Lizhen Hou

Synthesis and magnetic properties of Fe3C-C core-shell nanoparticles.

Fe3C-C core-shell nanoparticles were fabricated on a large scale by metal-organic chemical vapor deposition at 700 °C with ferric acetylacetonate as the precursor. Analysis results of x-ray diffraction, transmission electron microscope and Raman spectroscope showed that the Fe3C cores with an average diameter of ∼35 nm were capsulated by the graphite-like C layers with the thickness of 2-5 nm. The comparative experiments revealed that considerable Fe3O4-Fe3C core-shell nanoparticles and C nanotubes were generated simultaneously at 600 and 800 °C, respectively. A formation mechanism was proposed for the as-synthesized core-shell nanostructures, based on the temperature-dependent catalytic activity of Fe3C nanoclusters and the coalescence process of Fe3C-C nanoclusters. The Fe3C-C core-shell nanoparticles exhibited a saturation magnetization of 23.6 emu g(-1) and a coercivity of 550 Oe at room temperature.

The kinetic friction between a nanowire and a flat substrate measured using nanomanipulation with optical microscopy

The kinetic frictional force between a nanowire and its supporting flat substrate was measured using nanomanipulation with optical microscopy at ambient atmosphere. During testing, the nanowire was pushed at its center point by a sharp tip and thus exhibited an arc shape held by the frictional shear stress (kinetic friction per area). The arc-shaped nanowire slid along the supporting substrate with further pushing. The frictional shear stress was derived from the arc shape of the nanowire based on the theory of elasticity. The frictional shear stresses of Al2O3 nanowires on the Si and SiN substrates were measured to be 2.0 ± 0.2 and 1.5 ± 0.2 MPa, respectively. It was found that the lengths of the nanowires and their angular orientations with the substrate, the arc shapes being formed and the driving mode of the tip had insignificant effects on the measured frictional shear stress.

Facile synthesis and excellent microwave absorption properties of FeCo-C core–shell nanoparticles

FeCo-C core-shell nanoparticles (NPs) with diameters of 10-50 nm have been fabricated on a large scale by one-step metal-organic chemical vapor deposition using the mixture of cobalt acetylacetonate and iron acetylacetonate as the precursor. The Fe/Co molar ratio of the alloy nanocores and graphitization degree of C shells, and thus the magnetic and electric properties of the core-shell NPs, can be tuned by the deposition temperature ranging from 700 °C to 900 °C. Comparative tests reveal that a relatively high Fe/Co molar ratio and low graphitization degree benefit the microwave absorption (MA) performance of the core-shell NPs. The composite with 20 wt% core-shell NP obtained at 800 °C and 80 wt% paraffin exhibits an optimal reflection loss [Formula: see text] of -60.4 dB at 7.5 GHz with a thickness of 3.3 mm, and an effective absorption bandwidth (frequency range for RL ≤10 dB) of 9.2 GHz (8.8-18.0 GHz) under an absorber thickness of 2.5 mm. Our study provides a facile route for the fabrication of alloy-C core-shell nanostructures with high MA performance.