First-principles Study Of The Physical Properties Of One-dimensional Noble Metal Nanostructures

Metal is regarded as an indispensable material in people's life and production,in which noble metals(such as copper(Cu),silver(Ag),gold(Au))play an irreplaceable role in our life and production.Copper is a widely used commercial metal at present due to its excellent properties such as superior corrosion resistance,high strength and good malleability.Thus,it is widely used as interconnection lines of electronic devices in integrated circuits.Silver has the advantages of good thermal conductivity and malleability,its conductivity is the best one in all the metals.Gold is soft in texture and has good corrosion resistance,its malleability is the best one in the whole metals that we have learned about.In recent decades,with the rapid development of nano-science and technology,one-dimensional noble metal nanostructures and their alloy nanostructures have attracted considerable attention due to their electronic and mechanical properties differ greatly from those of bulk materials.Based on the first-principles calculations within the framework of density functional theory,the stability and electronic properties of one-dimensional noble metal nanostructures and their alloy nanostructures are studied in this paper.The following conclusions are obtained:(1)The stability,structural and electronic properties of multi-shell copper(Cu)nanowires have been systematically investigated.It is found that the equilibrium lattice constants are nearly same for all studied multi-shell Cu nanowires with different diameters.All the nanowires are metallic and the binding energy per atom and the quantum conductance show significant increase as the size of the nanowire increases.The results show that the electronic properties are bulklike for atoms on the inner shell of multi-shell Cu nanowires.However,lower coordinated atoms on the surface shell of the multi-shell nanowires have their electronic properties characterized by narrower 3d state shifted toward the Fermi energy.Finally,the charge density reveals that the interactions between the atoms of surface shell and their first nearest neighbor atoms are enhanced in multi-shell Cu nanowires as compared with those in bulk Cu.(2)We have systematically investigated the effects of adsorbates(CO molecule,O and N atoms)and defects(an attached atom and a monovacancy)on structural and electronic properties of the ultrathin(4,4)silver nanotube(AgNT).For CO adsorption,the top site is considered to be the most stable one from energy point of view.The donation-backdonation procedure between the CO and Ag states contributes to the forming of bonding/antibonding pairs,5?b/5?a and 2?b*/2?a*,respectively.After CO adsorption,the quantum conductance of AgNT decreases by 1G0.Both O and N atoms strongly interact with AgNT after adsorption,attributing to a 3G0 and 2G0 of decrease in quantum conductance,respectively,for the AgNT.High adsorption energy of attached one Ag atom and comparatively low formation energy of a monovacancy reveal that these two types of defects are likely to occur in the fabrication of AgNT.The quantum conductance of the AgNT keeps unchanged for attachment of one Ag atom,while for a monovacancy decreases by 1G0.(3)We have systematically investigated the structural stability and the electronic and optical properties of bimetallic Ag-Au,Cu-Au and Cu-Ag(4,2)alloy nanotubes(NTs).We found that the tip-suspended Ag-Au and Cu-Au alloy NTs were stable structures due to the existence of local minima in both the binding energies and the string tensions variation with their unit cell lengths and that the relative stability was enhanced when the content of Au was increased.However,a tip-suspended Cu-Ag alloy NT would be difficult to form in future experiments.We also found that both the relativistic effect of elemental gold and the string tension applied by the tip contacts play important roles in suppressing effectively the self-purification effect,leading to the formation of these coinage alloy NTs.The quantum conductance of the stable alloy NTs is increased by 1G0 as compared with that of the corresponding pure coinage-metal NTs.