Analyzing the Molecular Orientation of Ultrathin Organic Films by Polarized Transmission and Grazing Incidence Reflection Absorption IR Spectroscopy

Abstract

The rapid development of flexible electronics industry has stimulated a great deal of research interest on ultrathin organic films. To analyze the molecular orientation change of the ultrathin films or molecular layers under different conditions is essential for understanding the physics of the film growth or crystallization process and for optimizing the performance of the relevant devices. With this respect, IR spectroscopy seems more desirable than the various diffraction techniques due to its advantages of simple facility, ease of operation and nondestructive measurement, etc. In this short review, the basic experimental approaches and capabilities of two IR techniques, namely, polarized Transmission Infrared Spectroscopy (TIRS) and Infrared Reflection Absorption Spectroscopy (IRRAS), are briefly introduced. In particular, their application for analyzing the molecular orientation are demonstrated through examples of films of two typical organic materials used in flexible electronics: the small molecule semiconductor pentacene and the ferroelectric copolymer P(VDF-TrFE). Finally, two other relevant IR techniques, PM-IRRAS and polarized Attenuated Total Reflection FTIR (ATR-FTIR), are briefly discussed.

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