Pulse Dynamics of Electric Double Layer Formation on All-Solid-State Graphene Field-Effect Transistors
K Xu and MM Islam and D Guzman and AC Seabaugh and A Strachan and SK Fullerton-Shirey, ACS APPLIED MATERIALS & INTERFACES, 10, 43166-43176 (2018).
Electric double layer (EDL) dynamics in graphene field-effect transistors (FETs) gated with polyethylene oxide (PEO)-based electrolytes are studied by molecular dynamics (MD) simulations from picoseconds to nanoseconds and experimentally from microseconds to milliseconds. Under an applied field of approximately mV/nm, EDL formation on graphene FETs gated with PEO:CsClO4 occurs on the timescale of microseconds at room temperature and strengthens within 1 ms to a sheet carrier density of n(s) approximate to 10(13) cm(-2). Stronger EDLs (i.e., larger n(s)) are induced experimentally by pulsing with applied voltages exceeding the electrochemical window of the electrolyte; electrochemistry is avoided using short pulses of a few milliseconds. Dynamics on picosecond to nanosecond timescales are accessed using MD simulations of PEO:LiClO4 between graphene electrodes with field strengths of hundreds of mV/nm which is 100x larger than experiment. At 100 mV/nm, EDL formation initiates in sub-nanoseconds achieving charge densities up to 6 x 10(13) cm(-2) within 3 nanoseconds. The modeling shows that under sufficiently high electric fields, EDLs with densities similar to 10(13) cm(-2) can form within a nanosecond, which is a timescale relevant for high-performance electronics such as EDL transistors (EDLTs). Moreover, the combination of experiment and modeling shows that the timescale for EDL formation (n(s) = 10(13) to 10(14) cm(-2)) can be tuned by 9 orders of magnitude by adjusting the field strength by only 3 orders of magnitude.
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