Digging ditches in molecular strata.Digging ditches in molecular strata Most researchers use the scanning tunneling microscope scanning tunneling microscope, device for studying and imaging individual atoms on the surfaces of materials. The instrument was invented in the early 1980s by Gerd Binnig and Heinrich Rohrer, who were awarded the 1986 Nobel prize in physics for their work. (STM (Scanning Tunneling Microscope) A microscope that can image down to the atomic level. An STM uses a piezoelectric tube with a tiny sharp tip at the end that is moved within nanometers of the object being sampled. ) to probe molecular and atomic landscapes and to image materials at these smallest of structural scales. But some are beginning to use the atom-tipped instrument to sculpt sculpt v. sculpt·ed, sculpt·ing, sculpts v.tr. 1. To sculpture (an object). 2. To shape, mold, or fashion especially with artistry or precision: or even rearrange the diminutive landscapes. One recent afternoon, Bruce Parkinson of E.I. duPont de Nemours & Co. in Wilmington, Del., used his STM to etch a three-tiered pit of squares (left) into a tin diselenide crystal -- a stack of orderly molecular sheets, each separated by slightly more than 0.6 nanometers. A million of the inscribed in·scribe tr.v. in·scribed, in·scrib·ing, in·scribes 1. a. To write, print, carve, or engrave (words or letters) on or in a surface. b. To mark or engrave (a surface) with words or letters. micropits might fill a flattened sesame seed. Each side of the smallest and deepest square, lying six molecular sheets below the surface, measures 200 nanometers. The medium-sized tier, two sheets thick, has a square hole measuring 500 nanometers per side. The largest, uppermost tier includes three sheets and has a square hole 1,000 nanometers (1 micron) to a side. To date, the smallest pit Parkinson has etched measures 25 x 25 x 1.2 nanometers. On another afternoon, he used his STM to etch the less orderly pit shown on the right. Parkinson suggests in the Oct. 10 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
suffocation of piglets by the sow. The piglets may be weak from illness or malnutrition, the sow may be clumsy or ill, the pen may be inadequate in size or poorly designed so that piglets cannot escape. layers have completely disappeared. Because the STM tip itself rarely scratches the crystal surface, Parkinson says he suspects the etching process involves additional mechanisms, including heating and electrical field effects. |
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