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Characterization of conductive polycarbonate films

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Title:
Characterization of conductive polycarbonate films
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English
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Hokenek, Selma
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University of South Florida
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Subjects / Keywords:
Thin films
Organic dye
Transparent
BEDO-TTF dye
Iodine doping
Dissertations, Academic -- Biomedical Engineering -- Masters -- USF   ( lcsh )
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bibliography   ( marcgt )
non-fiction   ( marcgt )

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Abstract:
ABSTRACT: Transparency and conductivity are highly desirable qualities in materials for modern gas sensors. Polymer gas sensors have been developed in which the polymer acts as a solid electrolyte. However, these types of sensors are opaque, which limits their potential for integration with dichromatic materials. The development of a sensor integrating conductive polymer films and dichromatic materials requires the implementation of a transparent conductive polymer film. The potential of iodine-doped bisphenol-a polycarbonate films containing bis(ethylenedioxy)-tetrathiafulvalene (BEDO-TTF) dye for sensor applications will be tested through characterization of the films at various stages of their fabrication using Atomic Force Microscopy (AFM), Transmission Electron Microscopy (TEM), transmission Fourier Transform Infrared Spectroscopy (FTIR), Optical Microscopy (OM), and Four Point Probe conductivity measurements (FPP). FTIR results show that there is an interaction between the polycarbonate matrix and the dye-iodine complex. Measured resistivities of the iodine doped films range from 148 Omega-cm to 2.82 kOmega-cm depending on the concentration of the iodine and exposure time. The imaging techniques used show a significant difference in the structure and the surface of the iodine doped-PC-BEDO-TTF films with respect to the bare polycarbonate films or the films mixed with the organic dye. It is also clear that the surface roughness of the prepared conductive films increases with iodine loading. These films have the potential to be used in sensor or photovoltaic applications.
Thesis:
Thesis (M.S.B.E.)--University of South Florida, 2009.
Bibliography:
Includes bibliographical references.
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by Selma Hokenek.
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Title from PDF of title page.
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Document formatted into pages; contains 93 pages.

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ABSTRACT: Transparency and conductivity are highly desirable qualities in materials for modern gas sensors. Polymer gas sensors have been developed in which the polymer acts as a solid electrolyte. However, these types of sensors are opaque, which limits their potential for integration with dichromatic materials. The development of a sensor integrating conductive polymer films and dichromatic materials requires the implementation of a transparent conductive polymer film. The potential of iodine-doped bisphenol-a polycarbonate films containing bis(ethylenedioxy)-tetrathiafulvalene (BEDO-TTF) dye for sensor applications will be tested through characterization of the films at various stages of their fabrication using Atomic Force Microscopy (AFM), Transmission Electron Microscopy (TEM), transmission Fourier Transform Infrared Spectroscopy (FTIR), Optical Microscopy (OM), and Four Point Probe conductivity measurements (FPP). FTIR results show that there is an interaction between the polycarbonate matrix and the dye-iodine complex. Measured resistivities of the iodine doped films range from 148 Omega-cm to 2.82 kOmega-cm depending on the concentration of the iodine and exposure time. The imaging techniques used show a significant difference in the structure and the surface of the iodine doped-PC-BEDO-TTF films with respect to the bare polycarbonate films or the films mixed with the organic dye. It is also clear that the surface roughness of the prepared conductive films increases with iodine loading. These films have the potential to be used in sensor or photovoltaic applications.
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Characterization of Conduc tive Polycarbonate Films by Selma Hokenek A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Biomedical Engineering Department of Chemical a nd Biomedical Engineering College of Engineering University of South Florida Major Professor: Norma A. Alcantar, Ph.D. Julianne P. Harmon, Ph.D. John Wolan, Ph.D. Date of Approval: March 30, 2009 Keywords: thin films, organic dye, tran sparent, BEDO-TTF dye, iodine doping Copyright 2009, Selma Hokenek

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Dedication I would like to dedicate this work to my wonderful supporting family, who have helped me through all the stressful moments, to my wonderful co-workers, who helped me out when I hit a roadblock, and to those students who take up the thread of this research after me, may their roads be smooth.

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Acknowledgments I would like to thank Dr. Al cantar for giving me this opportunity, Parul Jain and Dr. Harmon, our co-workers in Chemistry, for their tireless efforts and help in so many different aspects of this project, and the National Science Foundation CBET grant 0808053 for supporting this research. I would also like to acknowledge Dr. Saddow and his research group for being so endlessly pati ent in letting me borrow their lab equipment at random intervals. Last, but certainly not le ast, I would like to thank all of the other members of my own research group for everythi ng they have done to help me get through the process of putting to gether this document.

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i Table of Contents List of Figures ............................................................................................................... ..... iii Abstract ...................................................................................................................... ........ ix Chapter One: Introduction .................................................................................................. 1 Chapter Two: Overview of Sensors .................................................................................... 6 2.1. Polycarbonate Sensors and Metal Particles ..................................................... 7 Chapter Three: General Char acterization Techniques ........................................................ 8 3.1. Fourier Transform Infrared Spectroscopy (FTIR) ........................................... 8 3.1.1. Attenuated Total Reflection Fourier Transform Infrared Spectroscopy (ATR-FTIR) ............................................................. 10 3.1.2. Transmission FTIR ......................................................................... 12 3.3. Transmission Electron Microscopy (TEM) ................................................... 12 3.4. Atomic Force Microscopy (AFM) ................................................................. 14 3.5. Four Point Probe ............................................................................................ 18 3.6. Ellipsometry ................................................................................................... 20 3.7. Optical Microscopy ........................................................................................ 20 Chapter Four: Experimental .............................................................................................. 22 4.1. Film Fabrication ............................................................................................. 22 4.2. Four Point Probe Experiments ....................................................................... 24 4.3. FTIR Settings and Information ...................................................................... 25 4.4. TEM Images................................................................................................... 26 4.5. AFM Surface Scans ....................................................................................... 26 4.6. Optical Microscopy ........................................................................................ 26 Chapter Five: Results and Analysis .................................................................................. 27 5.1. Four Point Probe Studies ............................................................................... 27 5.2. Imaging Analyses ........................................................................................... 37 5.3. FTIR Analyses and Their Correl ation with Imaging Results ........................ 47 Chapter Six: Possible Future Trends ................................................................................. 58 Chapter Seven: Summary ................................................................................................. 59 References .................................................................................................................... ..... 62

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ii Appendices .................................................................................................................... .... 66 Appendix A: Conductivity Data ........................................................................... 67 Appendix B: Optical Microscopy Data ................................................................. 73 Appendix C: AFM Imaging .................................................................................. 76 Appendix D: TEM Images .................................................................................... 93

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iii List of Figures Figure 1: Structure of Bis(ethylenedi oxy)-tetrathiafulvalene (BEDO-TTF). ......................2 Figure 2: Structure of Bisphenol-a Polycarbonate. ..............................................................4 Figure 3: Schematic of the Structure Pla nned for the Explosives Sensor Proposed ............5 Figure 4: Schematic of the Princi ples Behind AFM Surface Imaging. .............................15 Figure 5: Circuit Diagram for a Standard Wheatstone Bridge. .........................................16 Figure 6: Schematic Representation of a Piezoelectric Tube Scanner. .............................17 Figure 7: Probe Designations as Used in Four Point Probe Method. ................................18 Figure 8: Methods of Vapor Doping Used in This Study. .................................................24 Figure 9: Measurement Methods used to quantify the Resistan ce of Films doped with Method 1 and Method 2. ..........................................................................25 Figure 10: Method Used to Test F ilms Containing 1 wt% BEDO-TTF for Conductivity .....................................................................................................28 Figure 11: Current-Voltage Data for P-doped Silicon Wafer. ...........................................29 Figure 12: Current-Voltage Data for Op timization of Iodine Exposure for 12 mg/mL solution. ...............................................................................................30 Figure 13: Resistivity versus Expos ure Time for 12 mg/mL solution. ..............................31 Figure 14: Current-Voltage Data for 12 mg/mL Iodine Solution Concentration Exposed for Two Minutes using Method 1 ......................................................32 Figure 15: Current-Voltage Data for 12 mg/mL Iodine Solution Concentration Exposed for Three Minutes using Method 2.. ..................................................33 Figure 16: Resistance versus Distance for Films Doped Using Method 1. .......................34 Figure 17: Resistance versus Distance for Films Doped Using Method 2. .......................34

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iv Figure 18: Average Resistivities of Film s and Reference Materials: p-Si (100) Wafer, Polyaniline, Polypyrrole, Gold, and Copper ........................................36 Figure 19: Flowchart Showing the Change s in Transparency Before and After Doping..............................................................................................................38 Figure 20: AFM Images of the Polycar bonate Films With (right) and Without (left) BEDO-TTF Dye. .....................................................................................39 Figure 21: Optical Microscope Images of PC and PC/BEDO-TTF Films Under 100x and 400x Magnification. .........................................................................40 Figure 22: Optical Microscopy Images of the 8 mg/mL Doped Film Taken at 25x and 100x. ..........................................................................................................41 Figure 23: AFM Surface Topography and Ph ase Scans of Films Doped With Method 2. Images were taken in 0.5 m x 0.5 m size. ..................................42 Figure 24: Optical Microscopy Images of the Films Doped in the Three Different Iodine Solution Concentrations Taken at 100x and 400x. ...............................44 Figure 25: Surface Roughness Calculated From the AFM Images of Films Doped with Methods 1 and 2. ......................................................................................44 Figure 26: OM and TEM Images of the Polycarbonate and Polycarbonate/BEDOTTF Films. .......................................................................................................45 Figure 27: OM and TEM Images of the Film s Doped in the Three Different Iodine Solutions. .........................................................................................................46 Figure 28: FTIR Spectrum of U npurified Neat Polycarbonate ..........................................47 Figure 29: Numbered Structure of Bisphenol-A Polycarbonate ........................................48 Figure 30: FTIR Spectra of the Control Films and Doped Films for Method 1. ...............49 Figure 31: Expanded View of the Carbonyl Region of the Spectra Shown in Figure 30 ..........................................................................................................50 Figure 32: Expanded View of the Spect ral Peak From Figure 30 Which is Attributed to the Resonance Frequency of the Para-Substituted Phenol Rings. ...............................................................................................................51 Figure 33: FTIR Spectra of the Poly carbonate and Polycarbonate/BEDO-TTF Films ................................................................................................................52

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v Figure 34: FTIR Spectra of the F ilms Fabricated Using Method 2. ..................................53 Figure 35: Expanded View of the Carbonyl Region For Spectra of Films Made Using Method 2................................................................................................54 Figure 36: Expanded View of the Para-Substitution Peak Seen in the Spectra of Films Prepared Using Method 2 ......................................................................55 Figure 37: Expanded View of the Regi on of the Spectrum Surrounding the Thiol Ring Stretch Due to the BEDO-TTF Dye ........................................................56 Figure 38: Expanded View of the Spectra l Region Surrounding the Thiol (C-S) and Ether (O-C-O) Stretches Due to the BEDO-TTF Dye. .............................57 Figure 39: Current-Voltage Data fo r 12 mg/mL Solution Optimization. ..........................67 Figure 40: Resistivity versus E xposure Time for 12 mg/mL Solution Optimization.. ..................................................................................................67 Figure 41: Current-Voltage Data fo r 8 mg/mL Solution Optimization.. ...........................68 Figure 42: Resistivity versus Exposure Ti me for 8 mg/mL Solution Optimization. .........68 Figure 43: Current-Voltage Data fo r 4.3 mg/mL Solution Optimization. .........................69 Figure 44: Resistivity versus E xposure Time for 4.3 mg/mL Solution Optimization. ...................................................................................................69 Figure 45: Resistivity versus Exposure Time Optimization For All Three Solutions. .........................................................................................................70 Figure 46: Current-Voltage Data for 8 mg/mL Iodine Solution Concentration Exposed for Four Minutes using Method 1. ....................................................70 Figure 47: Current-Voltage Data for 8 mg/mL Iodine Solution Concentration Exposed for Four Minutes using Method 2. ....................................................71 Figure 48: Current-Voltage Data for 4.3 mg/mL Iodine Solution Concentration Exposed for Ten Minutes using Method 1 .......................................................71 Figure 49: Current-Voltage Data for 4.3 mg/mL Iodine Solution Concentration Exposed for Ten Minutes using Method 2. ......................................................72 Figure 50: OM Images of Polycarbonate Film at 25x, 100x, and 400x. ............................73

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vi Figure 51: OM Images of Polycarbonate/BEDO-TTF Film at 25x, 100x, and 400x..................................................................................................................73 Figure 52: OM Images of 12 mg/m L Doped Film at 25x, 100x, and 400x. ......................74 Figure 53: OM Images of 4.3 mg/m L Doped Film at 25x, 100x, and 400x. .....................74 Figure 54: OM Images of 12 mg/m L Doped Film at 25x, 100x, and 400x. ......................74 Figure 55: OM Images of 8 mg/mL Doped Film at 25x, 100x, and 400x. ........................75 Figure 56: OM Images of 4.3 mg /mL Doped Film at 100x, and 400x. .............................75 Figure 57: 10 m Square AFM Scan of Undope d Bis-phenol-a Polycarbonate Film. .................................................................................................................76 Figure 58: 10 m Square AFM Scan of Polycarbonate/BEDO-TTF Composite Film ..................................................................................................................76 Figure 59: 10 m Square AFM Scan of 12 mg/mL Doped Film .......................................77 Figure 60: 10 m Square AFM Scan of Noncond uctive Area of 8 mg/mL Doped Film. .................................................................................................................77 Figure 61: 10 m Square AFM Scan of Conductive Area of 8 mg/mL Doped Film.. ................................................................................................................78 Figure 62: 10 m Square AFM Scan of the conductive area of the 4.3 mg/mL Doped Film.. ....................................................................................................78 Figure 63: 5 m Square AFM Scan of the Polycarbonate Control Film.. .........................79 Figure 64: 5 m Square AFM Scan of the Polycarbonate/BEDO-TTF Control Film. .................................................................................................................79 Figure 65: 5 m Square AFM Scan of 12 mg/mL Doped Film. ........................................80 Figure 66: 5 m Square AFM Scan of the N onconductive region of the 8 mg/mL Doped Film. .....................................................................................................80 Figure 67: 5 m Square AFM Scan of the C onductive region of the 8 mg/mL Doped Film. .....................................................................................................81 Figure 68: 5 m Square AFM Scan of the C onductive region of the 4.3 mg/mL Doped Film. .....................................................................................................81

