RESUMO
The size effects on solidification and the formation mechanism of the segmented eutectic Bi-43Sn nanowires during in situ annealing have been investigated. A directional solidification along the wire axis limits the segmented eutectic nanowire to arrange axially during the in situ annealing processes due to directional solidification. In 70 nm nanowires, the small size confines the convection in liquid, which results in differences in the microstructure and composition profiles between 70 and 200 nm nanowires. In the vacuum hydraulic pressure injection process, the directional cooling helps the formation of single crystal, and the isotropic solidification leads to polycrystalline microstructure.
RESUMO
To investigate the properties of lead sulfide (PbS) nanocrystals, we have prepared PbS nanocrystals on/in the porous alumina membrane with a pore diameter 20 nm. Utilizing the reaction of Pb wires and the hydrogen sulfide (H2S) gas, PbS nanocrystals produced and grew as the reaction time increased. The composition identification of the nanocrystals was performed by the XPS and EDS analyses. More structure characteristics of the PbS nanocrystals obtained from the TEM analysis. As indicated in the PL spectra, an orange-red emission band appeared and the emission intensities were obviously related to the defects in the nanocrytals. A significant quantum confinement effect made the energy gap of PbS nanocrystals produce a blue shift from 0.41 eV to 1.89 eV. Furthermore, the growth mechanism of the PbS nanocrystals was also discussed.
RESUMO
Mg-5wt.% Sn alloy is often used in portable electronic devices and automobiles. In this study, mechanical properties of Mg-5wt.% Sn alloy processed by Equal Channel Angular Extrusion (ECAE) were characterized. More precisely, its hardness and wear behavior were measured using Vickers hardness test and a pin-on-disc wear test. The microstructures of ECAE-processed Mg-Sn alloys were investigated by scanning electron microscope and X-ray diffraction. ECAE process refined the grain sizes of the Mg-Sn alloy from 117.6 µm (as-cast) to 88.0 µm (one pass), 49.5 µm (two passes) and 24.4 µm (four passes), respectively. Meanwhile, the hardness of the alloy improved significantly. The maximum wear resistance achieved in the present work was around 73.77 m/mm³, which was obtained from the Mg-Sn alloy treated with a one-pass ECAE process with a grain size of 88.0 µm. The wear resistance improvement was caused by the grain size refinement and the precipitate of the second phase, Mg2Sn against the oxidation of the processed alloy. The as-cast Mg-Sn alloy with the larger grain size, i.e., 117.6 µm, underwent wear mechanisms, mainly adhesive wear and abrasive wear. In ECAE-processed Mg-Sn alloy, high internal energy occurred due to the high dislocation density and the stress field produced by the plastic deformation, which led to an increased oxidation rate of the processed alloy during sliding. Therefore, the oxidative wear and a three-body abrasive wear in which the oxide debris acted as the three-body abrasive components became the dominant factors in the wear behavior, and as a result, reduced the wear resistance in the multi-pass ECAE-processed alloy.
RESUMO
DNA is a one-dimensional nanowire in nature, and it may not be used in nanodevices due to its low conductivity. In order to improve the conducting property of DNA, divalent Ni(2+) are incorporated into the base pairs of DNA at pH≥8.5 and nickel DNA (Ni-DNA) is formed. Conducting scanning probe microscopy (SPM) analysis reveals that the Ni-DNA is a semiconducting biopolymer and the Schottky barrier of Ni-DNA reduces to 2 eV. Meanwhile, electrochemical analysis by cyclic voltammetry and AC impedance shows that the conductance of Ni-DNA is better than that of native DNA by a factor of approximately 20-fold. UV spectroscopy and DNA base pair mismatch analyses show that the conducting mechanism of Ni-DNA is due to electrons hopping through the π-π stacking of DNA base pairs. This biomaterial is a designable one-dimensional semiconducting polymer for usage in nanodevices.