ORIENTED CADMIUM DIHALIDE PARTICLES PREPARED IN LANGMUIR-BLODGETT-FILMS

Oriented arrays of CdI2, CdBr2, and CdCl2 particles have been synthesized in Langmuir-Blodgett (LB) films by the reaction of cadmium arachidate LB films with the corresponding hydrogen halide gas. Attenuated total reflectance FTIR (ATR-FTIR) shows that the conversions go to completion and that the organic film remains crystalline after reaction with the hydrogen halides. The cadmium halides are identified by transmission electron diffraction (TED) and X-ray photoelectron spectroscopy (XPS), and in each case only one inorganic species is formed. Transmission electron microscopy (TEM) and TED show that the CdI2 particles are formed exclusively with their [001] crystal axes perpendicular to the plane of the LB film, and for domain sizes up to several square micrometers, discrete particles have the same in-plane orientation. The CdBr2 and CdCl2 particles are each observed to form with a mixture of two orientations, [001] axis parallel and [001] axis perpendicular to the LB plane. As with the iodide, domains are observed where arrays of particles exhibit common in-plane orientations. It is proposed that the organized organic matrix is responsible for orienting the inorganic particles, and potential lattice matching between the inorganic particles and the organic matrix is discussed.