Scanning Angle Plasmon Waveguide Resonance Raman Spectroscopy for the Analysis of Thin Polystyrene Films

Abstract

Scanning angle (SA) Raman spectroscopy was used to characterize thin polymer films at a sapphire/50 nm gold film/polystyrene/air interface. When the polymer thickness is greater than ∼260 nm, this interface behaves as a plasmon waveguide; Raman scatter is greatly enhanced with both p-and s-polarized excitation compared to an interface without the gold film. In this study, the reflected light intensities from the interface and Raman spectra were collected as a function of incident angle for three samples with different polystyrene thicknesses. The Raman peak areas were well modeled with the calculated mean-square electric field (MSEF) integrated over the polymer film at varying incident angles. A 412 nm polystyrene plasmon waveguide generated 3.34× the Raman signal at 40.52° (the plasmon waveguide resonance angle) compared to the signal measured at 70.4° (the surface plasmon resonance angle). None of the studied polystyrene plasmon waveguides produced detectable Raman scatter using a 180° backscatter collection geometry, demonstrating the sensitivity of the SA Raman technique. The data highlight the ability to measure polymer thickness, chemical content, and, when combined with calculations of MSEF as a function of distance from the interface, details of polymer structure and order. The SA Raman spectroscopy thickness measurements agreed with those obtained from optical interferometery with an average difference of 2.6%. This technique has the potential to impact the rapidly developing technologies utilizing metal/polymer films for energy storage and electronic devices.

Scanning Angle Raman Spectroscopy of Poly(3-hexylthiophene)-Based Films on Indium Tin Oxide, Gold, and Sapphire Surfaces

“…Importantly, when other experimental variables are known, the pattern of the Raman signal as a function of incident angle provides an accurate measure of polymer thickness. 35 Panels A and B in Figure 6 show the calculated MSEF for a 512 nm 1:1 P3HT:PCBM film and a 700 nm P3HT film on a Figure 7 (only a subset of spectra are shown for clarity). Optical interferometry performed on the same polymer films generated thickness values of 570 ± 50 nm and 830 ± 40 nm, respectively.…”

Extracting interface locations in multilayer polymer waveguide films using scanning angle Raman spectroscopy

“…Similar trends are observed for sample 3-Bi ( Figure S2A) and sample 3-Tri ( Figure S3A). These representative calculated results suggest that it should be feasible to use SA Raman spectroscopy, with a signal that is proportional to the electric field intensity, [37][38][39][40]49,[53][54][55][56] to measure total film thickness as well as the location of polymer interfaces for both bilayer and trilayer films.…”

A Biosensor Using Coupled Plasmon Waveguide Resonance Combined With Hyperspectral Fluorescence Analysis

“…17,18 The resonances between guided light modes within the waveguide layer and surface plasmon polarizations (coupled plasmon waveguide resonance, CPWR) leads to narrower full width half-maximum (FWHM) of the re°ective curves and this in turn leads to increased resolution of the sensors by reducing the uncertainty of the resonance position. Besides, theoretical results indicate that CPWR also results in better performance no matter for detection range or for enhanced electromagnetic¯eld 19 which is highly suitable for background excitation of°uorescence to maintain an appreciable signal-to-noise ratio.…”