  |
|
Shown in Fig. A  is an enlargement of a line drawn by FSU's Peng Xiong onto the surface of a silicon wafer coated with nano-layers of aluminum and niobium. After the e-beam cuts a trench through the niobium layer, a caustic chemical is applied that eats into the aluminum layer but leaves the niobium intact. Then the niobium is oxidized (essentially rusted) electrochemically, a process that makes the exposed niobium expand and thus narrow the gap (Fig. B). Vaporized lead is then deposited onto the entire wafer, leaving an ultra-thin line at the bottom of the e-beam trench. The lead wire is thus electrically isolated from the other nearby metals. Xiong's method depends on an low temperature environment (minus 442 degrees F) that is necessary to control the deposition of vaporized lead and build atomically smooth wires.
There's a real fine line between what's possible and what isn't in nanotech-nology these days, and the line, in fact lines, are getting finer all the time. The nano-machines of tomorrow will run on "wires" that may be only a single atom wide. State-of-the-art in tiny wires today though are those depicted in the images here and a relatively new development called carbon nanotubes, basically hollow latticeworks of carbon atoms that show promise in microelectronics. A common method of making ultra-fine lines today is through a process called electron beam lithography (literally "stone writing") in which beams of electrons are used to draw patterns on various materials. The process borrows techniques from photography, where a light-sensitive film (or "resist") is spread over a silicon wafer which is exposed to electron beams and then processed. The result is an often intricate pattern of lines, which can form the blueprint for the integrated circuitry of computer chips. Though powerful and highly efficient, the technique has built-in resolution limits that curb how fine a line it can draw. In collaboration with materials scientists at the University of Florida, MARTECH researchers have developed a method for going beyond the resolution of e-beam lithography. Using the technique, FSU researcher Peng Xiong builds wires made of lead—an element that becomes superconducting at low temperatures—that are only 15 nanometers (15 billionths of a meter) wide, about the width of 50 atoms of lead. Nearly 7,000 of such lines, lying side by side, could fit across the width of a single human hair. —F.S. |