Orientation and nonlinear optical properties of 4-(N,N-dimethylamino)-3-acetamidonitrobenzene crystals on nanostructured poly(tetrafluoroethylene) substrates

The growth of 4-(N,N-dimethylamino)-3-acetamidonitrobenzene (DAN) crystals on nanostructured poly(tetrafluoroethylene) (PTFE) substrates has been inve stigated by means of x-ray, micro-FTIR (Fourier-transform infrared) and non linear optical ellipsometry techniques. Two types of structural arrangement s were identified, depending on growth conditions. In both cases, the (001) (DAN) plane contacts the (100)(PTFE) substrate plane. The major difference between both types of samples lies in the degree of azimuthal orientation a t the interface. For thin samples (thickness < 0.3 mu m), the average direc tion of the a crystallographic axes of the DAN crystals lies parallel to th e [001](PTFE) direction with a broad angular distribution, while thick samp les (thickness > 1 mu m) are characterized by a uniaxial orientation with a n isotropic random distribution in the plane of the layers. The comparison between various techniques used in this study to characterize the obtained thin films showed a remarkable agreement. In this context, second-harmonic generation was revealed once again as a powerful technique toward the study of orientation effects in crystalline layers of NLO organic materials, muc h beyond the possibilities of traditional linear polarization methods. (C) 2000 American Institute of Physics. [S0021-9606(00)70922-6].