John A. Osaheni

Efficient photogeneration of charge carriers in a layered photoreceptor using a conjugated polymer

The field‐dependent quantum efficiency φ(E) for photogeneration of charge carriers in a bilayer photoreceptor consisting of a poly(p‐phenylene benzobisthiazole) charge generation layer and a hole transporting layer has been measured by the xerographic photodischarge technique. φ(E) varied from 0.10 at low fields (<105 V/cm) to 0.32 at 106 V/cm. The conjugated polymer‐based photoreceptors have a photosensitivity of 13 ergs/cm2 and negligible dark decay (∼0.2 V/s). Photocarrier generation in the bilayer devices is suggested to be due to field‐assisted dissociation of exciplexes formed between the conjugated polymer and the hole transporting molecule.

Generation and drift of photocarriers in a conjugated ladder polymer

Abstract Generation and drift of photocarriers in thin films of the conjugated ladder polymer, poly(benzimidazobenzophenanthroline) (BBL), are explored by using transient photoconductivity methods. An estimation of a lower limit for photogeneration efficiency of mobile holes is found to be close to 10 −2 at an electric field of 5×10 5 V/cm. The drift of photogenerated carriers is found to be severely range limited by trapping events. In addition persistent decay of photocurrent is detected following the termination of a steadystate monochromatic illumination. The form of the persistent photocurrent suggests a broad range of release times of the trapped carriers which can be attributed to a disorder-induceddistribution of trapping sites.

Channel waveguides of insoluble conjugated polymers

We demonstrate a fast and simple technique of patterning insoluble, nonbleachable, conjugated polymer films into channel waveguides by striploading with photoresist. Two types of coupling gratings were tested for this new system. The coupling parameters, the linear losses and the beam confinement are discussed. This technique makes it possible to explore this class of materials in the field of integrated optics. A new data evaluation method for a more precise measurement of losses in slab waveguides is introduced.

Weak localization, electron-electron interaction, and metal-insulator transition in ion-implanted polymers

Abstract Kr + ion implanted rigid rod PBO, PBT and ladder BBL polymers show similar transport and optical behavior, with room temperature conductivities increasing from 10 −12 S/cm to ∼ 10 2 S/cm after implantation. A metal-insulator transition is observed at T c ∼ 30 K. Above T c , the results of a negative magnetoresistance ( ΔR / R ( H , T )), a weakly temperature dependent conductivity ( σ ( T ) α T p , 0.5 p T -dependent thermopower ( S ( T )), a Pauli spin susceptibility ( χ Pauli ), and a large microwave dielectric constant ( e mw ) resemble those of disordered metals in which weak localization and e-e interactions dominate the charge transport. Below T c , the changed behavior of positive ΔR / R , stronger T -dependent σ , and 1/ T -dependent S with a continued large and positive e mw all suggest an increased e-e interaction effect which opens up a ‘Coulomb’ gap (∼2meV), likely due to the enhanced localization. The density of states (DOS) is zero only at the center of the gap in accord with the theoretical prediction of the ‘Coulomb’ gap.

Nonlinear optical properties of thin film composite materials

Several groups have proposed the use of composite materials as a means of achieving large values of the third-order susceptibility /spl chi//sup (3/). One proposal involves forming a composite of alternating layers of two different materials with layer thicknesses much smaller than an optical wavelength. The angular dependence of the nonlinear optical response of this material can offer a means to determine quantitatively the extent to which the /spl chi/((3)) susceptibility is enhanced. In the present paper, we report the results of our experimental study of this angular dependence. We find that the angular dependence is in good qualitative agreement with theoretical predictions.<<ETX>>