ORIENTED CADMIUM DIHALIDE PARTICLES PREPARED IN LANGMUIR-BLODGETT-FILMS

Oriented arrays of CdI2, CdBr2, and CdCl2 particles have been synthesi zed in Langmuir-Blodgett (LB) films by the reaction of cadmium arachid ate LB films with the corresponding hydrogen halide gas. Attenuated to tal reflectance FTIR (ATR-FTIR) shows that the conversions go to compl etion and that the organic film remains crystalline after reaction wit h the hydrogen halides. The cadmium halides are identified by transmis sion electron diffraction (TED) and X-ray photoelectron spectroscopy ( XPS), and in each case only one inorganic species is formed. Transmiss ion 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 micro meters, discrete particles have the same in-plane orientation. The CdB r2 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 pa rticles exhibit common in-plane orientations. It is proposed that the organized organic matrix is responsible for orienting the inorganic pa rticles, and potential lattice matching between the inorganic particle s and the organic matrix is discussed.