First-principles Study Of The Structure And Electronic Properties Of Copper Nanowires And Nanotubes

One-dimensional(1D)copper nano-materials,such as nanowires and nanotubes,have attracted considerable attention due to their diverse structures and morphologies,as well as intriguing electronic,mechanical,optical and field emission properties.They are very promising building blocks in diverse fields,for example in flexible transparent electrode,solar cell,very large scale integration circuit,field-emission displays and catalysis.It is very important to explore the relationship between the microstructure and physical properties of 1D copper nano-material for application.Therefore,in this paper,the stablitiy and electronic properties of copper nanowires and nanotubes with different structures and morphologies have been investigated in detail by using the first-principles projector-augmented wave(PAW)potential within the density-functional theory(DFT)framework.The main conclusions can be summarized as follows.(1)We systematically investigated the structural and electronic properties of pure and defected Cus-i nanowire and Cu6-1 nanowire as well as Cus-i nanowire and Cu6-1 nanowire encapsulated in the BeO nanotube combined systems.The quantum conductances for optimized pure Cus-i nanowire and Cu6-1 nanowire are 5G0 and 6G0,respectively.In the case of adsorption for both nanowires,CO molecule prefers to bind on the top site,O atom prefers to adsorb on the center site,while Cu atom prefers to adsorb on the B1 site.After CO adsorption,the quantum conductance for Cus-inanowire remains unchanged while the quantum conductance for Cu6-1 nanowire shows a small decrease from 6G0 to 5 Go.O adatom strongly interact with neighboring Cu atom,leading to an obviously decrease of quantum conductance by 3G0 for both nanowires.Adsorption one extra Cu atom does not decrease the quantum conductance,while the Cu monovacancy leads to a drop of the quantum conductance.The hybridization between CO and the Cu states is dominated by the so-called donation/backdonation process,which leads to the formation of bonding/antibonding pairs,5 ? b/5 ? a and 2?b*/2?a*.The robust quantum conductance of the Cus-i and Cu6-1 nanowires,the insulating protection character of the(12,0)and(13,0)BeONTs and the highest stability of the tube-wire combined systems make the Cu5-1@(12,0)and Cu6-1@(13,0)combined systems are top-priority in the ULSI circuits and MEMS devices that demand steady transport of electrons.(2)We have systematically investigated the structural and electronic properties of an infinite linear monatomic Cu chain with an adsorbed CO molecule under stretch.We find that the bridge geometry is energetically favored not only when the Cu-Cu bond below the molecule is unstretched,but also for a wide range of dcu-cu up to about 4.20A,while the substitutional geometry is favored only in the hyperstretched situation dcu-cu>4.80A.The electronic structure properties can be described by the Blyholder's model,in terms of ?-donation of electron density from the nonbonding CO-5 ? orbital into empty metal orbitals and ?-backdonation from the occupied metal d orbitals to empty CO-2?*orbital.We have systematically investigated the structural and electronic properties of hydrogen(hydrogen atoms and H2 molecule)doped Cu chain nanowires and nanocontacts under stretch.These Cu chain nanowires and nanocontacts are stabilized by hydrogen impurities beyond their classical breaking point.The formed metal-impurity bond is much stronger than the metal-metal bond.Upon elongation,the doped Cu chain nanowire tends to break from the remote metal-metal bond and the doped Cu nanocontact will break from metal-metal chain bond.The interaction between hydrogen impurities and Cu atoms alters the interatomic bonding and hybridization of electronic states in Cu chain nanowires and nanocontacts..The total energy calculations reveal that after optimization,the aside horizontal configuration becomes the energetically preferred structure.Additionally,the dissociation of H2 molecule is observed when H2 molecule doped in Cu nanocontact,which can be used in catalytic application.(3)We present a systemic study of the structural and electronic properties of CuNWs with different Cu contents encapsulated inside zigzag(n,0)CNTs denoted as CuN@(n,0)(N=1,2,4 for n=6,7,8 and N=12,16 for n=10)combined systems.We find that CuNWs encapsulated inside the(6,0)CNTs prefers to form a linear chain along the tube axis,while those in(7,0)and(8,0)CNTs tend to form a zigzag chain.The larger diameter of the(10,0)CNT provides the wider space for encapsulating complex tubular CuNWs with three or four atomic strands.The quantum conductance of the Cu16@(10,0)combined system 3G0 is identical to that of the isolated Cui6 nanowire,but the outer CNTs can provide an effective barrier against oxidation and ensure long-term stability of the metal core.The asymmetry distribution of PDOS results in a net magnetic moment 0.59?B for the Cu2@(7,0)combined system.(4)The structural,energetic and electronic properties of(n,m)(3?6,n?m?n/2)single-wall copper nanotubes are investigated systematically.Due to the curvature effect,the diameter of the optimized nanotube D is lager than that of corresponding ideal nanotube rolled up from the triangular Cu(111)lattice sheet D0,while its axial cell length Lz is smaller than that of an ideal rolling up nanotube Lz0.The local maxima of the binding energy Eb for the(4,3)and(5,5)tubes indicate these tubes an enhanced stability compared to their immediate neighboring tubes.The local minima of string tension f indicate the(4,3)and(6,4)tubes are two long-lived "magic" copper nanotubes.A Cu(4,3)nanotube was found to be energetically stable and should be observed experimentally in both the free-standing and tip-suspended conditions,whereas the Cu(5,5)is expected to be observed only in free-standing condition,Cu(6,4)is expected to be observed in tip-suspended case.Analysis of band structure,quantum conductance,density of states and charge density suggests that the quantum conductance of single-wall Cu nanotubes sensitively depends on the atomic structures and chirality of the tubes.Current transporting states display different periods and chirality,the combined effects of which lead to weaker chiral currents on single-wall Cu nanotubes.