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vii Figure 69: 2 m Square AFM Scan of the Polycarbonate Control Film. ..........................82 Figure 70: 2 m Square AFM Scan of the Polycarbonate/BEDO-TTF Control Film. .................................................................................................................82 Figure 71: 2 m Square AFM Scan of the 12 mg/mL Doped Film.. .................................83 Figure 72: 2 m Square AFM Scan of the N onconductive Area of the 8 mg/mL Doped Film. .....................................................................................................83 Figure 73: 2 m Square AFM Scan of the Conductive Area of the 8 mg/mL Doped Film. .....................................................................................................84 Figure 74: 2 m Square AFM Scan of the Conductive Area of the 4.3 mg/mL Doped Film.. ....................................................................................................84 Figure 75: 10 m Square AFM Scan of Film Doped Using 12 mg/mL solution and Method 2 for 3 minutes. ...................................................................................85 Figure 76: 10 m Square AFM Scan of Film Doped Using 8 mg/mL solution and Method 2 for 4 minutes. ...................................................................................85 Figure 77: 10 m Square AFM Scan of Film Doped Using 4.3 mg/mL solution and Method 2 for 10 minutes. ..........................................................................86 Figure 78: 5 m Square AFM Scan of Film Doped Using 12 mg/mL solution and Method 2 for 3 minutes. ...................................................................................87 Figure 79: 5 m Square AFM Scan of Film Doped Using 8 mg/mL solution and Method 2 for 4 minutes. ...................................................................................87 Figure 80: 5 m Square AFM Scan of Film Doped Using 4.3 mg/mL solution and Method 2 for 10 minutes.. ................................................................................88 Figure 81: 2 m Square AFM Scan of Film Doped Using 12 mg/mL solution and Method 2 for 3 minutes. ...................................................................................89 Figure 82: 2 m Square AFM Scan of Film Doped Using 8 mg/mL solution and Method 2 for 4 minutes. ...................................................................................89 Figure 83: 2 m Square AFM Scan of Film Doped Using 4.3 mg/mL solution and Method 2 for 10 minutes. .................................................................................90 Figure 84: 0.5 m Square AFM Scan of Film Doped Using 12 mg/mL solution and Method 2 for 3 minutes. ............................................................................91

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viii Figure 85: 0.5 m Square AFM Scan of Film Doped Using 8 mg/mL solution and Method 2 for 4 minutes.. ..................................................................................91 Figure 86: 0.5 m Square AFM Scan of Film Doped Using 4.3 mg/mL solution and Method 2 for 10 minutes. ..........................................................................92 Figure 87: TEM – Iodine Deposit TEM Scans. .................................................................93

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ix Characterization of Conductiv e Polycarbonate Films Selma Hokenek ABSTRACT Transparency and conductivity are highly desirable qualities in materials for modern gas sensors. Polymer gas sensors have been developed in which the polymer acts as a solid electrolyte. However, these type s of sensors are opa que, which limits their potential for integration with dichromatic materials. The development of a sensor integrating conductive polymer films and dichromatic materi als requires the implementation of a transparen t conductive polymer film. The potential of iodine-doped bisphenol-a polycarbonate films containi ng bis(ethylenedioxy)-tetrathiafulvalene (BEDO-TTF) dye for sensor applications will be tested through ch aracterization of the films at various stages of their fabrica tion using Atomic Force Microscopy (AFM), Transmission Electron Microscopy (TEM), tr ansmission Fourier Transform Infrared Spectroscopy (FTIR), Optical Microscopy (OM), and Four Point Probe conductivity measurements (FPP). FTIR results show th at there is an inte raction between the polycarbonate matrix and the dye-iodine comple x. Measured resistivit ies of the iodine doped films range from 148 -cm to 2.82 k -cm depending on the concentration of the iodine and exposure time. The imaging techniqu es used show a significant difference in the structure and the surface of the iodine doped-PC-BEDO-TTF films with respect to the bare polycarbonate films or the f ilms mixed with the organic dye. It is also clear that the

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x surface roughness of the prepared conductive film s increases with iodine loading. These films have the potential to be used in sensor or photovolta ic applications.

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1 Chapter One: Introduction The aim in the development of sensors is to design a device which will minimize or even eliminate the time lapse between sa mple preparation and measurement that is inherent in traditional laborator y methods, and be of a configur ation that is ready for field studies. This miniaturization is necessary in order to provi de an easily portable device. Additional improvements are needed to ensure continuous quantitati ve or qualitative analysis, while maintaining the precision and accuracy of traditional laboratory methods. In the past, a variety of approaches have been used in the attempt to develop a good solution to this problem. One of the bi g successes has been in the development of microchips and integrated processors. The a dvantage of having microchips and integrated processors is their ability to conduct curre nt. Conductivity is a quality that is highly desirable in modern sensors. The application of polymer mate rials has also been proposed for a number of different applications in the field of sensors. Polymer sensors have been developed to measure a vast number of differe nt reactions and even cell types, ranging from the quantification of CD4+ lymphocytes [1], to piezoelectric sensors [2], and the sensing of nitrites [3]. There are also a number of different applic ations of polymers in the field of gas sensing, such as vapor-detection of organi c compounds [4]. Many of these polymer gas sensors generally rely on the conductive pr operties of the polymer itself, as a solid electrolyte [5]. There are no known organi c superconductors, but a number of organic superconducting charge-transfer complexes are known [6].

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2 Certain organic compounds, such as pol ymers, can be transformed to be conducting if they are exposed to iodine vapor s. These include polyacetylene [7], whose improved electrical properties were discove red in the late 1970s, and nanocomposites such as bisphenol-a polycar bonate and bis(ethylenedioxy) -tetrathiafulvalene (BEDOTTF) which were developed later [8]. The in crease in the conductivity of polyacetylene was marked, as shown by Shirakawa et al in 1997, and Chiang et al in 1978. The conductivity of the polya cetylene rose by a factor of about 11 orders of magnitude [9, 10]. At a doping of roughly 2%, using the iodine vapor treatment, the charge carriers are free to move along the polymer chains resulting in metallic behavior. Subsequently, in 1989, Suzuki et al. succeeded in making bi s(ethylenedioxy)-tetrathiafulvalene (BEDOTTF) [11]. A schematic of the st ructure of the dye used in th is project to induce electron movement is shown in Figure 1. This compound, mixed with polymer, has been shown to increase electron mobility after being dope d with iodine because the dye/iodine combination acts as a charge carrier, resulting in metallic behavior [8]. Figure 1: Structure of Bis(ethylene dioxy)-tetrathiafulvalene (BEDO-TTF). Tetrathiafulvalene and related molecu les, such as the BEDO-TTF shown in Figure 1, can function as electron donors sinc e they have short S-S contacts between molecules within their volume which provide the added dimensionality that must exist for superconducting coherence [6]. Work has been presented by Elsenbaumer et al. [6] that

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3 describes in detail the conceptual desi gn and methods of making conductive polymer films out of tetrathiaf ulvalene derivatives. The strong tendency of BEDO-TTF toward self-aggregation leads to the low energetic cost of the formation of two-dime nsional organic layers [12]. This, together with a low adiabatic ionization potential of 6.12 eV [13], is what allows BEDO-TTF to form conductive complexes with a wide variet y of organic acceptors and various anions [14]. Others use the approach of embeddi ng conductive nanomaterials within an insulating polymer matrix[15-17]. The polymer matrix is used to stabilize the particles in the form of a nanocomposite, which in turn is used for the fabrica tion of devices [18, 19]. The research that will be presented in Chapters Five and Six focuses on the characterization of thin po lycarbonate films that have been exposed to different concentrations of BEDO-TTF and iodine vapors. The long term goal of the project is the eventual development of a polycarbonate tran sparent and conductive thin film sensor for the detection of explosives, specifically nitroamines and peroxides, as will be shown in Figure 3. The baseline conductivity after the addition of the BEDOTTF dye, iodine, and gold nanoparticles is expected to reach levels high enough to enable the easy use of a voltimetric or amperometric approach to cr eate a sensor which will warn of any vapors that it comes into contact with, using, for example, a dichromatic substrate which will change color based on the voltage or current across the film. This would have a wide variety of applications in areas such as defense against chemical attacks or attacks that rely on improvised explosive devices (IEDs).

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4 The polycarbonate film itself is not exp ected to have a very good electrical conductivity, due to the nature of the pol ymer itself. Instead, polycarbonate has a reasonable resistance to changes in temper ature, good dimensional stability, and low creep. However, it has only a limited chemical resistance and tends to undergo environmental stress cracking [20]. Polycarbonate has the additional advantages of being transparent, allowing it to be used in conj unction with dichromatic materials, and being very easily available. The low cost and wi de availability are very desirable from a manufacturing standpoint, since they drama tically lower the cost of production. The structure of the polycarbonate used in this study is shown in Figure 2. Figure 2: Structure of Bisphenol-a Polycarbonate. Once the dye has been added to the pol ycarbonate film and doping with iodine has taken place, a transformation which renders the film conductive is expected to take place due to the formation of a complex between the iodine and the dye. Gold nanoparticles will be added to improve the conduc tivity of the films, but their preparation and characterization is out of the scope of this thesis.

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5 Polymer + dye Dopant Gold nanoparticles Gold nanoparticles Figure 3: Schematic of the Structure Planned fo r the Explosives Sensor Proposed. The sensor consists of three main components : the polymer matrix containing th e dye, the dopant, and the gold nanoparticles that will allow for the creat ion of surface active sites in future.

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6 Chapter Two: Overview of Sensors Generally speaking, the aim in developing se nsors is to minimize or eliminate the time lapse between sampling and analysis wh ere possible, thus providing continuous quantitative or qualitativ e analysis, while also maintaini ng the precision and accuracy of traditional laboratory methods of analysis [21]. Transparent polymers such as polycarbonate and gold nanoparticle s have been used in a variety of sensors in the past, including biosensors, as can be seen by the num ber of papers published that relate to the use of polycarbonate or gold for biosensors; for instance, nanopart icles and other nanoscale materials have been tested for applica tions in biosensors for analytical chemistry [22], biomolecular interacti on analysis [23], and the fa brication of enzyme-based biosensors [24-26], among others. Some of the most important applicati ons for sensors include how to detect explosives. For example, a sensor was developed by Doroshkin et al using cymantrene in a polystyrene matrix for the detection of explosives on surfaces [27]. The use of cymantrene is attractive in this application because it turns a brilliant blue after coming into contact with the explosives and bei ng exposed to UV light for a short time [28]. Similarly, sensors based on gold nanoparticles have been devi sed and their effectiveness has been probed by several groups [22, 29-33]. However, they generally tend to be very expensive or difficult to interpret. Zeo lites [34] and metallocene-doped conjugated polymers [27, 28, 35, 36] have also been used in similar applications.

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7 2.1. Polycarbonate Sensors and Metal Particles Polycarbonate has been used for a number of applications in the development of sensors. For example, as reported by Nanto et al., polycarbonate was incorporated into a device used to monitor for the presence of harmful gases [37]. Conductive polycarbonate composites have also been fabricated for the detection of dichloromethane (DCM) and toluene [38]. This type of sensing is base d on diffusion forces; the composite contains conducting pathways within its volume whose connections are broken when the solvent molecules that the composite is sensitive to diffuse through the composite [38]. It is expected that polyca rbonate films containing a n early even distribution of BEDO-TTF throughout its volume will form conducting pathways when doped with iodine. Most of these pathways will be near th e surface of the film, due to the tendency of the iodine to deposit on the film surface and form crystals. Polycarbonate has also been used as a matrix for the development of a process to prec ipitate nanoparticles in situ [39]. This precipitation process could potentially have applications in the refinement of the fabrication of our films, as regards th e incorporation of the gold nanoparticles. Additionally, De and Kundu [29] have repor ted on a gold nanocluster doped organicinorganic hybrid coating that was applied to polycarbonate substrates, where it acted as an abrasion resistant protective layer. This suggests that perhaps our films can be made abrasion resistant, as well, in turn making them more stable and robust as sensors.

