T. C. Clarke

Bio: T. C. Clarke is an academic researcher from IBM. The author has contributed to research in topics: Polyacetylene & Doping. The author has an hindex of 21, co-authored 39 publications receiving 1816 citations.

Preparation and characterization of neutral and oxidized polypyrrole films

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.

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

Abstract: 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.

Emergence of magnetism in graphene materials and nanostructures

Abstract: Magnetic materials and nanostructures based on carbon offer unique opportunities for future technological applications such as spintronics. This paper reviews graphene-derived systems in which magnetic correlations emerge as a result of reduced dimensions, disorder and other possible scenarios. In particular, zero-dimensional graphene nanofragments, one-dimensional graphene nanoribbons and defect-induced magnetism in graphene and graphite are covered. Possible physical mechanisms of the emergence of magnetism in these systems are illustrated with the help of computational examples based on simple model Hamiltonians. In addition, this review covers spin-transport properties, proposed designs of graphene-based spintronic devices, magnetic ordering at finite temperatures as well as the most recent experimental achievements.

New semiconductor device physics in polymer diodes and transistors

Abstract: Semiconductor devices have been made from polyacetylene, a conjugated polymeric semiconductor. The device operates in a novel way: charge is stored in localized soliton-like excitations of the polymer chain, which are introduced not by doping or photoexcitation but by the presence of a surface electric field. The formation of charged solitons changes the optical properties of the polymer, introducing optical absorption below the band gap. Combined with the processibility of the polymer, these new electro-optic effects may be exploited technologically in electro-optic modulators.

Highly conducting polyparaphenylene, polypyrrole, and polythiophene chains: An ab initio study of the geometry and electronic-structure modifications upon doping

Abstract: The effect of charge-transfer doping on the geometric and electronic structures of conjugated polymers has been investigated at the ab initio level with explicit consideration of the doping agents. Three systems were chosen for study as prototypical examples of conjugated polymers with nondegenerate ground states: polyparaphenylene, polypyrrole, and polythiophene. As a result of charge transfer with electron-donating dopants, extra charges appear on the polymer chains and induce strong geometry modifications. The lattice evolves from an aromatic structure towards a quinoid-like structure. Charged defects associated with lattice deformations such as spinless bipolarons are formed. The influence on the electronic structure of the polymer chains is such that with respect to the undoped case, new states appear within the gap. For the maximum doping levels experimentally achieved, band-structure calculations demonstrate that the states in the gap overlap to form bipolaron bands, a few tenths of an electron volt wide. The presence of these bipolaron bands is consistent with optical data as well as with magnetic data which suggest that the charge carriers in the highly conducting regime are spinless.