Growth of a well oriented layer of p-nitroaniline on the (100) plane of a p-cyanoaniline single crystal, studied by polarized absorption and second-harmonic generation

Microscopic calculation of surface-induced second-harmonic generation in crystals of para-nitroaniline

“…This provides semiquantitative support for the suggestion that the observed SHG is due to a new noncentrosymmetric phase that grows at the surface. 3,26 We find that only the first two layers of molecules contribute to the surface SHG: the contributions of deeper layers cancel, as expected for the bulk response. There are significant differences in the magnitude and direction of the response for different crystal directions, depending on the molecular orientations at each surface, and there are also modest differences between the responses for different terminations in the same direction.…”

“…It is known to occur in some promising NLO crystals, 17 and pNA gives NLC-active structures in a number of cases when crystals are grown with a second species. [23][24][25][26] In particular, layers of pNA grown on the surface of a crystal of para-cyanoaniline ͑pCA͒ yield more intense SHG than the surfaces of pNA or pCA by themselves. 26 The intensity also grows quadratically with the thickness of the layer, consistent with bulk SHG from a noncentrosymmetric form of pNA: surface SHG comes from the very top two or three molecules and once they are deposited does not depend on the thickness of the crystal or crystalline thin film.…”

“…[23][24][25][26] In particular, layers of pNA grown on the surface of a crystal of para-cyanoaniline ͑pCA͒ yield more intense SHG than the surfaces of pNA or pCA by themselves. 26 The intensity also grows quadratically with the thickness of the layer, consistent with bulk SHG from a noncentrosymmetric form of pNA: surface SHG comes from the very top two or three molecules and once they are deposited does not depend on the thickness of the crystal or crystalline thin film. Growth of a different noncentrosymmetric polymorph on a substrate or near physical defects in the pure pNA crystal is consistent with the different molecular interactions and packings in those environments.…”