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8 Chapter Three: General Characterization Techniques 3.1. Fourier Transform Infrar ed Spectroscopy (FTIR) In principle, Fourier Transform Infrared Spectroscopy is a reliable and relatively simple analytical technique. A beam of li ght with a known frequency in the infrared range is passed through a sample, and the am ount of light absorbed by the sample is measured by comparing the beam passing through the sample with a reference beam. This is repeated for wavelengths in the IR region. Another measurement commonly used in FTIR spectroscopy is called the wavenumber. It is easier to refer to the wavenumber at which a peak appears because wavenumbers corr elate to energy direc tly. This is not the case when using wavelengths, which have a more complicated relationship with the energy they correlate to [40] Wavenumbers are related to wavelength by the relationship: ) ( 10000 ) (1m wavelength cm wavenumber eq. 1 FTIR spectroscopy works by exploiting the very nature of the interatomic bond. All pairs of covalently bonded atoms have a characteristic frequency at which they will vibrate or rotate. These charac teristic frequencies are determ ined by the discrete energy levels, or vibrational modes, at which a given covalent bond can resonate. This is determined by a number of factors, including the masses of the atoms, and the presence of a dipole moment. A molecule is IR active if there is a permanent dipole moment,

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9 which is free to resonate when energy is adde d in the form of IR li ght [40]. As a result, the characteristic frequencies of the vibrations can be associated with a particular bond type. In the case of a simple diatomic mol ecule, there is only a single bond, which may stretch when energy is added, fo r example, in the form of in frared light. In more complex molecules, there are many bonds, and vibrations can be conjugated. This leads to the absorption of infrared light at characteris tic frequencies that correspond to chemical groups. For example, the atoms that comprise a CH2 group have six different, distinct, modes of vibration: symmetrical and asym metrical stretching twisting, rocking, scissoring, and wagging. According to the convention that has gr own around the use of spectroscopy, the wavelengths used in infrared spectroscopy have been classified into three broad categories: far-, mid-, and near-infrared. In far-infrared (FIR) spectroscopy, the wavenumbers examined range from 400 to 10 cm-1. FIR spectroscopy is useful mainly for the examination of the quantum vibrational stat es of gases [41]. In the mid-infrared range lie wavenumbers of 4000 to 400 cm-1, and in the near-infrared (NIR) 14000 to 4000 cm-1. Those wavelengths in the mid-infrared are usually used to study fundamental intramolecular vibrations, and the near-infrared can be us ed to excite overtone or harmonic vibrations in molecules. When a beam of IR light is generated, it is split into two separate beams using a half-silvered mirror. One of them is passe d through the sample, and the other through a reference. When working with liquid samp les, the reference used is usually the substance’s solvent. Then, both beams are direct ed back towards a splitter, which is used

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10 to quickly alternate which of the two beam s reaches the detector. The two signals are compared, and a plot of the absorbance is generated. The IR spectrum of a sample is collecte d by shining a monochromatic beam at the sample which changes wavelength over time, or by using a Fourier transform instrument which allows you to measure all wavelengths at once. Once this has been completed, the information is generally sent to a computer to be decoded using a program devoted to the task. After the transmittance at each wavelengt h has been calculated by the program, the spectrum of the sample is then displayed. The analysis of this signal yields much information about the molecular structure of the specimen of intere st. Samples with only a few IR active bonds and high levels of purity will generate simple spectra. The more complex the molecular structure, the more p eaks in the spectrum, and in some instances, the peaks need to be deconvoluted to extract all the information pres ent in the spectrum. The use of the reference prevents fluctuat ions in the output of the source from affecting the data, and allows the signal of th e solvent to be subtracted from the signal of the sample being analyzed, leaving only th e signal of the sample we wish to see. 3.1.1. Attenuated Total Reflection Fourier Tr ansform Infrared Spectroscopy (ATR-FTIR) Attenuated Total Reflection (ATR), is a spectroscopic technique that has the sensitivity to detect very low concentrations of sample near the crystal. In this study, ATR-FTIR is used to study the spectra of fabri cated films. The way measurements are performed is fa irly simple: a beam of IR light is passed through an ATR crystal, which is usually made from zinc selenide (ZnSe) or

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11 germanium. This crystal has th e property of being transparen t to the IR beam and has a relatively high refractive index. The IR beam is aimed in such a way that it is internally reflected within the crystal at least once. This reflection should take place where the crystal is in contact with the sample of interest for the best results. If this does not occur, the spectroscopic signal of the sample will not be well defined or clean. In the setup used for this study, the beam was bounced about twel ve times. This dramatically increases the likelihood that the sample will be in near the crystal in at l east one of the places where the beam bounces. The beam reflected by the sample is then collected by a detector once it has exited the crystal. The reflection of th e light beam off the in ternal surface of the crystal forms what is known as an evanescent wave, which penetrates into the sample to a depth of a few micrometers. This phenomenon is used in ATR-FTIR to examine the structure of the sample the wave comes in to contact with. After the evanescent wave interacts with the sample – liquid or solid – it passes back into the crystal and eventually back to the detector, where it is compared w ith the reference beam. This effect is most efficient when the crystal is made of a material whose optical properties include a refractive index higher than that of the samp le. A solid sample is simply pressed into contact with the crystal, and held in place using a clamp or a press to prevent trapped air from distorting the signal. In the case of a liquid sample, th ere must be a shallow layer over the crystal. This is achieved by injecting the liquid into a flow cell, which creates a thin layer of fluid on the crystal.

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12 3.1.2. Transmission FTIR Transmission FTIR is done primarily on so lid samples, such as polymer films, since it requires the sample to be perpendicula r to the beam of IR light, a feat that is difficult to accomplish with a liquid sample. In the case of liquid samples, it is customary to utilize a super-sealed liquid cell with plates made from i onic salts, such as calcium Fluoride (CaF2), which are transparent to IR light. In this method, the IR light beam is passed directly through the sample and to th e detector. The amount of light reaching the detector (I) through the sample is compared with the amount of light generated by the IR light source (I0) to calculate the transmittance of the sample. Transmittance follows the relationship: oI I T eq. 2 The results can be plotted as percent tran smittance, though absorbance is most commonly used. Absorbance is calculated us ing the following relationship: ) ( log log0 10 10I I T A eq. 3 3.3. Transmission Electron Microscopy (TEM) TEM has its roots in the years just preced ing the Great Depression. The very first TEM was built by Max Knoll, and Ernst Ru ska in Germany during 1931 [42]. The group

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13 went on to develop the first TEM with a re solving power greater than light two years later, and refining it into a commercial device in 1939. In TEM, a beam of electrons is directed at an ultra thin sample, where the electrons interact with the sample as they pass through it. The imaging is done by reconstructing an image of the sample ba sed on the electrons transmitted through the specimen. This image is magnified and pr ojected onto a device which can display and save the image, like, for example, a fluor escent screen, photographic film, or a CCD camera. TEM yields images of far greater magnifi cation than those that can be produced with an optical microscope, due to the di fference in the de Broglie wavelengths of electrons and photons. That is, the de Broglie wavelength of the electron is much smaller than that of the photon [43]. This is what allows the instrument to examine extremely small objects and fine detail, right down to a single column of atoms. The most common mode of operation for im aging with a TEM is what is known as bright field imaging mode. In bright field mode, the contrast formation can be said to be formed directly by the number and position of the electrons that penetrate the sample. This results in thicker regions of the samp le, or areas with a higher atomic number, appearing dark, while regions with no sa mple in the beam path appear bright. The technique of TEM does have some dr awbacks, however. One such limitation lies in the fact that many materials require extensive preparation before a sample thin enough to be electron transparent can be produced. Then there is also the possibility that the structure of the sample may be changed dur ing this processing or that the sample may be damaged by the electron beam, especially in the cases of bi ological or polymer

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14 samples. In addition to all of these limitations one must also keep in mind that the field of view is very small, and the region anal yzed is not necessarily characteristic of the whole sample. Of course, there is a very simple solution to this last problem: to take images of several regions of the sample. 3.4. Atomic Force Microscopy (AFM) In AFM, rather than using photons or el ectrons, one uses a nanoscale cantilever with a very sharp tip to raster scan the su rface of the specimen being imaged (this works like the record players of the 1960s and 70s but at the nano scale). This tiny cantilever is usually made from materials such as silicon or silicon nitride, and th e tip has a radius of curvature on the order of ten nanometers. Wh en the minuscule silic on tip is brought close to the sample surface to be imaged, the fo rces generated by the interactions between surface atoms and the tip cause the cantilever to bend. The de flection in the cantilever tip follows Hooke's law, due to the scale of th e distances involved. The image of the surface is created by a computer hooked up to a dete ctor, made up of an array of photodiodes, that tracks the movement of the cantilever using a laser that is reflected off the cantilever's surface near the tip. Any de flection of the cantilever results in a corresponding deflection in th e position of the laser beam reaching the detector. A schematic diagram of how the cantilever inte racts with the surface of a sample can be seen in Figure 4. Depending on the situation and specimen, a variety of different forces can be measured using AFM. These include mechani cal contact force, van der Waals forces,

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15 electrostatic forces, and magnetic forces, among others. We have used this technique to determine the morphological characte ristics of our conductive films. There are other methods, such as optical interferometry and pi ezoresistivity, that have been developed to improve the se nsitivity of the AFM measurements. A piezoelectric cantilever, acting as a mechano-electric transdu cer, adds a cross-check to the optical methods used to track the deflect ions of the laser beam improving the surface image accuracy. Figure 4: Schematic of the Prin ciples Behind AFM Surface Imaging. The cantilever tip is brought into contact with the surface, a nd then is moved back and forth ov er the surface. In the process of performing this scan, the cantilever will deflect ba sed on the height of th e surface features it encounters, thereby causing the beam of the infrared laser to deflect. From these deflections a 3-D image is generated. Using a Wheatstone bridge, the strain in the cantilever can be measured. This method is not as sensitive as laser deflecti on or interferometry. More information on how the Wheatstone Bridge works is referenced for the interested reader [44, 45].

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16 Briefly, the Wheatstone Bri dge is assembled out of two fixed resistors, one variable resistor, and the sample, as shown in Figure 5. When the current within the circuit is adjusted to zero by manipulating the variable re sistor, the resistance of the unknown sample may be calculated using Oh m’s Law[46] and the combination of Kirchoff’s Current Law[46] and Kirchoff’s Voltage Law[46]. In Figure 5, the known resistances are labeled R1, and R2. The name given to the variable resistor is R3. The source voltage is labeled Vs, and the unknow n resistance is labeled X. The current sourced is denoted by Is. In a nutshell, when the current sourced is zero, the resistances R1+R2 = R3+X. Since R1 and R2 are known valu es, and the resistance of the variable resistor can easily be determined, the resi stance of the sample can be calculated. Figure 5: Circuit Diagram for a Standard Wheatstone Bridge. Wh en Is is equal to zero, the resistances R1+R2 = R3 + X. From Ohm’s Law an d Kirchoff’s Current Law, the unknown resistance X can be calculated. Scanning a specimen with the cantilever kept at a fixed height can cause collisions between the cantilever and the surf ace, resulting in potentially severe damage

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17 to the cantilever tip. In order to minimize the risk of breaking the ti p of the cantilever, a feedback mechanism within the AFM machine is controlled with specialized software that is designed to automatically adjust a nd maintain the distance between the tip and the sample, as shown in Figure 4 [47]. Traditionally, the sample to be imaged is placed on a piezoelectric tube, as depicted in Figure 6, allowing the sample to move in the z-direc tion for the purpose of maintaining a constant force between the cantilever tip and the sample surface. In this case, the x and y directions are used for scanning the sample. Alternatively a configuration, known as a 'tripod' configuration, incorporating three piezoelectric crystals can be used. One piezoelectric crystal is respons ible for scanning in each of the x, y and z directions, as depicted in Figur e 6. This design eliminates so me of the distortion inherent in the use of a t ube scanner [48]. Figure 6: Schematic Representation of a Piezoelectric Tube Scann er. Shown are the five electrodes needed in +x, -x, +y, -y, and z. [48]

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18 The AFM can also be operated in a number of different imaging modes, depending on the material and morphology of the specimen: “static” or contact modes that are generally used for “hard” samples such as silicon carbide, and a variety of “dynamic” non-contact modes, such as tapping mode, which are more useful for “soft” surfaces such as polymers and biological cells [49]. 3.5. Four Point Probe A four point probe is an instrument with four elec trodes spaced evenly along a line. The design is based on a technique devi sed in the late 1950s by van der Pauw, an engineer working for Phillips [50, 51]. Th e four prongs of the four point probe are designated with a number as shown in Figure 7. Figure 7: Probe Designations as Used in Four Point Probe Method.

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19 The two outermost electrodes are used to supply a constant current, and the inner two are connected to a volt-meter. If we ta ke the spacing between the electrodes to be d t to be the film thickness, and the slab of material is assumed to be so much larger than the spacing as to appear infi nite, the resistivity, is given in micro-ohm-meters ( -m) by the following equations [52]: I dV 2 for t>>s eq. 4.a I tV ] 2 [ln for s>>t eq. 4.b A quick dimensional analysis of equations (4.a) and (4.b) yields the following: ] [ ] ][ [ A V m for t>>s eq. 5.a ] [ ] ][ [ A V m for s>>t eq. 5.b Both equations are given in units of vo lt-micrometers over amperes, which then can be readily converted into the conventional units of re sistivity by recognizing that volts over amperes are actually ohms ( ). This then leaves us with an equation that gives a result in units of -m. This technique could be used to measure a film's thickness, as might be inferred by the thickness term in equation (4.b), but it is generally used to measure the electrical conductivity of a thin layer, or th e bulk resistivity of bare wafers.

