Alice Mantlikova

Graphene wrinkling induced by monodisperse nanoparticles: facile control and quantification.

Controlled wrinkling of single-layer graphene (1-LG) at nanometer scale was achieved by introducing monodisperse nanoparticles (NPs), with size comparable to the strain coherence length, underneath the 1-LG. Typical fingerprint of the delaminated fraction is identified as substantial contribution to the principal Raman modes of the 1-LG (G and G’). Correlation analysis of the Raman shift of the G and G’ modes clearly resolved the 1-LG in contact and delaminated from the substrate, respectively. Intensity of Raman features of the delaminated 1-LG increases linearly with the amount of the wrinkles, as determined by advanced processing of atomic force microscopy data. Our study thus offers universal approach for both fine tuning and facile quantification of the graphene topography up to ~60% of wrinkling.

Highly efficient mesenchymal stem cell proliferation on poly-ε-caprolactone nanofibers with embedded magnetic nanoparticles

In this study, we have developed a combined approach to accelerate the proliferation of mesenchymal stem cells (MSCs) in vitro, using a new nanofibrous scaffold made by needleless electrospinning from a mixture of poly-ε-caprolactone and magnetic particles. The biological characteristics of porcine MSCs were investigated while cultured in vitro on composite scaffold enriched with magnetic nanoparticles. Our data indicate that due to the synergic effect of the poly-ε-caprolactone nanofibers and magnetic particles, cellular adhesion and proliferation of MSCs is enhanced and osteogenic differentiation is supported. The cellular and physical attributes make this new scaffold very promising for the acceleration of efficient MSC proliferation and regeneration of hard tissues.

Nanocomposites of monodisperse nanoparticles embedded in high-K oxide matrices – a general preparation strategy

We present a general approach, which enables preparation of multifunctional nanocomposites of monodisperse nanoparticles embedded in oxide matrices. The two-step route has been successfully applied to nanocomposites composed of CoFe2O4 nanoparticles embedded in high-K oxide matrices (ZrO2, Al2O3 and TiO2). First, hydrophobic CoFe2O4 nanoparticles were produced by hydrothermal synthesis and then their incorporation in the oxide matrix was completed by the sol–gel method using the corresponding alcoxides. The as-prepared samples were subjected to annealing at temperatures ranging from 200 to 700 °C, and characterized in detail by the Powder X-Ray Diffraction (PXRD), Energy Dispersive Analysis (EDX), Mossbauer Spectroscopy (MS) and magnetic measurements. The particle size does not change with the annealing temperature, while the amorphous matrices crystallize at temperatures above 400 °C. At much higher annealing temperatures, partial decomposition of the CoFe2O4 occurs accompanied by formation of additional phases. The magnetic measurements also confirmed presence and stability of the uniform CoFe2O4 nanoparticles in the matrices. Thus the proposed method allows preparation of new types of nanocomposites constituted of uniform nanoparticles of the desired type (magnetic, luminescent etc.) embedded in the favored oxide matrix.

INFLUENCE OF AGGREGATE COATING ON RELAXATIONS IN THE SYSTEMS OF IRON OXIDE NANOPARTICLES

We have investigated properties of systems of strongly interacting magnetic nanoparticles in order to estimate the influence of the inter-aggregate interactions on the collective phenomena. We have compared two systems composed of γ-Fe2O3 nanoparticles, prepared by thermal decomposition of an organic precursor and coprecipitation, respectively; with those prepared by coprecipitation, containing the particle aggregates coated by SiO2 layer of different thickness. Detailed magnetic studies of all samples such as the temperature dependence of magnetization and frequency-dependent a.c. susceptibility, recorded also in external magnetic field, revealed the blocking temperature close to 300 K and super-spin glass (SSG) or SSG-like nature of the systems. The slight minimization of the interaction strength in the system with increasing thickness of the SiO2 coating has been observed.

