Showing papers by "Mark S. Wrighton published in 1985"

Resistance of Polyaniline Films as a Function of Electrochemical Potential and the Fabrication of Polyaniline-Based Microelectronic Devices.

Abstract: : Anodic growth of polyaniline films on a Au microelectrode array has been carried out to add to the characterization of polyaniline and to fabricate polyaniline-based microelectronic devices, diodes and transistors, that function when the polyaniline-functionalized microelectrode array is immersed in an electrolyte solution. The microelectrode array is a set of eight Au electrodes, 0.1 micrometer thick, 4.4 micrometers wide and 50 micrometers long, each individually addressable and separated from each other by 1.7 micrometers. Polyaniline can be deposited in controlled amounts by electrochemical oxidation of aniline. When the polyaniline is deposited in sufficient amounts, two or more of the eight Au microelectrodes can be connected in the electrical sense. Current can pass between two connected microelectrodes when there is an applied potential between them. The magnitude of the current at a given applied potential depends on the electrochemical potential of the polyaniline. In 0.5 M NaHsSO4/H20 the current (at a fixed applied potential) is maximum at an electrochemical potential of approx. +0.4 V vs. SCE and declines by a factor of greater than 1,000,000 upon reduction to +0.1 or oxidation to +0,7 V vs. SCE. Owing to the large change in resistance upon change in electrochemical potential, the functionalized microelectrodes is crucial to device function, owing to the limited conductivity of the polyaniline. The switching time of a transistor-like device is faster than 0.1 s.

Poly(3-methylthiophene)-coated electrodes: optical and electrical properties as a function of redox potential and amplification of electrical and chemical signals using poly(3-methylthiophene)-based microelectrochemical transistors

Abstract: : Optical and electrical properties of anodically grown poly-3-methythiophene are reported as a function of redox potential in CH3CN/0.1M (n-Bu4N)ClO4. Poly-3-methylthiophene can be grown by the oxidation of 3-methylthiophene and deposited onto Au or Pt electrode surfaces. A pair of poly-3-methylthiophene-connected microelectrodes can function as a transistor where one of the electrodes is regarded as 'source' and the other as 'drain' with the source being referenced to the solution as a gate. The poly-3-methylthiophene is the analogue of the channel of a solid state field effect transistor, since its conductivity changes by 100,000,000 depending on the potential. Large optical (300-800 nm) and electrical changes for the poly-3-methylthiophene occur between approx. +0.3 V and approx. +0.8 V vs. SCE. The reduced material has an absorption maximum at 490 nm and the oxidized material has an absorption maximum at 750 nm. The optical density changes parallel the resistant changes that occur as the potential of the polymer changes between approx. +0.3 and approx. +0.8 V vs. SCE. The charging of a 1.5 micrometer thick film of poly-3-methylthiophene involves approx. 10,000 time more charge per unit of projected area then a smooth Pt electrode, consistent with a large effective internal surface area for the conducting polymer.

A microelectrochemical diode with submicron contact spacing based on the connection of two microelectrodes using dissimilar redox polymers

Abstract: : Closely spaced, 0.2-1 micrometer, Au microelectrodes on Si3N4 can be functionalized with polyvinylferrocene, PVFc(+)/(o), or with an N, N'- dibenzyl-4,4'-bipyridinium-based polymer, (BPQ(2+)/(+)n, derived from hydrolysis of N, N'-bis((P-trimethoxysilyl) benzyl)-4-4'bipyridinium, I. Two- or eight-microelectrodes arrays can be connected with either polymer in the sense that net current can pass from one microelectrode to another, through the polymer, when one electrode is held at a potential where the polymer is oxidized and the other electrode is held at a potential where the polymer is reduced. From such steady state current an estimate of the diffusion coefficient for charge transport, DCT, in the polymer can be made; values in the range .000000001- 10 to the --10 power sq cm/s are found and accord well with earlier measurements of DCT for te polymers studies. A two-terminal diode can be fabricated by coating one electrode with (BPQ(2+)/(+))n and an adjacent electrode with PVFc(+)/(o) such that there is a connection between the microelectrodes via the (BPQ(2+)/(+)n/PVFc(+)/(o) contact. Current passes when the applied potential is such that negative lead is attached to the PVFc(2+)/(+)n-coated electrode and the positive lead is attached to the PVFc(;)/(o)-coated electrode. The switching time of a microelectrochemical diode is controlled by the time required to oxidize and reduce the polymers.