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20 The drawback of this method is its te ndency to cause minor surface damage and leave small deposits of metal on the sample, and, while this damage is not severe, it is sufficient to render it useless for tests on wa fers or films meant for device fabrication [53]. 3.6. Ellipsometry Ellipsometry is an optical technique to measure the thickness and to probe the dielectric properties of thin films. It provides unsurpassed capabilities for the nondestructive and contact-free char acterization of thin films. This technique is based on the analysis of changes in the pol arization of light reflected by a sample. Thus, layers whose thickness is less than the wavelength of the light used to probe the sample can be analyzed, extending down to even monatomic layers [54, 55]. One caveat to keep in mind when using th is technique, however, is that it assumes discrete well-defined layers that are optically homogeneous and isotropic. If these assumptions are not true, a more complex variation of the technique is required. 3.7. Optical Microscopy In using an optical microscope which us es lenses, the theoretical resolving power is one half the wavelength of the light used to view the sample. This limit is never quite reached, however, as a result of the limitations imposed by the use of optical lenses. These include the finite dimensions of the lens act as an aperture restricting the acceptance of light rays from the sample, and loss of detail due to aberrations in the

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21 focusing properties of the lens [56]. Optical microscopes come in a variety of different types including polarized light microscope s, inverted light microscopes and phase contrast microscopes [57].

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22 Chapter Four: Experimental 4.1. Film Fabrication The materials to be used in this study are polycarbonate (P C) resin provided by Acros Organics with molecular we ight 45,000 (catalogue number: 178315000), Bis(ethy1enedioxy)tetrathiaf ulvalene (BEDO-TTF) made by Synchem OHG and having a purity of 99% (catalogue number: jg020), a nd the solvent, American Chemical Society grade dichloromethane (DCM), with a purit y of 99.9%, made by Fisher Scientific (catalogue number: D37-4). Also used was el emental iodine of purity 99.8%, provided by Sigma Aldrich (catalogue number: 207772). The films were fabricated by our collaborat ors in the Department of Chemistry, using a technique base d on that of Jeszka et al [8] The films were made by measuring out polycarbonate to appr oximately 1 wt% of the solvent, dissolving it in dichloromethane (DCM), and adding Bis(et hylenedioxy)-tetrathiafulvalene (BEDO-TTF) at a concentration of 1 wt% or 2 wt% of the polycarbonate. The solution was poured into molds and the solvent allowed to evaporate. Two different methods were used in th e process of vapor doping the films, as shown in Figure 8, so, at this point, the films were cut to 1.5 cm x 1.5 cm or 1 cm x 1 cm, for use in method 1 or method two, respectivel y, and then doped by the addition of iodine in a variety of different concentrations, usi ng vapor exposure at room temperature. This was done so that the effects of a concentra tion gradient on the film properties could be

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23 investigated. The use of method 1 caused the fo rmation of a concentrat ion gradient in the iodine, which lead to uneven doping of th e film surface, with most of the iodine depositing on the areas of the film closest to the solution. This allows the relationship between the distance from the iodine solution and the resistivity of the film to be studied. Method 2 was designed to allow exposure of th e films to iodine at equilibrium. Because the film is level relative to the surface of the iodine solution, there is only minimal concentration gradient induced when th e films are doped and they are doped as homogeneously as possible over their surfaces The properties of the film doped in the presence of a concentration gradient were compared to the propertied of the film doped using method 2. There is an additional difference in the two methods of vapor doping, besides the position of the film, however: the polycarbonate was used as obtained in method 1, and purified before use in method 2. The polycar bonate, as obtained, was not totally pure. This could potentially have an impact on the performance of the films fabricated without purifying the polycarbonate. Th erefore, the films prepared with method 1 were done on unpurified polycarbonate and those films dope d with method 2 were prepared using purified polycarbonate. The long term goal is to be able to co mbine the polycarbonate film with the gold nanoparticles, so that the conductiv ity of the film is increased. Various PC and PC-dye films were prepared. To ensure reproducibility and a good sampling average, at least three films fo r each concentration need to be prepared and characterized.

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24 Method 1 Method 2 Figure 8: Methods of Vapor Doping Used in This Study. In method 1, the film is exposed vertically in a non-equilibrium system open to the air. In method 2, the film is exposed horizontally, at equilibrium. 4.2. Four Point Probe Experiments Four point probe experiments were done using a Keithley 6221 sourcemeter, a Keithley 6514 electrometer, and a Signatone four point probe model S-301-4. The source meter was set to keep a compliance voltage of 105 V, while the current sourced was incrementally raised until the compliance voltage was reached. The voltages across the four point probe were noted down at each incr ement of the current, so that the resistance could be calculated for a given current s ourced. A 300mm diameter p-doped silicon (100) wafer, obtained from MEMC electronic mate rials and donated by Dr. John Wolan, with a nominal resistivity of 14-22 -cm was used as a reference. The differences in the two methods used to dope the films necessitated the use of two different measurement methods. The resis tivities of the films made with method 1 were measured at twelve locations on the film starting at the bottom of the film (nearest to the doping solution), and moving up the film (away from the doping solution) in

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25 increments of 1 mm. Films doped with method 2 were tested in a randomized fashion, and the locations of the tests were noted. The results for method 2 were averaged to calculate an average resistivity and conductiv ity of the films. These methods are shown schematically in Figure 9. The results are discussed in Section 5.1. x x x x x x x xtop Bottom x x x x x x x x x x x x x x x xtop Bottom Method 1 x x x x x x x x x x x x x x x x x x Method 2 Figure 9: Measurement Methods used to quantify th e Resistance of Films doped with Method 1 and Method 2. Because there is a concentration gradient present in the iodine when using met hod 1, the films were characterized using a series of measure ments taken along the center of the film, from bottom to top. Because method 2 produces nearly homogeneous films, the films were tested in ramdom positions across th eir surfaces, as shown. 4.3. FTIR Settings and Information The films were examined using a tr ansmission accessory in a Nicolet 6700 spectrophotometer. This allowed for the coll ection of data across the full spectrum of wavelengths provided by the machine: 4000 to 400 cm-1. This equates to a range of wavelengths from 2.5 m to 25 m. The films were also analyzed using ATR-FTIR. A zinc selenide (ZnSe) crystal was used, in conjunction with a flat plate accessory on a stand that incorporated potassium brom ide (KBr) windows. The use of the ATR accessory limits the range of wavenumbers that can be collected and tested to the range

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26 from 4000 cm-1 to 720 cm-1. Data gathered was analyzed using the Omnic 7.2a software distributed by Thermoscientific. 4.4. TEM Images TEM images were taken on a Morgagni 268D electron microscope, using settings of 100 kV, and 60 kV at a variety of magnifications. 4.5. AFM Surface Scans AFM images were taken on an XE-100 Advanced Scanning Probe Microscope. Images were taken in tapping mode using a classic silicon (Si) or silicon nitride (SiN4) cantilever. The scan sizes of the images were 10x10 m, 5x5 m, 2x2 m, and 0.5x0.5 m. 4.6. Optical Microscopy Optical microscope images of the films were taken using 25x, 100x, and 400x magnification.

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27 Chapter Five: Results and Analysis 5.1. Four Point Probe Studies The four point probe tests conducted were done to determine whether the films followed Ohm's law, and, if so, what the surface resistivity was before and after the polycarbonate/BEDO-TTF films had been doped. An overview of the results is as follows: Before going into any detail, there are some general observations worth noting. First, and foremost, before doping, the films ar e clear with an orange or pink tinge where the dye is concentrated. After doping, areas with higher dye concen trations turn into darker shades of purple, whereas areas with lower dye concentrations remained purplish. Secondly, during doping some films will ac quire a metallic sheen. These films show higher conductivity values than the films that do not have a metallic sheen. Thirdly, if the films are doped for too long, meaning that they have been overexpos ed to iodine, they will turn from purple to green, and are then no longer conductive. As a result, longer doping times do not necessarily mean better that the films will show better conductivity. Fourth, it was noted after several tests done on films containing 1 wt% of BEDO-TTF dye that the 12 mg/mL doped films were cons istently not conductive. As a result the concentration of the BEDO-TTF was raised to 2 wt% for all subsequent experiments.

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28 Lastly, if the films are shown to follow Ohm’s Law, it should be noted that the inverse of the slope of the plotted current and voltage data will be equal to the resistance of the film. The method used to test the films containing1 wt% BEDO-TTF was simply to place the four point probe in contact with the surface, and to source a current. The amount of that current that was transmitted was then observed. This experiment design is shown schematically in Figure 10. 12 mg/mLI28 mg/mLI24.3 mg/mLI2 Isrc= 4.53 mA Isrc= 4.53 mA Isrc= 4.53 mA Iout= 0 mA Iout= 2.00 mA Iout= 1.46 mA Figure 10: Method Used to Test Films Containi ng 1 wt% BEDO-TTF for Conductivity. Films were doped and then tested once with the FPP to determi ne whether they were conductive, and, if so, how much of the current sourced was transmitted. Testing of the four point probe, electro meter, and current source, using the pSilicon wafer as a reference showed that the setup was functioning properly. The nominal resistivity of the p-Silicon wafer was given by the manufacturer to be 14-22 -cm. The current-voltage data collected for the reference wafer is shown in Figure 11.

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29 0 0.002 0.004 0.006 0.008 0.01 00.020.040.060.080.10.12Voltage [V]Current [mA] Figure 11: Current-Voltage Data for P-doped Silicon Wafer. In order to ensure that our setup was working properly, a p-doped silicon wa fer with a known resistance of 14-22 -cm was tested, and the resistivity was caculated. A result of = 14.5 0.2 -cm was obtained. From the current-voltage data collect ed for the p-doped Silicon wafer, the resistance of the wafer can be calculated to be 91.091 This resistance is then multiplied by the interprobe distance of th e four point probe instrument, 0.0625 inches, and converted into the correct units as follo ws, and the error was calculated based on the repeat measurements which were taken in ot her randomly chosen lo cations on the wafer. d R eq. 6 = (91.091 )*(0.0625 in)*(2.54 cm/in) = 14.5 0.2 -cm The next step taken was to optimize th e iodine exposure time for each of the following concentrations: 12 mg/mL, 8 mg/mL, and 4.3 mg/mL. A film containing 2 wt%

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30 BEDO-TTF dye was doped for 30 seconds usi ng method 1, then conductivity data was taken in one place on the film. The same film was then doped with method 1 for another 30 seconds, and tested again. This cycle was repeated until the resistance of the film no longer showed large changes after each expos ure. The results for the 12 mg/mL solution are plotted in Figure 12. Results for the other two concentrations look similar, and can be found in Appendix A. 0 0.5 1 1.5 2 2.5 012345Current [mA]Voltage [V]0.5 min 1 min 1.5 min 2 min 2.5 min 3 min Figure 12: Current-Voltage Data fo r Optimization of Iodine Expo sure for 12 mg/mL solution. Plotted here is the current-voltage data for a film doped using meth od 1 for a variety of exposure times. The films were exposed to the iodine solution in increments of 30 seconds until the resistance (the inverse of the slope) no longer changed dramatically. One can easily see at a glance, keeping in mind that the slope is equal to the inverse of the resist ance of the film, that as the fi lms are doped for longer times, the resistance decreases until a tim e of two minutes is reached. Doping the films longer than

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31 two minutes, no longer decr eases the resistance. This can be seen illustrated in Figure 13, in which the resistivities for the 12 mg/mL film are plotted against the length of time for which they were exposed to the iodine soluti on. The values have been fitted with a power fit, to better illustrate the relationship be tween the resistivity and the exposure time. 0 0.5 1 1.5 2 00.511.522.533.5Resistivity [k-cm]Time [min] Figure 13: Resistivity versus Exposu re Time for 12 mg/mL solution. This plot presents the data from Figure 12 in a slightly different way, for clarity. Seen here is a plot of the calculated resistivities of the films against the length of ti me for which they were exposed. Because the sets of films doped with method 1 exhibit a large concentration gradient, as shown in Figure 13, to obtain an average value for the resistivity is meaningless. Figure 13 presents the data obtai ned for the 12 mg/mL iodine solution at an exposure time of two minutes. Shown in Figure 14 is the measurement data for the film

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32 doped in the 12 mg/mL solution using method 2. Similar data for the two remaining concentrations can be found in Appendix A. 0510152025 0 1 2 3 4 5 6 Voltage [V]Current [mA] Figure 14: Current-Voltage Data for 12 mg/mL Io dine Solution Concentration Exposed for Two Minutes using Method 1. Numbering of 1 to 12 represents distan ce along the film, where 1 is at the bottom, nearest the doping solution, and 12 is at the top, farthest away from the solution. The measurement data presented in Figur e 14 shows the increase in the resistivity as the distance from the doping solution incr eases. This seems to indicate that the resistance of the film increases as the amount of iodine deposited decreases. In the case of those films doped using method 2, a much more even deposition of iodine was seen, as was predicted. The effects of this homogeneity could be seen in the resistance, and, by extension, the resistivity and conductivity of the films. Where the resistance had a very wide range after doping with method 1, in f ilms doped with method 2, the resistances found at each position on the film surface we re clustered closely around one central Position:1 12

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33 value. The resistivity of the films doped with methods 1 and 2 are plotted in Figures 15 and 16 against the position on the film where the measurement was taken. 0246810121416 0 1 2 3 4 5 6 Voltage [V]Current [mA] Figure 15: Current-Voltage Data for 12 mg/mL Io dine Solution Concentration Exposed for Three Minutes using Method 2. It is immediately apparent from this plot that instea d of a range of resistances, as was seen in method 1, the resistances are tightly clustered around one average value. As can be seen by comparing Figures 15 a nd 16, the range of the resistances of the films in method one is not in evidence when method 2 is employed. Films doped with method 2 show a comparatively low resistance compared to films doped with method 1, as well as a much narrower range of values. Ap plying a linear curve fit to the data yields a set of three horizontal lines. This shows th at any error in the measurements is random and due to random processes, rather than be ing caused by the effects of a variable that has not been accounted for in taking the measurements.

