INVESTIGATION OF ELECTROACTIVE ULTRATHIN FILMS BY SURFACE PLASMON SPECTROSCOPY ZHANG NAN (M Eng., BUCT) A THESIS SUBMITTED FOR THE DEGREE OF MASTER OF SCIENCE DEPARTMENT OF MATERIALS SCIENCE NATIONAL UNIVERSITY OF SINGAPORE 2004 Acknowledgement I would like to express my gratitude to all the persons who made this thesis possible First of all, I gratefully acknowledge my supervisors, Prof Wolfgang Knoll and Prof Michael R Philpott for their invaluable guidance and support Their enthusiasm and active research interests are the constant source of inspiration to me During the course of this work, I have learnt much on how to research work I would also like to thank our group members Particularly, thanks to Dr Thomas Jakob for his support in high pressure SPS, Dr Akira Baba for his instruction and discussions in the electrochemistry, Amel and Menges for their support in imprinting gratings, Dr Ruediger Schweiss for his proof reading of this thesis In addition, special thanks to Dr Teng Jinghua and Jolynn for their help in grating fabrication in IMRE, to Agnes for her help in AFM and staff members in the Department of Materials Science for their assistance Last but not least, I would like to thank my husband, Zhilong, for his care, encouragement and his supporting all of my decisions i Table of Contents Table of Contents Acknowledgement.……………………………………………………………………i Table of Contents.……………………………………………………………….……ii Summary…………………………………………………………………………… iv List of Tables……………………………………………………………… …….…vi List of Figures…………………… …………… ………………………………… vii List of Symbols.…………………………………………………………… …… …x List of Abbreviation.…………………………………………………………… …xii Chapter Introduction ……………………………………………………… ……1 Chapter Introduction to Basic Principles………………………………… …….3 2.1 Plasmon Surface Polariton.……………………………………………………… 2.1.1 Maxwell equations……………………… …………………………………4 2.1.2 Excitation of surface plasmon………………………………………………6 2.1.2.1 Prism coupling…………………………………………………….8 2.1.2.2 Grating coupling………………………………………………… 10 2.1.2.3 Factors affecting surface plasmon resonance…………………12 2.1.2.4 Addition of dielectric layers…………………………………….15 2.2 Refractive Index Variable as Thermodynamic Function ……………………….16 2.2.1 Lorenz-Lorentz equation………………………………………………….17 2.2.2 Tait equation……………………………….……………………………….20 2.3 Evaluation of Grating Coupling Experiments………………… ……………….22 2.4 Cyclic Voltammetry………………………………………………………………23 References……………………………………………………………………………27 Chapter Experimental Methods …………………………………………………29 3.1 Sample Characterization Techniques……………………………………………29 3.1.1 Surface plasmon spectroscopy…………………………………………….29 3.1.2 Electrochemical-surface plasmon spectroscopy……………………… 32 3.1.3 High pressure surface plasmon spectroscopy with electrochemical cell…33 3.1.5 Atomic force microscopy…………………………………………………36 3.2 Sample Preparation Techniques…………………………………………………36 3.2.1 Fabrication of gratings…………………………………………………….37 3.2.1.1 Photolithography………………………………………………… 37 3.2.1.2 Hot embossing lithography………………………………………38 3.2.2 Cleaning procedure………………………………………………… ……39 3.2.3 Thermal evaporation of metal layers………………………… …………40 3.2.4 Cyclic voltammetry……………………………………………….……… 40 3.2.5 Layer-by-Layer self-assembly process…………………………………… 41 References………………………………………………………………………… 42 Chapter Electropolymerization of Bithiophene…………………………………44 4.1 Experiments………………………………………………………………………45 4.2 Results and Discussions……………………………………………………… 45 4.2.1 Reference solution………………………………………………………….45 4.2.2 Electropolymerization process of bithiophene …………………………….48 4.2.2.1 Cyclic voltammgram………………………………………………49 ii Table of Contents 4.2.2.2 Angular-dependent scan of SPS……………………… …………50 4.2.2.3 Time-dependent scan of SPS…………………………………… 53 4.2.3 p-Doped state……………………………………………………………….58 4.2.4 Reversibility of polythiophene film ………………………………………61 4.3 Summary………………………………………………………………… …….61 References……………………………………………………………………… ….62 Chapter Polyaniline / Sulfonated Polyaniline Multilayer Film Under Elevated Pressure…………………………………………… ……………… 65 5.1 Introduction………………………………………………………………… ….65 5.2 Experiments………………………………………………………………………66 5.2.1 Grating fabrication by photolithography………………………………… 66 5.2.2 Grating fabrication by hot embossing lithography……………………… 66 5.2.3 Polycation and polyanion preparation…………………………………… 67 5.2.4 Layer-by-Layer adsorption……………………………………………… 68 5.3 Results and Discussions……………………………………………….