Nanocharacterization of Relaxation Properties in Organic Thin Film Electronic Materials
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Nanocharacterization of Relaxation Properties in Organic Thin Film Electronic Materials Tomoko Gray and René M. Overney Department of Chemical Engineering University of Washington Seattle, WA 98195, U.S.A. ABSTRACT With increased molecular complexity of organic thin film electronics, novel characterization methods are required to provide nanoscale material property information. Particularly important in polymer thin film electronics are methods characterizing the mobility properties of materials that are in amorphous unsteady states. If the unsteady nature of materials is paired with dimensional and interfacial constraints in anisotropic systems, such as thin films, it produces material systems of great challenges with enormous engineering potentials. Two examples are addressed in this paper, involving desired and undesired supramolecular alignments in polymer thin films, the spectral stability in organic blue-light emitting diodes and the electro-optical (EO) activity in organic non-linear optical (NLO) materials, in conjunction with novel scanning probe microscopy (SFM) based characterization tools. The nanoscopic methods discussed here, i.e., shear modulation force microscopy (SM-FM), and nanoscale isothermal friction analysis (NIFA), offer a quantitative approach for investigating the mobility/stability of organic semiconductor polymer films. Thereby, local properties such as energy barriers for submolecular motions (relaxations) and critical transition temperatures can be directly inferred from organic films that are used in actual electronic devices.
INTRODUCTION Supramolecular alignments are crucial for organic electro-optic and optoelectronic applications. While for non-linear optical (NLO) materials, partial intramolecular mobility is essential during the poling process to achieve strong electro-optical (EO) properties; molecular mobility is often a nuisance in optoelectronic materials, as it fosters undesired supramolecular aggregations. Supramolecular Alignment and EO Activity for Photonic Applications From vacuum tubes to transistors, and to integrated circuits, electronics has continually met our expanding needs. However, to keep up with our growing demand for higher data processing rates and larger data transmitting capacities, new technologies must emerge. Thereby, photonics is one approach, with great potential in broadband communication, involving ultrahigh speed electro-optical (EO) switches.[1, 2] In particular, organic and polymer based photonic devices have been of interest, due to their superior EO properties, attractive mechanical and processing advantages of polymers, and most importantly, because of their tunability of EO properties upon molecular design.[3-5] In general, the pursuit for highly efficient photonic materials is classified by two major objectives: (a) to obtain nonlinear optical (NLO) chromophores with large nonlinearities that
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have chemical susceptibility and thermal stability and (b) to achieve large EO activity. EO activity is induced by acen
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