title: The Substrate is a pH-Controlled Second Gate of Electrolyte-Gated Organic Field-Effect Transistor.
abstract: 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.
authors.affiliation: Dipartimento di Scienze della Vita, Università di Modena e Reggio Emilia , Via G. Campi 103, 41125 Modena, Italy.
authors.forename: Michele
authors.initials: M
authors.lastname: Di Lauro
authors.affiliation: Dipartimento di Scienze della Vita, Università di Modena e Reggio Emilia , Via G. Campi 103, 41125 Modena, Italy.
authors.forename: Stefano
authors.initials: S
authors.lastname: Casalini
authors.affiliation: Dipartimento di Scienze della Vita, Università di Modena e Reggio Emilia , Via G. Campi 103, 41125 Modena, Italy.
authors.forename: Marcello
authors.initials: M
authors.lastname: Berto
authors.affiliation: Consiglio Nazionale delle Ricerche, Istituto per lo Studio dei Materiali Nanostrutturati (CNR-ISMN) , Via P. Gobetti 101, 40129 Bologna, Italy.
authors.forename: Alessandra
authors.initials: A
authors.lastname: Campana
authors.affiliation: Dipartimento di Fisica e Astronomia, Alma Mater Studiorum-Università degli Studi di Bologna , Viale Berti-Pichat 6/2, 40127 Bologna, Italy.
authors.forename: Tobias
authors.initials: T
authors.lastname: Cramer
authors.affiliation: Consiglio Nazionale delle Ricerche, Istituto per lo Studio dei Materiali Nanostrutturati (CNR-ISMN) , Via P. Gobetti 101, 40129 Bologna, Italy.
authors.forename: Mauro
authors.initials: M
authors.lastname: Murgia
authors.affiliation: Dipartimento di Scienze della Vita, Università di Modena e Reggio Emilia , Via G. Campi 103, 41125 Modena, Italy.|Department of Physics and Astronomy, University of Sheffield , Hounsfield Road, Sheffield S3 7RH, U.K.
authors.forename: Mark
authors.initials: M
authors.lastname: Geoghegan
authors.affiliation: Dipartimento di Scienze della Vita, Università di Modena e Reggio Emilia , Via G. Campi 103, 41125 Modena, Italy.|Consiglio Nazionale delle Ricerche, CNR-NANO Via Campi 213/a, 41125 Modena, Italy.
authors.forename: Carlo A
authors.initials: CA
authors.lastname: Bortolotti
authors.affiliation: Dipartimento di Scienze della Vita, Università di Modena e Reggio Emilia , Via G. Campi 103, 41125 Modena, Italy.
authors.forename: Fabio
authors.initials: F
authors.lastname: Biscarini
keywords: EGOFET; bioelectronics; biosensors; capacitive coupling; pentacene