……….69 5.3.1 Characterization of grating profile………………………………… …….69 5.3.1.1 Grating fabricated by photolithography………………………….69 5.3.1.2 Grating fabricated by hot embossing lithography……………… 74 5.3.2 Investigation of PANI / SPANI multilayer film under elevated pressure….77 5.3.2.1 Layer-by-Layer self-assembly process………….…………………77 5.3.2.2 Electroactivity of multilayer film in neutral solution… …… …79 5.3.2.3 Pressure effect on medium…………………………… ………….82 5.3.2.4 Electroactivity of multilayer film under elevated pressure…… …84 5.3.2.4 Optical property of multilayer film under elevated pressure 84 5.4 Summary…………………………………………………………………………88 References……………………………………………………………………………89 Chapter Conclusion……………………………………………………………….92 iii Summary Summary Surface Plasmon Spectroscopy (SPS) in combination with electrochemical techniques was used to investigate several electroactive polymer films, in particular, polybithiophene and polyaniline / sulfonated polyaniline (PANI / SPANI) multilayers SPS has been shown to be a technique of high sensitivity for characterizing ultrathin films at the nanometer scale In this work, a combination of SPS and electrochemical technique was used to in-situ investigate the manipulation of an electrode/electrolyte interface A high pressure cell adapted for SPS and electrochemical experiments could be utilized to perform the SPS and electrochemical measurements under pressure up to 50 MPa The electropolymerization of 2,2’-bithiophene was investigated by electrochemical-surface plasmon spectroscopy (EC-SPS) A shift of the resonance angle was observed, which indicated a continuous deposition of polymer on the electrode The anion doping and dedoping were monitored during the electropolymerization of bithiophene at the electrode surface in the time-dependent scan of SPS During the anodic scan, the anion doping resulting in a decrease in reflectivity gave rise to swelling of the polymer film The dedoping of the anion caused a slope change of the reflectivity during the cathodic scan The gratings used as the surface plasmon coupler were fabricated by photolithography or hot embossing lithography The surface profile of the grating was characterized by atomic force microscopy (AFM) In hot embossing lithography, the profile of the iv Summary master grating was successfully transferred to a polymethylmethacrylate (PMMA) film spin-coated on the quartz glass Gratings fabricated by these two methods could be used for the surface plasmon coupling The process of PANI / SPANI multilayer film manipulated on the Au surface by the Layer-by-Layer technique was investigated by EC-SPS With the increased number of deposited bilayer, a continuous deposition of the polyelectrolyte was observed The SPS angular scan of the reference system (bare gold in phosphate-buffered saline (PBS) solution (pH = 7.0)) was fitted well by just changing the refractive index of PBS without varying other parameters The behavior of the PBS medium under pressure was modeled by the Lorenz-Lorentz and Tait equations The parameters in these two equations were obtained by fitting the data of the refractive index to the Lorenz-Lorentz / Trait equations No deviation of these parameters from those of water was found After the PANI / SPANI multilayer film was introduced into the high pressure SPS with an electrochemical cell, the cyclic voltammograms and SPS angular scans of the PANI / SPANI / PBS system at different pressures were measured and compared It was found that the peak current decreased with elevated pressure This change indicated that the film became more compact and ion transfer within the film became more difficult It was observed that the shift of minimum angle was larger than that in the reference system This was due to the interaction of the refractive index change and the thickness change of the film The former increased with elevated pressure while the later decreased Further experiments are on going to separate these factors v List of Tables List of Tables Table 5.1 Parameters resulting from fitting the data of the refractive index to the Lorenz-Lorentz / Tait equations Table 5.2 Critical angle and minimum angle of the bare gold / PBS system and those of the PANI / SPANI / gold / PBS system vi List of Figures List of Figures Fig 2.1 Dispersion