Date of Award

Spring 1-1-2010

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Mechanical Engineering

First Advisor

Conrad R Stoldt

Second Advisor

Victor M Bright

Third Advisor

David R Kassoy

Abstract

Porous silicon (PS) is a silicon (Si) based material composed of pores with diameters ranging from several nanometers to several micrometers. Typically PS is formed by electrochemically etching a Si wafer in a hydrofluoric acid (HF) based electrolyte. This route requires a custom built etch cell and a power supply and is difficult to integrate with the batch processing techniques of conventional Microsystems fabrication. In the first part of this work, a galvanic etching approach is used to fabricate PS in which neither a power supply nor custom etch cell are required. Galvanic etching methods are developed to fabricate thick, mechanically stable PS on lightly doped p-type Si wafers. A detailed characterization of galvanic PS, including specific surface area measurements, etch rates, high resolution transmission electron microscopy, and photoluminescence measurements, is also presented. As a means to model galvanic Si etching (corrosion) on Si Microsystems, we present a finite element method (FEM) enabled simulation.

In the second half of this work, galvanic PS for nanoenergetics is investigated. Nanoenergetic composite materials are composed of nanometer-scale fuel and oxidizer components that have energy release rates much greater than the bulk materials. In this case, PS fuel is impregnated with sodium perchlorate (NaClO4) oxidizer to yield a nanoenergetic composite. The data presented here include the first measurements of nanoenergetic PS using thermal analysis techniques including bomb calorimetry and differential scanning calorimetry (DSC). Additionally, the reaction products are revealed to be composed of nearly spherical, interconnected nanoparticles of amorphous silica. Using bomb calorimetry, the heat of reaction of galvanic PS-NaClO4 nanoenergetic composites is determined to be 9.9 ± 1.8 kJ/g and 27.3 ± 3.2 kJ/g of PS when ignited under N2 and O2, respectively. DSC, coupled with Fourier transform infrared spectroscopy (FTIR) data, reveals that the energy output is dependent on the hydrogen termination of the PS. Lastly, the flame propagation velocity of the PS-NaClO4 composite is measured with a novel on-chip diagnostic technique and high-speed video data taken at 930,000 frames per second. A velocity averaging ~3,050 m/s is observed, and is currently the fastest velocity reported for nanoenergetic materials.

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