and the structures derived from them. In addition, I have restricted as much as possible the material presented to papers published in the last few years. Comprehensive reviews
Nanoparticle Preparations Supercritical Solvents The use of supercritical solvents h
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