The Substrate is a pH-Controlled Second Gate of Electrolyte-Gated Organic Field-Effect Transistor.
Michele Di Lauro, Stefano Casalini, Marcello Berto, Alessandra Campana, Tobias Cramer, Mauro Murgia, Mark Geoghegan, Carlo A Bortolotti, Fabio Biscarini
Author Information
Michele Di Lauro: Dipartimento di Scienze della Vita, Università di Modena e Reggio Emilia , Via G. Campi 103, 41125 Modena, Italy.
Stefano Casalini: Dipartimento di Scienze della Vita, Università di Modena e Reggio Emilia , Via G. Campi 103, 41125 Modena, Italy.
Marcello Berto: Dipartimento di Scienze della Vita, Università di Modena e Reggio Emilia , Via G. Campi 103, 41125 Modena, Italy.
Alessandra Campana: Consiglio Nazionale delle Ricerche, Istituto per lo Studio dei Materiali Nanostrutturati (CNR-ISMN) , Via P. Gobetti 101, 40129 Bologna, Italy.
Tobias Cramer: Dipartimento di Fisica e Astronomia, Alma Mater Studiorum-Università degli Studi di Bologna , Viale Berti-Pichat 6/2, 40127 Bologna, Italy.
Mauro Murgia: Consiglio Nazionale delle Ricerche, Istituto per lo Studio dei Materiali Nanostrutturati (CNR-ISMN) , Via P. Gobetti 101, 40129 Bologna, Italy.
Mark Geoghegan: Dipartimento di Scienze della Vita, Università di Modena e Reggio Emilia , Via G. Campi 103, 41125 Modena, Italy.
Carlo A Bortolotti: Dipartimento di Scienze della Vita, Università di Modena e Reggio Emilia , Via G. Campi 103, 41125 Modena, Italy.
Fabio Biscarini: Dipartimento di Scienze della Vita, Università di Modena e Reggio Emilia , Via G. Campi 103, 41125 Modena, Italy.
Electrolyte-gated organic field-effect transistors (EGOFETs), based on ultrathin pentacene films on quartz, were operated with electrolyte solutions whose pH was systematically changed. Transistor parameters exhibit nonmonotonic variation versus pH, which cannot be accounted for by capacitive coupling through the Debye-Helmholtz layer. The data were fitted with an analytical model of the accumulated charge in the EGOFET, where Langmuir adsorption was introduced to describe the pH-dependent charge buildup at the quartz surface. The model provides an excellent fit to the threshold voltage and transfer characteristics as a function of the pH, which demonstrates that quartz acts as a second gate controlled by pH and is mostly effective from neutral to alkaline pH. The effective capacitance of the device is always greater than the capacitance of the electrolyte, thus highlighting the role of the substrate as an important active element for amplification of the transistor response.
