INVESTIGATION OF THIN MOLECULAR FILMS BY SURFACE ENHANCED VIBRATIONAL SPECTROSCOPY DISSERTATION Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University By Hong Tian, M.S. ***** The Ohio State University 2008 Dissertation Committee: Approved by Professor James V. Coe, Advisor Professor Richard L. McCreery, Coadviser _________________________________ Professor Susan V. Olesik Advisor Graduate Program in Chemistry Professor Heather A. Allen ABSTRACT The use of surface enhanced vibrational spectroscopy to characterize structures, investigate interactions at interface and measure thickness of nanocoatings has been investigated. The structural development of pyrolyed photoresist films (PPF) was characterized by both IR and Raman spectroscopy. The physicochemical properties of these films changed as a function of the pyrolysis temperature. PPF pyrolyzed at 1000 ℃ formed highly defective nanocrystalline carbons with a significant contribution from various sp2, sp3 type carbons and aromatic rings of the original polymer. Dilute solution of photoresist was used as an excellent starting material for the manufacture of optically transparent pyrolyzed photoresist films (OTPPF). OTPPF offers the possibility of sensitive, reproducible, and stable measurements in both UV-Vis and infrared regions of the electromagnetic spectrum. It provides the information of structures of molecules, interaction of adsorbed molecules and the substrate at air-solid interfaces. A study of surface enhanced vibrational spectroscopy on 4-nitroazobenzene (NAB) has been conducted. A new strategy of surface enhanced infrared absorption spectroscopy (SEIRA) has been developed based on the extraordinary transmission effect of metal microarrays. The intensity and position of transmission resonances of double stacked Ni meshes can be tuned by rotating one mesh relative to the other. When the resonances shift ii to the vibrational frequencies of NAB, the corresponding absorption features are greatly enhanced. Nanocoatings of TiO2 were applied to one side of free standing Ni meshes. Shifts, attenuation and broadening of the transmission resonances have been observed versus coating thickness. New modes have been developed to correlate the optical response of Ni mesh with coating thickness. The Ni meshes exhibit potential as sensors for nanoscale coating thickness. iii DEDICATION This work is dedicated to my family and friends. Thank you all for your love, understanding and encouragement. iv ACKNOWLEDGMENTS Many people have contributed to this dissertation. I would like to express my gratitude to them for their guidance, support and friendship during my graduate studies at the Ohio State University. I am very grateful to my advisors, Dr. Richard L. McCreery and Dr. James V. Coe. I have been fortunate to have two advisors, and both of them offered me guidance and support through these years. I would like to thank Dr. McCreery for his guidance and assistance in getting my graduate career started on the right foot and building my foundation as an analytical chemist. I especially want to thank his cooperation after he moved to University of Alberta. I am particularly grateful for being accepted into Dr. Coe’s research group. Dr. Coe taught me how to question thoughts and express ideas. He continually stimulated my analytical thinking and interest in research. His patience and support helped me overcome many crisis situations and finish this dissertation. I would also like to thank all of the members of both Dr. McCreery and Dr. Coe’s research group, especially Belinda Hurley, Haihe Liang, Jing Wu, Jeremy Steach, Aletha Nowak, Franklin Anariba, William McGovern, Andrew Bonifas, Solomon Ssenyange, Kenneth Rodriguez, Joseph Heer, Shannon Teeters-Kennedy, Katie Cilwa, and Marin Malone. They listened and gave me good advices, offered a lot of help in experiments, v assisted me in adjusting to a foreign country and a new culture, and provided genuine friendship. I especially want to thank Kenneth Rodriguez and Haihe Liang, for their cooperation, informative discussion and sharing data with me. I am also grateful to Dr. Gordon Renkes and Dr. Lisa Hommel for teaching me how to use their instruments and helping me with experiments. I would like to thank Dr. Umit Ozkan and her students in the department of chemical engineering who were willing to help me with Raman experiments even I was a stranger to them. I extend many thanks to the faculty of this department who have provided good graduate education to me. I would like to acknowledge graduate studies office, especially Dr. David Hart, Dr. Robert Coleman, Judith Brown, Jennifer Hambach and Martha McDowell, for their support and assistance. I am also thankful to all the staff