Improved Fabrication Of Crystalline Films

Researchers in Japan have developed a simple method for preparing rare-earth hydroxide films by trapping crystallites of one such material at a solvent interface and then uniformly transferring them to a substrate (Chem. Commun., DOI: 10.1039/b812111g). The resulting films are of much better quality in terms of orientation and coverage than crystalline films prepared by traditional methods, such as solvent evaporation or spin-coating. Takayoshi Sasaki of the National Institute for Materials Science and coworkers had previously synthesized Eu(OH)_2.5Cl_0.5•_0.9H₂O, which forms micrometer-sized platelike crystals. The team's film-fabrication method begins by dispersing the crystallites in water and then adding hexane, which results in a two-phase system. When a few drops of ethanol are added, the crystallites form a monolayer at the water-hexane interface. When a pretreated substrate is dipped into the solution, the crystallites adhere to the substrate, forming a monolayer film; multiple layers are deposited by repeatedly dunking the substrate. Subjecting the film to ultrasound treatment serves to create uniform layers of the large crystallites. Well-organized films of the type made by the Japanese team, which are photoluminescent and readily undergo anion exchange for further modification, have potential applications in optical devices and chemical sensing.