1,807 research outputs found
Is Small Perfect? Size Limit to Defect Formation in Pyramidal Pt Nanocontacts
We report high resolution transmission electron microscopy and ab initio
calculation results for the defect formation in Pt nanocontacts (NCs). Our
results show that there is a size limit to the existence of twins (extended
structural defects). Defects are always present but blocked away from the tip
axes. The twins may act as scattering plane, influencing contact electron
transmission for Pt NC at room temperature and Ag/Au NC at low temperature.Comment: 4 pages, 3 figure
A comprehensive study of electric, thermoelectric and thermal conductivities of Graphene with short range unitary and charged impurities
Motivated by the experimental measurement of electrical and hall
conductivity, thermopower and Nernst effect, we calculate the longitudinal and
transverse electrical and heat transport in graphene in the presence of unitary
scatterers as well as charged impurities. The temperature and carrier density
dependence in this system display a number of anomalous features that arise due
to the relativistic nature of the low energy fermionic degrees of freedom. We
derive the properties in detail including the effect of unitary and charged
impurities self-consistently, and present tables giving the analytic
expressions for all the transport properties in the limit of small and large
temperature compared to the chemical potential and the scattering rates. We
compare our results with the available experimental data. While the qualitative
variations with temperature and density of carriers or chemical potential of
all transport properties can be reproduced, we find that a given set of
parameters of the impurities fits the Hall conductivity, Thermopower and the
Nernst effect quantitatively but cannot fit the conductivity quantitatively. On
the other hand a single set of parameters for scattering from Coulomb
impurities fits conductivity, hall resistance and thermopower but not Nernst
Surface Effects on the Mechanical Elongation of AuCu Nanowires: De-alloying and the Formation of Mixed Suspended Atomic Chains
We report here an atomistic study of the mechanical deformation of AuxCu(1-x)
atomic-size wires (NWs) by means of high resolution transmission electron
microscopy (HRTEM) experiments. Molecular dynamics simulations were also
carried out in order to obtain deeper insights on the dynamical properties of
stretched NWs. The mechanical properties are significantly dependent on the
chemical composition that evolves in time at the junction; some structures
exhibit a remarkable de-alloying behavior. Also, our results represent the
first experimental realization of mixed linear atomic chains (LACs) among
transition and noble metals; in particular, surface energies induce chemical
gradients on NW surfaces that can be exploited to control the relative LAC
compositions (different number of gold and copper atoms). The implications of
these results for nanocatalysis and spin transport of one-atom-thick metal
wires are addressed.Comment: Accepted to Journal of Applied Physics (JAP
Low Temperature (ln2) And Uhv Mechanically Controllable Break Junction Setup To Study Quantum Electrical Transport Of Atomic-size Metal Nanowire
Reliable metal nanowire studies requires experimental stringent conditions, as clean samples and environment. In this sense, we have designed and built a dedicated instrument to study electrical transport properties of atomic-size metal contacts based on the mechanically controlled break junction technique, operating at ultra-high-vacuum conditions. Here we describe the chosen setup, its implementation and performance. © 2008 IOP Publishing Ltd.100PART 5Landauer, R., (1957) IBM J. Res. Dev., 1, p. 223Agrait, N., Yeyati, A.L., Van Ruitenbeek, J.M., (2003) Phys. Rep., 377, p. 81Rodrigues, V., Fuhrer, T., Ugarte, D., (2000) Phys. Rev. Lett., 85, p. 4124Hansen, K., Lægsgaard, E., Stensgaard, I., Besenbacher, F., (1997) Phys. Rev. B, 56, p. 2208De Heer, W.A., Frank, S., Ugarte, D., (1997) Z. Phys. B, 104, p. 469Rodrigues, V., Bettini, J., Rocha, A.R., Rego, L.G.C., Ugarte, D., (2002) Phys. Rev. B, 65, p. 153402Rego, L.G.C., Rocha, A.R., Rodrigues, V., Ugarte, D., (2003) Phys. Rev. B, 67, p. 045412Gonzalez, J.C., Rodrigues, V., Bettini, J., Rego, L.G.C., Rocha, A.R., Coura, P.Z., Dantas, S.O., Ugarte, D., (2004) Phys. Rev. Lett., 93, p. 126103Lagos, M., Rodrigues, V., Ugarte, D., (2007) J. Electron Spectroscopy and Related Phenomena, 20, pp. 156-158Rubio, G., Agraït, N., Vieira, S., (1996) Phys. Rev. Lett., 