Large Sensitivity Enhancement: Incorporation of Ultra-Fine Metal Nanoparticles into Organic Field Effect Transistor and Single Electron Transistor Based Sensors

We report pentacene-based field effect transistor devices with remarkable improvement in sensitivity towards trace nitroaromatic vapors through the incorporation of high density, sub-2 nm metal nanoparticles (NPs). Exploiting the unique electrical properties of these NPs, we have demonstrated a detection limit of 2,4-dinitrotoluene (DNT) vapor to be 56.6 parts per billion while control samples (without any embedded NPs) showed no observable DNT sensitivity. We attribute this remarkable enhancement in sensitivity to the ability of these NPs to function as discrete nodes, participating in charge transfer with adsorbed nitroaromatic molecules. To further improve sensor performance, we reduced the feature size of the channel down to sub-10 nm level by electron beam lithography. A pentacene nanoflower structure with average size of 300 nm was deposited on top of the sub-2nm Au NPs between the nanogap as the tunneling barrier to reduce the tunneling resistance. With this device configuration, the size-dependent Coulomb charging energies of 0.48 eV (for 0.5 nm size of Au NPs) to 0.11 eV (for 1.93 nm of Au NPs) are much larger than thermal energy under 300 K (0.0259 eV), allowing us to observe single electron tunneling behaviors by simple current-voltage (I-V) measurements at room temperature. The single electron interaction between the SET and the target molecules as well as the sensor performance have also been investigated.