C. K. Chiang

Synthesis of electrically conducting organic polymers: halogen derivatives of polyacetylene, (CH)x

When silvery films of the semiconducting polymer, trans‘polyacetylene’, (CH)x, are exposed to chlorine, bromine, or iodine vapour, uptake of halogen occurs, and the conductivity increases markedly (over seven orders of magnitude in the case of iodine) to give, depending on the extent of halogenation, silvery or silvery-black films, some of which have a remarkably high conductivity at room temperature.

Conducting Polymers: Halogen Doped Polyacetylene.

A study of the electrical conductivity of the halogen doped transpolyacetylene system, (CH)x, is reported. When films of trans‐ (CH)x are exposed to chlorine, bromine, or iodine vapor, uptake of halogen occurs; and the conductivity increases markedly, over eleven orders of magnitude in the case of iodine. The behavior of the halogenated polyacetylene is like that of a series of semiconductors with activation energies which vary with halogen content. The results are discussed in terms of a model of the doping process based on charge transfer.

Polyacetylene, (CH)x: n‐type and p‐type doping and compensation

A series of experiments are reported which demonstrate that donors or acceptors can dope polyacetylene to n type or p type, respectively, and that the two kinds of dopants can compensate one another. The formation of a rectifying p‐n junction is demonstrated. These results suggest the possibility of utilizing doped polyacetylene in a variety of potential semiconductor device applications.

Electrical conductivity of (SN)x

Abstract Measurements of the b -axis conductivity of polymeric sulfur nitride (SN) x from 4.2–300K are reported for samples having different polymerization times. A general increase in the conductivity was found with longer polymerization times leading to room temperature conductivities 1200–3700 (Ω-cm) −1 and resistance ratios 50–205. The temperature dependence of the resistivity can be represented by Matthiessens rule showing the intrinsic resistivity over a broad temperature range 15 T T 2 form which is discussed in terms of electron-electron scattering.

Semiconductor-metal transition in doped (CH)x: Thermoelectric power☆

Thermoelectric power studies of polyacetylene have been carried out as a function of dopant concentration and temperature. The thermopower of pure trans-(CH)x is large (S = +850 μ V°K) and positive consistent with p-type material. With iodine doping, (CHIy)x, the thermopower remains positive over the full range of concentration 0 < y < 0.22. The semiconductor-metal transition is clearly observed at nc ≅ 3 mole %; S falls dramatically from S = +850 μ V°K at y = 0.003 to S = +30 μ V°K at y = 0.03. At higher concentrations, S remains nearly constant saturating at +18 μ V°K in the heavily doped metallic polymer. Temperature dependences are consistent with metallic behavior at the highest dopant concentrations and hopping transport in the undoped and lightly doped polymer.

Junction formation with pure and doped polyacetylene

A variety of rectifying junctions have been fabricated using doped and undoped (CH)x. Schottky diodes formed between metallic AsF5‐doped (CH)x and n‐type semiconductors indicate high [CH(AsF5)y]x electronegativity. The p‐type character of undoped trans‐ (CH)x is confirmed by Schottky‐barrier formation with low‐work‐function metals. An undoped p‐ (CH)x : n‐ZnS heterojunction has been demonstrated with an open‐circuit voltage of 0.8 V. These results point to the potential of (CH)x as a photosensitive material for use in solar‐cell applications.

Anomalous electrical properties of linear chain mercury compounds

Abstract The electrical resistivity of Hg 2.86 AsF 6 has been studied as a function of temperature. At room temperature, the resistivity along the chain direction is 10 −4 Ω-cm with an anisotropy of about 10 2 . This incommensurate linear chain system remains metallic at low temperatures with resistance ratio ϱ ab (300 K)/ ϱ ab (1.4 K) ≅ 3000 and still increasing with no apparent sign of residual resistivity. A large anisotropic magnetic field dependence of the resistivity is observed below 30 K. Near 4 K, the c-axis resistance drops abruptly more than three orders of magnitude, apparently to zero, while ϱ ab is continuous. The c-axis transition is suppressed in a small magnetic field.

A ‘metallic’ derivative of polymeric sulphur nitride: poly(thiazyl bromide), (SNBr0·4)x

Crystals and films of (SNBr0·4)x, a derivative of polymeric sulphur nitride, (SN)x, have been characterized; visible and i.r. reflectance and room-temperature conductivity are consistent with metallic behaviour.

Magnetic field induced residual resistivity in quasi-one-dimensional Hg3−δAsF6☆

Abstract The â-b plane resistivity of the Hg-chain compound, Hg3−δAsF6, has been measured as a function of temperature and magnetic field using a contactless ac technique. The data imply a magnetic field dependent residual resistivity which goes to zero as the field is reduced to zero. The results are discussed in terms of the quasi-one-dimensional electronic and structural features of this novel linear chain compound.

Effect of uniaxial stress on electrical conductivity of sulphur nitride polymer

Abstract The effect of uniaxial stress on the room temperature electrical conductivity of polymeric sulfur-nitride is reported. The results provide additional evidence of the importance of interchain coupling on the electrical properties of (SN) x and demonstrate that the perpendicular transport is limited by interfiber contacts.