| Description |
Organic semiconductors offer tremendous potential for detecting airborne chemicals. Planar, π-conjugated molecules, such as perelyene diimide derivatives, are especially appealing because they can form nanofibers through self-assembly. Depositing these structures onto a substrate creates a porous network. This network is easily penetrable and offers a large surface area for interaction with the target chemical, leading to enhanced sensitivity when used as a gas sensor. Furthermore, the π-conjugation provides electronic conductivity, which enables the use of these ma- terials as chemiresistors. Finally, because the building blocks are organic molecules, there are virtually limitless structural possibilities; molecules can be engineered to interact with a specific chemical by modifying the side groups. Using these materials, our group has demonstrated vapor-phase detection of explosives, chemical warfare agents, narcotics, and toxic gases at concentrations extending into the low parts per trillion range. While organic semiconductors have many strengths, major barriers have limited their utility to the lab. First, the conductivity is intrinsically low. Oftentimes, it is too low to be read by commercial electronics (picoampere scale). Secondly, because of the random way the nanofibers deposit, device-to-device variation is difficult to control. In this dissertation, we will discuss early-stage work to address these issues. Three strategies were investigated and will be presented: 1) integrating sensor molecules with conductive materials, 2) integrating sensor molecules with conductive devices, and 3) controlled deposition to align the nanofibers across the electrode gap. In the first strategy, we explore the fundamental properties of the sensing material interface with carbon nanotubes. The formation of charge transfer complexes and unexpected charge transfer were observed. Next, sensor molecules were used to gate field effect transistors. The result is a sensitive, selective device compatible with production-scale manufacturing. Finally, we will discuss nanofiber alignment using dielectrophoresis. Removing the randomness from deposition is a potential means to reduce device-to- device variation while increasing the conductivity. These investigations may produce a route from the lab to the real world for sensors based on organic semiconductors. |
