Orientation analysis of polymer thin films on metal surfaces via IR absorbance of the relative transition dipole moments

Abstract

Modern technology has increasing requirements for thin film based electronic devices. Many surface and electronic properties strongly depend on the orientation of the material. Industrial development has a need for cheap, non-destructive, and fast orientation analysis in different conditions. Infrared-orientation analysis is less represented in literature compared to other orientation methods, while offering a lot of unique advantages. In this respect for thin polymeric films, we propose infrared (IR) absorbance-spectroscopy near metal surfaces to distinguish the orientation of different molecular segments. By use of the ratio method, the calculation of the orientation becomes mostly independent from the angle of incidence and averages out aperture errors of the measurement setup, hence the given solutions are generally applicable for many setups. For the most common point groups, the hereby-presented mathematical solution is valid for thin films cast on metal surfaces. Extensive quantum mechanical calculations of the transition dipole moments are avoided for known IR spectroscopy bands. The detailed application of the given IR orientation analysis is demonstrated for the polymers polystyrene, polyethylene glycol, poly(methyl methacrylate) and polyvinyl acetate. Each segment of these polymers is analyzed for the preferred molecular orientation in respect to the surface.