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Spatial, Temporal, and Chemical Aspects of Vapor Detection

Using Conductive Composite Chemically Sensitive Resistors

Thesis by Shawn M. Briglin

In Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy

California Institute of Technology Pasadena, California

2003

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Acknowledgements

When I first arrived at Caltech I was unsure of what group I wanted to join, but

after I walked past the Lewis group labs for the first time, I was immediately certain of

where I wanted to do my thesis research, and I’ve never regretted it. I am grateful to my

thesis advisor, Prof. Nathan Lewis, whom I thank for his support and for his supply of

many excellent suggestions. He’s there when you need him and not when you don’t... the

two most important qualities in a thesis advisor and mentor.

Every member in the Lewis group and several other people at Caltech have also

helped me out at some point, making it impractical to thank them all. Greg Sotzing and

Mike Freund got me started, and I am indebted to both of them for getting me over the

first few hurdles.

I thank my parents for teaching me so much when I was growing up. They

provided me with just the right combination of science books, Lego’s™, and broken-down

kitchen appliances necessary to prepare me for graduate school.

Contrary to what you see in film and television about how boring people are at

places like Caltech, I met some unbelievably cool people there. They know who they are,

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Abstract

We have investigated the vapor response properties of chemically sensitive thin film resistors prepared from conductor-insulator composites. A new sensor type was developed from alkylamine-capped gold nanocrystals, and films of this composite, which are composed of nanometer-scale gold cores separated by regions of insulating

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Table of Contents

Acknowledgements... iii

Abstract... iv

Table of Contents... v

List of Tables... vii

List of Figures... viii

Chapter 1: Introduction...1-1

Overview... 1-2 Organization of Thesis... 1-6 References... 1-7

Chapter 2: Detection of Mercaptan Vapors Using Thin Films of

Alkylamine-Passivated Gold Nanocrystals... 2-1

Abstract... 2-2 Introduction... 2-3 Experimental... 2-7 Results and Discussion... 2-11 Conclusions... 2-15 Acknowledgements... 2-15 Tables... 2-16 Schemes and Figures... 2-17 References... 2-27

Chapter 3: Exploitation of Spatiotemporal Information and Geometric

Optimization of Signal/Noise Performance Using Arrays of Carbon Black-Polymer Composite Vapor Detectors... 3-1

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Results... 3-18 Discussion... 3-29 Conclusions... 3-35 Acknowledgements... 3-36 Tables... 3-37 Schemes and Figures... 3-39 References... 3-59 Appendices... 3-61

Chapter 4: Characterization of the Temporal Response Profile of Carbon

Black-Polymer Composite Detectors to Volatile Organic Vapors... 4-1

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List of Tables

Chapter 2

Table 1 Standardized Human Olfactory Thresholds and Maximum Workplace Concentrations for Several Mercaptan Gases and Vapors ... 2-16

Chapter 3

Table 1 Responses, Noise, and S/N for Two Types of Polymer-Carbon Black Composite Detectors with Geometrically Optimized Form Factors... 3-37 Table 2 Limits of Detection for Carbon Black Polymer Composite

Detectors and Polymer Film SAW Detectors... 3-38

Chapter 4

Table 1 Parameters for, and Results of, Comparisons between Time Profiles of Calculated Responses and the Experimental Responses of Four Different Film Thickness PEVA Detectors... 4-30 Table 2 Response Times and Effective Film Thickness Calculations for a

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List of Figures

Chapter 2

Fig. 1 UV-VIS Absorbance Spectra of a Dodecylamine-Capped Gold Nanocrystal Film Sensor before and after Exposure to Propanethiol Vapor... 2-19 Fig. 2 Resistance vs. Time of a Typical Dodecylamine-Capped Gold

Nanocrystal Sensor on Exposure to 4 ppb CH3SH... 2-20

Fig. 3 Resistance vs. Time of a Typical Dodecylamine-Capped Gold Nanocrystal Sensor on Exposure to 150 ppb CH3SH... 2-21

Fig. 4 Explanation of the Response Descriptor ... 2-22 Fig. 5 Response Descriptor vs. Concentration of CH3SH... 2-23

Fig. 6 Resistance vs. Time of a Dodecylamine-Capped Gold Nanocrystal Sensor on Exposure to 20 ppm Octanethiol Vapor... 2-24 Fig. 7 Resistance vs. Time of a Dodecylamine-Capped Gold Nanocrystal

Sensor on Exposure to 8.6 ppm H2S... 2-25

Fig. 8 Resistance vs. Time of a Dodecylamine-Capped Gold Nanocrystal Sensor on Exposure to Vapors of Acetone, Toluene, and Acetic Acid... 2-26

Chapter 3

Fig. 1 Noise Power Spectral Density vs. Frequency for Seven Different Area PEVA Detector Films... 3-45 Fig. 2 Relative Noise Power Spectral Density vs. Film Volume for Seven

PEVA and Seven PCL Detector Films... 3-46 Fig. 3 QCM Frequency Shift vs. Methanol and Hexane Concentration for

PEVA and PCL Films... 3-47 Fig. 4 Position Sensitive Responses of PEVA Detectors for Three

Different Vapor Pressure Analyte... 3-49 Fig. 5 Position Sensitive Responses of PEVA Detectors for Different

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Fig. 7 Position Sensitive Responses of PEVA and PCL Detectors as a Function of Air Flow-Rate... 3-54 Fig. 8 Responses of PEVA and PCL Detectors with Different Form

Factors and Different Positions in a Vapor Stream... 3-57

Chapter 4

Fig. 1 Shapes of Short Vapor Pulses... 4-35 Fig. 2 Experimental and Calculated Sensor Responses on an Ultrathin

PEVA Detector Film... 4-37 Fig. 3 Experimental and Calculated Sensor Responses on a 510 nm

Thick PEVA Detector Film... 4-39 Fig. 4 Experimental and Calculated Sensor Responses on an 870 nm

Thick PEVA Detector Film... 4-41 Fig. 5 Experimental and Calculated Sensor Responses on a 1030 nm

Thick PEVA Detector Film... 4-43 Fig. 6 Experimental and Calculated Sensor Responses on a 5700 nm

Thick PEVA Detector Film... 4-45 Fig. 7 Log-Log Plot of Sensor Response Times vs. the Squared Film

References

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