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34 0 10 20 30 40 50 60 02468101214Resistance, R [k ]Distance [mm] 12 mg/mL 8 mg/mL 4.3 mg/mL Figure 16: Resistance versus Distance for Films Doped Using Method 1. Shown in this plot is the relationship between the resistivity and the distance away from the iodine solution. The resistance rises dramatically as distance from the solution increases for two of the three concentrations. 0 10 20 30 40 50 60 02468101214Resistance, R [k ]Distance [mm] 12 mg/mL 8 mg/mL 4.3 mg/mL Figure 17: Resistance versus Distance for Films Doped Using Method 2. Shown in this plot is the relationship between the resistivity and the positi on on the film where each measurement was taken. The resistance stays within a very narrow range, comp ared to that of method 1, with only very small variations.

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35 Because the resistance of the films dope d using method 2 is almost homogeneous over the film surface, as shown by the measurements presented in Figure 17, and because any error in the measurements can be attr ibuted to the inherent randomness in the deposition of iodine using the process of vapor doping, it is po ssible to take an average of the calculated resis tivities without bias ing the calculation. The calculated average resistivitie s of these films ranged from 148 -cm, in the case of the film doped in the 4.3 mg/mL solution for 10 minutes, to 1060 -cm for the film doped in the 8 mg/mL solution for 4 minutes, to 2822 -cm for the film doped in the 12 mg/mL solution for 2 minutes. Calcula ting the conductivities for the three doped films, values of 35.4, 94.3, and 67.2 mS-cm-1 are found for the 12, 8, and 4.3 mg/mL solutions, respectively. The conductivities of the three doped f ilms, two types of conducting polymer, and two commonly used co nductive metals are plotted in Figure 17, for ease of interpretation. Compared to the resistivities of copper or gold, which are 1.68x10-9 -cm and 2.214 x10-9 -cm, respectively, the resis tivity of our polymer films is very high, but when compared to th e two conducting polymers, the difference in conductivity is not as great., There is poten tial that the doped polycarbonate films will match the conductivities of polyaniline or polypyrrole after doping optimization and the addition of the gold nanoparticles. The attentive reader will note that th e film which was doped with the most concentrated iodine solution shows the lowest conductivity, while th e film doped with the least concentrated iodine solu tion shows the highest conductivity. This is believed to be a result of the length of time the film was exposed to the doping solution. The film doped

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36 with the 4.3 mg/mL iodine solution was dope d for a period of 10 minutes, whereas the film doped with the 12 mg/mL solution wa s only doped for a period of 2 minutes. Figure 18: Average Resistivities of Films and Ref erence Materials: p-Si (1 00) Wafer, Polyaniline, Polypyrrole, Gold, and Copper. When compared to polyaniline or polypyrrole, the films fabricated in this study do not quite reach the same levels of conductivity. There is g ood potential that they might do so after optimization of all components has been done. There is an additional optimization that must take place besides the optimization of the film conductivity, if these films are to be used in conjunction with dichromatic materials as sensors in the future : that of the f ilm transparency. Before doping, the polycarbonate films are transparent in the visible range, and acquire a pink/orange tinge after the addi tion of the BEDO-TTF dye. After doping, the

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37 films darken, picking up brilliant colors. Wh ere the iodine is de posited on the film surface, the dye goes from little pink/orange to purple, as seen in the film doped for two minutes in the 12 mg/mL solution, depicted in Figure 19 (bottom ri ght image), and then, as more iodine is deposited, the films develop a dark green metallic sheen, as seen in the film doped in the 4.3 mg/mL solution for 10 minutes, also shown in Figure 18 (bottom left image). In the boxes below the images of the films in Figure 19 are given the average conductivity values found for each doping concentr ation and time, as well as the ratio of the conductivity to the highest value found in terms of pe rcentage. Meaning that the conductivity value for th e film doped in the 4.3 mg/mL solution for 10 minutes was taken as 100%, and the values for th e other two films were then calculated from this value. It can be readily seen that, if a film is to be developed that will be both transparent and conducting, some work needs to be done to determine what the highest conductivity is that can be achieved while maintaining the tr ansparency of the film. This would lead us to speculate that, since its tr ansparency is the highest of the three conductive films, the 12 mg/mL doped film should be the one chosen for optimization. 5.2. Imaging Analyses Images of the polycarbonate films, before and after doping, taken by three different imaging techniques will be discussed in this section. Images of the films were taken using AFM, TEM, and optical micr oscopy, hereafter referred to as OM.

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38 PC w/dye Doping Solution Concentrations 4.3 mg/mL 8 mg/mL 12 mg/mL 67.2 mS cm 1 9.47 mS cm 1 3.54 mS cm 1 Conductivity: Relation to 4.3 mg/mLConductivity: 14% 5.3% PC w/dye Doping Solution Concentrations 4.3 mg/mL 8 mg/mL 12 mg/mL 67.2 mS cm 1 9.47 mS cm 1 3.54 mS cm 1 Conductivity: Relation to 4.3 mg/mLConductivity: 14% 5.3%Figure 19: Flowchart Showing the Changes in Tran sparency Before and After Doping. Also shown are the conductivities measured for each film and the percentages relative to the 4.3 mg/mL conductivity. In Figure 20, images of the film topogra phies and phase analyses are presented for the undoped polycarbonate and polycarbonate/B EDO-TTF films. The topography of the polycarbonate film shows a very smooth surf ace with what appear to be some uneven areas in the bottom left corner. The phase anal ysis of the polycarbonate film reveals that there are no inclusions of other forei gn materials on the polycarbonate surface.

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39 100 nm 10 5 0 nmPC PC + BEDO-TTF 100 nm 10 5 0 nm 100 nm 100 nm -33 -35 deg -31 -60 -80 deg -40 100 nm 100 nm 100 nm 10 5 0 nmPC PC + BEDO-TTF 100 nm 100 nm 100 nm 10 5 0 nm 10 5 0 nm 100 nm 100 nm -33 -35 deg -31 -60 -80 deg -40 100 nm 100 nm 100 nm 100 nm 100 nm 100 nm -33 -35 deg -31 -33 -35 deg -31 -60 -80 deg -40 -60 -80 deg -40 Figure 20: AFM Images of the Polycarbonate Films With (right) and Without (left) BEDO-TTF Dye. Top right and left images are of the film topograp hy, and the two bottom images are of the phase analysis. The PC presents a v ery smooth surface, while the PC/BEDO-TTF composite shows the appearance of pore-like structures. Once the BEDO-TTF dye has been added, the co mposite film shows st ructures appearing on its surface that resemble pores. The phase s can of the same film shows the appearance of a different material within the largest of the pore-like structures, which suggests that the BEDO-TTF dye could be aggregating there. In OM images taken of the same two films, similar structures were observed, as shown in Figure 20. The polycarbonate film presents a very smooth surface and shows some features similar to the pores seen in the poly carbonate/BEDO-TTF film, though they are less in number. The polycarbonate/BE DO-TTF film displays the same features,

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40 but in higher density. More f eatures appear in the same area, and the surface appears rougher, as a result. 20 m 20 m 20 m 20 m 200 m 200 m 200 m 200 m PC PC + BEDO-TTF 20 m 20 m 20 m 20 m 200 m 200 m 200 m 200 m PC PC + BEDO-TTF Figure 21: Optical Microscope Images of PC and PC/BEDO-TTF Films Under 100x and 400x Magnification. Features similar to the pore-like st ructures seen in the AFM images are present in both films. OM images of the films doped with method 1 show a very clearly defined interface between the area on the film where th e iodine has been deposited on the surface, and the area where it has not. An example is shown in Figure 22, which presents the images taken of the film doped with the 8 mg /mL solution for four minutes. Images of the films doped using the other two solution concentrations can be found in Appendix B.

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41 1000 m 200 m 200 m 200 m 1000 m 200 m 200 m 200 m 200 m 200 m 200 m Figure 22: Optical Microscopy Images of the 8 mg/mL Doped Film Taken at 25x and 100x. The transition between the heavily and lightly doped regi ons of the film is shown. The very dark area contains more iodine than the lighter one. AFM surface scans of films doped with me thod two reveal that as the exposure time increases and the iodine solution concen tration decreases, the crystal sizes observed in the deposits on the film surface increase. Figure 22 presents the topography and phase scans of the films exposed to the three different iodine solu tions. From the images, it can be readily seen that the increase in the surface roughness seen as the doping time increases corresponds to a drama tic increase in the crystallinity of the iodine deposited on the film surface. In the case of the film doped for two minutes in the 12 mg/mL solution, nucleation sites can be seen that appear to be the precursors of iodi ne crystals, but there are no crystals, as of yet, and the features seem to be lacking a long range order. When the film doped in the 8 mg/mL solution for four minutes is considered, more defined

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42 crystal-like structures can be seen, but the features remain indistinct. The jump to an exposure time of ten minutes at a concentrati on of 4.3 mg/mL brings with it the formation of large well-defined crystals, and a large in crease in the conductivity of the film. This seems to suggest that the formation of the io dine crystals results in higher film surface conductivity. 25 0 -50 deg -25 20 10 0 nm 100 nm 100 nm 100 nm12 mg/mL 8 mg/mL 4.3 mg/mL 100 nm 100 nm 100 nm 25 0 -50 deg -25 25 0 -50 deg -25 20 10 0 nm 20 10 0 nm 100 nm 100 nm 100 nm 100 nm 100 nm 100 nm12 mg/mL 8 mg/mL 4.3 mg/mL 100 nm 100 nm 100 nm 100 nm 100 nm 100 nm Figure 23: AFM Surface Topography and Phase Scan s of Films Doped With Method 2. Images were taken in 0.5 m x 0.5 m size. Images in the top row are top ographical scans, and images in the bottom row are the phase scans of the same areas. An increase in the cryst allinity of the iodine depositions as well as in the surface roughness can be seen with increasing exposure time and iodine loading. The phase scans show that the only material being scanned is iodine and the entire film surface has been covered by the iodine. The phase scans show that there are no changes in the material that the AFM cantilever tip encounters as it scans the surface: all it sees is iodine This indicates that there is a homogeneous layer of iodine forming, confirming the validity of the FPP conductivity measurements.

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43 OM images of the films doped with met hod 2 show a trend as well. Presented in Figure 23 are images taken using the OM of the films doped in the three different concentrations of iodine solution. Instead of displaying surface characteristics that have to do with the crystallinity of the iodine de posited on the film surf ace, the films show an increase in the surface roughness that parall els the increase in surface roughness that is predicted by calculations done using the AFM imaging software. The surface roughness values for the films doped with methods 1 a nd 2 are shown in Figure 24. Also shown in the upper right corner of the plot for met hod 1 is an image of the film doped using method 1 in the 4.3 mg/mL iodine solution for ten minutes. In the images of the th ree doped films, there is an increase in the surface roughness and conductivity as the iodine concen tration in the soluti on decreases and the time the film is exposed to th e solution increa ses. This suggests that longer exposure times and lower iodine concentrations allow the iodine atoms more time to self-assemble into crystalline structures on the film. When method 1 is employed, uneven random depositions of iodine that do not form crystals are seen. Interestingly, there appears to be a threshold exposure time or iodine crystal size between four minutes and ten minutes at which the polycarbonate film buckles and forms maze-like wrinkles.

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44 20 m 20 m 20 m 20 m 20 m 20 m 20 m 20 m 20 m 200 m 200 m 200 m 200 m 200 m 200 m12 mg/mL 8 mg/mL4.3 mg/mL 12 mg/mL8 mg/mL4.3 mg/mL Figure 24: Optical Microscopy Images of the Film s Doped in the Three Different Iodine Solution Concentrations Taken at 100x and 400x. There is a dramatic increase in the surface roughness of the films as the exposure time and iodine loading increas e. This increase also correlates to an increase in the surface roughness and the film conductivity. 0 5 10 15 20 1052Surface Roughness, Rq [nm]Scan Side Length [um] 0 5 10 15 20 1052Surface Roughness, Rq [nm]Scan Side Length [um]Method 1Method 2 0.12g iodine 10 mLDCM 2-3 minutes 0.12g iodine 10 mLDCM 2-3 minutes 0.043g iodine 10 mLDCM 10 minutes 0.043g iodine 10 mLDCM 10 minutes 0.08g iodine 10 mLDCM 4 minutes 0.08g iodine 10 mLDCM 4 minutes Figure 25: Surface Roughness Calculated From the AFM Images of Films Doped with Methods 1 and 2. Shown in the inserts are images of the films fabricated with each method. In these plots, the surface roughnesses calculated from the AFM scan s are presented in graphical form. The tendency toward increasing surface roughness as the iodine loading is clearly shown for both methods.

