Development of Bi-Metallic Fe-Bi Nanocomposites: Synthesis and Characterization

Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) is a widely used technique for assessing tissue physiology. Spoiled gradient echo (SPGR) pulse sequences are one of the most common methods for acquisition of DCE-MRI data, providing high temporal and spatial resolution with strong T(1)-weighting. Conversion of SPGR signal to concentration is briefly reviewed, and a new closed-form expression for concentration measurement uncertainty for finite signal-to-noise ratio (SNR) and baseline scan time is derived. This result is applicable to arbitrary concentration-dependent relaxation rate and is valid over the same domain as the theoretical SPGR signal equation. Expressions for the lower and upper bounds on measurable concentration are also derived. The existence of a concentration- and tissue-dependent optimal flip angle that minimizes concentration uncertainty is demonstrated and it is shown that, for clinically relevant pulse sequence parameters, this optimal flip angle is significantly larger than the corresponding Ernst angle. Analysis of three pulse sequences from the DCE-MRI literature shows that optimization of flip angle using the methods discussed here leads to potential improvements of 10-1166% in effective SNR over the 0.5-5.0 mM concentration range with minimal or no loss of measurement accuracy down to 0.1 mM. In vivo data from three study patients provide further support for our theoretical expression for concentration measurement uncertainty, with predicted and experimental estimates agreeing to within +/- 30%. Equations for concentration bias resulting from biases in flip angle and from pre-contrast relaxation time and contrast relaxivity (both longitudinal and transverse) are also derived in closed-form. The resulting equations show the potential for significant contributions to bias in concentration measurement arising from even relatively small mis-specification of flip angle and/or pre-contrast longitudinal relaxation time, particularly at high contrast concentrations

Organometallic Synthesis of β\beta-CoAl Nanoparticles and β\beta-CoAl/Al Nanoparticles and Their Behaviour upon Air Exposure

Nanocolloids of the intermetallic beta-CoAl phase were prepared by a soft organometallic route. They were fully characterized by (HR)TEM, EDX, WAXS, XAS and SQUID magnetometry. Their exposure to air led to an increased saturation magnetization in agreement with Co/Al segregation and the formation of Co/Al(2)O(3) nanocomposite. Furthermore, the beta-CoAl nanoparticles could be used as seeds to grow an aluminum overlayer, which passivated the alloyed core against oxidation. These nanoparticles yielded stable colloidal solutions in aromatic solvents

Formation of Bimetallic FeBi Nanostructured Particles: Investigation of a Complex Growth Mechanism

cited By 7International audienceMagnetic bimetallic Fe-Bi composites, synthesized by decomposition of organometallic precursors under amine borane and dihydrogen, formed regular nanospheres with mean diameter of 150 ± 30 nm. The nanospheres display a core-shell like chemical distribution in which bismuth is mainly concentrated in the core, as demonstrated through elemental mapping X-ray energy dispersive spectroscopy while the shell is formed by aggregated 3 nm wide iron nanoparticles. The close environment of the different elements was analyzed through complementary techniques such as extended X-ray absorption fine structure, wide-angle X-ray scattering, and 57Fe Mössbauer and X-ray photoelectron spectroscopies. Despite their iron-rich shell, the Fe-Bi nanospheres present both good magnetic properties and enhanced resistance to oxidation during air exposure. To uncover the growth mechanisms leading to the formation of this compound, a series of samples taken at different steps of the synthesis process was analyzed. The role of metallic iron to promote the reduction of the bismuth precursor from the early stages of the synthesis is emphasized. Remarkably, this process promotes the formation of a metastable Fe-Bi nanoalloy. © 2012 American Chemical Society

Effect of a Side Reaction Involving Structural Changes of the Surfactants on the Shape Control of Cobalt Nanoparticles

International audienceCobalt nanoparticles with different sizes and morphologies including spheres, rods, disks, and hexagonal prisms have been synthesized through the decomposition of the olefinic precursor [Co(η3-C8H13)(η4-C8H12)] under dihydrogen, in the presence of hexadecylamine and different rhodamine derivatives, or aromatic carboxylic acids. UV–vis spectroscopy, X-ray diffraction, low and high resolution transmission electron microscopy, and electron tomography have been used to characterize the nanomaterials. Especially, the Co nanodisks formed present characteristics that make them ideal nanocrystals for applications such as magnetic data storage. Focusing on their growth process, we have evidenced that a reaction between hexadecylamine and rhodamine B occurs during the formation of these Co nanodisks. This reaction limits the amount of free acid and amine, usually at the origin of the formation of single crystal Co rods and wires, in the growth medium of the nanocrystals. As a consequence, a growth mechanism based on the structure of the preformed seeds rather than oriented attachment or template assisted growth is postulated to explain the formation of the nanodisks