ORNL Technology Detects Explosives With Mini-Explosions (February 2000)

An instrument that can detect nano-explosions could lead to an inexpensive hand-held device to screen people and luggage at airports or to detect land mines. The device, being developed at the Department of Energy's Oak Ridge National Laboratory, is based on miniature micro-machined silicon cantilevers one-tenth the width of a human hair that can detect tiny forces caused by heat-induced nano-explosions. The instrument, which boasts parts-per-trillion sensitivity, works by absorbing TNT molecules given off by explosives. As the semiconductor material absorbs the TNT and is heated with power from a simple battery, the TNT molecules undergo tiny explosions that are detected by an optical beam. Developer of the technology, Thomas Thundat of the Biochemistry and Biophysics Section of Life Sciences Division, envisions a device that will make it more feasible to locate and remove unexploded land mines that litter millions of acres in Third World countries. While other technologies exist to locate land mines and detect explosives, Thundat believes the nano-explosion device offers several advantages, including low cost and ultra-high sensitivity. The instrument also regenerates itself after each use for continuous operation. The key to the device's exceptional sensitivity is a revolutionary micro-mechanical sensor that is micro-machined from single-crystal silicon and can be heated to very high temperatures quickly. When the temperature of the cantilever is increased with current from a battery to 575 degrees Celsius - the characteristic temperature of TNT - the adsorbed TNT molecules explode. Because the thermal mass of cantilevers is small, they can be heated to more than 700 degrees Celsius in a millisecond with just a micro-watt of power. A diode laser beam similar to those used in compact disc players but 1,000 times more responsive detects the vibrations caused by the tiny explosions. The high sensitivity is a result of the cantilever's ability to respond to extremely small mechanical or tiny thermal disturbances. Therefore, even traces of TNT are sensed quickly. By scanning an appropriate temperature range, researchers can use this technology to detect many explosive molecules, including those with low vapor pressures such as those used in plastic explosives. Others contributing to the project are Moonis Ally of the Energy Division, Jerry Hu a Visiting Scientist in the Life Sciences Division, and Panos Datskos of the Engineering Technology Division. (Contact: Thomas Thundat, 574-6201, thundattg@ornl.gov; Funding Source: funded by the Federal Aviation Administration through the National Safe Skies Alliance; funding from the Laboratory's seed money program, funded by DOE, and other DOE program money also contributed to this discovery) Note: a press release was issued on February 21.