Analysis of metal catalyst content in magnetically filtered SWCNTs by SQUID magnetometry

Removal of the residual magnetic metal catalyst from the single-wall carbon nanotubes (SWCNTs) is important prerequisite for many further applications. We present here a facile analysis method enabling direct control of the removed fraction of the catalyst nanoparticles (NPs) after purification. Determination of distribution of the magnetic moments attributed to the catalyst NPs enables proper interpretation of the efficiency and mechanism of the used purification process. The study has been performed on the SWCNTs containing magnetic metal NPs, exposed to sonication and magnetic filtration. Two different SWCNT precursors (HiPco and laser ablation SWCNTs), three solvents and multiple filtration steps, respectively, have been tested. Magnetic property measurements are supported by the results of thermal decomposition and Raman spectroscopy.

Magnetic Force Microscopy Studies of Superparamagnetic Nanoparticles

We have tested ability of superparamagnetic nanoparticles embedded in matrix to be detected by the magnetic force microscopy (MFM). The sample was characterized by X-ray diffraction and by further magnetic studies such as the temperature and field dependence of magnetization (M) that served as the starting point for an optimal setup for the MFM imaging. To demonstrate the magnetic origin of the phase contrast, the images were taken both with the magnetic and non-magnetic probes. Because of the strong inter-particle interactions arising from the small distances among the particles, only the clusters of the magnetic nanoparticles have been imaged. The optimization of scanning parameters that depend on the sample properties, as well as the possibility to measure the contrast arising from the single particle embedded in matrix will be discussed.

Nanocomposite of CeO2 and High-Coercivity Magnetic Carrier with Large Specific Surface Area

We succeeded in the preparation of CoFe2O4/CeO2 nanocomposites with very high specific surface area up to 264 g/m2. First, highly crystalline nanoparticles NPs of CoFe2O4 4.7 nm were prepared by hydrothermal method in water-alcohol-oleic acid system. The oleate surface coating was subsequently modified by ligand exchange to citrate. Then the NPs were embedded in CeO2 using heterogeneous precipitation from diluted Ce3+ sulphate solution. Dried samples were characterized by Powder X-Ray Diffraction, Energy Dispersive X-Ray Analysis, Scanning and Transmission Electron Microscopy, Mossbauer Spectroscopy, and Brunauer-Emmett-Teller method. Moreover, detailed investigation of magnetic properties of the bare NPs and final composite was carried out. We observed homogeneous embedding of the magnetic NPs into the CeO2 without significant change of their size and magnetic properties. We have thus demonstrated that the proposed synthesis method is suitable for preparation of extremely fine CeO2 nanopowders and their nanocomposites with NPs. The morphology and magnetic nature of the obtained nanocomposites make them a promising candidate for magnetoresponsive catalysis.

Origin of high-coercivity in nanocomposites by single-precursor sol-gel method

We have fabricated high-coercivity nanocomposites constituted of Fe2O3 or CoFe2O4 nanocrystals embedded in amorphous silica matrix by a single-molecule precursor sol-gel method. Our approach enables smooth variation of the Fe(Co) : Si ratio up to 40 weight % of the magnetic phase, resulting in high density nanocomposite. Final crystallite size and phase composition was adjusted by subsequent heat treatment. The Fe2O3/SiO2 samples annealed at 1000 and 1100 °C revealed coercivity, Hc ~ 2 T at 300 K due to formation of the metastable -Fe2O3 phase. The CoFe2O4/SiO2 composites exhibit enhancement of the Hc value with increasing annealing temperature. Origin of the large coercivity in the two types of the magnetically hard nanocomposites will be discussed.

High-Coercivity Iron Oxide Based Nanocomposites - Particle Shape and Magnetic Structure by Synchrotron and Neutron Scattering

We report on advanced investigation of structure and magnetism of high-coercivity Fe2-xAlxO3/SiO2 (x = 0 − 0.75) nanocrystals obtained by a smart sol-gel route. The substitution of Fe by Al originates suppression of the high-to-low coercivity crossover at 120 K typical for the -Fe2O3 phase. Our neutron scattering experiment revealed, that the high-coercivity collinear magnetic structure of the -Fe2O3 persists in the Al-doped nanocrystals down to low temperatures, while an incommensurate magnetic structure develops in the low-coercivity phase in the undoped -Fe2O3 only. The size and shape of the nanocrystals was obtained by advanced profile analysis of the high-quality S-PXRD data.