MOLECULAR PACKING IN NEW LANGMUIR-BLODGETT SYSTEMS INVESTIGATED BY X-RAY SPECULAR REFLECTIVITY AND GRAZING-INCIDENCE X-RAY-DIFFRACTION

In this work we investigate the periodic arrangement and crystalline o rder of Langmuir-Blodgett multilayers of a perylene-3,4,9,10-tetracarb oxyldiimide derivative (PTCDI-Opent) and of a long chain ammonium salt of 12-phosphomolybdate (PMo12O403-) deposited on (111)-oriented Si su bstrates by X-ray specular reflectivity (XSR) and grazing incidence X- ray diffraction measurements (GIXD), This is the first experimental st udy of the structural order performed on these complex compounds, Our results show that both films are quite uniform in thickness as demonst rated by well defined Kiessig fringes collected in the XSR spectra. Th e presence of sharp specular Bragg peaks in the XSR measurements of th e PMo12O403-, film indicates a very good crystalline order in the grow th direction, For the PTCDI-Opent structure, an unexpected molecular r eorganization in the film along the growth direction is found if compa red to the molecular conformation at the air-water interface and the t ransfer ratios. Both films can be identified as monophasic structures, Moreover, the in-plane structural arrangement derived by GIXD shows d omains of 70-140 Angstrom lateral size.