Role of initial morphology in H2S treated cadmium arachidate Langmuir - Blodgett films

To examine the issues like the shape of the CdS clusters, time and thickness dependence of chemical conversion and to study the correlation between the pre and post sulfidation structure of the LB films on CdS formation, a set of multilayer cadmium arachidate LB films grown with different morphology and thickness have been studied using AFM, TEM, X-ray reflectivity and XPS. Microscopic evidence of formation of nearly uniform CdS nanoparticles of around 4.5 nm in the LB matrix was observed. In relatively compact films, mount like structures were found to develop due to out-of-plane molecular motion, whereas, for non compact films, expansion and molecular rearrangement appears to reduce the height non-uniformity and smooth out the surface as a result of sulfidation. Full conversion of cadmium arachidate to CdS was not achieved in the LB matrix even after a long exposure and the time required for conversion was found to be independent of film thickness, both contrary to the earlier observation. A partial conversion of a maximum of around 60% could be achieved in the films of various thickness and compactness indicating that partial survival of the layered structure after sulfidation may be possible in initially compact films.