Nanomaterials characterization and bio-chemical sensing using microfabricated devices.

摘要

A variety of nanostructured materials have been synthesized in recent years. These nanomaterials have potential applications in areas spanning computing, energy conversion, sensing, and biomedicine. Because of size confinement effects, furthermore, these nanomaterials are expected to show very different physical properties from those of their bulk counterparts. The measurement of their properties, however, has been very challenging due to their small dimensions. Similarly, it remains a challenge to detect chemical and biomolecular species due to their small dimensions.; This dissertation presents the development of microelectromechanical systems (MEMS) devices for the characterization of thermophysical properties of nanomaterials and for the detection of chemical species and biological cells.; The thermophysical property of one-dimensional (1D) nanomaterials was measured using a batch-fabricated microdevice consisting of two adjacent symmetric silicon nitride membranes suspended by long silicon nitride beams. Three methods were developed to assemble nanomaterials with the measurement devices. Those three methods include a wet deposition process, an in-situ chemical vapor deposition technique, and an electric-field-assisted assembly method. During the measurement, one membrane is Joule-heated to cause heat conduction through the nanomaterials to the other membrane, allowing for the measurement of thermal conductance and Seebeck coefficient. The electrical conductance can also be measured using the microdevice. The temperature-dependent properties of an individual single-wall carbon nanotubes (SWCNs) and SWCN bundles were measured. Measurement sensitivity, errors, and uncertainty were examined. The obtained thermal conductivity of an individual SWCN is found to be much higher than bundles of SWCNs in the range of 2000--11000 W/m-K at room temperature, in agreement with theoretical predictions. Furthermore, the thermal conductivity of bundles of SWCNs are found to be suppressed by contact resistance between interconnected SWCNs in the bundle.; The microdevice has also been integrated with metal oxide nanobelts for chemical sensing. The sensing mechanism is based on surface oxidation-reduction (redox) processes that change the electrical conductance of the nanobelt. The sensor was found to be highly sensitive to inflammable and toxic gas species including nitrogen dioxide (NO2), ethanol, and dimethyl methylphosphonate (DMMP). (Abstract shortened by UMI.)