Scanning angle Raman spectroscopy: Investigation of Raman scatter enhancement techniques for chemical analysis
Over the past 25 years Raman spectroscopy has transitioned from a technically challenging and time consuming research technique to a valuable and practical method of chemical analysis. During this time span, coined the `Raman renaissance' by Dr. Richard McCreery, enhancement techniques and improvements to near-infrared detectors have played a significant role in extending the utility of this analytical technique. This thesis outlines advancements in Raman scatter enhancement techniques by applying evanescent fields, standing-waves (waveguides) and surface enhancements to increase the generated mean square electric field, which is directly related to the intensity of Raman scattering. These techniques are accomplished by employing scanning angle Raman spectroscopy (Chapter 2-4) and surface enhanced Raman spectroscopy (Chapter 5). In Chapter 6, a 1064 nm multichannel Raman spectrometer is discussed for chemical analysis of lignin. Extending dispersive multichannel Raman spectroscopy to 1064 nm reduces the fluorescence interference that can mask the weaker Raman scattering. Overall, these techniques help address the major obstacles in Raman spectroscopy for chemical analysis, which include the inherently weak Raman cross section and susceptibility to fluorescence interference.
Chapter 1 is a general introduction to total internal reflection (TIR) Raman spectroscopy and scanning angle (SA) Raman spectroscopy. Brief introductions to surface enhanced Raman spectroscopy and 1064 nm multichannel Raman spectroscopy are provided in their respective Chapters, 5 and 6. In Chapters 2-4, the utility of scanning angle Raman spectroscopy is put into practice for compositional and thickness measurements of thin polymer films. SA-Raman spectroscopy can be classified as an enhancement technique that can be used for measuring interfacial phenomena with chemical specificity. With improvements to modern technology, scanning angle Raman spectroscopy can provide a practical and adaptable technique for applications where surface enhanced Raman spectroscopy (SERS) is impractical. In Chapters 3-4, the total internal reflection Raman spectroscopy configuration is expanded to include surface plasmon resonance and plasmon waveguide resonance Raman spectroscopy. Chapters 2-6 contain published manuscripts. This work develops a foundation of applied chemical measurements for numerous devices, including thin polymer films and photovoltaic devices.
Chapter 7 provides general conclusions to the preceding chapters as well as the future prospects of SA-Raman spectroscopy measurements. The appendix describes recent developments in SERS substrates with a primary focus on applications for single cell analysis. It is a section published in a review paper entitled "Single Cell Optical Imaging and Spectroscopy" in Chemical Reviews.