Coated Metal Nanoparticles Research Articles

Metal nanoparticle plasmonics inside reflecting metal films

Oxide coated metal nanoparticles buried within a thin metal layer support a surface plasmon resonance. A local dip occurs in spectral reflectance along with a switching off of the film’s plasmonic response. Models are introduced in which these resonances are tunable by altering the ratio of oxide thickness to core particle radius. The optical response of two experimental examples is presented and modeled using effective medium theory. Beyond the resonance zone the doped layer switches back to the plasmonic response of a nanoporous version of the host metal whose effective plasma frequency arises only from the percolating component.

Advanced Piezoresistance of Extended Metal-Insulator Core-Shell Nanoparticle Assemblies

Assembled metal-insulator nanoparticles with a core-shell geometry provide access to materials containing a large number (>10(6)) of tunneling barriers. We demonstrate the production of ceramic coated metal nanoparticles exhibiting an exceptional pressure-sensitive conductivity. We further show that graphene bi- and trilayers on 20 nm copper nanoparticles are insulating in such a core-shell geometry and show a similar pressure-dependent conductivity. This demonstrates that core-shell metal-insulator assemblies offer a route to alternative sensing materials.

Plasma Synthesis of Coated Metal Nanoparticles with Surface Properties Tailored for Dispersion

AbstractA method to produce copper nanoparticles coated with an organic plasma polymer layer is presented. The reaction mechanism for plasma polymerization of ethylene glycol is elucidated, and hydroxyl, methanol and ethanol radicals are shown to be present in the RF discharge. UV radiation is shown to have a significant effect on radical formation. Empirical evidence suggests that nanoparticles exhibit enhanced reactivity. Contact angle measurements of coated particles deposited onto copper collection surfaces show hydrophilic or hydrophobic properties when ethylene glycol or ethane, respectively, is used as the precursor gas. Such properties facilitate dispersion into other media by improving the interaction between the solid and liquid phases.magnified image

Characterization and magnetic property of carbon coated metal nanoparticles and hollow carbon onions fabricated by CVD of methane

This work focuses on the structural characterization and magnetic property of carbon onions, which were synthesized via catalytic decomposition of methane over Ni/Al catalyst. The results showed that the small microcrystalline planar is 3.2 nm for the obtained carbon onions according to calculation from Raman. The saturation magnetization at room temperature of the carbon onions is 27.12 emu/g, which is 53% of the bulk ferromagnetic element counterpart due to the inclusive phases of carbon and magnetic effect of small particles with larger surface to volume ratio. The coercive force at room temperature of the carbon onions is 141.6 Oe, while the ratio of remnant to saturation magnetization M r/ M s is about 0.247.

Catalytic synthesis of carbon nanostructures using Fe(OH)3/Al as catalyst precursors

Abstract Fe(OH) 3 /Al with different Fe contents was prepared using a new deposition–precipitation reaction. Then mixed oxides were obtained by calcination of these precursors, and their catalytic activities were examined during synthesis of various carbon nanostructures. It was found that carbon nanotubes were synthesized using a Fe/Al 2 O 3 catalyst with 10 wt% Fe, while carbon coated metal nanoparticles resulted from Fe/Al 2 O 3 catalyst with 15 wt% Fe, but for the Fe/Al 2 O 3 catalyst with 5 wt% Fe, only amorphous carbon has been obtained.

Insulator coated metal nanoparticles with a core/shell geometry exhibit a temperature sensitivity similar to advanced spinels

The preparation of carbon-coated copper nanoparticles with different carbon layers resulted in materials with a highly sensitive pressure and temperature dependent conductivity. The core/shell geometry of these carbon/metal composites afforded two distinctly different electrical behaviors depending on the carbon layer properties. Graphene layers with a predominant sp 2 character showed an ill-defined bandgap structure as evidenced by UV–vis diffuse reflectance spectroscopy. The resulting composites were weak conductors with low sensitivity. Use of predominately insulating carbon layers with a well-defined bandgap of above 1.9 eV resulted in composites with a material constant β of over 4700 K which is comparable to currently used commercial spinels. A theoretical analysis and detailed material characterization by Raman spectroscopy, X-ray diffraction, 13C NMR spectroscopy and thermoanalysis suggested a tunneling based conduction mechanism in these core/shell materials. This interpretation was supported by a good correlation between experimental data and the estimated effects arising from the theoretical analysis of the tunneling effects.