Solvation Effects on the Electrical Properties of a Microfluid-Assisted Solution Field-Effect Transistor with Atomically Thin MoS2 Layers

A microfluid-assisted solution field-effect transistor(FET) withnanoscale channels of atomically thin MoS2 layers was constructed.The source-drain current (I (d)) vsgate voltage (V (g)) characteristics (I (d)-V (g)) wereexamined with a focus on the threshold voltage (V (th)) at the onset of the I (d)-V (g) curve. I (d)-V (g) changed when the channelcontacted the tetracyanoquinodimethane (TCNQ) and 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane(F4-TCNQ) solutions in isopropyl alcohol (IPA), acetonitrile (ACN),and dimethyl sulfoxide (DMSO). The shift in V (th) from the pure solvent condition (& UDelta;V (th)) increased monotonically with the concentration, whichwas successfully simulated using Langmuir-type adsorption kinetics.We conclude that the TCNQ and F4-TCNQ solutes were partially solvatedby the solvent and adsorbed on the MoS2 channel. Simultaneously,the saturated & UDelta;V (th) value revealeda significant difference between the TCNQ and F4-TCNQ solutes. Theratio of saturated & UDelta;V (th) of F4-TCNQcompared to that of TCNQ showed a decrease of 4.2, 1.7, and 1.3 forIPA, ACN, and DMSO, respectively. These results coincided with theorder of the dielectric constants of these solvents (18.0, 36.0, and46.6, respectively). The solutes produced the I (d)-V (g) curve by both chargetransfer and the gating effect, the latter of which was screened bythe presence of a solvent. This study demonstrates that a solutionFET can be employed in solid-solution interface chemistry.