Templated growth of nanoparticles using mixed Langmuir-Blodgett films

Nanoparticles have unusual optical and electronic properties as compared to bulk materials. One of the major challenges to nanotechnology is to create nanoscale building blocks with precisely controlled size and composition and assemble them into larger useful structures. In this study, our goal is to explore the possibility of using a mixed Langmuir-Blodgett (LB) film as a template to control the size, and assembly structure of nanoparticles. Langmuir isotherm was used to identify compatible amphiphiles to form stable mixed LB film. Arachidic acid (AA)/octadecylamine (ODA) was found to be a well-mixed, stable system and used to prepare three-layer mixed LB film with the subphase containing Cd2+ or Fe3+ ions. The cations containing films were then reacted with hydrogen sulfide to form CdS or Fe₂S₃ nanoparticles. Atomic Force Microscope was used to characterize the mixed LB film and characterize the size and assembly structure of the nanoparticles.; Our results indicate that the compatibility in the tail and head group of AA and ODA is required for a well-mixed Langmuir film. The LB film of cadmium arachidate exhibited crystalline lattice and the CdS particles were observed to form a regular superlattice. The LB film of cadmium arachidate mixed ODA appeared to be an amorphous film, while randomly distributed CdS nanoparticles were observed with reduced size. In the absence of ODA, the iron arachidate LB trilayer film was a highly crystalline structure, and a superlattice of Fe₂S₃ nanoparticles was revealed. More importantly, iron arachidate mixed ODA still maintain a crystalline structure, and the lattice constant increases as the ODA:AA ratio increases. Accordingly, the superlattice of Fe₂S₃ nanoparticles formed are also with an increased lattice constant.; It is concluded that (1) Langmuir isotherms are useful in identifying well mixed amphiphiles system; (2) There is a direct correlation between the ordering in the LB template and the assembly structure of the nanoparticles and the charge of cation plays a vital role in determining the LB template structure; and (3) Mixed LB films are promising in synthesizing the superlattice of nanoparticles of limited sizes.