We present novel three-dimensional (3D) hierarchical ZnO and ZnAl2O4 nanostructures produced by multitransformation reactions using Zn as the starting material. In two representative instances selected for illustrating this strategy, various Zn precursors like Zn nanowires and polyhedral Zn microcrystals were first prepared by physical vapor deposition without any catalyst. Subsequently, we successfully synthesized branched ZnO nanowires and hollow ZnO polyhedrons with vertically aligned ZnO nanowires by oxidizing Zn nanowires and polyhedral Zn microcrystals, respectively, under optimal conditions. The growth of both ZnO nanobranches and vertically aligned nanowires was suggested as a self-supplying and self-catalytic process following the vapor transport solid condensation mechanism. Furthermore, the obtained ZnO nanostructures were homogeneously covered by a shell of amorphous Al2O3 using atomic layer deposition. Through the solid–solid interfacial reaction of ZnO and Al2O3, the 3D nanostructures were transformed to hierarchical ZnAl2O4 nanostructures conserving the shape of the corresponding ZnO nanostructures. Particularly, all the ZnAl2O4 nanobranches or vertically aligned 1D structures exhibited a tubular structure, which was induced by the nanoscale Kirkendall effect. This work demonstrates a simple and efficient pathway to design hierarchical ZnO and complex hollow zinc spinel nanostructures, which are expected to have potential applications in nanotechnology.
In this study, a highly ordered gold nanoparticle (AuNP) monomer array based on a gold-coated conical anodic aluminum oxide (AAO) template was fabricated to produce a ring-shaped hot line between the gold layer and AuNPs instead of the existing hot spot between the metal nanoparticles. The surface-enhanced Raman scattering signal of the synthesized nanostructured template was 80 times higher than that of a flat gold surface and 3.7 times higher than that of ordered AuNP monomers arranged by the conical AAO template. The template was also fabricated based on a wet chemistry process, which allows for considerably easier and quicker production of large-area templates. KEYWORDS: surface-enhanced raman scattering (SERS), Raman spectroscopy, finite-difference time-domain (FDTD) method, anodic aluminum oxide (AAO) template, gold nanoparticles, plasmonic nanoparticle
Three types of nanostructured silicon carbide ceramics were prepared with additives of Al 2 O 3 and Y 2 O 3 as the primary sintering additives, together with 1 mass! CaO, 1 mass! MgO or 0.73 mass! AlN. The silicon carbides SiC containing tens of nanometers of grains were successfully fabricated using a two-step sintering process. The mechanical properties and contact damages of the nanostructured SiC ceramics were investigated in this study. The nanostructured SiC ceramics exhibited a hardness of Ĭ20 GPa, a strength of 400-700 MPa, and a toughness of 3.0 MPaெm 12. The nature of the contact damage exhibited classical ring or cone cracks formed in a region of weak tension outside the contact rather than microcracks in the diffuse quasi-plastic zones as observed in heterogeneous microstructures consisting of micron-sized elongated grains.
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