G. M. Chow

Carboxyl group (–CO2H) functionalized ferrimagnetic iron oxide nanoparticles for potential bio-applications

A new approach to prepare surface-functionalized magnetic nanoparticles by synthesis of poly(methacrylic acid) (PMAA) coated maghemite nanoparticles in aqueous solution is reported. Maghemite (γ-Fe2O3) nanoparticles with an average diameter of 8 ± 2 nm were fabricated and subsequently coated with PMAA by emulsion polymerization. The FTIR study and thermal analysis confirmed the chemical adsorption of methacrylic acid on the maghemite nanoparticle surface, and suggested a symmetrical carboxylate bonding. The free carboxyl group of PMAA, which was verified by FTIR spectroscopy and zeta potential measurement, provided the site for immobilization of foreign molecules. The PMAA coated maghemite nanoparticles were demonstrated as potential magnetically targeted drug carriers by adsorbing an anti-cancer drug (carboplatin) via the ion–dipole interaction between CO2− of PMAA and carboplatin.

Nanocrystalline metallic powders and films produced by the polyol method

Abstract The polyol method has been extended to synthesize metallic powders of Ru, Rh, Sn, Re, W, Pt, Au, Fe-Cu, Co-Cu, Ni-Cu, in addition to powders of Fe, Co, Ni, Cu, Pd and Ag which were previously prepared by others using this method. This method can also be used to deposit nanocrystalline metallic films on a variety of substrates, including PyrexTM, KaptonTM, TeflonTM, aluminum nitride, carbon fibers and alumina fibers. This can be a viable catalyst-free method for the deposition of conductive metallic films on non-conductive substrates.

Colloidal LaF3:Yb,Er, LaF3:Yb,Ho and LaF3:Yb,Tm nanocrystals with multicolor upconversion fluorescence

The IR-to-visible upconversion fluorescent nanocrystals, Yb–Er, Yb–Ho and Yb–Tm co-doped LaF3 were chemically synthesized and investigated. The ligand-capped nanocrystals were easily dispersed in organic solutions and subsequently formed a transparent colloidal solution. Under 980 nm IR excitation, green, red and blue emission bands were observed from these colloidal solutions, respectively. Compared with the recently reported colloidal NaYF4:Yb,Er nanocrystals, our nanocrystals produced a fluorescence output which was 5 times higher. These nanocrystals have potential applications as bio-probes and displays.

Low temperature deposited L10 FePt–C (001) films with high coercivity and small grain size

FePt–C films with high coercivity, (001) texture, and small grain size were deposited on MgO∕CrRu/glass substrate by cosputtering FePt and carbon at 350°C. The out-of-plane coercivity measured at room temperature increased from 9.6to15.1kOe when C concentrations increased from 0% to 15%. Further increasing the C contents to 20% and 25% caused the decrease of coercivity to 13.6 and 11.8kOe, respectively. With C doping, a two-layer structure of FePt–C films was formed and fcc-phase FePt particles were found. By optimizing the sputtering process, FePt–C (001) film with coercivity higher than 14.4kOe and columnar FePt grains of 7.5nm in diameter was obtained, which are suitable for ultrahigh density perpendicular recording.

High coercivity L10 FePt films with perpendicular anisotropy deposited on glass substrate at reduced temperature

The microstructures and magnetic properties of FePt films grown at 350°C on glass substrates with MgO (200) intermediate layer and CrRu (200) underlayer were investigated. The film with 1nm MgO intermediate layer showed higher degree of chemical ordering than that with 4nm MgO layer due to the compression of the lattice constant of 1nm MgO intermediate layer along the [100] direction. Isolated FePt particles were formed when nominal thickness of FePt was 4nm. The room temperature coercivity of isolated FePt particles with 1nm MgO intermediate layer was as high as 12kOe, significantly larger than that with 4nm MgO intermediate layer (6.3kOe).

