Application of scanning angle Raman spectroscopy for determining the location of buried polymer interfaces with tens of nanometer precision

Abstract

Near-infrared scanning angle (SA) Raman spectroscopy was utilized to determine the interface location in bilayer films (a stack of two polymer layers) of polystyrene (PS) and polycarbonate (PC). Finite-difference-time-domain (FDTD) calculations of the sum square electric field (SSEF) for films with total bilayer thicknesses of 1200-3600 nm were used to construct models for simultaneously measuring the film thickness and the location of the buried interface between the PS and PC layers. Samples with total thicknesses of 1320, 1890, 2300, and 2750 nm and varying PS/PC interface locations were analyzed using SA Raman spectroscopy. Comparing SA Raman spectroscopy and optical profilometry measurements, the average percent difference in the total bilayer thickness was 2.0% for films less than ∼2300 nm thick. The average percent difference in the thickness of the PS layer, which reflects the interface location, was 2.5% when the PS layer was less than ∼1800 nm. SA Raman spectroscopy has been shown to be a viable, non-destructive method capable of determining the total bilayer thickness and buried interface location for bilayer samples consisting of thin polymer films with comparable indices of refraction.

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

“…[37] Raman scattering is proportional to the square of the electric field, so SA Raman spectra are modeled by plotting the square of the electric field intensity integrated over the thickness of each polymer layer (i.e., sum square electric field [SSEF]) as a function of the incident angle. The current work expands the bilayer polymer film work reported by Damin et al [39] in two important ways. First, we apply the SA Raman amplitude ratio between peaks for each polymer in the film, which has been previously proposed by us to measure mixed polymer films, [40] and recursive SSEF calculations to reduce the computational time required to model the SA Raman data.…”

“…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.…”

“…Scanning angle (SA) Raman spectroscopy is a technique that couples a sample to a prism (a schematic is shown in the top of Figure ), and a data set consists of the Raman spectra as a function of the incident angle of the excitation light. SA Raman spectroscopy has been used to measure polymer waveguide thicknesses, buried bilayer film interfaces, and mixed polymer film chemical composition . Other reported methods that are similar to SA Raman spectroscopy, variable‐angle internal reflection, and ATR Raman spectroscopy have been used to measure bilayer polymer films .…”

“…SA Raman spectroscopy has been used to measure polymer waveguide thicknesses, buried bilayer film interfaces, and mixed polymer film chemical composition. [37][38][39][40] Other reported methods that are similar to SA Raman spectroscopy, variable-angle internal reflection, and ATR Raman spectroscopy have been used to measure bilayer polymer films. [41][42][43] More recently, a solid immersion lens has been used to collect the near-field Raman scattering (providing a 30× improvement in sampling depth compared to far-field illumination and collection) from bilayer films with less than 200 nm polystyrene on a microns thick polycarbonate substrate using an ATR Raman microscope.…”

Combined measurement of directional Raman scattering and surface-plasmon-polariton cone from adsorbates on smooth planar gold surfaces

“…Furthermore, the multidimensionality of the data (cone diameter and intensity and Raman scattering as a function of incident angle) provides the ability to measure more sample properties compared to either SPR or Raman scattering techniques alone. This is highlighted by our related previous work using a technique called scanning angle Raman spectroscopy, [37][38][39][40][41][42][43][44][45] whereby the incident light is scanned over a wide range of angles while simultaneously collecting the reflected light from the prism side and Raman scattering on the sample side of the interface. Scanning angle Raman spectroscopy (in the absence of a gold film) was used to identify buried interfaces in a multi-layered system with ~10s of nanometer spatial resolution.…”