Preparation of plasma poly(1-isoquinolinecarbonitrile) thin film and its ultrafast nonlinear optical property

Abstract

How to get a uniform, defect-free, and reproducible conjugated polymer thin films is now becoming the main fabrication problem for the practical application of these materials as the fast switches and modulators in opto-electronic devices. In this research, a novel plasma-polymerized 1-isoquinolinecarbonitrile (PPIQCN) thin film was prepared by plasma polymerization under different glow discharge conditions. The effect of the discharge power on the chemical structure and surface compositions of the deposited PPIQCN films was investigated by Fourier transform infrared (FTIR), UV-Visible absorption spectra and X-ray photoelectron spectroscopy (XPS). The results show that a high retention of the aromatic ring structure of the starting monomer in the deposited plasma films is obtained when a low discharge power of 10 W was used during film formation. In the case of higher discharge power of 30 W, more severe monomer molecular fragmentation can be observed, which results in a decrease in the effective conjugation length of PPIQCN film. The morphology characterized by atomic force microscopy (AFM) indicates that a fine, homogenous PPIQCN film could be obtained under a relatively low discharge power. A femtosecond time-resolved optical Kerr effect technique at a wavelength of 820 nm has been applied to investigate the third-order nonlinearity of the plasma PPIQCN film. For the first time, a non-resonant optical Kerr effect and ultrafast response of the PPIQCN film was observed.