Brilliant Infrared Light Sources for Micro-ellipsometric Studies of Organic Thin Films
Micro-ellipsometric studies in the infrared spectral range are of increasing interest in particular for the determination of the optical constants of organic films and multilayers as in these cases the composition, thickness or roughness often vary on micro- and mesoscopic length scales. In cases where the aforementioned properties change across the probed spot, the degree of polarization of the reflected beam is deteriorated and sophisticated models have to be employed to derive the optical constants or other parameters from the determined ellipsometric angles. The achievable spot size in an ellipsometric set-up is now limited by the necessity of performing a specular reflectance measurement with a reasonably defined angle. In the optimal case the infrared radiation can be focused to near diffraction limited spot sizes with opening angles in the incoming beam of less than 7\(^\circ \). In other words such an experiment turns out to be limited by a source property that is typically called brilliance or brightness and makes the technique particularly suited for the use of accelerator based infrared sources such as 3rd generation synchrotron storage rings. The current status of such activities will be reviewed on the example of different pilot experiments. An outlook on future developments will also be given.
Critical reading and fruitful discussions by and with K. Hinrichs (ISAS), T. Kampfrath (FHI) and G.P. Williams (Thomas Jefferson Laboratory) is gratefully acknowledged. B. Green (HZDR) is acknowledged for proofreading the manuscript.
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