Two-dimensional synthesis of anisotropic nanoparticles

A novel approach for the synthesis of nanoparticles has been introduced in which nanoparticles are fabricated via decomposition of an insoluble precursor compound in a monolayer at the gas/liquid interface, and nanoparticle growth is an example of a two-dimensional (2-D) process where true 2-D diffusion of precursor molecules, active intermediates, metal atoms and its complexes, nucleus and growing nanoparticles, surfactants and additives occurs only in the plain of the monolayer. In the present contribution, two possible example embodiments of the approach are described. First, magnetic iron-containing nanoparticles were photochemically generated by the ultraviolet decomposition of a volatile precursor compound iron pentacarbonyl in a mixed Langmuir monolayer. Secondly, nanoparticles were produced by the chemical reduction of palladium from Pd-3(CH3COO), molecules and of gold from Au(P(C6H5)(3))Cl in the mixed monolayers. Stearic acid, arachidic acid or octadecyl amine were used as surfactants to form Langmuir monolayers on the aqueous sub-phase surface and to stabilize the growing nanoparticles. Nanoparticles were formed in the 2-D gas phase of a monolayer (at very low or no surface pressure). The morphology of the nanoparticles synthesized was characterized by atomic force microscopy and transmission electron microscopy. It was established that the shape, size and crystallinity of the resulting nanoparticles were dependent substantially on the monolayer composition and state during the growth process. It was demonstrated that the shape of the magnetic nanoparticles can be changed from 2-D isotropic plate and ring-like to the field-aligned ellipsoidal and needle-like when external magnetic field parallel to the plane of particulate monolayer was applied during the synthesis. The effects of self-organization of nanoparticles and formation of 2-D nanostructures are also presented. It is shown that controlling the mixed monolayer composition and compression state opens wide possibilities for the growth regulation of the 2-D growth of nanoparticles and self-organization processes to obtain inorganic nanostructures with various and unique morphologies. (C) 2002 Elsevier Science B.V. All rights reserved.