Orientation and nonlinear optical properties of N-4-nitrophenyl-(L)-prolinol crystals on nanostructured poly(tetrafluoroethylene) substrates

摘要

Thin crystalline films of N-4-nitrophenyl-(L)-prolinol (NPP) were grown on nanostructured highly oriented poly(tetrafluoroethylene) (PTFE) substrates. Depending on the growth conditions, two types of crystalline orientation were observed. Thinnest samples (<0.2 #mu#m), directly grown from the vapor phase, are made of numerous highly ordered crystallites presenting a (110)_(NPP)||(100)_(PTFE) interfacial relationship and an almost perfect azimuthal orientation. Thicker layers (>1 #mu#m) could be obtained from deposition-annealing procedures and exhibit a (101)_(NPP) planar orientation but with a lack of azimuthal orientation. The full characterization of these various samples was performed by analysis of x-ray diffraction data obtained in #theta#-2#theta# and grazing incidence geometry, the latter being used to determine the azimuthal orientation. Furthermore, the proposed orientations were fully consistent with the nonlinear optical (NLO) properties of the layers, deduced from optical second harmonic generation measurements. The combination of x-ray diffraction and nonlinear ellipsometry technique thus proved once again to be a powerful method to analyze oriented structures obtained with NLO molecules.