Formation of nanoparticles and one-dimensional nanostructures in floating and deposited Langmuir monolayers under applied electric and magnetic fields

Effects of applied electric and magnetic fields on the two-dimensional (2-D) growth of colloid nanoparticles have been studied. 2-D photochemical generation of amorphous iron-containing magnetic nanoparticles was carried out via ultraviolet decomposition of a volatile organometallic compound iron pentacarbonyl in a mixed Langmuir monolayer at the gas/water interface with stearic acid as a surfactant matrix. During the formation of nanoparticles the monolayer was in the 2-D gas phase state (at very low or no surface pressure). Magnetic properties of nanoparticulate multilayer Langmuir-Blodgett films were studied using electron paramagnetic resonance technique, and ferromagnetic resonance and superparamagnetic signals were observed in the material. Scanning tunneling microscopy and transmission electron microscopy analyses of deposited nanoparticulate films showed that the size and shape of synthesized nanoparticles can be changed dramatically from plate-like to aligned acicular when external magnetic field parallel to the plane of monolayer was applied during the synthesis of nanoparticles. Effects of synergistically applied electric and magnetic fields were also observed. The data obtained and model calculations give evidence that anisotropic interparticle dipole-dipole interactions and kinetic factors can play substantial role in the dipolar nanoparticle growth reactions under applied external fields. Controlling morphology of nanostructures by synthesis under applied fields could prove to be a promising approach for nanophase engineering and nanotechnology. (C) 2002 Elsevier Science B.V. All rights reserved.