Transistor microelectrochemical

In this article we report the synthesis and electrochemical properties of the polymer derived from oxidation of X, poly(I), and the characteristics of a microelectrochemical transistor based on the polymer. Poly(I), which is formed by electrochemical oxidation of X, Equation 1, consists of a conducting polymer backbone, polythiophene. 

Recently, several molecule-based microelectrochemical devices have been developed by the Wrighton group.(14.15.21-22) A microelectrode array coated with poly(I) results in a microelectrochemical transistor with the unique characteristic that shows "turn on" in two gate potential, Vq, regimes, one associated with the polythiophene switching from an insulator to a conductor upon oxidation and one associated with the v2+ + conventional redox centers. 

Scheme IV, A poly(I)-based microelectrochemical transistor that turns on when VG is moved from VG (ie +0.4 V vs. Ag+/Ag) where polythiophene is reduced and insulating to Vq4 (ie +0.7 V vs. Ag+/Ag) where polythiophene is oxidized and conducting. This transistor also turns on to a smaller extent at E0/ (V2+/+), Vq1 = -0.63 V vs. Ag+/Ag. At VG significantly (>0.2 V) more negative (Vq2 < -0.8 V vs. Ag+/Ag) or positive (+0.4 V > Vq > -0.4 V vs. Ag+/Ag) of E° (V2+/+) only the reduced or oxidized form of viologen redox centers is present, respectively, and this device is...

The poly(I)-based transistor is the first illustration of a microelectrochemical transistor based on a combination of a conducting and a conventional redox polymer as the active material. The transistor "turns on" at VG corresponding to oxidation of the polythiophene backbone. The resistivity of poly(I) declines by a factor of 105 upon changing VG from 0.4 V to 0.8 V vs. Ag+/Ag. When Vg is moved close to the one-electron reduction potential of V2+/+, the conventional redox conductivity gives a small degree of "turn on". A sharp Iq-Vq characteristic results, with an Ip(peak) at Vq = E° (V2+/+). Though the microelectrochemical devices based on conventional redox conduction have both slow switching speed and a... 

Figure 11. Drain current, Id, vs. gate voltage, Vg, for various drain voltages, Vq (25, 50, 100 mV) for a poly(I)-based microelectrochemical transistor. The gate voltage, Vq was scanned at 1 mV/s.

Fig. 13. Microelectrochemical device, (a) Schematic illustration of the microelectrochemical transistor based on polyaniline (thickness of the polyaniline layer 5 pm, electrode width 1-2 pm, distance 2-4 pm) (b) characteristic curve of the polyaniline transistor (Id versus Vg at Vd = 0.18 V). (Redrawn from Wrighton, 1986).

Not long ago,this group first described microelectrochemical devices, which are based on microfabricated arrays of electrodes, connected by electroactive materials. Because the active components of these devices are chemical in nature, many of these devices are chemically sensitive,and comprise a potentially useful class of chemical sensors. Devices showing sensitivity to pH, 02r 2 f and Na" have been demonstrated. These devices are, typically, operated in fluid solution electrolytes. If this class of devices is to be useful as gas sensors, systems which are not dependent on liquid electrolytes need to be developed. We have recently reported solid state microelectrochemical transistors, which replace conventional liquid electrolytes with polymer electrolytes based on polyethyleneoxide (PEG) and polyvinylalcohol (PVA). In this report, we discuss additional progress toward solid-state devices by employing a new polymer ion conductor based on the polyphosphazene comb-polymer, MEEP (shown below). By taking advantage of polymer ion conductors we have developed microelectrochemical devices, where all of the components of the device are confined to a chip. 

Figure 1. A conducting polymer-based microelectrochemical transistor. P3MeT connects two wires of a microfabricated array. Electrodes 1 and 2 are source and drain, respectively. At left, Vq is such that the polymer is neutral... 

Figure 5 shows an example from a new class of solid-state microelectrochemical transistors, which are based on redox-active molecules dissolved in the polymer. The redox-active material is N,N,N, N -tetramethyl-p-phenylenediamine (TMPD) which is sublimed into the MEEP/LiCF3S03 film. Here, the MEEP/LiCF3S03 acts as both polymer host and electrolyte. The transistor characteristic of this device is also shown in Figure 5. Below 0.0 V vs. Ag, the device is off, Iq = 0, since all the TMPD is neutral. As TMPD is oxidized, the device turns on, with a maximum Iq near /2 TMPD" /. We have...

Figure 13.13 / -[conc.] plot of an ion-selective microelectrochemical transistor... 

The characteristics of the polymer-based microelectrochemical transistors are as follows. The current between source and drain. Ip, is a function of the potential between source and drain, Vp, at various fixed gate potentials, Vq. When the Vg using poly(3-methylthiophene) or PP is held at negative potentials where the polymer... 

Gaponik NP, Shchukin DG, Kulak AI, Sviridov DV (1997) Polyaniline-based microelectrochemical transistor with the electrocatalytic gate. Mendeleev Commun 7(2) 70-71 Geim AK, Novoselov KS (2007) The rise of graphene. Nat Mater 6 183-191... 

A pH-sensitive microelectrochemical transistor [288] is based on the pH dependence of the reduction potential of a 4,4 -bipyridine-substituted polypyrrole. At a fixed gate voltage, file source-drain current is pH-dependent, as a result of the reversible protonation of the bipyridinium group. 

Sulfur-ojqrgen interactions have been proposed as a possible cause for the considerable stability of polyalkojQfthiophenes, based on ex situ investigations of a large selection of substituted thiophenes and their polymers [843]. The amplification of chemical and electrical signals has been applied in a microelectrochemical transistor based on poly(3-methylthiophene) [844]. 

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