Surface diffusion is intimately correlated with crystal orientation and surface structure. Fast surface diffusion accelerates phase transformation and structural evolution of materials. Here, through in situ transmission electron microscopy observation, we show that a copper nanowire with dense nanoscale coherent twin-boundary (CTB) defects evolves into a zigzag configuration under electric-current driven surface diffusion. The hindrance at the CTB-intercepted concave triple junctions decreases the effective surface diffusivity by almost 1 order of magnitude. The energy barriers for atomic migration at the concave junctions and different faceted surfaces are computed using density functional theory. We proposed that such a stable zigzag surface is shaped not only by the high-diffusivity facets but also by the stalled atomic diffusion at the concave junctions. This finding provides a defect-engineering route to develop robust interconnect materials against electromigration-induced failures for nanoelectronic devices.
NAND flash is the most widely used non-volatile memories due to its low cost and rewritable properties. However, some problems exist in NAND flash that need to be solved, such as low writing and reading speed, high operating voltage, and relatively large cell dimensions. Next generation memories, especially resistive random access memory (RRAM) could improve these problems. The technologies of 3D vertical architecture have made a major breakthrough in establishing high-density memory structures. Combined with an array structure, a 3D high density vertical resistive random access memory (VRRAM) cross-point arrays are able to efficiently increase the device density in vertical direction. In this work, a novel 3D VRRAM arrays which contains two VRRAM cells (Pt/ ZnO/ Al and Pt/ ZnO/ Ti) and one normal layered RRAM (Al/ Al2O3/ Ti) at each cross point were constructed. The Al2O3 based device could operate under a lower compliance current, where contained higher resistance than ZnO based cells. With the controlling of compliance current, the leakage current between VRRAM cells and Al/ Al2O3/ Ti cell could be effectively reduced, therefore, the neighboring cells could be operated independently. We demonstrated the introducing of VRRAM structure could achieve high density advantage in vertical direction, and the adjacent cells in 3D vertical structure could be operated independently with scarcely leakage current. The shrinkage of leakage current enhance the stability of devices and increase the feasibility of high density VRRAM structure applications. Figure 1
The Mo5O14-type structure is an important and representative to the MoO-based catalyst in the selective oxidation process. In the petrochemical industries, the MoO-based catalyst has been widely doped with other elements like V, Nb and Te to have distinct properties with high activity, selectivity and conversion efficiency. The specific facet and bonding relationship would affect the catalyst properties and functionality. The catalyst is usually synthesized as nanoparticles, which have random configuration and uniformity. Therefore, we successfully synthesized the single-crystalline Mo5O14 nanowires, which have uniform structure and controllability about diameter and length by CVD process. Besides, nanowire catalyst with nanoporous structure could possess both advantages of nanoparticles and nanowires. Therefore, we aimed at systematically analyzing Mo5O14 nanowires and then fabricating nanoporous structure in nanowires by e-beam irradiation. Utilizing advanced TEM techniques could reveal the overall atomic structure, which have intrinsic tunnel structure and unique periodicity. In addition, the e-beam irradiation on the intrinsic tunnel structure is observed by in-situ TEM. During the e-beam irradiation process, the oxygen atoms would be removed and result in the structure transformation. Using this technology, the irradiation region could be definable and controllable by electron beam size to define the distribution of nanoporous in nanowires. These results would benefit to realizing the catalytic selective oxidation related with Mo5O14-type structure but also fabricating nanoporous nanowires with rapid and convenient methods. Figure 1
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