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45 It can be seen that all three of the im aging techniques used show a general trend of increasing surface roughness with increasing i odine loading of the films. This increase of the surface roughness also correlates w ith increasing conductiv ity. This correlation implies strongly that the surface roughness may be directly related to the conductivity of the films fabricated. This could potentially follow the same principles as the phenomenon seen in other conducting materials, such as th in metal films and semiconductors [58, 59]. In comparing the OM and TEM images, we again see that the features appearing in the OM images also appear in the TEM images. However, the use of TEM allows for closer study of the pore-like st ructures appearing on the surf ace of the undoped films, as shown in Figure 25. Now it can be seen that wh at appeared to be pore-like structures in the AFM and OM images are, in actuality, possible phase separation domains. 20 m 20 m 10 m 20 m 20 m 10 mPC PC + BEDO-TTF 20 m 20 m 10 m 20 m 20 m 10 mPC PC + BEDO-TTF Figure 26: OM and TEM Images of the Polycarbonate and Polycarbonate/BEDO-TTF Films. The upper row of images are taken using the OM at 400x, and the lower two images were taken on the TEM at a magnification of 2.2k x and 100 kV. Shown here are higher magnification images of the phase separation phenomena taking place in the undoped films. In the composite film, small subdomains are observed.

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46 In the case of the polycarbonate film, show a wide range of sizes from about 1 m to roughly 4 m. These phase separation domains remain in evidence in the polycarbonate/ BEDO-TTF film, and their si ze increases slightly to an average of about 5 m. The domains in the film containing the BEDO-TTF dye also exhibit the formation of small subdomains within the larger ones, as well as the formation of larger domains due to the fusion of several smaller domains. 200 m 200 m 200 m 200 m 200 m 200 m 5 m 5 m 5 m12 mg/mL 8 mg/mL 4.3 mg/mL 200 m 200 m 200 m 200 m 200 m 200 m 5 m 5 m 5 m12 mg/mL 8 mg/mL 4.3 mg/mL Figure 27: OM and TEM Images of the Films Doped in the Three Different Iodine Solutions. The upper row of images was taken using the OM at 1 00x, and the lower two images were taken on the TEM at a magnification of 4.4kx an d 60 kV. Presented here are images that depict th e change that takes place on exposure to iodine : the phase separation effects disa ppear and dark iodine deposits appear in the TEM images, and th e OM images show increasing surf ace roughness, as in the data calculated from the AFM scans and presented in Figure 25. These phase separation domains disappear once the iodine is added. This is demonstrated by the images prepared in Figure 27. In the upper row of images in the figure, OM images of the films are shown, and in the lower row, TEM images of the same films are displayed. These images demons trate that as the iodine loading on the film surface increases, the number of iodine deposit s on the film decreases, and the size of the

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47 deposits increases, going from about 0.5 um in the case of the 12 mg/mL doped film to as large as 1.5 um in th e 4.3 mg/mL doped film. 5.3. FTIR Analyses and Their Co rrelation with Imaging Results FTIR analyses were conducted on the purified and unpurified neat polycarbonate films, the polycarbonate/BEDO-TTF films, and the doped films in transmission. The results were compared and will be discu ssed as follows: The peak finder algorithm included in the Thermo software (Omnic) was used to guide the placement of the peaks in the spectra that are referred to in this section. Let us be gin with the neat polycarbonate spectrum that was taken as a control. The absorbance peaks exhibited by this film are given in Figure 28. It should be noted that the spectrum presented in Figure 28 is of the unpurified polycarbonate used for the experiments done with method 1. 0 0.5 1 1.5 2 2.5 3 500 1000 1500 2000 2500 3000 3500 4000Absorbance [a.u.]Wavenumber [cm-1]O O O CH3CH3 n CH3stretch CH3stretch C=O stretch C=O stretch Phenol ring stretch Phenol ring stretch C-O stretch Para-substituted phenol ring stretch Para-substituted phenol ring stretch Figure 28: FTIR Spectrum of Unpurified Neat Po lycarbonate. The peaks corresponding to the monomeric functional groups are la beled. The structure of the polycarbonate monomer is given in the upper left corner for reference.

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48 All of the functional groups that make up the molecule are represented. The peaks in the spectrum correspond to those expected from a polymer with the structure shown in the upper left hand corner of Figure 28. Figure 29: Numbered Structure of Bisphenol-A Polycarbonate. The carbons of the polymer backbone are numbered for easier identification in the discussion. The two methyl groups bonded to car bon atom seven and the hydrogen atoms bonded to the carbons in the two phenol rings ge nerate the first peak in the spectrum, which appears at 2969 cm-1. Similarly, the oxygen atom double bonded to carbon atom number 14 resonates at about 1776 cm-1, generating the signatur e carbonyl peak in the spectrum. At 1506 cm-1, the resonance frequency of the two phenol rings is reached. Several very strong peaks appear between 1290 and 1015 cm-1. These are a result of the different vibrational modes of the oxygen atoms bonded to carbon atom fourteen. The carbon-oxygen stretch ty pically appears in two or mo re bands in the 1300 to 1000 cm-1 range. The last peak of interest that a ppears in this spectrum appears at 831 cm-1. This peak is attributed to the presence of para -substituted phenol rings in the backbone of the polycarbonate polymer.

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49 PC PC/BEDO-TTF 0.12g I20.08g I20.043g I2 0 0.5 1 1.5 2 2.5 3 3.5 500 1000 1500 2000 2500 3000 3500 4000Absorbance [a.u.]Wavenumber [cm-1] Figure 30: FTIR Spectra of the Control Films and Doped Films for Method 1. No easily observable peaks are seen appearing or disappearing. There is a peak shift occurring in the carbonyl peak and a shoulder is appearing in the para-substitution peak. In Figure 30, the spectra for all of the doped and undoped films are plotted. It can be easily seen that there are no obvious change s. No easily observable peaks are seen to be appearing or disappearing. The two regions of the spectra shown in Figure 30 that will be further analyzed are those encompassing th e carbonyl and para-sub stitution regions, as labeled in Figure 28. These two regions corres pond to fundamental vibrations associated with the bonds of the carbons numbered 1, 4, 8, 11, and 14. The carbonyl region of the spectra is pl otted in Figure 31. At a glance it is apparent that the addition of the BEDO-TTF dye has not caused any changes to take place other than an increase in the intensity of the peak. This simply tells us that there are more carbonyl bonds available in the sample to absorb IR light. Since no carbonyl bonds exist in the BEDO-TTF dye, reason dictates that there must be more carbonyl bonds

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50 present due to the presence of more polycarbon ate molecules. This, in turn, leads to the conclusion that this increase in intensity is mo st probably due to a s light increase in the film thickness from the neat polycarbona te film to the polycarbonate/BEDO-TTF composite film. Doping for two minutes in the 12 mg/mL solution results in a peak shift of three reciprocal centimeters. As the iodi ne loading increases, however, the carbonyl peak does undergo a slight shift. The peak after doping for four minutes in the 8 mg/mL solution reveals a shift to the right of about 6 reciprocal centimeters. This shift increases again in the case of the 4.3 mg/mL dope d film, to 9 reciprocal centimeters. 0 0.5 1 1.5 2 2.5 3 3.5 1700 1750 1800 1850Absorbance [a.u.]Wavenumber [cm-1] Figure 31: Expanded View of the Carbonyl Region of the Spectra Shown in Figure 30. There is a negligible peak shift on the addition of the BED O-TTF dye to the neat po lycarbonate film. As the iodine loading of the film increases, the peak shif t also increases, showing th at the addition of the iodine causes an interaction to take place between the carbonyl bond of th e monomer and the iodine complexes formed. PC PC/BEDO-TTF 12 mg/mL I2 8 mg/mL I2 4.3 mg/mL I2

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51 This increase with the iodine loading on th e film surface seems to indicate that the formation of the BEDO-TTF/iodine complex re sults in a weak interaction between the complex and the carbonyl groups present in the polycarbonate matrix. The increases in the peak shifts observed correspond to the in creases in film conductivity, as well, which implies that the interaction between th e polycarbonate and the BEDO-TTF/iodine complex could potentially have an impact on how well the films conduct electricity. 0 0.5 1 1.5 2 2.5 3 3.5 700 750 800 850 900Absorbance [a.u.]Wavenumber [cm-1] Figure 32: Expanded View of the Spectral Peak From Figure 30 Which is Attributed to the Resonance Frequency of the ParaSubstituted Phenol Rings. The peak in question appears between 800 and 865 cm-1. As in the case of the carb onyl peak, there is a negligible peak shift on the addition of the BEDO-TTF dye to the neat polycarbonate film, and as the iodine loading of the film increases, the peak shift also increase s, showing that the additi on of the iodine causes an interaction to take place between the carbonyl bond of the monomer and the iodine complexes formed. The expanded view of the para-substitution region of the spectra presented in Figure 30, shown here in Figure 32, shows a pr ogression just as the carbonyl region does. The difference between the two regions is th at in the carbonyl region, there was a peak PC PC/BEDO-TTF 12 mg/mL I2 8 mg/mL I2 4.3 mg/mL I2

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52 shift, whereas in the para-substituted region there is a new peak appearing. The shoulder appearing on the left side of the para-subs titution peak grows more pronounced as the iodine loading on the film surface increases. This peak is not present in the spectra of the polycarbonate or the polycarbona te/BEDO-TTF films, but app ears after the films have been exposed to the iodine solutions us ed to vapor dope the film surfaces. The appearance of this peak is believed to be due to the formation of the BEDO-TTF-iodine complex after exposure of the film to the iodine solution [60, 61]. A variety of differences are visible when the spectra taken of the films fabricated using method 1 are compared with those of the films made using method 2. The superimposed spectra of the polycarbona te and polycarbonate/BEDO-TTF films are shown in Figure 33 for comparison. Some diffe rences are apparent that were not seen when making films with he unpurified polycarbonate. 0 1 2 3 4 5 6 7 500 1000 1500 2000 2500 3000 3500 4000Absorbance [a.u.]Wavenumber [cm-1]PC PC/BEDO-TTF CH3stretch CH3stretch C=O stretch C=O stretch Phenol ring stretch Phenol ring stretch C-O stretch Para-substituted phenol ring stretch Figure 33: FTIR Spectra of the Po lycarbonate and Polycarbonate/BE DO-TTF Films. Shown here are the spectra of the control films p repared using method 2. In method 2, purifie d polycarbonate resin is used as the matrix for all film s. As previously, the peaks correspond ing to the functi onal groups of the molecules present are labeled. Several clear differences are evident between this spectrum and that of the films made using method 1. The carbonyl peak now shows a clear shift on the addition of the dye, as does the para-substitution peak. There is also a new peak appearing between 1200 and 1150 cm-1 as a result of the C-S bonds within the dye.

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53 When the spectra of the doped films are superimposed on the two spectra just presented, as seen in Figure 34, severa l regions show difference worthy of further discussion. These include the carbonyl and pa ra-substitution regions, as were noted when method 1 was used, as well as those regions impacted by the addition of the dye, where peaks are visible now that the po lycarbonate has been purified. 0 1 2 3 4 5 6 7 500 1000 1500 2000 2500 3000 3500 4000Absorbance [a.u.]Wavenumber [cm-1] Figure 34: FTIR Spectra of the Films Fabricated Usin g Method 2. Shown here are the spectra of all the films prepared using method 2. For clarity, th e labels of the functional groups are replaced with a legend, since the peaks corresponding to the functional groups have not changed from the previous figure. The carbonyl region of the f ilms made with method 2 shows a dramatic shift in the spectral peak before and after the a ddition of the BEDO-TTF dye. An expanded view of this region is plotted in Figure 35. This shift disappears ag ain after the films have been doped, broadening and becoming attenuated. Th is would seem to indicate that on the PC PC/BEDO-TTF 12 mg/mL I2 8 mg/mL I2 4.3 mg/mL I2

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54 addition of the BEDO-TTF there is a strong in teraction between the dye and the carbonyl region of the polycarbonate monomer. The disappearance of the peak shift when the iodine is deposited on the film surface implie s that, not only is the interaction between the BEDO-TTF and the carbonyl bond disappearing, but the carbonyl bond itself is being attacked by the iodine. The attenuation of the carbonyl peak as the iodine loading increases suggests that the intensity of the carbonyl peak is dropping due to the disappearance of carbonyl bonds pr esent in the molecule due to the electrophilic nature of the iodine atoms. 0 1 2 3 4 5 6 7 1700 1750 1800 1850Absorbance [a.u.]Wavenumber [cm-1] Figure 35: Expanded View of the Carbonyl Region For Spectra of Films Made Using Method 2. This peak corresponds to the stretch as sociated with carbon 14 of the monomer, as labeled in Figure 29. There is a clear shift on the addition of the BEDOTTF dye, which is replaced by a sharp attenuation of the peak after exposure to iodine. This indicate s an interaction between the carbonyl group of the polycarbonate monomer and the BEDO-TTF dye fo rms and is then broken after doping. The attenuation of the peak suggests that the iodine is breaking the carbonyl bonds present in the polymer matrix.

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55 The para-substitution region of the film s doped with method 2 shows a similar trend to that seen in the carbonyl region. Th ere is a peak shift af ter the addition of the dye, which subsequently disappears again after the films are exposed to iodine. The parasubstitution peak also shows attenuation, like the carbonyl peak, suggesting that the resonating double bonds in the phenol rings of the polycarbonate are being broken by the iodine that is deposited on the film surface. This seems to indicate that, before the purification of the polycarbonate the iodine was forming complexes with the dye and the impurities in the film. After the purification, the sharp attenuation of the peaks indicates that the iodine is breaking bonds within the polycarbonate monomers due to a decrease in the number of bonds to attack in the impurities. It is possible that these interactions between the iodine and the polycarbonate could have some impact on the physical charac teristics of the polycarbonate film. Further study is needed to determine what effect, if any, the deposition of the iodine has on the structural properties of the polycarbonate. 0 1 2 3 4 5 6 7 700 750 800 850 900Absorbance [a.u.]Wavenumber [cm-1] Figure 36: Expanded View of the Para-Substitution Peak Seen in the Spect ra of Films Prepared Using Method 2. The peak in question appears between 800 and 865 cm-1. This peak corresponds to the stretch associated with carbon 1, 4, 8, and 11 of the monomer, as labeled in Figure 29.

