Determining the electronic properties of surface enhanced raman spectroscopy substrates

Whelan, Liam David (2015) Determining the electronic properties of surface enhanced raman spectroscopy substrates. Masters thesis, Memorial University of Newfoundland.

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Abstract

Surface Enhanced Raman Spectroscopy (SERS) is an ultra-sensitive technique for optical detection of target analytes. Our work focuses on detecting oil in water using SERS, with this thesis using phenanthrene as a model compound. SERS is a technique which takes advantage of the optical properties of metal substrates to greatly increase the intensities of adsorbed analytes’ vibrational modes. The rapid development of novel materials as SERS active substrates requires an efficient screening method. SERS Enhancement Factor (EF) does correlate somewhat with surface morphology and UV-Vis absorption, however we present a technique which shows an even stronger correlation and is ultimately a better screening tool: Kelvin Probe Force Microscopy (KPFM). This technique maps the electronic properties of a substrate to its surface morphology. This thesis covers two classes of SERS substrates: annealed bimetallic systems and nanosphere patterned mono- and bimetallic systems. The ability to directly map the electronic properties of a substrate to its morphological properties is of critical importance in determining a key link between the macroscale SERS sensor response and the microscale substrate structure. Our major findings indicate that when Au/Cr nanostructured films’ work function is near the calculated and experimental values for the HOMO-LUMO gap of the target analyte, phenanthrene, the observed SERS intensity reaches a maximum.

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