Scanning angle Raman spectroscopy measurements of thin polymer films for thickness and composition analyses |
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| Affiliation: | 1. Ames Laboratory, U.S. Department of Energy, Ames, IA 50011-3111, United States;2. Department of Chemistry, Iowa State University, Ames, IA 50011-3111, United States;1. Institute of Chemistry, Saint Petersburg State University, RU–198504 Saint Petersburg, Russia;2. Department of Analytical Chemistry, University of P.J. Šafárik, SK-04154 Košice, Slovakia;1. Graduate School of Technology, Industrial and Social Sciences, Tokushima University, Tokushima, 770-8506, Japan;2. Laboratory of Advanced Science and Technology for Industry, University of Hyogo, Kamigori, Hyogo, 678-1205, Japan;3. Chubu University, Kasugai, Aichi, 487-8501, Japan;4. Nichia Corporation, Anan, Tokushima, 774-0044, Japan;1. Laboratório de Nanoestruturas Plasmônicas, Núcleo de Espectroscopia e Estrutura Molecular, Departamento de Química, Universidade Federal de Juiz de Fora, R. José Lourenço Kelmer s/n, Martelos, CEP 36036-900, Juiz de Fora, MG, Brazil;2. Departamento de Física, Universidade Federal de Juiz de Fora, R. José Lourenço Kelmer s/n, Martelos, CEP 36036-900, Juiz de Fora, MG, Brazil;1. Department of Physics, Government College University, Faisalabad, Pakistan;2. Department of Physics, Quaid-i-Azam University, Islamabad, Pakistan;3. Department of Physics, Women University of Azad Jammu & Kashmir, Bagh, Pakistan;4. Department of Physics, School of Science and Engineering, LUMS, Lahore, Pakistan |
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| 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°. 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 μm. 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. |
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