relation of free photons in a dielectric and in a coupling prism Fig 2.2 Otto and Kretschman configuration for high refractive index prism Fig 2.3 Sketch of the diffraction induced by a grating surface Fig 2.4 SPS angular scan for different metals with and without adsorbed layer Fig 2.5 Comparison of typical angular scan by prism coupling and grating coupling Fig 2.6 Sketch of two processes to excite a surface plasmon Fig 2.7 Scheme of the potential wave form and the cyclic voltammogram Fig 3.1 Sketch of a standard SPS set-up Fig 3.2 Sketch of the flow cell for the excitation of surface plasmons in SPS Fig 3.3 Comparison of angular and kinetic scans during adsorption of additional layer Fig 3.4 Sketch of the cell in EC-SPS Fig 3.5 Sketch of an evaporation mask used to evaporate the working and counter electrode on the substrate Fig 3.6 Sketch of high-pressure SPS with the electrochemical cell Fig 3.7 (a) Fabrication procedure of shallow gratings by photolithography (b) Optical set-up used to fabricate holographic gratings Fig 3.8 Schematic procedure of the film deposition by LbL process Fig 4.1 SPS kinetic scans and cyclic voltammograms for reference solution Fig 4.2 Corresponding SPS angular scans taken after the cyclic sweep Fig 4.3 Scheme of electropolymerization with thiophene as the monomer Fig 4.4 Cyclic voltammograms of electropolymerization of bithiophene vii List of Figures Fig 4.5 Cyclic voltammogram of electropolymerization of bithiophene in first cycle Fig 4.6 SPS angular scans taken in solution with or without bithiophene monomer Fig 4.7 SPS angular scans taken after each cyclic sweep Fig 4.8 Plot of polymer layer thickness vs number of cycles Fig 4.9 Scheme of doping / dedoping process Fig 4.10 SPS kinetic scans and cyclic voltammograms in each cyclic sweep Fig 4.11 SPS angular scans of polybithiophene films at different fixed potentials Fig 4.12 SPS angular scans of bare gold surface at different fixed potentials Fig 4.13 p-Doping process of polybithiophene Fig 4.14 Simultaneous observation of SPS kinetic scan and current change during the repeated cyclic sweep Fig 5.1 Molecular structures of employed PANI and SPANI Fig 5.2 AFM pictures of grating profiles on photoresist before and after evaporation of metal layer Fig 5.3 AFM pictures of grating profiles before and after etching Fig 5.4 SPS angular scans in different media by using the grating as coupler Fig 5.5 Thickness of spin-coated PMMA film vs concentration of the solution Fig 5.6 AFM pictures of grating profiles by hot embossing lithography Fig 5.7 SPS angular scans taken after each bilayer polyelectrolyte deposition Fig 5.8 Thickness of multilayer film vs number of deposited bilayer Fig 5.9 Molecular structures of PANI at different state Fig 5.10 Cyclic voltammograms of Au electrode modified with bilayers of viii List of Figures PANI / SPANI film Fig.5.11 SPS kinetic scan of PANI / SPANI multilayer film in PBS Fig 5.12 SPS angular scans of an evaporated gold layer in PBS at different pressures Fig 5.13 Refractive index of PBS at different pressures fitted by Lorenz-Lorentz / Tait equations Fig 5.14 Cyclic voltammograms of PANI / SPANI / PBS system at different pressures Fig 5.15 Cationic peak current vs square root of the scan rate at different pressures Fig 5.16 SPS angular scans of PANI / SPANI multilayer film in PBS at different pressures ix Chapter Polyaniline / Sulfonated Polyaniline Multilayer Film Under Elevated Pressure PANI / SPANI film with bilayers fabricated on the grating substrate They were recorded in 0.1 mol/L phosphate-buffered saline (PBS) solution with different scan rates The inset shows the plot of the anodic peak current versus the square root of the scan rate A linear relationship is found, indicating a solution redox process Prior to the peak potential, it is electron transfer control After the peak potential, it is diffusion control 30 Current density / µA/cm 20 10 mv/s 16mv/s 36mv/s 49mv/s -10 70 60 data linear fit 50 40 30 20 R=0.997 10 -20 -30 -40 -50 -60 -0.4 -0.2 0.0 0.2 0.4 0.6 Potential E (vs Ag/AgCl(saturated) ) / V Fig 5.10 Cyclic voltammograms of Au electrode modified with bilayers PANI / SPANI multilayer film recorded in 0.1 mol/L PBS buffer at a scan rate of 9,16,36,49 mV/s, receptively Inset shows the relationship between anodic peak currents and the square root