Nanostructure Templating in Inorganic Solids with Organic Lyotropic Liquid Crystals

Various nanoscale semiconducting superlattices have been generated by direct templating in a lyotropic organic liquid crystal. These include superlattices of CdS, CdSe, and ZnS, templated in a liquid crystal formed by oligoethylene oxide oleyl ether amphiphiles and water. The semiconductor growth process copied the symmetry and characteristic dimensions of the original mesophase by avoiding growth of mineral within regularly spaced hydrophobic regions. The final product was a superlattice structure in which a mineral continuum was featured with hexagonally arranged cylindrical pores 2-3 nm in diameter and 5 nm apart. Most importantly, the superlattice morphology of the nanostructured systems in contact with the mesophase was found to be thermodynamically stable with respect to the solid lacking nanoscale features. We also found that both the morphology of features in the nanostructured solids and their dimension can be controlled through the amphiphile’s molecular structure and water content in the liquid crystal. The semiconducting solids CdS, CdSe, and ZnS were all directly templated, while Ag2S, CuS, HgS, and PbS were produced only as nonfeatured solids using identical synthetic methodologies. We propose that interactions of polar segments in template molecules with the precipitated mineral and with its precursor ions are necessary conditions for direct templating. This is based on the absence of templating in the more covalent minerals and also in the presence of salts known to bind precursor ions.