Yun Hao Xu

FeCo–Au core-shell nanocrystals

A one-step synthesis of heterostructured high magnetic moment FeCo–Au nanocrystals was demonstrated. The nanocrystals possess a cubic shape and have an average size of 30nm. Compositional analysis revealed the detailed distribution of each element within the nanocrystal. The crystalline structure of the components and their epitaxial relationship were determined by structural analysis. The heterostructured FeCo–Au nanocrystals are promising in biomedical applications as well as in fundamental studies of interactions in the nanoscale.

In Vitro and In Vivo Lung Deposition of Coated Magnetic Aerosol Particles

The magnetic induced deposition of polydispersed aerosols composed of agglomerated superparamagnetic particles was measured with an in vitro model system and in the mouse trachea and deep lung for the purpose of investigating the potential of site specific respiratory drug delivery. Oleic acid coated superparamagnetic particles were prepared and characterized by TEM, induced magnetic moment, and iron content. The particles were dispersed in cyclohexane, aerosolized with an ultrasonic atomizer and dried by sequential reflux and charcoal columns. The fraction of iron deposited on glass tubes increased with particle size and decreasing flow rate. High deposition occurred with a small diameter tube, but the deposition fraction was largely independent of tube size at larger diameters. Results from computational fluid dynamics qualitatively agreed with the experimental results. Enhanced deposition was observed in the mouse lung but not in the trachea consistent with the analysis of the aerodynamic time allowed for deposition and required magnetic deposition time.

Cubic and Spherical High-Moment FeCo Nanoparticles With Narrow Size Distribution

FeCo nanoparticles with controllable shapes and narrow size distribution were fabricated by using a plasma-gas-condensation technique. Either cubic shape or spherical shape were obtained when the magnetic field distribution above the sputtering target were well controlled. Meanwhile, the size distribution of these FeCo nanoparticles was also controllable, and a narrow size distribution of 4.9% was obtained at the optimized conditions. The Fe-Co nanoparticles with different shapes showed different magnetic behaviors.

Nanocluster deposition for high density magnetic recording tape media

A technique for the fabrication of ultra-high density magnetic recording tape media with no risk of heating polymer substrate is reported. In this approach magnetic nanoparticles were generated by combining gas-phase nanocluster deposition and on-line heating techniques and deposited onto polymer substrate. Magnetic properties of the nanoparticles were optimized during their flight in vacuum prior to deposition. This technique is materials independent and it can fabricate nanocomposite films with high coercivity and very small film thickness. The fabricated magnetic nanoparticles have a uniform size distribution [for CoPt, 8.4% (standard deviation)] and well-defined spherical shape.

(FeCo)3Si?SiOx core?shell nanoparticles fabricated in the gas phase

A method of fabricating core?shell nanoparticles by using an integrated nanoparticle deposition technique in the gas phase is reported. The principle of the method is based on nanoparticle growth from the vapour phase, during which elements showing lower surface energies prefer to form the shells and elements showing higher surface energies prefer to stay in the cores. This method was applied successfully to the Fe?Co?Si ternary system to fabricate core?shell-type nanoparticles. The nanoparticles were exposed in air after collection to achieve oxidation. The analysis results based on transmission electron microscopy (TEM), Auger electron spectroscopy (AES), x-ray diffraction (XRD), and a superconducting quantum interference device (SQUID) showed that the core parts are magnetic materials of body-centred cubic (bcc) structured (FeCo)3Si of 15?nm in diameter, and the shell parts are amorphous SiOx of 2?nm in thickness. These core?shell-type nanoparticles show a magnetic anisotropy constant of about 7 ? 105?erg?cm?3 and a saturation magnetization of around 1160?emu?cm?3, which is much higher than that of iron oxide. After annealing at 300 ??C in air, (FeCo)3Si?SiOx core?shell-type nanoparticles showed a little bit of a drop in magnetic moment, while pure FeCo nanopariticles totally lost their magnetic moment. This means that the shells of SiOx are dense enough to prevent the magnetic cores from oxidation.

FeCo nanoparticles assembled film

FeCo is a material attracting the interest of many because its very high saturation magnetization (up to 2.45T). In this study, FeCo nanoparticles assembled films with a matrix (carbon) were prepared by an integrated nanocluster deposition system with a gas aggregation cluster source and dc magnetron co-sputtering guns. The nanoparticles are produced from a Fe65Co35 alloy target. The average particle size is controlled to vary from 5to12nm. The size distribution is less than 10%. Transmission electron microscope images show the change of crystallinity upon online heating. FeCo nanoparticles with cubic shape are formed with online heating. Hc is found to increase with the carbon matrix deposited.

Magnetic Properties of Heterostructured Co–Au Nanoparticles Direct-Synthesized From Gas Phase

Heterostructured Co-Au nanoparticles are direct synthesized from gas phase. Magnetic properties of Co-Au nanoparticles are characterized. Low-temperature and room-temperature hysteresis loops show that the magnetic properties of Co are kept in Co-Au nanoparticles. A blocking temperature of 290 K is measured for Co-Au particles with an average size of 12 nm. A field-cooled low-temperature hysteresis loop of Co-Au nanoparticles indicates the existence of oxide, even the particles have a core-shell-like structure

A core-shell nanomaterial with endogenous therapeutic and diagnostic functions

In the present communication, we report the fabrication of a unique core-shell inorganic nanomaterial with potential therapeutic and diagnostic functions. It contains an iron–cobalt (FeCo) core that demonstrates magnetic resonance imaging (MRI) contrast property and a thin nanoshell of gold that inhibits the function of a pro-angiogenic growth factor, VEGF165. Au(FeCo) core-shell nanomaterials are fabricated in the gas phase and characterized using transmission electron microscopy, energy dispersive spectrum, inductively coupled plasma analysis, and MRI. Inhibition of VEGF165 function by Au(FeCo) is demonstrated against VEGF165/VPF-induced signaling cascades and proliferation of human umbilical vein endothelial cells (HUVECs). The self-contrast property of Au(FeCo) is determined in vitro by MRI after incubating HUVECs with Au(FeCo), demonstrating intrinsic contrast property of this potentially therapeutic nanomaterial. In brief, we report here the successful fabrication of an inorganic core-shell nanomaterial with potential therapeutic and diagnostic functions. It inhibits the function of VEGF165 and functions as a MRI contrast agent.

Iron nitride nanoparticles by nanocluster deposition

Fe16N2 has been reported to have a saturation magnetization as high as 2.8–3.0T based on molecular beam epitaxy deposited single crystal film. We report on Fe nitride nanoparticles prepared with a gas-aggregation nanocluster deposition technique, which could potentially generate pure metastable Fe16N2 phase nanoparticles. Nitrogen gas has been used to nitride the particles after they have been formed in the cluster source. X-ray diffraction patterns show a peak split of α-Fe (110) at 52.4° (2θ), which indicates the formation of Fe3N phase.

Exchange Coupling in Synthetic Antiferromagnetic Multilayers for Magnetic Write Head

Fine tuning of exchange coupling constants was demonstrated in synthetic antiferromagnetic multilayers consisting of three ferromagnetic layers and two spacer layers. The effects of interfacial roughness on both the bilinear and biquadratic exchange coupling constants were studied. A model was developed to simulate the behavior of such synthetic antiferromagnetic multilayer system. Detailed exchange coupling constants, both bilinear and biquadratic, were extracted from experimental data by using the model and compared for different samples.