ZnS nanoclusters in LB multilayers

Zinc arachidate (ZnA) LB multilayers have been exposed to H2S to form ZnS nanoclusters within the layered matrix of arachidic acid (AA). The as-deposited ZnA multilayer consists of arachidate molecules packed in a hexagonal layer cell, with the alkyl chain tilted at about 32° away from the layer normal. FTIR and UV–vis studies show that the conversion of arachidate salt into arachidic acid and the formation of ZnS is completed in 2–3 h. Blue shift in absorption onset and excitonic peak ∼290 nm indicates nanocrystalline nature of ZnS. TEM studies show that ZnS nanoclusters of size ∼5 nm are formed. X-ray reflection and grazing angle diffraction studies and changes in the nature of CH2 scissoring mode peak of ZnS–AA composite multilayer show that the molecular packing corresponds to a closely packed structure based on orthorhombic subcell in which the chains are tilted by ∼27° towards nearest neighbours. This is in contrast to a loose ‘rotator phase like’ packing of molecules in the precursor ZnA multilayer.