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Polyimide Surface Bombarded with Ar Atomic Beam

The alignment mechanism of a polyimide surface bombarded with an atomic beam is investigated. Atomic beam treatment of polyimide films allows a liquid crystal (LC) to align parallel to the beam direction. This alignment mechanism is demonstrated by the selective destruction of double bonds in polyimide. The optical retardation measurement using a photoelastic modulator (PEM) indicates that the in-plane crystalline order of the polyimide chain that occurred by rubbing is not created by atomic beam exposure. The atomic force microscopy (AFM) image of the polyimide surface modified by atomic beam exposure shows that its directional topography does not appear. The binding energy of core electrons of each element measured by X-ray photoelectron spectroscopy (XPS) describes the variation of the chemical bonding state on the polyimide surface exposed to atomic beam. These experimental results illustrate that LC alignment is achieved from the overlap of the p-orbitals of polyimide and LC.