Scanning angle (SA) Raman spectroscopy is applied to study polymer films to simultaneously measure polymer thickness, chemical composition and structure with tens of nanometer spatial resolution in the axial direction. A benefit of SA Raman spectroscopy over other (e.g., 180-degree backscatter) illumination geometries for the measurement of 10 nm to 1 micron thick polymer films is a one to two order of magnitude signal enhancement.  This enables the collection of thin film Raman spectra with second acquisition times and signal-to-noise ratios that exceed 100. The SA Raman technique uses a prism on which the polymer is coated. Raman spectra are collected as the incident angle of the excitation laser is precisely varied from 30 to 70�. This range represents angles that span above and below the critical angle for total internal reflection. The SA Raman technique is applied to study polymer films used in organic photovoltaic devices, such as poly(3-hexylthiophene) and phenyl-C61-butyric acid methyl ester blend films, where the nanoscale morphology is critical for device function. The width of the ~1450 cm-1 C=C stretch is sensitive to polymer order and is used to measure film morphology on several substrates, including interfaces representing functional organic photovoltaic devices. SA Raman spectroscopy is also used to locate buried interfaces in stacked polymer layers of tens to hundreds of nanometer thickness with tens of nanometer accuracy. The experimental measurements are modeled with calculations of the interfacial mean square electric field to determine the distance dependence of the SA Raman signal and polymer film properties. Scanning angle Raman spectroscopy is a versatile method applicable whenever the chemical composition, structure and thickness of interfacial thin films needs to be measured.  This work is supported by the Department of Energy, Office of Basic Energy Sciences.

Scanning angle Raman spectroscopy for thin film measurements

248th National Meeting (2014)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.