title: High Fidelity Nano-Hole Enhanced Raman Spectroscopy.
abstract: Surface Enhanced Raman Spectroscopy (SERS) is a sensitive technique that can even detect single molecules. However, in many SERS applications, the strongly inhomogeneous distribution of intense local fields makes it very difficult for a quantitive assessment of the fidelity, or reproducibility of the signal, which limits the application of SERS. Herein we report the development of exceptionally high fidelity Hole-Enhanced Raman Spectroscopy (HERS) from ordered, two-dimensional hexagonal nanohole arrays. We take the fidelity f to be a measure of the percent deviation of the Raman peaks from measurement to measurement. Overall, area averaged fidelities for 12 gold array samples ranged from f ~ 2% - 15% for HERS using aqueous R6G molecules. Furthermore, intensity modulations of the enhanced Raman spectra were measured for the first time as a function of polarization angle. The best of these measurements, which focus on static laser spots on the sample, could be consistent with even higher fidelities than the area-averaged results. Nanohole arrays in silver provided supporting polarization measurements and a more complete enhanced Raman fingerprint for phenylalanine molecules. We also carried out finite-difference time-domain calculations to assist in the interpretation of the experiments, identifying the polarization dependence as possibly arising from hole-hole interactions. Our results represent a step towards making quantitative and reproducible enhanced Raman measurements possible and also open new avenues for a large scale source of highly uniform hot spots.
authors.affiliation: Biosciences Division, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Illinois 60439.
authors.forename: John T
authors.initials: JT
authors.lastname: Bahns
authors.forename: Qiti
authors.initials: Q
authors.lastname: Guo
authors.forename: Jason M
authors.initials: JM
authors.lastname: Montgomery
authors.forename: Stephen K
authors.initials: SK
authors.lastname: Gray
authors.forename: Heinrich M
authors.initials: HM
authors.lastname: Jaeger
authors.forename: Liaohai
authors.initials: L
authors.lastname: Chen