A method for controlled synthesis of anisotropic nanoparticles and nanosystems

In the present work it has been shown that the shape of ultrafine metallic magnetic particles is controlled by applied magnetic and/or electric fields and the state of reaction media during the nanoparticles formation. The ulraviolet (UV) decomposition of volatile organometallic compound iron pentacarbonyl was used to produce amorphous metallic nanoparticles. The two-dimensional photochemical synthesis of nanoparticles was carried out in a mixed Langmuir monolayer at the gas/water interface with stearic acid as surfactant matrix and also in a mixed film deposited onto graphite substrate. Scanning tunneling microscopy analysis of deposited nanoparticulate monolayers showed that the size and shape of nanoparticles formed were dependent on the initial mixed monolayer content, compression extent and exposure time to UV, and were changed dramatically from isotropic plate-like to aligned ellipsoidal and needle-like when external magnetic and/or electric fields were applied during the synthesis. Magnetic nanoparticles with diameter exceeding 5 nm formed chain structures alignable by external fields. The one-dimensional aligned metallic string-like nanostructures (nanowires) with cross-section size about 10 divided by 20 nm were also formed at elevated temperatures under synergistically applied magnetic and electric fields. Magnetic properties of nanoparticulate multilayer Langmuir-Blodgett films were studied using electron paramagnetic resonance technique. The ferromagnetic resonance and superparamagnetic signals were observed in the material.