Network


Latest external collaboration on country level. Dive into details by clicking on the dots.

Hotspot


Dive into the research topics where T. C. Clarke is active.

Publication


Featured researches published by T. C. Clarke.


Molecular Crystals and Liquid Crystals | 1982

Preparation and characterization of neutral and oxidized polypyrrole films

G. B. Street; T. C. Clarke; M. Krounbi; K. Keiji Kanazawa; Victor Y. Lee; P. Pfluger; J. C. Scott; G. Weiser

Abstract Oxidized and neutral films of polypyrrole have been prepared electrochemically in the absence of oxygen and water. The neutral films are insulating and can be readily oxidized by chemical oxidizing agents to give films of greater conductivity than can be achieved by electrochemical oxidation. Optical spectroscopy provides evidence for the similarity of the polymeric carbonium ion produced by both types of oxidation. NMR studies are consistent with the α,α’ bonding in these polymers; they also show the expected downfield shifts relative to the neutral polymer on both chemical and electrochemical oxidation. ESR studies of both the electrochemically oxidized and the neutral polymer suggest the presence of highly mobile spins.


Journal of Chemical Physics | 1983

Optical study of polypyrrole perchlorate

K. Yakushi; L. J. Lauchlan; T. C. Clarke; G. B. Street

The optical transmittance spectra of polypyrrole perchlorate have been measured at various stages in the reduction to neutral polypyrrole at 300 and 120 K and at high pressure. Analysis of the results suggests that the polypyrrole chain is composed of conjugated segments of various lengths. The optical conductivity spectrum of polypyrrole perchlorate was obtained by the Kramers–Kronig transformation of the transmittance data from 0.025 to 6.25 eV. The spectrum is not consistent with Drude‐like free carriers. The conduction mechanism probably involves hopping between the conjugated segments.


Journal of Chemical Physics | 1979

Vibronic intensity enhancement in the infrared spectra of heavily doped (CH)x and (CD)x

J. F. Rabolt; T. C. Clarke; G. B. Street

Fourier Transform IR transmission spectroscopy has been utilized to elucidate the nature of the polymer–dopant interaction in doped (CH)x. Significant changes in the IR spectrum occur after doping and several intense bands at 1385, 1295, and 832 cm−1 have been observed and their shifts studied upon deuteration. The origin of these intense features can be attributed to a vibronic activation and enhancement of the totally symmetric Raman active Ag modes in the IR spectrum.


Solid State Communications | 1980

Phototransport effects in polyacetylene, (CH)x

T. Tani; P.M. Grant; W. D. Gill; G. B. Street; T. C. Clarke

Abstract We have made the first comprehensive measurements of the photovoltaic and photoconductivity effects in polyacetylene in that we have extended the spectral range originally covered by Matsui and Nakamura [17] to include the visible region as well. The photovoltaic experiments were done on Schottky barrier junctions formed between AsF5 lightly-doped p-type trans-(CH)x and a low work function metal, the first junctions of this type to be produced in semiconducting polyacetylene. The observation of a photovoltaic response threshold at 1.48 eV provides the first definitive measurement of the single-particle band gap in trans-(CH)x. In addition, we have found the existence of a peak at 1.35 eV in the photoconductivity spectrum of undoped trans-(CH)x which may be due either to extrinsic sources or to thermal dissociation of a weakly bound Wannier exciton.


Journal of Applied Physics | 1981

Properties of metal/polyacetylene Schottky barriers

Paul M. Grant; T. Tani; W. D. Gill; M. Krounbi; T. C. Clarke

Rectifying barriers of undoped and lightly doped trans‐(CH)x films with low work function metals have been investigated. I‐V and C‐V measurements were used to explore the junction properties. The junction characteristics were found to be Schottky‐like in the large sense accompanied by significant differences in detail. Using C‐V measurements to determine the carrier concentration, we found the carrier mobility to be concentration dependent.


Solid State Communications | 1978

Conductivity and Hall effect measurements in doped polyacetylene

K. Seeger; W. D. Gill; T. C. Clarke; G. B. Street

Abstract Conductivity and Hall effect measurements are reported for polyacetylene films heavily doped with AsF5. The Hall coefficient is anomalously small, however, it is p-type and relatively temperature insensitive in the range 4–300 K indicative of metallic conduction. The effects of film degration by heating and air exposure are also investigated.


Solid State Communications | 1979

Transport properties of heavily AsF5 doped polyacetylene

J.F. Kwak; T. C. Clarke; R. L. Greene; G. B. Street

Abstract We report measurements of the temperature dependence of the thermoelectric power and electrical conductivity for polyacetylene heavily doped (more than 10%) with arsenic pentafluoride. The thermopower is small, positive and linear with temperature. The conductivity is very large for a polymeric system, about 1000 (Ω cm) -1 at room temperature, and as temperature is decreased drops in value by less than a factor of two, becoming essentially temperature independent below 4 K. The samples exhibited ohmic behavior at the current densities used and did not show any frequency dependence up to 1000 Hz. No evidence for superconductivity was found down to 30 mK. The results are interpreted as the first conclusive evidence for the existence of a metallic state at all temperatures in this material.


Synthetic Metals | 1980

The chemical nature of polyacetylene doping

T. C. Clarke; G. B. Street

Abstract The chemical mechanisms involved in oxidative doping of polyacetylene, (CH) x , have been investigated using a variety of spectroscopic techniques. A common feature in doping by halogens, silver rats, and AsF 5 is electron transfer from the polymer to the dopant to give a polyolefinic cation and a reduced form of the dopant which intercalates between the polymer chains. The infrared spectrum of the oxidized polymer shows several intense features arising from vibronic activation and enhancement of totally symmetric Raman active A g modes in the i.r. The implications of these observations on the structure of the polyacetylene chains after doping are discussed.


Solid State Communications | 1982

Spin dynamics in trans-polyacetylene

N. S. Shiren; Y. Tomkiewicz; T.G. Kazyaka; A.R. Taranko; H. Thomann; L. R. Dalton; T. C. Clarke

Abstract Detailed spin-echo and cw EPR measurements on trans -(CD) x and trans -(CH) x are reported. The magnitude of the on-chain diffusion rate, and its temperature dependence are evaluated. The results do not agree with predictions of the soliton model nor with results evaluated from recent NMR measurements.


Synthetic Metals | 1979

The mechanism of arsenic pentafluoride doping of polyacetylene

T. C. Clarke; R. H. Geiss; W. D. Gill; P.M. Grant; H. Morawitz; G. B. Street; D. E. Sayers

Abstract Doping of polyacetylene with arsenic pentafluoride is found to involve oxidation of the polymer according to the mechanism: 2(CH)x + 3AsF5 → 2(CH)+x + 2AsF−6 + AsF3. The AsF−6 ions intercalate beteeen the polymer chains in a nonrandom fashion. Oxidation of the polymer is accompanied by replacement of the original interband transition in the visible by a featureless transition extending into the infrared. Treatment of the doped polyacetylene with ammonia destroys the enhanced conductivity and regenerates a visible spectrum similar to that of the undoped polymer but somewhat blue-shifted. Possible explanations are offered for these results in terms of the proposed mechanism of doping.

Collaboration


Dive into the T. C. Clarke's collaboration.

Researchain Logo
Decentralizing Knowledge