Scanning angle Raman spectroscopy measurements of thin polymer films for thickness and composition analyses

TitleScanning angle Raman spectroscopy measurements of thin polymer films for thickness and composition analyses
Publication TypeJournal Article
Year of Publication2013
AuthorsMeyer MW, Nguyen VHT, Smith EA
Journal TitleVibrational Spectroscopy
Volume65
Pages94-100
Date Published03
Type of ArticleArticle
ISBN Number0924-2031
Accession NumberWOS:000315760100012
Keywordsfields, integrated-optics, optical-wave-guides, Polystyrene films, Radiative polymer waveguide, RESONANCE, Thickness calibration curve, total internal reflection, VIBRATIONAL SPECTROSCOPY
Abstract

Scanning angle (SA) Raman spectroscopy was used to measure the thickness and composition of polystyrene films. A sapphire prism was optically coupled to a sapphire substrate on which 6-12% (w/v) polystyrene in toluene was spin coated. Raman spectra were collected as the incident angle of the p-polarized, 785-nm excitation laser was varied from 56 to 70 degrees. These angles span above and below the critical angle for a sapphire/polystyrene interface. The thickness of the polystyrene film was determined using a calibration curve constructed by calculating the integrated optical energy density distribution as a function of incident angle, distance from the prism interface and polymer thickness. The calculations were used to determine the incident angle where waveguide modes are excited within the polymer film, which is the angle with the highest integrated optical energy density. The film thicknesses measured by SA Raman spectroscopy ranged from less than 400 nm to 1.8 mu m. The average percent uncertainty in the SA Raman determinations for all films was 4%, and the measurements agreed with those obtained from optical interferometery within the experimental uncertainty for all but two films. For the 1270-nm and 580-nm polystyrene films, the SA Raman measurements overestimated the film thickness by 5 and 18%, respectively. The dependence of the calibration curve on excitation polarization and composition of the polymer and bulk layers was evaluated. This preliminary investigation demonstrates that scanning angle Raman spectroscopy is a versatile method applicable whenever the chemical composition and thickness of interfacial polymer layers needs to be measured. (c) 2012 Elsevier B.V. All rights reserved.

URL<Go to ISI>://WOS:000315760100012
DOI10.1016/j.vibspec.2012.11.020