First-principle Study Of The Structural Stability And Electronic Properties Of Alloy Atomic Chains

In recent years,with the gradually shrinking in size of electronic and mechanical devices,one-dimensional metal nanowires have attracted extensive interest due to their novel mechanical,electrical and optical properties as well as potential application in nanotechnology and nanoscience.Among them the nobel-metal(such as Au,Ag and Cu)nanowires and their alloyed nanowires attract extensively experimental and theoretical attention.The suspended atomic chains being an ultimate one dimensional nanowire have been produced in experiment.Using first-principles calculations,we have investigated the structure stability,band structures,density of states and electronic properties and magnetic properties of one-dimensional Au-Ag,Au-Cu and Ag-Cu alloy monoatomic chains as well as alloy Cu-Fe monoatomic chains.The research contents and conclusions can be summarized as follows:(1)The structural stability and electronic properties of Au-Ag,Au-Cu and Ag-Cu alloy monoatomic chains have been systematically investigated via first-principles calculations.We used the string tension criterion,rather than the energy criterion,to identify the stability of tip-suspended and finite alloy chains.We found that the tip-suspended Ag-Au and Cu-Au alloy monoatomic chains were stable zigzag structures due to the existence of local minima in the string tensions variation with their lattice constant.However,a tip-suspended Ag-Cu alloy monoatomic chain would be difficult to form in future experiments due to the nonexistent of local minima in the string tensions.The electronic structure revealed that the atomic chains with different structures exhibit metallic behavior.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 the Au-Ag and Au-Cu alloy monoatomic chains.(2)The structure stability and magnetic properties of uniformly and nonuniformly alloyed Cu-Fe monoatomic chains under a tension strain along the wire-axis direction have been investigated.The uniformly alloyed Cu-Fe monoatomic chain composed of regularly alternating Cu and Fe atoms is stable under stretching up to large interactomic distances.While the nonuniformly alloyed Cu-Fe*monoatomic chain is less stable due to the easily formation of Fe2 dimer.For the uniformly Cu-Fe monoatomic chain subjected to stretching tension,there exists a transition of the chain from the zigzag configuration to the linear configuration,which is accompanied by a transition from ferromagnetic to antiferromagnetic state.The electronic structure revealed that strong hybridization between the Cu and Fe states as well as the electron transfer from Fe atom to Cu atom are responsible for the high stability of alloyed Cu-Fe monoatomic chain.