Organic lateral heterojunction devices for vapor-phase chemical detection

Abstract

As the U.S. is engaged in battle overseas, there is an urgent need for the development of sensors for early warning and protection of military forces against potential attacks. On the battlefields, improvised explosive devices (IEDs) have resulted in 54% of all coalition deaths in Iraq and 59% in Afghanistan. The U.S. military has responded with an intensive program of technology development, spending $12.4 billion over the past three years on counter-IED equipment, technology R&D, training, and other measures through the Joint Improvised Explosive Device Defeat Organization (JIEDDO). Snifing"technology, based on fluorescent polymers, has emerged as one of the most sensitive tools in the military's explosives-detecting arsenal. Fluorescent polymer sensors have demonstrated effective ultra-trace, vapor-phase detection of trinitrotoluene (TNT) at security checkpoints and during vehicular sweeps, achieving sensitivity levels comparable to the canine nose. In this sensor scheme, a large contribution to the noise signal is the inefficient transduction of the polymer's chemically sensitive, photoluminescent signal into an electrical signal. The poor optical coupling of the polymer's photoluminescence into a photodetector, reduces the signal-to-noise ratio (SNR) and overall sensor performance. In this work we have developed a novel transduction mechanism and device structure that enable more efficient photon-to-electron conversion resulting in direct transduction of the chemical signature into an electrical signal. Device models detailing the physical processes of device operation will be presented along with supporting experimental evidence.

(cont.) In addition, detection of as little as 1 picogram of TNT has been demonstrated. Ultimately, this work results in a solid-state sensor platform that can be readily engineered to accept any chemosensitive fluorescent polymer for a variety of ultra-trace sensing applications with potential uses in the medical diagnostic, industrial processing, environmental, and defense industries.