Selective study of polymer/dielectric interfaces with vibrationally resonant sum frequency generation via thin-film interference

A technique for selective characterization of the structure of free and buried thin-film interfaces by vibrationally resonant sum frequency generation spectroscopy is described. Manipulation of Fresnel coefficients by choice of film thickness on a reflecting substrate allows simultaneous optimization of the signal from the desired interface and minimization of the signal from other interfacial sources. This technique is demonstrated for the free polystyrene (PS)/air and the buried PS/spin-on glass interfaces. Our spectra show that the pendant phenyl group orientation is similar at the buried and free interfaces, with the phenyls pointing away from the bulk PS at each interface.