Properties and applications in chemical sensing: Modification of porous silicon interfaces

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Baker, Caitlin
Gole, James L.
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This thesis will discuss the design of PSi chemical sensors, the enhancement of the sensitivity and selectivity through metal oxide nanostructure depositions, and probe the applications of this technology as a tool to explore interface interaction dynamics. Using the nanostructure-directed modification of the Lewis acid/base character of an analyte-extrinsic PSi semiconductor interface, we have developed the ability to control the degree of electron transduction between an extrinsic semiconductor interface and interacting analyte gases. Based on {the inversion of the} hard/soft acid/base theory (HSAB), the careful selection of nanostructure directed modifications can enhance or impair electron transduction, which can be made to precisely control the increase or decrease the sensor response to a given analyte. This concept has led creation of a general road map, the Inverse Hard/Soft Acid Base (IHSAB) concept, for sensor design. We have demonstrated that the change in conductometric response allows a more detailed monitoring of the interaction of various materials deposited to an extrinsic semiconductor interface in contrast to standard characterization methods such as X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray spectroscopy (EDX). We are now extending the application of PSi sensors to the identification of organic solvents using impedance spectroscopy. Through the use of an equivalent circuit model, we can explore the physical changes of the PSi sensors with a diversity of distinctly interacting metal oxide nanostructure depositions and upon exposure to various organic solvents. Through mobile PSi sensor device development and formulation of a table cataloging materials' effects on interface interactions, we can create a complete interfacial analysis system with applications as a materials characterization tool, a research project starter, and a classroom demonstration of basic and advanced solid state and condensed matter physics concepts.
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