Georgia Basina

Different modulated structures of topological defects stabilized by adaptive targeting nanoparticles

It is demonstrated that interactions between nanoparticles and topological defects induce a twist-grain boundary phase in a chiral liquid crystal. The occurrence of this phase, the analogue of the Shubnikov phase in type-II superconductors, is driven by direct interactions between surface-functionalized CdSe quantum dots and screw dislocations. It is shown that, within an adaptive-defect-core-targeting mechanism, nanoparticles of appropriate size and functionalization adapt to qualitatively different cores of topological defects such as disclination lines and screw dislocations. This mechanism enables the effective reduction of the energetically costly, singular defect core volume, while the surrounding phase ordering remains relatively weakly affected. The findings suggest new pathways towards the controlled assembly of superstructures in diverse, symmetry-broken, condensed-matter systems, ranging from nanoparticle-decorated liquid crystals to superconductors.

Synthesis of air stable FeCo nanoparticles

Nanoparticulate FeCo alloys have been synthesized by Fe(CO)5 and Co2(CO)8 thermal decomposition in paraffin oil in the presence of oleic acid and oleyl amine. The crystal structure and morphology of the nanoparticles were confirmed by powder x-ray diffraction and transmission electron microscopy. The size and crystallinity of the particles was found to depend on the reaction conditions such as the precursors concentration, reaction time, and carbonyls injection temperature. Also the Fe/Co ratio can be easily controlled by controlling the Fe and Co carbonyls ratio. The as-made nanoparticles were annealed at 500 °C under CH4 stream in order to be protected from future oxidation. This treatment leads to the formation of a graphitic shell around the particles which also protects them from sintering. Additionally, these particles can be functionalized with 1-pyrenebutiric acid in order to be soluble in various solvents.

Direct chemical synthesis of L10 FePt nanoparticles

Ordered faced-centered tetragonal (fct) FePt nanoparticles were successfully synthesized by a chemical method using presynthesized Au nanoparticles as the “catalyst.” The reaction temperature was also studied and it seems that there is an optimum value of 360 °C where the fct structure is formed. The particles have a mean diameter of 3.5–15 nm and the x-ray diffraction patterns exhibited (001) and (110), which signified the tetragonal phase formation. Room temperature magnetic hysteresis loops show that the FePt particles have coercive fields between 0.68 and 2.8 kOe.

Water-Soluble Spinel Ferrites by a Modified Polyol Process as Contrast Agents in MRI

Magnetic nanoparticles have recently been very attractive for biomedical applications. In this study, we have synthesized ferrite nanoparticles for application as contrast agents in MRI experiments. Fe3O4 and MnFe2O4 spinel ferrites with a mean size of 11–12 nm, were prepared by a modified polyol route in commercially available polyethylene glycol with molecular weight 600 (PEG‐600). The reaction takes place in the presence of water soluble and non‐toxic tri‐block copolymer known as Pluronic® F‐127 (PEO100‐PPO65‐PEO100). The nanoparticles have saturation magnetization values of 52 and 68 emu/g for MnFe2O4 and Fe3O4, respectively. Both the Fe3O4, and MnFe2O4 nanoparticles make stable solutions in water known as ferrofluids. Preliminary data demonstrated the capability of these nanoparticles to induce imaging contrast in T2 weighted MRI experiments, making these materials suitable for biomedical applications such as medical MRI.