of the scan rate The redox behavior of PANI / SPANI multilayer film in PBS was also investigated by SPS Fig.5.11 shows the SPR reflectivity change of such film during cyclic sweeps The reflectivity increases during the anodic potential scan and decreases during the cathodic scan The change is due to the doping / dedoping processes, which results in a change of the dielectric constant and the density of the film, thus causing the change of reflectivity - 80 - Chapter Polyaniline / Sulfonated Polyaniline Multilayer Film Under Elevated Pressure 0.54 (a) 0.52 Reflectivity R 0.50 0.48 0.46 0.44 0.42 0.40 50 100 150 200 250 300 Time / s 0.54 (b) Reflectivity R 0.52 0.50 0.48 0.46 0.44 0.42 -0.4 -0.2 0.0 0.2 0.4 0.6 Potential E (Ag/AgCl (saturated)) / V Fig.5.11 SPS kinetic scan of bilayers PANI / SPANI measured in PBS (a) SPS kinetic scan (b) Reflectivity vs Potential (3rd cyclic sweep) - 81 - Chapter Polyaniline / Sulfonated Polyaniline Multilayer Film Under Elevated Pressure 5.3.2.3 Pressure effect on the medium Before we studied the PANI / SPANI multilayer film at elevated pressure, the pressure medium’s behavior and pure gold layer’s behavior under pressure need to be investigated first in order to serve as the reference Studies of pressure effects on the optical properties of liquid phases have been performed for a long time [38, 39] The theoretical Lorenz-Lorentz equation and Tait equation have been demonstrated to be suitable to fit the behavior of liquid under high pressure [2, 3] We recorded SPS angular scans of the bare gold in 0.1 mol/L PBS buffer under four different pressures, as shown in Fig 5.12 A shift of the minimum angle to higher values with an elevated pressure can be noticed This shift of the SPS spectrum can be completely fitted by changing refractive index of PBS only When increasing the pressure, the density of PBS increases and consequently the refractive index of PBS increases During the fitting, the dielectric constants of gold were not changed The minimum angle can be observed during the whole pressure range So the gold layer is stable and its optical property remains in aqueous environment up to pressure of 37.7 MPa Fig 5.13 depicts the refractive index of the PBS buffer as a function of pressure up to 37.7 MPa With the increasing pressure, the compression leads to an increased density of the medium and thus an increased refractive index This behavior was evaluated with the Lorenz-Lorentz / Tait equation The result of this evaluation is shown in Table 5.1 Although the buffer contains small amounts of salts, the absolute values of the parameters in these two equations are comparable to those found for pure water No significant deviation was found from the values of water - 82 - Chapter Polyaniline / Sulfonated Polyaniline Multilayer Film Under Elevated Pressure 0.83 0.8 0.82 0.81 8.8MPa 18.4MPa 28.1MPa 37.7MPa 0.80 0.79 Reflectivity R 0.6 0.78 3.8 4.0 4.2 4.4 4.6 0.4 8.8MPa 18.4MPa 28.1MPa 37.7MPa 0.2 0.0 12 15 18 21 Incident angle θ ⁄ ° Fig 5.12 SPS angular scans of an evaporated gold layer in PBS at different pressures 1.339 data ⎯ Lorenz-Lorentz/Tait Fit Refractive index 1.338 1.337 1.336 1.335 1.334 10 15 20 25 30 35 40 Pressure / MPa Fig 5.13 Refractive index of PBS buffer at different pressures The solid line is the Lorenz-Lorentz / Tait equations fit to the data - 83 - Chapter Polyaniline / Sulfonated Polyaniline Multilayer Film Under Elevated Pressure Table 5.1 Parameters resulting from fitting the data of the refractive index to the Lorenz-Lorentz/Tait equations T/ ºC 25 v0 / cm3g-1 1.00317 RLL / cm3g-1 0.2063±0.0002 B / MPa 262.54±89 κ0 / GPa 0.41087±0.01 The value for v0 is extrapolated from CRC Handbook of Chemistry and Physics v0: RLL: Lorenz-Lorentz constant B: Temperature depending parameter κ0: Bulk compressibility at standard conditions 5.3.2.4 Electroactivity of multilayer film under elevated pressure Next, the PANI / SPANI multilayer film was introduced into the high pressure SPS with an electrochemical cell The cyclic voltammograms of the PANI / SPANI / PBS system at different pressures were measured and compared Fig 5.14 shows the cyclic voltammograms of such system with the scan rate of 20 mV/s It can be seen that the peak current decreases from 0.1 MPa to 8.6 MPa and the peak separation increase These are due to the increased