The Analytical and Surface Chemistry Program supports this project by Prof. Reginald Penner at the University of California at Irvine on the synthesis of nanowires of various metals and an evaluation of their use as chemical sensors. Nanowires are to be fabricated by the procedure of electrochemical step decoration, which has been demonstrated for molybdenum to make wires that are up to 150 micrometers in length, hemicylindrical in cross-section, and removable from the surfaces on which prepared. The high-aspect ratio nanowires, with diameters ranging from 10 to 500 nanometers, can be prepared size-selective on stepped graphite surfaces, transferred to a polystyrene film, and then electrodes attached. The conductivity is similar to that of bulk metal. As a sensor, the nanowires function by exposure of the metal surface to an analyte while measuring the electrical conductivity of the nanowires. For example, molybdenum wires are reactive with oxygen yielding a substantial, but stable drop in conductivity as a metal oxide coating is made. The future research directions include preparation of noble metal nanowires. One synthetic scheme to be tested is metal wire preparation via a mercury amalgam. Then, sensors are to be fabricated with nanowires, either bare metal or with a metal oxide overlayer. Yet to be determined is the physical model to connect analyte concentration with the change in metal nanowire conductivity.
New generation chemical sensors will have a wide range of applications, from biomedical to pollution control. As nanotechnology moves from the laboratory to practical applications, the synthesis of devices must be improved; faster, cheaper, better. There is a great need for reliable and efficient synthesis of nanowires. Electrochemical step decoration is an application of fundamental knowledge of electrochemistry with the known step features naturally occurring on a clean graphite surface. The graphite provides a template for the controlled growth of an electrochemically grown metal wire. The nanowires have an extremely high surface area in relation to the number of metal atoms in the wire. For this reason, electrical conductivity depends upon the number and kind of molecules attached to the surface, making nanowires a logical component of new generation sensors.