in instrumentation support group, machine shop, and computer support group for always providing good services. Many thanks to my friends, especially Rich Mendola, Hu Lan, Sophia Lee, Saihong Jiang, Lanhao Yang, Xiaodan Su, Chen Ren, Yali Li, and Ya-Ting Kao. They have helped me to overcome many difficulties during years of my graduate study at OSU. I deeply appreciate their support and care. They have been such a blessing to me. There are many people helped me during the past years not being mentioned in this acknowledgment, I appreciate your kindness to me, and remember all of you. Finally, I would like to thank my family. My parents, sister, brother-in-law and nephew have been a constant source of love, concern, joy, strength and support. vi VITA May 16, 1978. .Born – Xinxiang, China 1998. .B.S. Zhengzhou University 2001. .. M.S. Lanzhou Institute of Chemical Physics, Chinese Academy of Science 2001 – 2002. Research Associate, Shanghai Institute of Organic Chemistry, Chinese Academy of Science. 2002 – Present. Graduate Teaching and Reasearch Asstiate, The Ohio State University. PUBLICATIONS Research Publications 1. J. V. Coe, J. Heer, S. Teeeters-Kennedy, H. Tian, K. R. Rodriguez. “Extraordinary transmission of metal films with arrays of subwavelength holes.” Annu. Rev. Phys.Chem., 2008, 59, 179-202. 2. H. Tian, A. J. Bergren, R. L. McCreery. “UV-vis Spectroelectrochemistry of Chemisorbed Molecular Layers on Optically Transparent Carbon Electrodes.” Applied Spectroscopy, 2007, 61(11), 1246-1253. 3. H. Liang, H. Tian, R. L. McCreery. “Normal and surface-enhanced raman spectroscopy of nitroazobenzene submonolayers and multilayers on carbon and silver surfaces.” Applied Spectroscopy, 2007, 61(6), 613-620. 4. K. R. Rodriguez, H. Tian, J. M. Heer, J. V. Coe. “Extraordinary Infrared Transmission Resonances of Metal Microarrays for sensing Nanocoating Thickness.” J. Chem.Phys.C, 2007, 111, 12106-12111. vii 5. K. R. Rodriguez, H. Tian, J. M. Heer, S. Teeters-Kennedy, J. V. Coe. “Interaction of an infrared surface plasmon with an excited molecular vibration.” J. Chem.Phys., 2007, 126(15), 151101/1-151101/5. 6. J. V. Coe, K. R. Rodriguez, S. Teeeters-Kennedy, K. Cilwa, J. Heer, H. Tian, S.M. Williams. “Metal Films with Arrays of Tiny Holes: Spectroscopy with Infrared Plasmonic Scaffolding.” J. Chem.Phys.C, 2007, 111(47), 17459-17472. FIELDS OF STUDY Major Field: Chemistry viii TABLE OF CONTENTS P a g e Abstract. ii Dedication. .iv Acknowledgments . .v Vita . .vii List of Tables. .. xii List of Figures . .. .xiii List of Abbreviations. xviii Chapters 1. Introduction . .1 1.1 Surface Properties of Pyrolyzed Photoresist Films (PPF) . .. .2 1.2 Optically Transparent Electrodes (OTE) . 6 1.3 Extraordinary Transmission of Sub-Wavelength Hole Arrays. 8 1.3.1 What are surface plasmons . 8 1.3.2 Extraordinary transmission through sub-wavelength hole arrays. .. 10 1.3.3 Metal films with periodic sub-wavelength hole arrays. .12 1.3.4 SP dispersion curves and front-back coupling of metallic arrays of sub-wavelength holes. .15 1.4 Raman spectroscopy . .. .19 1.4.1 Surface Raman spectroscopy . .. .19 1.4.2 Resonance Raman spectroscopy . .. .21 1.5 Surface enhanced Infrared absorption (SEIRA) . .. .. .23 1.6 Research objectives . .. .25 ix 2. Characterization of Carbon Film Evolution with Temperature by Infrared and Raman Spectroscopy . .38 2.1 Introduction. .. .38 2.2 Experimental. .. .40 2.3 Raman Spectroscopy of Photoresist Evolution. .. .43 2.4 Infrared Spectroscopy of Photoresist Evolution. .. .47 2.5 Characterization of Pyrolyzed Photoresist Films Using the Extraordinary Infrared Transmission of Metallic Arrays of Sub-wavelength Aperture . .54 2.6 Formation Mechanism of Pyrolyzed Photoresist Films . .. .58 2.7 Conductivity of Pyrolyzed Photoresist Films . .59 2.8 Comparison of Pyrolyzed Photoresist Films with Evaporated Carbon Films . .. .59 2.9 Conclusions. .. .. .64 3. Optically Transparent Pyrolyzed Photoresist Film and its Application in Electrochemistry, Uv-Vis and Infrared Spectroscopy. .73 3.1 Introduction. .. .73 3.2 Experimental. .. .74 3.3 Optical Properties of Optically Transparent Pyrolyzed Photoresist Films. .. .81 3.4 UV-Vis Spectra of Molecules Chemisorbed onto Optically Transparent Pyrolyzed Photoresist Films . .. .84 3.5 Free and Adsorbed Molecular Spectra . .. .86 3.6 IR Spectroscopy of Chemisorbed Molecules on Optically Transparent Pyrolyzed Photoresist Films. .. .. .90 3.7 Conclusions. .. .97 4. Surface Enhanced Vibrational Spectroscopy of 4- Nitroazobenzene . .100 4.1 Introduction. 100 4.2 Experimental. .. .101 4.3 UV-Vis Spectra of NAB on Various Substrates . .104 4.4 Raman Spectra of NAB on Various Substrates . .. .106 4.5 Infrared Spectra of NAB on Single Mesh. .109