Date of Award

Summer 2007

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Micro and Nanoscale Systems

First Advisor

Cheng Luo

Abstract

Conducting polymers, since their discovery, have attracted significant attention due to their promise of replacing silicon and metals in building devices. They have been shown to have wide applications for biological and chemical sensing as well as for electronic devices. Previous and current efforts have concentrated on building devices of a specific function. When multiple micropatterns of different conducting polymers are fabricated on a common substrate, a versatile microsystem can be envisioned. The existing conducting polymer patterning techniques present some technical challenges of degradation, low throughput, low resolution, depth of field, and residual layer in producing conducting polymer microstructures. To circumvent these challenges in the existing technology, the Intermediate-Layer Lithography (ILL) method is proposed in this study. This approach overcomes the "depth of field" and "residual layer" issues of the traditional hot embossing process.

Conducting polymer micropatterns of various dimensions have been fabricated. The conducting polymers used for patterning include polypyrrole (PPy), poly(3,4-ethylenedioxythiophen)-poly(4-styrenesulphonate) (PEDOT-PSS), and sulphonated polyaniline (SPANI). Straight and serpentine microwires of various dimensions were fabricated and the embossing recipe was finalized for a stable reproduction of the imprinting results. The fabricated microwires were used for sensing applications using the "chemiresistor" principle. Sensitivities of conducting polymer films and microwires were compared after they were exposed to different levels of humidity. The microwires were found to be more sensitive than films at lower humidity levels. Two sets of microwires of PPy, PEDOT-PSS, and SPANI were imprinted on a common substrate. The imprinted microwires were used for sensing methanol, toluene, and acetone, individually and in mixtures of two gases. Each of the three different conducting polymer microwires was found to be more sensitive to methanol and acetone compared to toluene. An additional layer of glucose oxidase was coated over the PPy microwires to sense for glucose. The response current of the PPy microwires increased with increasing concentration of glucose (0.2 mg/ml–0.8 mg/ml). The relationship between the surface-to-volume ratio of the microwires and their sensitivities was also investigated. PPy and PEDOT-PSS microwires of various dimensions were fabricated and exposed to acetone vapor at low concentrations. The microwires with higher surface-to-volume ratio were found to be most sensitive at lower concentrations of acetone.

PPy nanowires were fabricated effectively using the ILL method. The widths of the wires were 100 nm and 500 nm with lengths of 20 μm. In the near future, we would like to fabricate several different conducting polymer nanowires on a common substrate for sensing operations. Multiple sensors on a common substrate would result in a more functional sensor capable of sensing multiple analytes at very low concentrations.

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