Date of Award
Chemistry and Biochemistry
Aroca, Ricardo (Chemistry and Biochemistry)
Materials Characterization, Analytical.
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The present work explores vibrational Raman spectroscopy. Vibrational Raman and vibrational infrared are the most commonly used spectroscopies for detection and identification of molecules with their vibrational fingerprint. Under certain conditions, molecules display unique florescence and Raman scattering behavior when they are close to metal nanostructures sustaining localized surface plasmon resonances (LSPR), giving rise to surface-enhanced Raman scattering (SERS) and surface-enhanced resonance Raman scattering (SERRS). The utilization of LSPR in metallic nanoparticles, in particular silver and gold nanostructures, is a remarkable means of improving the efficiency of Raman scattering enhancing optical signals in SERS and SERRS. Correspondingly, the fabrication and characterization of silver and gold island films are first presented, and SERS signals enhancement of an organic dye on these metal nanostructured films are demonstrated. The excitations are characterized by UV-Vis absorption spectroscopy, while the morphology is revealed by atomic force microscopy (AFM). To control the surface coverage of the metal nanostructures, the Langmuir-Blodgett (LB) technique is used to coat the SERS substrate with monomolecular layers of several target systems, such as dyes and phospholipids. The most important results in this work are in the field of single molecule detection (SMD) using two spectroscopic approaches: LB-SERRS and LB-SERS. LB-SERRS improves the scattering efficiency from the electronic resonances (resonance Raman) of dye using silver island film with a plasmon absorption overlapping the molecular absorption. Several experiments are designed to the statistical average of LB-SERRS spectra, and the statistical breakdown observed in spectral characteristics when SMD is approached. The development of other SERS-substrates was attempted to control plasmonic using LSPR. A convenient method was pursued using a self-assembly of silver colloidal nanoparticles on a silanized glass surface. The SERS spectral evidence is presented to validate the substrate development. Surface-enhanced florescence (SEF) was also used for single molecule studies. Shell-isolated nanoparticles (SHINs) are used to produce SEF that named SHINEF. Using mixed LB monolayers of perylene tetracarboxylic (PTCD) derivatives, we report single molecule fluorescence and single molecule SERRS. In addition, overtones and combinations of fundamental vibrational modes are seen with atypical relative intensity in the LB-SERRS spectra of PTCDs.
Moula, Golam, "Plasmon-Enhanced Raman and Resonance Raman Scattering and Single Molecule Detection in Langmuir-Blodgett Monolayers" (2011). Electronic Theses and Dissertations. 395.