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56 There are several other regi ons of the spectra generate d by the films made using method 2, however: those containing peaks generated by the BEDO-TTF dye. For example, the first peak that appears as a resu lt of the addition of th e dye, and the subtlest, shows up at 1648 cm-1. This peak can be attributed to a stretch that takes place in the five-membered rings within the dye. An e xpanded view of the region surrounding this peak is shown in Figure 37. 0 1 2 3 4 5 6 7 1600 1620 1640 1660 1680 1700Absorbance [a.u.]Wavenumber [cm-1] Thiol ring stretch Thiol ring stretch Figure 37: Expanded View of the Region of the Spe ctrum Surrounding the Thiol Ring Stretch Due to the BEDO-TTF Dye. The structure of the dye is sh own in the upper right corner, for reference, and the rings causing the spectral peak have been highlighted with a red box. Another region of interest is that of the symmetric C-O stretch. This can be seen in Figure 38. The addition of the BEDO-TTF dye causes a series of peaks due to C-S

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57 stretching to appear in the region previously only attri buted to C-O stretching. The intensity of the peak due to the ether stretche s present in the film jumps on the addition of the BEDO-TTF dye. This rise in the intensity of the peak is directly attributable to the presence of more ether bonds after the addition of the dye, because the di-substituted sixmembered rings in the dye contribut e to the intensity of this peak. 0 1 2 3 4 5 6 7 1050 1100 1150 1200 1250 1300Absorbance [a.u.]Wavenumber [cm-1] Ether stretch C-S stretch 0 1 2 3 4 5 6 7 1050 1100 1150 1200 1250 1300Absorbance [a.u.]Wavenumber [cm-1] Ether stretch Ether stretch C-S stretch C-S stretch Figure 38: Expanded View of the Spectral Region Surrounding the Thiol (C-S) and Ether (O-C-O) Stretches Due to the BEDO-TTF Dye. The structure of the dye is shown in the lower left corner, for reference.

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58 Chapter Six: Possible Future Trends Though the future of the field of sensor s, biological and otherwise, is very uncertain given the current pr ecarious state of the worldwide economy, the conditions are currently looking relatively good. The number of publications has been consistently increasing in recent years, particularly in the last three to five years, and shows no signs of slowing. Of course, the number of papers bei ng published is not th e only criterion on which an analysis should be based. The complim entary aspect to that of academic papers published in journals is natura lly that of industry, and the actual production of the devices so painstakingly developed by researchers. So any prediction made must account for the fact that after the research and developmen t are over, and production begins, it is the combination of simplicity of operation, speed, acc uracy, and price that will be the keys to a successful production run. It is after all, usually the sensor that can strike the best balance between these characteristics that will gain a larger market share than the others in the end.

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59 Chapter Seven: Summary The selection of materials for modern gas sensors is based upon their physical and chemical characteristics. Two qualities in particularly high demand are transparency and conductivity. This is due to the fact that, while polymer gas sensors, in which the polymer acts as a solid electrolyte, have been devel oped, these types of sensors are opaque. As a direct consequence of their opacity, the potential for thei r use in sensors combining conductive polymers with dichroma tic materials is limited. To provide a resolution to this dilemma, the development of a method for the production of a tr ansparent conductive polymer film is necessary. Past research has shown that it is pos sible to create polymer films containing conductive networks using iodine-doped bi sphenol-A polycarbonate films containing bis(ethylenedioxy)-tetrathiafu lvalene (BEDO-TTF) dye. The feasibility of the use of these types of films for sensor applications was tested. It is the goal of this researcher to help create a sensor which will identify molecu les of explosives in the air, sensitively enough and robustly enough to make the sensor useful in public settings, such as shopping centers and mass transit stations, as a warning of an improvised explosive device (IED). Polymer sensors can be difficult to fabric ate if they are being used in complex applications. However, the sensor whos e beginning stages of development are

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60 characterized in this work promises to be easily fabricated once the process has been optimized and all of the components have been added to the system. Based on the results presented in Chap ter Five, given optimization of the conductivity and the transparency the films fabricated could be used for the design and development of a sensor for the detection of chemical vapors. It wa s found in this study that: FTIR spectra show an interaction betw een the polycarbonate matrix and the dyeiodine complex when method 1 is used in the fabrication, based on the shifts seen in the carbonyl and para-substitution peaks The use of method 2 shows a different inte raction, with a p eak shift appearing when the dye is added to the neat pol ycarbonate films, which disappears again after the addition of the i odine, to be replaced with a sharp attenuation of the peaks. From FPP measurements, the re sistivities of the doped f ilms have been shown to range from 148 -cm in the case of the film w ith the longest exposure time to 2.82 k -cm in the case of the film w ith the shortest exposure time. The imaging techniques used show a general trend of increasing surface roughness with increasing iodine loadi ng of the films which correlates with increasing conductivity. Future work to be done on these films w ould be to optimize the transparency and conductivity of the films to fine tune the fabrication pro cess to produce the best film for application in a vapor sensor sensitive to expl osives. The next steps would be to add gold

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61 nanoparticles to the surface of the doped film, and to then optimize the concentration of the gold particles and the conductivity of the films.

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62 References 1. Thorslund S, Larsson, R., Bergquist, J ., Nikolajeff, F., Sanchez, J. Biomed Microdevices 2008(10):851-857. 2. Farrar D, West, J. E., Busch-Vishniac, I. J., Yu, S. M. Scripta Materialia 2008;59(10):1051-1054. 3. Almeida MG, Silveira, C. M., Moura, J. J. G. Biosensors and Bioelectronics 2007;22(11):2485-2492. 4. Wei Q-B, Luo, Y-L., Zhang, C-H., Fan, L-H., Chen, Y-S. B-Chemical Sensors and Actuators 2008;134(1):49-56. 5. Adhikari B, Majumdar, S. Prog. Polym. Sci. 2004;29(7):699-766. 6. Elsenbaumer RL, Pomerantz, M ., Marynick, D.S., Sharma, S.C. 1996. 7. Adhikari B, Majumdar, S. Prog. Polym. Sci. 2004;29(7):708. 8. Jeszka JK, Tracz, A., Sroczynska, A., Kryszewski, M., Yamochi, H., Horiuchi, S., Saito, G., Ulanski J. Synthetic Metals 1999;106(2):75-83. 9. Chiang CK, Park, Y.W., Heeger, A.J., Sh irakawa, H., Louis, E.J., MacDiarmid, A.G. J Chem Phys 1978;69:5098-5104. 10. Shirakawa H, Louis, E.J., MacDiarm id, A.G., Chiang, C.K., Heeger, A.J. J Chem Soc Chem Comms 1977:578-580. 11. Suzuki T, Yamochi, H., Srdanov, G., K. Hinkelmann, G., Wudl F. J. Am. Chem. Soc. 1989;111 (8):3108-3109. 12. Horiuchi S, Yamochi, H., Saito G., Sakaguchi, K.-I., Kusunoki, M. J. Am. Chem. Soc. 1996;118(36):8604. 13. D.L. Lichtenberger RLJ, K. Hinkelmann, T. Suzuki, F. Wudl J. Am. Chem. Soc. 1990;112(9):3302. 14. Golub M, Graja, A., Jzwiak K. Synthetic Metals 2004;144 201-206. 15. Arshak K, Moore, E., Cunniffe C., Nicholson, M., Arshak A. Superlattices and Microstructures 2007;42(1-6):479-488.

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63 16. Epifani M, Giannini, C., Tapfer, L., Vasanelli, L. J. Am. Ceram. Soc. 2000;83(10):2385-2393. 17. Torsi L, Pezzuto, M., Siciliano, P., Rella, R., Sabbatini, L., Valli, L., Zambonin, P.G. Sensors and Actuators B 1998;48:362-367. 18. Beecroft L. L. O, C. K. Chem. Mater. 1997;9(6):1302. 19. Foss CA, Hornyak, G. L., Stockert, J A., Martin, C. R. Adv. Mater. 1993;5(2):135. 20. Biswas A, Marton, Z., Kanzow, J., Kr use, J., Zaporojtchenko, V., Faupel, F., Strunskus, T. Nano Letters 2003;3(1):69. 21. Monk DJ, Walt, D. R. Anal Bioanal Chem. 2004;379:931-945. 22. Pereira FC, et al. Qum. N ova [online] 2006;29(5):1054-1060. 23. Carion Oea ChemBioChem 2007;8:315 322. 24. Cusm A, et al. Materials Scien ce and Engineering C 2007;27(5-8):1158 1161. 25. Lu Y, et al. Bioelect rochemistry 2007;71(2):211 216. 26. Tripathi Aea Anal. Chem. 2007;79(3):1266-1270. 27. Dorozhkin LM, Nefedov, V.A., Sabelni kov, A.G., Sevastjanov, V.G. Sensors and Actuators B 2004;99:568-570. 28. Nefedov VA, Marina V. Polyakova, M.V., Rorer, J., Sabelnikov, A. G., and Kochetkov, K. A. Mendeleev Communications 2007;17:167-169. 29. De G, and Kundu, D. Chem. Mater. 2001;13(11):4239-4246. 30. Kawaguchi T, Shankaran, D. R., Kim, S. J., Matsumoto, K., Toko, K., Miura, N. Sensors and Actuators B 2008;133:467-472. 31. Martinu L, Biedermann, H., Ze mek J. Vacuum 1985;35(4-5):171. 32. Pipino ACR, Silin, V. Chemical Physics Letters 2005;404:361-364. 33. Vrs NM, Patakfalvi, R., Dkny, I. Colloids and Surfaces A 2008;329:205-210. 34. Urbiztondo MA, Pellejero, I., Villarroya M., Ses, J, Pina, M.P., Dufour, I., Santamara, J. Sensors and Actuat ors B 2009;137:608-616.

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64 35. Vorotyntsev MA, Vasilyeva, S. V. A dvances in Colloid and Interface Science 2008;139:97-149. 36. Sutarlie L, Yang, K.-L. Sens ors and Actuators B 2008;134:1000-1004. 37. Nanto H, Yokoi, Y., Mukai, T., Fuji oka, J., Kusano, E., Kinbara, A., Douguchi, Y. Materials Science and E ngineering C 2000;12(1-2):43-48. 38. Zribi K, Feller, J. F., Elleuch, K., Bourmaud, A., Elleuch, B. Polym. Adv. Technol. 2006 17:727-731. 39. Valmikanathan OP, Ostroverkhova, O., Mu lla, I.S., Vijayamohanan K., Atre, S.V. Polymer 2008;49(16):3413-3418. 40. Pavia DL, Lampman, G. M., Kriz, G. S. Introduction to Spectroscopy: A Guide For Students of Organic Chamistry, 3rd Ed. ed. Australia: Thomson Learning, Inc., 2001. 41. Skoog DA, West, D. M. Principles of Instrumental Analysis. New York: Holt, Rinehart and Winston, Inc., 1971. 42. Mongillo J. Nanotechnology 101: Greenwood Press, 2007. 43. Thornton ST, Rex, A. Modern Physics for Scientists and Engineers. Australia: Thomson Learning, Inc., 2002. 44. Laboratory NHMF. Wheatstone Bridge. Magnet Lab, 2008. 45. Nilsson JW, Riedel, S. A. Elect ric Circuits: Prentice Hall, 2008 46. Hayt Jr. WH, Kemmerly, J. E., Durbin, S. M. Engineering Circuit Analysis, Sixth Edition ed.: Tata McGraw Hill, 2002. 47. Fatikow S. Automated Nanohandl ing by Microrobots: Springer, 2007. 48. Morris V. J. KAR, Gunning A. P. At omic Force Microscopy for Biologists: Imperial College Press, 1999. 49. Morita S, Wiesendanger, R., Meye r, E., Eds. Noncontact atomic force microscopy: Springer, 2002. 50. Korenivski V. The van der Pauw Technique. vol. 2009, 2003. 51. van der Pauw LJ Philips Technical Review 1958/59;20(8):220-224. 52. Bautista K. Thin Film Deposition. The University of Texas at Dallas, 2004.

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65 53. Schroder DK. Semiconductor Material and Device Characterization, 3rd Ed.: Wiley-IEEE, 2006. 54. Tompkins HG, Irene, E. A. Handbook of ellipsometry: Springer Science & Business, 2005. 55. Tompkins HG. A User's Guide to El lipsometry: Dover Publications, 2006. 56. Cherry RJ. New techniques of optic al microscopy and microspectroscopy: CRC Press, 1991. 57. Nickell J, Fischer, J. F. Crime science: methods of forensic detection: University Press of Kentucky, 1998. 58. Ganesan S, Pecht, M. Lead-free El ectronics: John Wiley and Sons, 2006. 59. Wissmann P, Finzel, H.-U. Electrical resistivity of thin metal films: Springer, 2007. 60. Graja A, Swietlik, R., Polomska, M., Brau, A., Farges, J.-P. Synthetic Metals 2002;125:319-324. 61. Sommer W, Moldenhauer, J., Schweitzer D., Heinen, I., Keller, H.J. Synthetic Metals 1995;68:133-139.