iR drop in the cell and indicate that the film becomes more compact under elevated pressure and the transfer of ions becomes more difficult For the PANI / SPANI multilayer film, the PANI is doped by the negatively charged SPANI, which is the charge carrier in the film The H+ around the SPANI chain keeps the electroactivity of the PANI / SPANI film in neutral solution In order to investigate the system further, the sweep rate was varied at constant pressure In Fig 5.15, the current peak is plotted as a function of the square root of the sweep rate It can be fitted by a straight line, indicating a solution redox process 5.3.2.4 Optical property of multilayer film under elevated pressure The optical property of PANI / SPANI multilayer films under elevated pressure was also studied Fig 5.16 shows the SPS angular scans for such an ultrathin polymer film at different pressures It can be seen that the minimum angle shifts to a higher angle This shift was compared with the reference system, bare gold / PBS system The - 84 - Chapter Polyaniline / Sulfonated Polyaniline Multilayer Film Under Elevated Pressure results are depicted in Table 5.2 It can be noticed that the shifts of minimum angle are larger in the gold / PANI / SPANI/ PBS system than that in the bare gold / PBS system This shift cannot be fitted by just changing the refractive index of PBS The changes of multilayer film under pressure also contribute to the shift The refractive index of PBS increases with the elevated pressure, as discussed in 5.3.2.3 The multilayer film’s change is the density change itself The density change of the film leads to the change of both the thickness and the refractive index of the film However, only a set of parameters (n, d) could be derived from such SPS angular scan These two parameters are correlated and cannot be separated just by these SPS angular scans because a thin film with a high refractive index might have the same surface plasmon resonance as a thick film with a low refractive index However, by virtue of the electrochemical results of this system, we give a qualitative explanation to the result From the investigation of the electroactivity of the PANI / SPANI film, we know that the film becomes more compact under pressure and accordingly the film density increases Therefore, the refractive index of the film increases, which makes the minimum angle shift to higher angle Further experiments are needed to separate the thickness change and refractive index change quantively Table 5.2 Comparison of the critical angle and minimum angle of the bare gold/PBS system with those of the PANI /SPANI multilayer film system Bare gold PANI/SPANI film θc : critical angle θc/° θm/° θc/° θm/° 0.1 MPa MPa 18 MPa 28 MPa 38 MPa / / 4.95 15.4 4.00 14.7 5.0 15.55 4.05 14.8 5.05 15.7 4.1 14.9 5.1 15.85 4.2 15 5.15 16.0 θm : minimum angle - 85 - Chapter Polyaniline / Sulfonated Polyaniline Multilayer Film Under Elevated Pressure 1.5 0.1 MPa 8.6 MPa 28.6 MPa Current density / µA/cm 1.0 0.5 0.0 -0.5 -1.0 -1.5 0.0 0.1 0.2 0.3 0.4 0.5 Potential E (vs Ag) / V Current density / µΑ/cm2 Fig 5.14 Cyclic voltammograms of PANI /SPANI / PBS system at different pressures with same scan rate 5 data at 18.6MPa linear fit data at 8.6MPa linear fit data at 0.1MPa linear fit Square root of sweep rate (mV/s)1/2 Fig 5.15 Cathodic peak current versus square root of the scan rate at different pressures The solid lines are linear fits to the data - 86 - Chapter Polyaniline / Sulfonated Polyaniline Multilayer Film Under Elevated Pressure a) 0.95 0.1 MPa 8.8 MPa 18.6 MPa 28.6 MPa 37.9 MPa 0.90 Reflectivity R 0.85 0.80 0.75 0.70 0.65 0.60 0.55 10 12 14 16 18 20 22 24 Incident angle θ / ° b) 0.92 0.1 MPa 8.8 MPa 18.6 MPa 28.6 MPa 37.9 MPa 0.91 Reflectivity R 0.90 0.89 0.88 0.87 0.86 0.85 4.2 4.5 4.8 5.1 5.4 5.7 6.0 Incident angle θ / ° c) 0.65 0.1 MPa 8.8 MPa 18.6 MPa 28.6 MPa 37.9 MPa 0.64 Reflectivity R 0.63 0.62 0.61 0.60 0.59 0.58 0.57 12 13 14 15 16 17 18 Incident angle θ / ° Fig 5.16 SPS angular scans of a PANI / SPANI multilayer film in PBS at different pressures (a) full scan (b) critical angle part (c) resonance angle part - 87 - Chapter Polyaniline / Sulfonated Polyaniline Multilayer Film Under Elevated Pressure 5.4 Summary Gratings used for SPS were fabricated by photolithography or hot embossing lithography These