The Morphology of Electroless Ni Deposition on a Colloidal Pd(II) Catalyst

The surface morphology of a surface-bound colloidal Pd(II) catalyst and its effect on the particle sizes with the largest particles reaching approximately 50 nm in diameter. Catalyst surface coverages as low as 20% are found to be sufficient to initiate complete and homogeneous metallization. The distribution of particle sizes for the electroless metal deposit, found to be a function of plating time, is broad with the maximum Ni particle size exceeding 120 nm. Results indicate controlling the size of the bound catalyst is the principal determining factor in controlling the particle size of the electroless deposit. Modification of the surface by depleting the concentration of surface functional groups capable of binding catalyst is used to shift the size distribution of bound catalyst to smaller values. A resulting three-to fourfold reduction in the particle size of the electroless deposit is demonstrated.

Structural, morphological, and magnetic study of nanocrystalline cobalt-copper powders synthesized by the polyol process

Nanocrystalline Co{sub {ital x}}Cu{sub 100{minus}{ital x}}(4{le}{ital x}{le}49 at.%) powders were prepared by the reduction of metal acetates in a polyol. The structure of powders was characterized by x-ray diffraction (XRD), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), extended x-ray absorption fine structure (EXAFS) spectroscopy, solid-state nuclear magnetic resonance (NMR) spectroscopy, and vibrating sample magnetometry (VSM). As-synthesized powders were composites consisting of nanoscale crystallites of face-centered-cubic (fcc) Cu and metastable face-centered cubic (fcc) Co. Complementary results of XRD, HRTEM, EXAFS, NMR, and VSM confirmed that there was no metastable alloying between Co and Cu. The NMR data also revealed that there was some hexagonal-closed-packed (hcp) Co in the samples. The powders were agglomerated, and consisted of aggregates of nanoscale crystallites of Co and Cu. Upon annealing, the powders with low Co contents showed an increase in both saturation magnetization and coercivity with increasing temperature. The results suggested that during preparation the nucleation of Cu occurred first, and the Cu crystallites served as nuclei for the formation of Co.

Synthesis of nir-sensitive Au-Au2S nanocolloids for drug delivery

Abstract Near IR (NIR) sensitive Au–Au2S nanocolloids were prepared by mixing HAuCl4 and Na2S in aqueous solutions. An anti-tumor drug, cis-platin, was adsorbed onto Au–Au2S nanoparticle surface via the 11-mercaptoundecanoic acid (MUA) layers. The results show that the degree of adsorption of cis-platin onto Au–Au2S nanoparticles was controlled by the solution pH value, and the drug release was sensitive to near-infrared irradiation. The cis-platin-loaded Au–Au2S nanocolloids can be potentially applied as NIR activated drug delivery carrier.

The process‐controlled magnetic properties of nanostructured Co/Ag composite films

Nanostructured Co/Ag composite films were prepared by magnetron sputtering using a single target. The average crystallite sizes of Co and Ag in the films depend on the deposition conditions. As the substrate temperature increases from 100 °C to 600 °C, the average Ag crystallite size increases from 39 to 452 A, and the average Co crystallite size increases from <30 to 297 A in the film with 39 vol. % of Co. The films with 39 vol. % of Co and prepared at 400 °C substrate temperature showed a maximum magnetic coercivity of 565 Oe at 6 K. We have studied the correlation between the structure and magnetic properties of these films.

Magnetic and hardness properties of nanostructured Ni–Co films deposited by a nonaqueous electroless method

Nanostructured NixCo100−x films were deposited on Cu substrates by reducing the constituent metal salts in refluxing ethylene glycol at 194 °C. The average crystallite size increased with x, and reached a maximum of 64 nm when x=100. The coercivity Hc of the films measured in the direction perpendicular (⊥) to the plane of the film was higher than that in the parallel (∥) direction. For the sample of x=50, Hc⊥ was 379 Oe, which was six times that of Hc∥. Saturation magnetization Ms in the film plane was 1016 emu/cm3, and the remanent magnetization Mr 636 emu/cm3, giving a squareness ratio of 0.63. This film also had a Vickers hardness of 193.