By using first-principles calculations,we have systematically investigated the structural stability and electronic properties of a single oxygen atom adsorbed on the surface of foursquare Cu nanowires for a wide range of adsorption sites.In view of binding energy maximization,we found that the long bridge site at the edge of the Cu nanowires is the most stable site for oxygen adsorption,which is always slightly energetically favorable compared with the hollow site at the surface.The electron transferring from Cu atoms to O adatom and a significant polarization indicate the O-Cu chemical bond,showing some degree of ionic character.In addition,the hybridization between O-2p and Cu-3d states implies the O-Cu bond which also shows some degree of covalence character.The main factors which affect the oxygen preferred adsorption site are analyzed from the local geometrical configurations and electronic properties.
We have performed the first-principles calculations onto the structural,electronic and magnetic properties of seven 3d transition-metal(TM=V,Cr,Mn,Fe,Co,Ni and Cu) atom substituting cation Zn in both zigzag(10,0) and armchair(6,6) zinc oxide nanotubes(ZnONTs).The results show that there exists a structural distortion around 3d TM impurities with respect to the pristine ZnONTs.The magnetic moment increases for V-,Cr-doped ZnONTs and reaches maximum for Mn-doped ZnONTs,and then decreases for Fe-,Co-,Ni-and Cu-doped ZnONTs successively,which is consistent with the predicted trend of Hund's rule for maximizing the magnetic moments of the doped TM ions.However,the values of the magnetic moments are smaller than the predicted values of Hund's rule due to strong hybridization between p orbitals of the nearest neighbor O atoms of ZnONTs and d orbitals of the TM atoms.Furthermore,the Mn-,Fe-,Co-,Cu-doped(10,0) and(6,6) ZnONTs with half-metal and thus 100% spin polarization characters seem to be good candidates for spintronic applications.
Variation of stress in attached copper film with an applied strain is measured by X-ray diffraction combined with a four-point bending method.A lower slope of the initial elastic segment of the curve of X-ray measured stress versus applied strain results from incomplete elastic strain transferred from the substrate to the film due to insufficiently strong interface cohesion.So the slope of the initial elastic segment of the X-ray stress (or X-ray strain directly) of the film against the substrate applied strain may be used to measure the film-substrate cohesive strength.The yield strength of the attached copper film is much higher than that of the bulk material and varies linearly with the inverse of the film thickness.
Under the generalized gradient approximation,the electronic structures and magnetic properties of Fe (1-x) Cox alloy nanowires encapsulated inside zigzag (10,0) carbon nanotubes (CNTs) are investigated systematically using first-principle density functional theory calculations.For the fully relaxed Fe (1-x) Cox /CNT structures,all the C atoms relax outwards,and thus the diameters of the CNTs are slightly increased.Formation energy analysis shows that the combining processes of all Fe (1-x) Cox /CNT systems are exothermic,and therefore the Fe (1-x) Cox alloy nanowires can be encapsulated into semiconducting zigzag (10,0) CNTs and form stable hybrid structures.The charges are transferred from the Fe (1-x) Cox nanowires to the more electronegative CNTs,and the Fe-C/Co-C bonds formed have polar covalent bond characteristics.Both the spin polarization and total magnetic moment of the Fe (1-x) Cox /CNT system are smaller than those of the corresponding freestanding Fe (1-x) Cox nanowire,and the magnetic moment of the Fe (1-x) Cox /CNT system decreases monotonously with increasing Co concentration,but the Fe (1-x) Cox /CNT systems still have a large magnetic moment,implying that they can be utilized in high-density magnetic recording devices.
By using the first-principles calculations,we have systematically investigated the adsorption of atomic oxygen on Cu(111) surface for a wide range of coverages Θ(from 0.11 to 1.00 ML) and adsorption sites.We found that the fcc-hollow site is the most stable site for oxygen adsorption.The adsorption energy decreases with increasing oxygen coverage due to the increasing repulsive interaction in the overlayer O adatoms.Except for coverage of 1.00 ML,the oxygen-induced lateral relaxations and bucklings are found in the outermost three Cu layers,and the hillock-like as well as ridge-like bucklings are also found for Θ=0.25 ML and Θ=0.75 ML as well as Θ=0.50 ML,respectively.With an increasing oxygen coverage,the work function increases and the surface dipole moment decreases.Electron transfer from the first layer Cu atoms to O adatoms indicates the O-Cu bond having some degree of ionic character,while the hybridization between O 2p and Cu 3d orbitals implies that it also has some degree of covalence character.Moreover,with the increasing oxygen coverage,more Cu 3d and O 2p states are empty thus weakening the binding of O/Cu(111) system,but increase in the PDOS at the Fermi level.This implies an enhancement in the metallic character of the O/Cu(111) system.
