W. D. Gill

Drift mobilities in amorphous charge‐transfer complexes of trinitrofluorenone and poly‐n‐vinylcarbazole

Hole and electron drift mobilities have been measured in thin films of charge‐transfer complexes of 2,4,7‐trinitro‐9‐ fluorenone (TNF) with poly‐n‐vinylcarbazole (PVK). The film compositions ranged from pure PVK to mixtures of TNF : PVK in a 1.1 : 1 molar ratio with respect to the monomer unit. Measurements have also been made on amorphous films of pure TNF. The drift mobilities are extremely low (< 10−6 cm2/V sec) and are strongly field and temperature dependent. The field dependence is due to the measured activation energies decreasing as the square root of the applied field from zero‐field values of about 0.7 eV for both carriers. The field dependence of the mobilities is similar to that observed for conductivity modified by the Poole‐Frenkel mechanism; however, several objections make this model unacceptable for this case. At this time, no satisfactory explanation of the observed field dependence can be given. As the TNF concentration is increased, the hole mobility decreases rapidly, while the electron mobility increases. The results suggest that charge carriers are highly localized with transport taking place by a thermally assisted intermolecular hopping process as for the case of small ppolaron motion. Hole transport is apparently due to hopping via uncomplexed carbazole states, while electron transport is due to hopping between TNF sites which may be complexed or uncomplexed. Estimates of the charge‐carrier localization obtained from the exponential dependence of mobility on the site separation give characteristic distances of 1.1 × 10−8 cm for holes and 1.8 × 10−8 cm for electrons.

Polypyrrole: An electrochemically synthesized conducting organic polymer

Abstract The simple, one-step electrooxidation of pyrrole from an organic solvent on a platinum electrode results in the formation of a flexible, metallic polymer. The black films stripped from the electrode are found to be unchanged under ambient storage and thermally stable to temperatures exceeding 300 °C. They are space filling, unlike the fibrillar (CH)x and show considerable disorder. The room temperature conductivity ranges from 10–100 (ohm cm)−1. The thermopower is small and positive, decreasing linearly with decreasing temperature, consistent with p-type metallic conduction. The very small Hall constant is anomalous in both sign and magnitude.

‘Organic metals’: polypyrrole, a stable synthetic ‘metallic’ polymer

Highly stable, flexible films of polypyrrole with p-type conductivities of 100 Ω–1 cm–1 have been prepared by electrolytic oxidation of the appropriate pyrrole monomers; similarly prepared films of mixtures of pyrrole and N-methylpyrrole have conductivities between 5 × 10–3 and 100 Ω–1 cm–1 depending upon the composition.

Phototransport effects in polyacetylene, (CH)x

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.

Properties of metal/polyacetylene Schottky barriers

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.

Conductivity and Hall effect measurements in doped polyacetylene

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.

The preparation and characterization of crystals of the superconducting polymer, (SN)x

Abstract A technique is described for growing (SN) x crystals which have superior electrical properties to those reported previously. The room temperature electrical conductivity has increased, so has the ratio of the room temperature and 4°K resistivities. There is no conductivity maximum in the region 20–30°K and the superconducting transition temperature is higher.

The mechanism of arsenic pentafluoride doping of polyacetylene

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.

Photoconductivity and function properties of polyacetylene films

Abstract Photoconductivity and photovoltaic effects of AsF 5 -doped and undoped trans -(CH) x films have been measured at room temperature in the wavelength region from 0.3 to 3.5 μm. The photovoltaic response threshold at 1.48 eV, measured on Schottky barrier junctions with a low work function metal, is interpreted as the single particle band-gap of trans -(CH) x . I-V and C-V characteristics of the junctions indicate that good Schottky barriers are formed between lightly doped p-type (CH) x and low work function metals. Evidence for ∼ 2 × 10 18 cm −3 deep traps in both doped and undoped trans -(CH) x is obtained from analysis of these characteristics.

Modification of the electronic properties of (SN)x by halogens; properties of (SNBr0·4)x

The electrical and optical properties of (SN)x have been modified by reaction with Br2, ICl, and I2.