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66 Appendices

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67 Appendix A: Conductivity Data A1. Method 2 Optimizations: 02468101214 0 1 2 3 4 5 6 30 seconds 1 minute 1.5 minutes 2 minutes 2.5 minutes 3 minutes 3.5 minutes 4 minutes Voltage [V]Current [mA] Figure 39: Current-Voltage Data for 12 mg/mL Solution Optimization Each plotted data set (each line) corresponds to a different exposure time that was tested. 0 0.02 0.04 0.06 0.08 0.1 012345Resistivity, [k -cm]Time [min] Figure 40: Resistivity versus Exposure Time for 12 mg/mL So lution Optimization. Here the calculated resistivity is plot ted against the exposure time.

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68 Appendix A, continued 02468101214 0 1 2 3 4 5 6 0.5 min 1.5 min 2.5 min 3.5 min 4.5 min Voltage [V]Current [mA] Figure 41: Current-Voltage Data fo r 8 mg/mL Solution Optimization Each plotted data set (each line) corresponds to a different exposure time that was tested. 0 0.02 0.04 0.06 0.08 0.1 012345 8 mg/mLResistivity, [k -cm]Time [min] Figure 42: Resistivity versus Ex posure Time for 8 mg/mL Solution Optimization. As for the 12 mg/mL optimization, here the calculated resist ivity is plotted agai nst the exposure time.

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69 Appendix A, continued 00.20.40.60.811.21.4 0 1 2 3 4 5 6 0.5 min 1 min 2 min 4 min 6 min 8 min 10 min 12 min 14 min 16 min 18 min 20 min 22 min Voltage [V]Current [mA] Figure 43: Current-Voltage Data for 4.3 mg/mL Solution Optimization Each plotted data set (each line) corresponds to a different exposure time that was tested. 0 0.2 0.4 0.6 0.8 1 0510152025Resistivity, [k -cm]Time [min] Figure 44: Resistivity versus Expo sure Time for 4.3 mg/mL Solution Optimization. As was done for the other concentrations, here the calculated resis tivity is plotted against the exposure time. A different profile is seen because, after the film ha s been exposed for 12 minutes, the effects of the iodine deposition cause the resistivity to increase. Th e dotted line is fitted to the data points from 0.5 to 12 minutes to demonstrate the trend ex pected based on the other concentrations.

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70 Appendix A, continued Figure 45: Resistivity versus Exposure Time Op timization For All Three Solutions. Here the calculated resistivity is plotted against the exposure time for all three films for ease of comparison. A2. Comparing Methods Post-Optimization: 0510152025 0 1 2 3 4 5 6 Voltage [V]Current [mA] Figure 46: Current-Voltage Data fo r 8 mg/mL Iodine Solution Co ncentration Exposed for Four Minutes using Method 1. Th e current-voltage data for all 12 positi ons on the film tested is shown. Positions1 12

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71 Appendix A, continued 00.511.522.5 0 1 2 3 4 5 6 Voltage [V]Current [mA] Figure 47: Current-Voltage Data fo r 8 mg/mL Iodine Solution Co ncentration Exposed for Four Minutes using Method 2. The current-voltage data fo r all 12 randomized posi tions tested is shown. 00.511.522.5 0 1 2 3 4 5 6 Voltage [V]Current [mA] Figure 48: Current-Voltage Data fo r 4.3 mg/mL Iodine Solution Concentration Exposed for Ten Minutes using Method 1. Th e current-voltage data for all 12 positi ons on the film tested is shown. Positions1 12

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72 Appendix A, continued 00.511.522.5 0 1 2 3 4 5 6 Voltage [V]Current [mA] Figure 49: Current-Voltage Data fo r 4.3 mg/mL Iodine Solution Concentration Exposed for Ten Minutes using Method 2. The current-voltage data fo r all 12 randomized posi tions tested is shown.

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73 Appendix B: Optical Microscopy Data B1. Images of Films Prepared Using Method 1 The images contained herein depict characte ristic areas of a given sample which was fabricated using method 1. The surface features seen in the images of the polycarbonate before and after the addition of the BEDO-TTF dye are the postulated phase separation domains. Images of the doped films are ta ken at the area where the transition from heavily doped to less doped occu rs. This is visible as a mu ch darker area of the film where the iodine is more heavily deposite d, and a lighter area where less iodine has deposited. The features seen in the 4.3 mg/m L doped film are defects that are caused by the FPP testing. Each of those lighter areas re presents the point of contact of one of the four probes. 1000 m200 m 20 m Figure 50: OM Images of Polycarbonate Film at 25x, 100x, and 400x. 20 m 20 m 200 m 200 m 1000 m 1000 m 1000 m200 m 20 m Figure 51: OM Images of Polycarbonate/BEDO-TTF Film at 25x, 100x, and 400x.

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74 Appendix B, continued 1000 m 200 m 20 m Figure 52: OM Images of 12 mg/mL Doped Film at 25x, 100x, and 400x. 1000 m200 m 20 m Figure 53: OM Images of 4.3 mg/mL Doped Film at 25x, 100x, and 400x. B2. Images of Films Prepared Using Method 2 The images contained herein depict characteri stic areas of a given sample prepared using method 2. What is emphasized in the images of these films is the homogeneity of the iodine deposition. There was no clear in terface between heavily doped and less doped regions as was seen when method 1 was used. 20 m 200 m 1000 m 1000 m200 m 20 m Figure 54: OM Images of 12 mg/mL Doped Film at 25x, 100x, and 400x.

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75 Appendix B, continued 1000 m200 m 20 m Figure 55: OM Images of 8 mg/mL Doped Film at 25x, 100x, and 400x. 20 m 200 m 200 m 20 m Figure 56: OM Images of 4.3 mg/mL Doped Film at 100x, and 400x.

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76 Appendix C: AFM Imaging C1. Surface Scans of Films Prepared Using Method 1 10x10 m surface scans: Figure 57: 10 m Square AFM Scan of Undoped Bis-phen ol-a Polycarbonate Film. The slight scratching of the surface is due to the use of FPP testing. Figure 58: 10 m Square AFM Scan of Polycarbonate/ BEDO-TTF Composite Film. The surface features seen are damage to the film surface due to the use of FPP testing. FPP has been known to leave behind deposits of metal and other foreign materials.

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77 Appendix C, continued Figure 59: 10 m Square AFM Scan of 12 mg/mL Doped Film. From this image it can be deduced that the iodine deposited at this exposure time and concentration using method 1 does not tend to form crystallites. Figure 60: 10 m Square AFM Scan of Nonconductive Area of 8 mg/mL Doped Film. As in the 12 mg/mL film shown in Figure 59, the iodine deposi ted at this exposure time and concentration using method 1 does not tend to form cry stallites in the nonconducting re gion. (The nonconducting region forms as a result of the concentration gradient in the iodine in method 1.)

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78 Appendix C, continued Figure 61: 10 m Square AFM Scan of Conductive Area of 8 mg/mL Doped Film. Unlike the 12 mg/mL film shown in Figure 59, and the nonconducti ng area of the same film, the iodine deposited does not tend to form a continuous layer. There is no formation of crystallites, either, due to the effects of the concentration gradient on the deposition of the iodine. Figure 62: 10 m Square AFM Scan of the conductive area of the 4.3 mg/mL Doped Film. In the image some crystal-like structures are observed, but no long range order. This is most likely also due to the non-equilibrium effects of doping using method 1.

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79 Appendix C, continued 5x5 m surface scans: Figure 63: 5 m Square AFM Scan of the Polycarbonate Co ntrol Film. In the image some pore-like structures are observed, similar to what is seen in the OM and TEM images presented in the text. Figure 64: 5 m Square AFM Scan of the Polycarbonate/BEDO-TTF Control Film. In the image some pore-like structures are observ ed, similar to what is seen in the OM and TEM images presented in the text. There are also some scratches, due to the use of FPP testing on the control films.

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80 Appendix C, continued Figure 65: 5 m Square AFM Scan of 12 mg/mL Doped Film This image is a more magnified region of that shown in Figure 59. Figure 66: 5 m Square AFM Scan of the Nonconductive region of the 8 mg/mL Doped Film. This image is a more magnified region of that shown in Figure 60.

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81 Appendix C, continued Figure 67: 5 m Square AFM Scan of the Conductive region of the 8 mg/mL Doped Film. This image is a more magnified region of that shown in Figure 61. The deposit in the low er center of the image is believed to be another instance of damage caused by FPP testing. Figure 68: 5 m Square AFM Scan of the Conductive region of the 4.3 mg/mL Doped Film. This image is a more magnified region of that shown in Figure 62.

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82 Appendix C, continued 2x2 m surface scans: Figure 69: 2 m Square AFM Scan of the Polycarbonate Co ntrol Film. At this scale most of the surface features are no longer easily visible, so no further magnification will be done. Figure 70: 2 m Square AFM Scan of the Polycarbonate/ BEDO-TTF Control Film. This image is a more magnified region of that shown in Figure 64. The small bumps seen are suspected to be small aggregated of BEDO-TTF dye molecules.

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83 Appendix C, continued Figure 71: 2 m Square AFM Scan of the 12 mg/mL Dope d Film. This image is a more magnified region of that shown in Figure 65. It can be seen from this scan that the iodine is not forming crystallites, and that the surface is very uneven. Figure 72: 2 m Square AFM Scan of the Nonconductive Area of the 8 mg/mL Doped Film. This image is a more magnified region of that shown in Figure 66. This area of the film shows that the entire surface is coated with iodi ne, but also that it is uneven, and that no crys tallites are formed.

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84 Appendix C, continued Figure 73: 2 m Square AFM Scan of the Conductive Area of the 8 mg/mL Doped Film. This image is a more magnified region of that shown in Figure 67. This area of the film shows that, as in the case of the nonconductive area, the enti re film surface is coated with io dine, and that the deposits are larger. Figure 74: 2 m Square AFM Scan of the Conductive Area of the 4.3 mg/mL Doped Film. This image is a more magnified region of that shown in Figure 68. This area of the film shows deposits of iodine with more order than in the case of the other two concentrations, but no crystallites.

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85 Appendix C, continued C2. Surface Scans of Films Prepared Using Method 2 10x10 m surface scans: Figure 75: 10 m Square AFM Scan of Film Doped Using 12 mg/mL solution and Method 2 for 3 minutes. Because the film was do ped at equilibrium, the beginnings of crystallite formation can be seen. The texture of the surface is due to the form ation of nucleation sites where the iodine deposits. Figure 76: 10 m Square AFM Scan of Film Doped Using 8 mg/mL solution and Method 2 for 4 minutes. Similar to Figure 75, the beginnings of crystallite formation are more defined than before.

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86 Appendix C, continued Figure 77: 10 m Square AFM Scan of Film Doped Using 4.3 mg/mL solution and Method 2 for 10 minutes. Here, crystallite formation has occurred, and deposits with long ra nge order are visible.

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87 Appendix C, continued 5x5 m surface scans: Figure 78: 5 m Square AFM Scan of Film Doped Using 12 mg/mL solution and Method 2 for 3 minutes. This is a magnified area of the scan presented in Figure 75. Figure 79: 5 m Square AFM Scan of Film Doped Using 8 mg/mL solution and Method 2 for 4 minutes. This is a magnified area of the scan presented in Figure 76.

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88 Appendix C, continued Figure 80: 5 m Square AFM Scan of Film Doped Using 4.3 mg/mL solution and Method 2 for 10 minutes. This is a magnified area of the scan presented in Figure 77.

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89 Appendix C, continued 2x2 m surface scans: Figure 81: 2 m Square AFM Scan of Film Doped Using 12 mg/mL solution and Method 2 for 3 minutes. This is a magnified area of the scan pres ented in Figure 78. At this magnification the details of the locations of the nucleation sites and the ed ges of the crystallites are more clearly defined. Figure 82: 2 m Square AFM Scan of Film Doped Using 8 mg/mL solution and Method 2 for 4 minutes. This is a magnified area of the scan presented in Figure 79. The morphology of this concentration and exposure time can be seen to look very similar to that of the 12 mg/mL doped film seen in Figure 81, in such criteria as the size and density of the crystallites.

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90 Appendix C, continued Figure 83: 2 m Square AFM Scan of Film Doped Using 4.3 mg/mL solution and Method 2 for 10 minutes. This is a magnified area of the scan presen ted in Figure 80. In this scan it is clearly visible that the crystallites are now fully formed and that more nucleation sites are forming on their surface. The formation of these secondary nucleation sites seem s to imply that the formation of a second layer of crystallites could potentially form on top of the first.

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91 Appendix C, continued 0.5x0.5 m surface scans: Figure 84: 0.5 m Square AFM Scan of Film Doped Using 12 mg/mL solution and Method 2 for 3 minutes. This is a magnified area of the scan pres ented in Figure 81. This image is presented here for the purpose of emphasizing the form ation of the iodine nucleation sites. Figure 85: 0.5 m Square AFM Scan of Film Doped Using 8 mg/mL solution and Method 2 for 4 minutes. This is a magnified area of the scan presented in Figure 82. The progression to more defined crystallites with iodine loading can be seen when comparing the image of this film to the 12 mg/mL doped film and the 4.3 mg/mL doped film.

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92 Appendix C, continued Figure 86: 0.5 m Square AFM Scan of Film Doped Using 4.3 mg/mL solution and Method 2 for 10 minutes. This is a magnified area of the scan p resented in Figure 83. Consistent with the other images taken of this film, the crystallites are more defined than in either of the other two films.

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93 Appendix D: TEM Images 2000 nm 2000 nm 500 nm Figure 87: TEM – Iodine Deposit TEM Scans. Sh own are three images of successively higher magnification of an iodine deposit on the 4.3 mg/mL film.