gratings can be used for surface plasmon coupling Photolithography is a costly way to get gratings with a good surface profile and the grating profile will have small differences from each other after etching However, a grating with a good surface profile can be reused many times and only the top layers like gold films and the dielectric layers need to be removed Hot embossing lithography is a fast method for the parallel replication of gratings with low cost The profile of the master grating can be transferred to the thin PMMA film successfully However, such gratings cannot be reused The deposition process of the PANI / SPANI multilayer film by LbL technique was studied by SPS A continuous deposition of the polyelectrolyte was observed With the assumption of a fixed refractive index of the film, a linear relationship between the film thickness and the number of bilayers was obtained Compared with the values in the literature, the relatively small absolute value of each bilayer thickness is due to the corrugated grating surface profile The electroactivity of PANI / SPANI multilayer film in neutral solution was investigated by CV and SPS A linear relationship between the peak current and the square root of the scan rate was found, indicating a solution redox process The SPR reflectivity increased during the anodic potential scan and decreased during the cathodic scan The change is due to the doping / dedoping processes which result in the change of the dielectric constant and the density of the film The behavior of bare gold / PBS systems under elevated pressure was studied first, - 88 - Chapter Polyaniline / Sulfonated Polyaniline Multilayer Film Under Elevated Pressure which was used as the reference to the gold /PANI /SPANI / PBS system A shift of the minimum angle with an elevated pressure was observed This shift could be completely fitted by varying the refractive index of PBS without changing other parameters The behavior of the PBS medium under pressure was evaluated by the Lorenz-Lorentz / Tait equations The parameters in the two equations were obtained by fitting to the data of the refractive index to the Lorenz-Lorentz / Tait equations These parameters were found to have no much deviation from those of water The PANI / SPANI multilayer film’s electrochemical and optical properties under elevated pressure were investigated by high pressure SPS with an electrochemical cell The cyclic voltammograms of the PANI / SPANI film under different pressures were compared It was found that the peak current decreased with elevated pressure This indicated that the film became more compact and ion transfer became more difficult The electrochemical behavior of the mutilayer film under elevated pressure was also diffusion control The SPS angular scans for such an ultrathin polymer film at different pressures were recorded The minimum angle shifted to a higher angle, which was much higher than that in the reference system It could not be fitted by just changing the refractive index of PBS Under elevated pressure, the thickness of the film decreased and refractive index of the film increased All of these changes contribute to the shift of the minimum angle Further experiments are needed to separate them quantitatively References (1) Drickamer, H G High Pressue Chemistry, Biochemistry and Materials Science Winter, R.; Jonas, J ed NATO ASI Series, 1992, p67 (2) Kleideiter, G.; Lechner, M D.; Knoll, W Macromol Chem Phys 1999, 200, 1028 - 89 - Chapter Polyaniline / Sulfonated Polyaniline Multilayer Film Under Elevated Pressure (3) Kleideiter, G.; Sekkat, Z.; Kreiter, M.; Lechner, M D.; Knoll, W J Molecular Structure 2000, 521, 167 (4) Ulrich, F.; Thomas, J.; Thorleif B.; Wolfgang, K.; Matthias, B Fluid Phase Equilibria 2002, 200, 147 (5) (8) Kiyoshi, M.; Acheson, M R Organic Synthesis at High Pressure John Wiley & Sons, Inc 1991 Maria, T C.; Harry, G D.; Larry, R F J Phys Chem 1992, 96, 9888 Thomas, J G R.; Hans-U, S.; Wolfgang H M.; Gerhard W Chem Phys Letters 1998, 283, 15 Ferreira, M.; Cheung, J H.; Rubner, M F Thin Solid Films 1994, 244, 806 (9) Ferreira, M.; Rubner, M F Macromolecules 1995, 28, 7107 (6) (7) (10) Knoll, W Curr Opin Colloid Interface Sci 1996, 1, 137 (11) Ferreira, M.; Rubner, M F.; Mater Res Soc Symp Proc 1994, 328, 119 (12) Onoda, M.; Yoshino, K J Appl Phys 1995, 78, 