Potentiometry in Gas Phase

Properties of organic semiconductors (OS) are controlled by the primary and secondary doping^1,2. These highly versatile materials have found sensing application in modern potentiometric sensors for ions as well as for potentiometric sensing of gases. Operation of the equilibrium ion sensors is governed by the modulation of the potential at the interface between the solution and the OS, according to the Nikolskij-Eisenman equation. Exchange of ions with the OS can be seen as a form of primary doping of the latter. For the operation of such potentiometric sensors a stable and well-defined external reference electrode is needed².

When a dry, solid state OS is exposed to a gas or a vapor that can donate or accept electrons, a charge transfer complex is formed between the OS and the gas. Such interaction is called secondary doping, which results in modulation of work function (WF) of the OS. Such interaction can be measured with a Kelvin Probe or with a field-effect transistor. From the sensing point of view the biggest difference and advantage of WF-FET vis-à-vis ion sensors is the fact that no external reference electrode is needed because silicon is used as reference and its WF is stable under normal operating conditions. That fact alone makes the WF-FETs ideally suited for miniaturization, leading to gas-sensing arrays³.

1. Jiri Janata and Mira Josowicz, J.Solid State Electrochem. 13 (2009) 41-49,  “Organic Semiconductors in Potentiometric Gas Sensors”
2. Jiri Janata, Principles of Chemical Sensors, 2^nd Edition, Springer, 2009, New York
3. Jiri Janata, Coll.Czechoslov..Chem.Commun. 
2009, 74, 1623–1634, Potentiometry in gas phase