| Nano science and technology make the means and ability of understanding and rebuilding the material world extend to the field of atoms and molecules. When one of the dimensions of nano-materials reaches the nanometer magnitude, there are unique physical and chemical characters that can be different from the bulk. One-dimensional functional nano-materials-nanowire and carbon nanotube, have the very important potential applications in the field of nano-mesoscopic devices. They can be used as a scanning tunneling microscope tip, nano devices and integrated circuits to connect large, optical fiber, sensitive materials and so on, Therefore the development of nano-electronic devices based on one-dimensional functional nano-materials will become the focus of the content of this century.In the present work, the relaxed structures and electronic properties for Au nanowires with cross-sections of 3×3,5×5,7×7,9×9 and 11×11 atomic layers as well as the binding and electronic properties of a single copper atomic chain bound in armchair (6,6) or zigzag(10,0) CNTs have been investigated by using the first-principles PAW potential within DFT framework. Following conclusions are obtained:(1)For all five-size nanowires, the relaxed structures still have the tetragonal symmetry and with increasing initial distance of the atoms away from the central axis of the nanowires, the relaxation amount has an increasing tend. Furthermore, the relaxation direction changes from inward for diagonal atoms to outward for median atoms shows there is a "round corner" phenomenon. The vanishing of the neighbor atoms outside nanowire, on the one hand, accompanies with the vanishing of their electrons which are originally shared with the surface atoms, so the total charge of the surface atoms is reduced. On the other hand, the surface atoms will contribute themselves electrons which are originally shared with the vanishing neighbors to remaining neighbor atoms, so an enhanced interaction presents between the surface atoms as well as the surface atoms and their first nearest neighbor atoms. We term this phenomenon "skin effect", which enhance the mechanical and the electronic transport properties of the nanowire compared to bulk. Furthermore, the vanishing of the neighbor atoms outside nanowire accompanies also the vanishing of their restrictions onto the electrons of the surface atoms so most of them range in higher energy region of the occupancy state. In fact, the conclusions drawn here are applicable to not only the nanowires but also the other cases existed surface, such as nanobelts, nanotubes, nanocables, clusters, thin films and so on.(2) The armchair (6,6) and zigzag(10,0) nanotubes are nearly ideal to bind a single Cu atomic chain especially on their center axis. The insertion processes are completely exothermic in these two kinds of nanotubes. We expect that more than one linear Cu atomic chain would be pulled spontaneously into wider nanotubes by forces amounting to a fraction of a nano-Newton. In Cu(1)@(6,6) and Cu(2)@(10,0) combined systems, the charge density is not completely a superposition of that of pristine CNT and isolated Cu atomic chain, reflecting a very weak interaction still exits between two components of each combined system. The accumulated charges between components of the combined system indicate Cu-CNT bonds may be regarded as weak covalent and the depleted charge from the Cu atomic chain has a 3d character. As a result of the nonvanishing interaction, (6,6) and(10,0) CNTs do not act as "perfectly inert" containers for the Cu atomic chain. The electronic band structures and DOS of either the Cu(1)@(6,6) or Cu(2)@(10,0) combined system are not a simple superposition of their components, also indicating a very weak interaction exists between the outer CNT and the inner Cu atomic chain. A reverse effect is observed between the Cu atomic chain and CNT. The restriction of the CNT makes the highest peak of the Cu chain slightly shift towards the lower energy region, that is from-0.554eV of isolated Cu(1)atomic chain to-0.624eV of Cu(1)@(6,6) combined system and from-0.914eV of isolated Cu(2) atomic chain to-1.122eV for Cu(2)@(10,0) combined system. In reverse, the strong metallic character of the Cu atomic chain enhances also the metallic character of the combined system as indicated by both a broader flat plateau of the (6,6) CNT around the Fermi level changing to a narrower flat plateau of the Cu(l)@(6,6) combined system and a semiconducting(10,0) CNT with a small gap changing to a metallic Cu(2)@(10,0) combined system without gap. Compared with the DOS of the Cu(1)chain, the Cu(2) chain with higher Cu-concentration and thus stronger interactions between Cu atoms, presents not only a shift towards lower energy region for all peaks but also a new peak appeared near Fermi level EF in DOS of Cu(2) and consequently Cu(2)@(10,0) combined system. Appearance of this new peak near EF enhances the DOS at the Fermi level D(EF)(in units of states/eV-cell) from 1.89 for the Cu(1) chain to 3.02 for the Cu(2) chain and consequently from 1.97 for the Cu(l)@(6,6) combined system to 3.99 for the Cu(2)@(10,0) combined system. So the Cu(2)@(10,0) combined system is better than the Cu(1)@(6,6) combined system in future utilization of nanoelectronics. |
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