Date of Award

Spring 2004

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Micro and Nanoscale Systems

First Advisor

Hai-Feng Ji

Abstract

The objective of this work is to design and fabricate an advanced silicon dioxide microcantilever sensor and to investigate chemical and biological sensing by microtechnology.

Microcantilever sensor technology has many advantages including fast response time, lower cost of fabrication, the possibility of sensor arrays with small overall dimensions, the ability to explore microenvironments, and improved portability for field applications. For all of these advantages, microcantilever chemical and biological sensors have drawn more and more attention.

So far, all other microcantilevers were designed and fabricated for AFM applications. We developed a novel SiO2 microcantilever especially for chemical and biological sensor applications. First of all, a round tip was added at the end of the microcantilever to ease laser beam injection and 2 μm in thickness was designed to reduce noise disturbance in chemical or biological sensing. Secondly, the SiO2 microcantilever induces much larger deflection compared with the commonly used Si microcantilever due to the SiO2's lower Young's modulus. The SiO2 microcantilever thus has much higher sensitivity than the commonly used Si microcantilevers. So, for the chemically specific reaction between SiO2 and HF, it is feasible to detect femtomolar concentrations of hydrogen fluoride using SiO2microcantilever.

Silicon plasma dry etching was employed to release the SiO2 cantilever from bulk silicon. The spring constant of the cantilevers was measured to be 0.104 N/m.

A fabricated SiO2 microcantilever was used to detect femtomolar concentrations of hydrogen fluoride (HF), a decomposition component of nerve agents.

Also, a SU-8 polymer microcantilever was made by microfabrication techniques. Besides optical detection of microcantilever deflection in a microcantilever sensor system, another detection method known as piezoresistive detection was also developed. A piezoresistive microcantilever was successfully designed and fabricated.

The microcantilever was also developed to monitor impulses. In related research, a superhydrophobic perfluorocarbon nanoneedle surface was successfully synthesized. The water contact angle of this perfluorocarbon surface was measured at 179.8°, which is a record-high contact angle. This research aims at developing microcantilevers with one side covered by superhydrophobic film. In microcantilever surface modification, usually in solution, one surface is fully modified while another side keeps integrated. Maximum differential surface stress is then induced. The superhydrophobic surface was synthesized for this purpose.

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