4456 (13) Tian, J.; Wu, C C.; Thompson, M E.; Stum, J C.; Marcella, M J.; Swager, T M Adv Mater 1995, 7, 395 (14) Hong, H.; Davidov, D.; Avany, Y.; Chayet, H.; Faraggi, E Z.; Neumann, R Adv Mater 1995, 7, 846 (15) Ho, P K H.; Kim, J S.; Burroughes, J H.; Becker, H.; Li, S F Y.; Brown, T M.; Cacialli, F.; Friend, R H Nature 2000, 404, 481 (16) Advincula, R.; Frank, C W.; Roitman, D.; Sheats, J.; Moon, R.; Knoll, W Mol Cryst Liq Cryst 1998, 316, 103 (17) Mark, H.; Rubinson, J F Conducting Polymer Films as Electrodes In Interfacial Electrochemistry; Principles and Applications; Wieckowski, A., Ed.; Marcel Dekker: New York, 1999; pp 839 (18) Ross, S.; Seliskar, C.; Heineman, W Anal Chem 2000, 72, 5549 (19) MacDiarmid, A G.; Chiang, J C.; Halpern, M.; Huang, W S.; Mu, S L.; Somasiri, N L D.; Wu, W.; Yaniger, S I Mol Cryst Liq Cryst 1985, 121, 173 (20) Chen, S A.; Fang, W G Macromolecules 1991, 24, 1232 (21) Nguyen, M T.; Dao, L H J Electroanal Chem 1980, 111, 111 (22) Gustafassom, G.; Treacy, Y C.; Klavetter, N C.; Heeger, A J Synth Metal 1993, 57, 4123 (23) Bartlett, P N.; Wallace, E N K J Electroanal Chem 2000, 486, 23 (24) Simon, E.; Hallwell, C M.; Toh, C S.; Cass, A E.; Bartlett, P N - 90 - Chapter Polyaniline / Sulfonated Polyaniline Multilayer Film Under Elevated Pressure Bioelectrochemistry 2002, 55, 13 (25) Raitman, Q A.; Katz, E.; Buckmann, A F.; Willner, I J Am Chem Soc 2002, 124, 6487 (26) Chou, S Y.; Krauss, P.; Renstron, J J Vac Sci Technol B 1996, 14, 4129 (27) Decher, G Science 1997, 277, 1232 (28) Baba, A.; Park, M.; Advincula, R.C.; Knoll, W Langmuir 2002, 18, 4648 (29) Advincula, R IEICE Trans Electron 2000, 7, 1104 (30) Baba, A.; Kaneko, F.; Advincula, R C Colloids Surf 2000, 173, 39 (31) Wilbur, J L.; Kumar, A.; Kim, E.; Whitesides, M Adv Mater 1994, 6, 600 (32) Lin, L; Cheng, Y T.; Chiu, C J Microsystem Technologies 1998, 4, 113 (33) Heydeman, L J.; Schift, H.; David, C.; Gobrecht, J.; Schweizer, T Microelectronic Engineering 2000, 54, 229 (34) Bird, R B.; Armstrong, R C.; Hassager, O in: Fluid Mechanics, Dynamics of Polymeric Liquids, Vol 1, John Wiley, 1987 (35) Tian, S J.; Baba, A.; Liu, J Y.; Wang, Z H.; Knoll, W.; Park, M K.; Advincula, R Adv Func Mater 2003, 13, 473 (36) Master, J G.; Sun, Y.; MacDiarmid, A G Synth Met 1991, 41, 715 (37) Tripathy, S K.; Kumar, J.; Nalwa, H S Polyelectrolytes, Their Characterization, Polyelectrolyte Solutions Dimitriev IN Handbook of Polyelectrolytes and Their Applications Vol 2:, p65 (38) Gibson, R E.; Loeffler, O H J Am Chem Soc 1941, 63, 898 (39) Rosen, J S J Opt Soc Am 1947, 37, 932 - 91 - Chapter Conclusion Chapter Conclusion Surface plasmon spectroscopy (SPS) has been shown to be a technique with high sensitivity for the characterization of ultrathin films at the nano-scale Several kinds of other techniques have been combined with it to simultaneously detect the changes of films on the metal surface In this thesis, the possibility of performing a combination of SPS with cyclic voltammetry (CV) for the in-situ evaluation of electrochemical processes of conducting polymers on a flat electrode substrate was demonstrated; in particular, electropolymerization of 2,2’-bithiophene was investigated The high pressure SPS with an electrochemical cell was utilized to investigate polyaniline / sulfonated polyaniline (PANI / SPANI) multilayer film The instrument can perform standard SPS measurement under elevated pressure up to 50 MPa and can additionally perform electrochemical experiments at the same time The electropolymerization process of 2,2’-bithiophene and the doping / dedoping process were investigated by electrochemical-surface plasmon spectroscopy (EC-SPS) From our studies, the 2,2’-bithiophene monomer did not form a self-assembled monolayer on the electrode surface The cyclic sweeps resulted in a continuous deposition of the polybithiophene With the assumption that the thickness was independent of refractive index, a linear relationship between the thickness of the film and the number of the cycle was obtained In the first cycle, the increase of the roughness mainly contributed to the reflectivity’s increase In the following cycles, the reflectivity’s increase was due to the aggregation of the polybithiophene film on the electrode surface The anion doping and dedoping processes during the electropolymerization at