Mohamed S. A. Abdou

Laser, direct-write microlithography of soluble polythiophenes

Abstract Focused laser light of wavelength 442 nm was used to induce photochemical crosslinking in thin films of poly(3-hexylthiophene). Irradiated regions were insoluble and thus patterns of micron resolution could be achieved by dissolution of unexposed regions. The minimum gel dose required to leave an insoluble residue was 7.7 mJ cm −2 and the dose required for 50% gel formation was 61 mJ cm −2 . Patterns of the polymer were oxidized with nitrosonium tetrafluoroborate. The resistance of oxidized polymer channels having dimensions 40 μm wide, 90 nm thick and 200 μm long was 150 kΩ. The bulk conductivity of deposited and oxidized polymer was ∼ 6 Ω −1 cm −1 . Two dominant photochemical mechanisms are present during photolysis: photosensitization of singlet oxygen and Diels-Alder addition of singlet oxygen to thienyl residues; photo-oxidation of the alkyl side chain. The latter is believed to be responsible for crosslinking and photo-insolubilization.

Oxidation of π-conjugated polymers with gold trichloride: enhanced stability of the electronically conducting state and electroless deposition of Au0

Abstract Oxidative doping of thin π-conjugated polymer films using acetonitrile solutions of gold trichloride yields electronically conductive polymers (15 Ω −1 cm −1 ) containing the AuCl 4 − counter ion. Thin oxidized films containing counter ions are orders of magnitude more stable in ambient atmosphere at 25 °C than polymers oxidized using AuCl 4 − conventional oxidants such as iron trichloride. Oxidation of polymer films using solutions of AuCl 3 in nitromethane results in electroless deposition of zero-valent gold in addition to formation of AuCl 4 − -doped polymer. Thick films (> 1 μ m) afford growth of a homogeneous and continuous metallic layer on top of the polymer film. As a result, conductivities of the metal/polymer bilayers are as high as 11 000 Ω −1 cm −1 . Mechanisms of oxidative doping and deposition of gold metal are described.

Microlithography of π-conjugated polymers

In this work the photochemistry and photoimaging of derivatized polythiophenes will be described. Poly(3-alkylthiophenes) are inherently photolabile. One of the photochemical products leads to cross-linking, which can be utilized in photolithography. During this process, (pi) -conjugation remains virtually intact, and conductivities remain the same as the pristine polymer. The photosensitivity of this polymer to cross-linking, and thereby, insolubilization, can be enhanced by copolymerization with thienyl moieties possessing the methacryoyl functionality. In addition to photoimaging, the stability of the conducting state will be discussed. Strategies for enhancing stabilization will be addressed with a view to assimilating organic wires into integrated circuitry.