15 research outputs found
The role of structural evolution on the quantum conductance behavior of gold nanowires during stretching
Gold nanowires generated by mechanical stretching have been shown to adopt
only three kinds of configurations where their atomic arrangements adjust such
that either the [100], [111] or [110] zone axes lie parallel to the elongation
direction. We have analyzed the relationship between structural rearrangements
and electronic transport behavior during the elongation of Au nanowires for
each of the three possibilities. We have used two independent experiments to
tackle this problem, high resolution transmission high resolution electron
microscopy to observe the atomic structure and a mechanically controlled break
junction to measure the transport properties. We have estimated the conductance
of nanowires using a theoretical method based on the extended H\"uckel theory
that takes into account the atom species and their positions. Aided by these
calculations, we have consistently connected both sets of experimental results
and modeled the evolution process of gold nanowires whose conductance lies
within the first and third conductance quanta. We have also presented evidence
that carbon acts as a contaminant, lowering the conductance of one-atom-thick
wires.Comment: 10 page
Magnetic phenomena in 5d transition metal nanowires
We have carried out fully relativistic full-potential, spin-polarized,
all-electron density-functional calculations for straight, monatomic nanowires
of the 5d transition and noble metals Os, Ir, Pt and Au. We find that, of these
metal nanowires, Os and Pt have mean-field magnetic moments for values of the
bond length at equilibrium. In the case of Au and Ir, the wires need to be
slightly stretched in order to spin polarize. An analysis of the band
structures of the wires indicate that the superparamagnetic state that our
calculations suggest will affect the conductance through the wires -- though
not by a large amount -- at least in the absence of magnetic domain walls. It
should thus lead to a characteristic temperature- and field dependent
conductance, and may also cause a significant spin polarization of the
transmitted current.Comment: 7 pages, 5 figure
Towards unified understanding of conductance of stretched monatomic contacts
When monatomic contacts are stretched, their conductance behaves in
qualitatively different ways depending on their constituent atomic elements.
Under a single assumption of resonance formation, we show that various
conductance behavior can be understood in a unified way in terms of the
response of the resonance to stretching. This analysis clarifies the crucial
roles played by the number of valence electrons, charge neutrality, and orbital
shapes.Comment: 2 figure
Gold nanowires and the effect of impurities
Metal nanowires and in particular gold nanowires have received a great deal of attention in the past few years. Experiments on gold nanowires have prompted theory and simulation to help answer questions posed by these studies. Here we present results of computer simulations for the formation, evolution and breaking of very thin Au nanowires. We also discuss the influence of contaminants, such as atoms and small molecules, and their effect on the structural and mechanical properties of these nanowires
Magnetism-induced ballistic conductance changes in palladium nanocontacts
We present first-principles calculations of the effects of magnetism on the ballistic conductance of a model Pd nanocontact, made of a short Pd monatomic stretched chain placed between two Pd leads, simulated by semi-infinite (100) slabs. The stretching makes the suspended Pd chain generally ferromag- netic. The spin-resolved ballistic conductance, calculated according to the Landauer-Bu ̈ttiker formula is found to be 0.85G0 for the spin-up and 1.15G0 for the spin-down electrons (G0 = 2e2/h is the conductance quantum). The total conductance ∼2G0 is lower, but still relatively close to that of the nonmagnetic Pd nanocontact with the same geometry, calculated to be 2.3G0. To illustrate how magnetism and conductance depend on structural details, we change the three atom chain docking from the top to a hollow surface site, where at the same stress the Pd contact is nonmagnetic and the conductance decreases to 1.8G0. Overall we find these calculated ballistic conductance values of very similar magnitude to the first histogram peak in the experimental data obtained for Pd at low temperature in mechanically controllable break junctions. We conclude that the 15% conductance changes caused by the onset or the demise of local magnetism, similar in magnitude to geometry-related conductance changes, are probably too small to be used as a diagnostic for the presence or absence of nanocontact magnetism