Contrasting responses of Organic Transistors to Nerve Gas and Explosive Simulant Vapors

We describe chemically sensitive organic transistors in which the semiconductor film consists of a base layer of a high mobility p- or n-channel molecular solid, and an overlayer contains analogous compounds terminated with hydroxy functional groups. Such devices respond to dimethyl methylphosphonate at concentrations on the order of 100 ppb and on time scales < 1 minute. Semiconductor cores include diphenylbithiophene and naphthalenetetracarboxylic diimide, with OH end groups in some cases. End groups include both alkyl and phenolic OH. Devices are as thin as four monolayers. Sensitivity is highly gate dependent, and means of ensuring the gate setting for maximum response are proposed. Contrasting response to dinitrotoluene, a component of nitroaromatic explosive vapors, is reported. Finally, the influence of the channel versus near-contact regions on the vapor-induced changes in resistance is evaluated.