Electrochemical characterization of surface-bound redox polymers derived from 1,1'-bis(((3-(triethoxysilyl)propyl)amino)carbonyl)cobaltocenium: charge transport, anion binding, and use in photoelectrochemical hydrogen generation

Abstract: This paper describes the behavior of electrode-bound redox material derived from the hydrolysis of the -Si(OEt)/sub 3/ groups of 1,1'-bis(((3-(triethoxysilyl)propyl)amino)carbonyl)cobaltocenium (I). Surfaces of the conventional electrodes SnO/sub 2/ and Pt derivatized with I have a reversible electrochemical response in H/sub 2/O/electrolyte; the E/sup 0/' is pH independent at -0.62 V vs. SCE. The photoelectrochemical behavior of p-type Si photocathodes derivatized with I reveals that the photoreduction of the cobaltocenium derivative can be effected at an electrode potential approx. 500 mV more positive than on metallic electrodes, consistent with the known behavior of p-type Si photocathodes. When polymer from I is deposited on p-type Si and subsequently coated with a small amount of Rh or Pd (approx. 10/sup -7/ mol/cm/sup 2/), the photoelectrochemical generation of H/sub 2/ is possible with 632.8-nm (approx. 15 mW/cm/sup 2/) radiation and efficiencies in the vicinity of 2%. The polymer derived from I is more optically transparent and more durable at negative potentials than redox polymers derived from vilogen monomers. Potential-step measurements and steady-state-current measurements for mediated redox processes show that the charge-transport rate for the polymer derived from I is about the same as for polymers from viologen monomers. 32 references, 8 figures.

Photochemistry of (alkene)pentacarbonyltungsten(0) complexes in rigid alkane at low temperature: relative importance of dissociative loss of alkene and carbon monoxide

Abstract: Irradiation UV (254 ou 213 nm) de complexes W(CO) 5 (alcene) avec alcene=C 2 H 4 , C 3 H 6 et pentene-1 dans le methylcyclohexane. La perte relative de l'alcene est deux fois plus importante a 313 nm qu'a 254 nm. En outre la perte en compose ethylenique est triplee selon l'ordre C 2 H 4

Apparatus for production of hydrogen peroxide

Abstract: An apparatus for the production of hydrogen peroxide is disclosed. In one preferred embodiment, high surface area circulating elements derivatized with a quinone catalyst are reduced in an electrolytic cell where the cathode may also be derivatized with a quinone catalyst and a solution quinone at low concentration is used as a mediator. Once reduced, the circulating elements are separated and used to form hydrogen peroxide from molecular oxygen in an aqueous, electrolyte-free, environment. The circulating elements can be cycled repeatedly. Particular, novel naphthoquinone compounds are also disclosed.

Electrostatic binding of bicarbonate and formate in viologen-based redox polymers: importance in catalytic reduction of bicarbonate to formate

Abstract: The relative importance of electrostatic binding of CO3H and HCO2 in a redox polymer derived from an N,N'-dialkyl-4,4'-bipyridinium monomer has been investigated by Fourier transform infrared (FTIR) spectroscopy. At 298 K and a total concentration of C-containing species of 0.1 M the two species are equally firmly bound in a polymer immobilized on a single-crystal Si electrode surface. When the concentration of C-containing species is 1.0 M, the CO3H ion is more firmly bound by about a factor of 2.5, and at a total concentration of 3.0 M the CO3H ion is about 7 times more firmly bound than the HCO2 ion. The HCO2 and Cl anions are equally firmly bound at 1.0 M total anion concentration. On the basis of the lack of change in the cyclic voltammetry response of a derivatized electrode in 1.0 M Na(CO3H) or Na(HCO2) compared to 1.0 M NaCl, the exchange rate of the C-containing anions does not appear to be a factor that would limit the rate of reduction of the CO3H ion at an electrode modified with the polymer and impregnated with Pd(0).

Photochemistry of (alkene)pentacarbonyltungsten(0) complexes in rigid alkane at low temperature: relative importance of dissociative loss of alkene and carbon monoxide

Abstract: Irradiation UV (254 ou 213 nm) de complexes W(CO) 5 (alcene) avec alcene=C 2 H 4 , C 3 H 6 et pentene-1 dans le methylcyclohexane. La perte relative de l'alcene est deux fois plus importante a 313 nm qu'a 254 nm. En outre la perte en compose ethylenique est triplee selon l'ordre C 2 H 4

Chemical derivatization of microelectrode arrays by oxidation of pyrrole and n-methylpyrrole: fabrication of molecule-based electronic devices

Abstract: : An array of eight Au microelectrodes, each approximately 0.12 microns thick, 3 microns wide, and 140 microns long separated from each other by a distance of 1.4 micron has been fabricated on a 0.45 micron thick Si02 layer grown on a single crystal Si substrate using standard microfabrication techniques. Each electrode can be individually addressed and characterized electrochemically. The individual electrodes can b functionalized with polypyrrole or with poly-N-methylpyrrole by oxidation of pyrrole or N-methylpyrrole, respectively, using conditions similar to those for macroscopic electrodes. The amount of polymer deposited can be controlled and it is possible to electrically connect adjacent microelectrodes with deposited polymer. Since the reduced forms of these polymers are insulating and the oxidized forms are electronically conducting it is possible to prepare electronic devices that are analogous to diodes and transistors using adjacent microelectrodes connected with polymer.