Nanoscale Mapping of the Conductivity and Interfacial Capacitance of an Electrolyte Gated Organic Field Effect Transistor under Operation

Probing nanoscale electrical properties of organic semiconducting materials at the interface with an electrolyte solution under external applied voltages is key in the field of organic bioelectronics. It is demonstrated that the conductivity and interfacial capacitance of the active channel of an Electrolyte Gated Organic Field Effect Transistor (EGOFET) under operation can be probed at the nanoscale using Scanning Dielectric Microscopy in force detection mode in liquid environment. Local electrostatic force vs gate voltage transfer characteristics at each point on the device are obtained and correlated with the global current-voltage transfer characteristics of the EGOFET. The nanoscale maps of the conductivity of the semiconducting channel shows the dependence of the channel conductivity on the gate voltage and its variation along the channel due to the space charge limited conduction. The maps reveal very small electrical heterogeneities, which correspond to local interfacial capacitance variations due to an ultrathin non-uniform insulating layer resulting from a phase separation in the organic semiconducting blend. Present results offer insights on the transduction mechanism at the organic semiconductor/electrolyte interfaces at scales down to ~100nm, which can bring substantial optimization of organic electronic devices for bioelectronic applications such as electrical recording on excitable cells or label-free biosensing.