Publication Date

Spring 2010

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Chemistry

Advisor

Roger H. Terrill

Keywords

capillary, condensation, distribution, modeling, porosimetry, porous silicon

Subject Areas

Chemistry, Analytical; Chemistry, Physical

Abstract

In this study a set of porous silicon (pSi) interferometric vapor sensor were made from p+ (~1 ohm-cm) and p++ (~0.005 ohm-cm) B-doped Si. The pSi layers were prepared electrochemically, stabilized either by ozone oxidation or 1-octene derivatization, and then characterized. FTIR reflection spectroscopy, scanning electron microscopy, and x-ray spectroscopy of pSi layer cross sections confirmed the completeness of the ozone oxidation and 1-octene hydrosilation. The performance of the pSi layers as interferometric ethanol vapor sensors was assessed by constructing calibration curves of optical thickness change versus ethanol partial pressure and using these to assess the detection limits for ethanol vapor sensing. The interferometric calibration curves were analyzed by fitting them to a BET adsorption and capillary condensation model. The model fits the calibration curves using four parameters: two thermodynamic parameters describing physisorption, plus a mean radius and standard deviation describing the pore size distribution. Acceptable fits were obtained for the p+ Si only, and these fits yielded reasonable mean radii that clearly contracted in response to the octene hydrosilation.

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