Hot-Wire Synthesis of Gold Nanoparticles

Gold nanoparticles were synthesized by a hot-wire generator at atmospheric pressure using a gold-platinum composite wire. At low gas flow velocities the nanoparticles were found to be agglomerates of partially sintered primary particles. By reducing the tube size via the insertion of a nozzle with a throat diameter of 3 mm, the hot-wire generator was found to produce small (<10 nm diameter) crystalline gold particles. Elemental and x-ray photoelectron spectroscopy analysis of the particles showed that they were composed of gold with no platinum impurity. Charging analysis of the “as-produced” nanoparticles showed that fewer than 10% of the particles were charged, but the charge fraction increased as the applied power increased, as did the ratio of negatively-to-positively-charged particles.     

关于聚焦诱导立体显示器的研究

传统的立体显示是通过聚焦诱导,进行深度视觉模糊调节,从而达到立体视觉效果。现在,科研人员开发了一种新型技术——聚焦修正。通过这项技术,将聚焦诱导和深度视觉模仿同步进行,可以使立体景象显示更加快速、准确,同时减轻观看者的视觉疲劳度。     

Dislocation plasticity and phase transformations in Si-SiC core-shell nanotowers

Vapor-liquid-solid (VLS) Si nanotowers were coated with nanocrystalline SiC to form a Si-SiC core-shell composite. Due to a mismatch in the coefficients of thermal expansion (CTE), the Si core was under a compressive stress following the deposition. The composite tower was then cross-sectioned using focused ion beam milling, exposing the Si core. Indentation into the Si showed an increased toughness as a function of diameter compared to similar sized Si nanotowers and nanospheres. This result is explained through enhanced dislocation and phase transformation plasticity in the Si core from the CTE compressive stresses.     

Analysis of nanostructured coatings synthesized by ballistic impaction of nanoparticles

SiC nanostructured coatings were synthesized by ballistic impaction of nanoparticles using a process called hypersonic plasma particle deposition (HPPD). X-ray diffraction spectra of typical samples showed the presence of crystalline SiC and Si. Grain sizes obtained through transmission electron microscopy showed particles in the sub 10 nm range with primarily crystalline β-SiC and some crystalline Si particles present. These results correlate well with particle size distributions measured using an aerosol sampling probe coupled to a scanning electrical mobility spectrometer. Interestingly, particle size distributions indicated only small changes in the particle size distributions when Si deposition was compared to SiC. Examination of adhesion characteristics highlighted the importance of a chemically bound interlayer during SiC deposition on Mo and steel substrates.     

Strain-hardening in submicron silicon pillars and spheres

Measurements of submicron spheres and pillars of silicon single crystals have exhibited a strain-hardening capacity equal to or greater than their metallic counterparts. Stress–strain characteristics are reported for diameters ranging from 40 to 400 nm. Evaluations were performed with nanoindentation-based atomic force, scanning and transmission electron microscopies. Values of strain-hardening exponents up to unity in nanospheres are attributed to a size effect variation on the rate of increase of contact area with deformation. A surface-mediated dislocation nucleation concept is shown to be consistent with length scale effects partially modified by geometry as well as size. It is proposed, but not proven, that the modification relates to greater constraint in compact spheres as opposed to tall pillars.