the electrode surface were observed by the time-dependent - 92 - Chapter Conclusion scan of SPS During the positive scan, the reflectivity’s decrease was the result of anion doping, which was equal to the swelling of the polymer film During the negative scan the slope change of the reflectivity was due to the dedoping of the anion After putting the electrode with polybithiophene film into a monomer free electrolyte solution, the p-doped state of the polybithiophene was investigated The minimum angle in the SPS spectrum shifted to lower angle in p-doped state After redox cycling for three times, there was no reflectivity change, which indicated that the polybithiophene film had good reversibility from the p-doped state to the undoped state The gratings used as the surface plasmon coupler were fabricated by photolithography or hot embossing lithography The surface profiles of gratings were characterized by AFM Gratings fabricated by these two methods can be used for SPS It is costly in time and resources to get a good grating surface profile by photolithography and additionally gratings have small difference from each other after etching However, such gratings with good features can be reused for many times just by removing the top layers The hot embossing process is a fast method for grating fabrication with low cost With a single master grating, the profile of the master grating was successfully transferred to the thin PMMA film spin-coated on the quartz glass The parallel replication of gratings can be achieved However, such gratings cannot be reused The deposition process of the PANI / SPANI multilayer film by the LbL technique was studied by SPS A continuous deposition of the polyelectrolyte was observed With the assumption of a fixed refractive index of the film, a linear relationship - 93 - Chapter Conclusion between the film thickness and the number of bilayer was obtained The electroactivity of PANI / SPANI multilayer film in neutral solution was investigated by CV and SPS A linear relationship between the peak current and the square root of the scan rate was found, indicating a solution redox process The SPR reflectivity increased during the positive potential scan and decreased during the negative potential scan This change was due to the ion doping / dedoping processes The behavior of the pressure medium (PBS) was studied by high pressure SPS It was observed that the minimum angle shifted to a higher angle with elevated pressure The shift of minimum angle was completely fitted by varying the refractive index of PBS without changing other parameters in SPS spectrum simulation (Winspall) This behavior was evaluated by the Lorenz-Lorentz / Tait equations The parameters in these two equations were obtained by fitting the data of the refractive index to these equations No deviation of these parameters from those of water was found The electrochemical and optical properties of PANI / SPANI multilayer film under elevated pressure were investigated by high pressure SPS with an electrochemical cell It was found that the peak current decreased and peak separation increased with elevated pressure, which indicated that more iR dropped in system and the film became more compact and charge transfer became difficult In SPS angular scans, the shift of the minimum angle was observed It was a result of the interaction of the following factors: increased refractive index of the pressure medium; increased refractive index of polymer film and decreased thickness of polymer film In next step, SPR results by two lasers with different wavelength for the PANI / SPANI system must be obtained and analyzed further in order to separate these factors quantitatively - 94 - ... Techniques……………………………………………29 3.1.1 Surface plasmon spectroscopy? ??………………………………………….29 3.1.2 Electrochemical -surface plasmon spectroscopy? ??…………………… 32 3.1.3 High pressure surface plasmon spectroscopy with electrochemical... convenience and ? ?surface plasmon? ?? is used for short The aim of this study is to combine surface plasmon spectroscopy (SPS) with other techniques to investigate electroactive polymer films Therefore,... Gratings fabricated by these two methods could be used for the surface plasmon coupling The process of PANI / SPANI multilayer film manipulated on the Au surface by the Layer -by- Layer technique