title: Reversible and Irreversible Responses of Defect-Engineered Graphene-Based Electrolyte-Gated pH Sensors.
abstract: We have studied the role of defects in electrolyte-gated graphene mesh (GM) field-effect transistors (FETs) by introducing engineered edge defects in graphene (Gr) channels. Compared with Gr-FETs, GM-FETs were characterized as having large increments of Dirac point shift (∼30-100 mV/pH) that even sometimes exceeded the Nernst limit (59 mV/pH) by means of electrostatic gating of H(+) ions. This feature was attributed to the defect-mediated chemisorptions of H(+) ions to the graphene edge, as supported by Raman measurements and observed cycling characteristics of the GM FETs. Although the H(+) ion binding to the defects increased the device response to pH change, this binding was found to be irreversible. However, the irreversible component showed relatively fast decay, almost disappearing after 5 cycles of exposure to solutions of decreasing pH value from 8.25 to 6.55. Similar behavior could be found in the Gr-FET, but the irreversible component of the response was much smaller. Finally, after complete passivation of the defects, both Gr-FETs and GM-FETs exhibited only reversible response to pH change, with similar magnitude in the range of 6-8 mV/pH.
authors.affiliation: Division of Materials Science and Engineering, Hanyang University , Seoul 04763, Korea.
authors.forename: Sun Sang
authors.initials: SS
authors.lastname: Kwon
authors.affiliation: Division of Materials Science and Engineering, Hanyang University , Seoul 04763, Korea.
authors.forename: Jaeseok
authors.initials: J
authors.lastname: Yi
authors.affiliation: Division of Materials Science and Engineering, Hanyang University , Seoul 04763, Korea.
authors.forename: Won Woo
authors.initials: WW
authors.lastname: Lee
authors.affiliation: Division of Materials Science and Engineering, Hanyang University , Seoul 04763, Korea.
authors.forename: Jae Hyeok
authors.initials: JH
authors.lastname: Shin
authors.affiliation: Division of Materials Science and Engineering, Hanyang University , Seoul 04763, Korea.
authors.forename: Su Han
authors.initials: SH
authors.lastname: Kim
authors.affiliation: Division of Materials Science and Engineering, Hanyang University , Seoul 04763, Korea.
authors.forename: Seunghee H
authors.initials: SH
authors.lastname: Cho
authors.affiliation: Department of Mechanical Science and Engineering, University of Illinois, Urbana-Champaign , Urbana, Illinois 61801, United States.
authors.forename: SungWoo
authors.initials: S
authors.lastname: Nam
authors.affiliation: Division of Materials Science and Engineering, Hanyang University , Seoul 04763, Korea.
authors.forename: Won Il
authors.initials: WI
authors.lastname: Park
keywords: defect passivation; defect-mediated chemisorption; electrolyte-gated field effect transistor; graphene; graphene mesh; nanosensor; pH sensor