76, p. 2302Smit, R.H.M., Noat, Y., Untiedt, C., Lang, N.D., Van Hemert, M.C., Van Ruitenbeek, J.M., (2002) Nature, 419, p. 906VaLkering A, M.C., Mares, A.I., Untiedt, C., Gavan, K.B., Oosterkamp, T.H., Van Ruitenbeek, J.M., (2005) Review of Scientific Instruments, 76, p. 103903Zhou, C., Muller, C.J., Deshpande, M.R., Sleight, J.W., Reed, M.A., (1995) Appl. Phys. Lett., 67, p. 1160Hansen, K., Nielsen, S.K., Brandbyge, M., Lægsgaard, E., Stensgaard, I., Besenbacher, F., (2000) Appl. Phys. Lett., 77, p. 708Hakkinen, H., Barnett, R.N., Landman, U., (1999) J. Phys. Chem. B, 103, p. 8814Legoas, S.B., Rodrigues, V., Ugarte, D., Galvao, D.S., (2004) Phys. Rev. Lett., 93, p. 216103Novaes, F.D., Da Silva A, J.R., Fazzio, A., Da Silva, E.Z., (2005) J. Appl. Phys. A, 81, p. 1551Barnett, R.N., Hakkinen, H., Scherbakov, A.G., Landman, U., (2004) Nano Lett., p. 41845Hakkinen, H., Barnett, R.N., Scherbakov, A.G., Landman, U., (2000) J. Phys. Chem. B, 104, p. 9063Rodrigues, V., Bettini, J., Silva, P.C., Ugarte, D., (2003) Phys. Rev. Lett., 91, p. 096801Costa-Kramer, J.L., Garcia, N., Olin, H., (1997) Phys. Rev. B, 55, p. 1291
Personalised Trachea Stent Designer: a Knowledge Feature
Modelling of anatomical parts is usually tackled through triangulated models with specialised Bio-CAD applications. If features beyond anatomy are required, geometry is usually translated into NURBS geometry for further modification in parametric feature based design CAD systems. But, they remain quite unmanageable yet. The authors present, validate and implement into a knowledge feature a methodology that generates an anatomically personalised trachea stent based a point cloud data extracted from a Computerised Axial Tomography with an open-source medical data visualisation application
Current sheets at three-dimensional magnetic nulls:effect of compressibility
The nature of current sheet formation in the vicinity of three-dimensional
(3D) magnetic null points is investigated. The particular focus is upon the
effect of the compressibility of the plasma on the qualitative and quantitative
properties of the current sheet. An initially potential 3D null is subjected to
shearing perturbations, as in a previous paper [Pontin et al., Phys. Plasmas,
in press (2007)]. It is found that as the incompressible limit is approached,
the collapse of the null point is suppressed, and an approximately planar
current sheet aligned to the fan plane is present instead. This is the case
regardless of whether the spine or fan of the null is sheared. Both the peak
current and peak reconnection rate are reduced. The results have a bearing on
previous analytical solutions for steady-state reconnection in incompressible
plasmas, implying that fan current sheet solutions are dynamically accessible,
while spine current sheet solutions are not.Comment: to appear in Physics of Plasmas. This version contains updated
figures and references, additional discussion, and typos are fixed. This is
the second in a series of papers - the first of which (by the same authors)
is located at astro-ph/0701462. A version with higher quality figures can be
found at http://www.maths.dundee.ac.uk/~dpontin
Evidence of spontaneous spin polarized transport in magnetic nanowires
The exploitation of the spin in charge-based systems is opening revolutionary
opportunities for device architecture. Surprisingly, room temperature
electrical transport through magnetic nanowires is still an unresolved issue.
Here, we show that ferromagnetic (Co) suspended atom chains spontaneously
display an electron transport of half a conductance quantum, as expected for a
fully polarized conduction channel. Similar behavior has been observed for Pd
(a quasi-magnetic 4d metal) and Pt (a non-magnetic 5d metal). These results
suggest that the nanowire low dimensionality reinforces or induces magnetic
behavior, lifting off spin degeneracy even at room temperature and zero
external magnetic field.Comment: 4 pages, 3 eps fig
A spectroscopic look at the gravitationally lensed type Ia SN 2016geu at z=0.409
The spectacular success of type Ia supernovae (SNe Ia) in SN-cosmology is
based on the assumption that their photometric and spectroscopic properties are
invariant with redshift. However, this fundamental assumption needs to be
tested with observations of high-z SNe Ia. To date, the majority of SNe Ia
observed at moderate to large redshifts (0.4 < z < 1.0) are faint, and the
resultant analyses are based on observations with modest signal-to-noise ratios
that impart a degree of ambiguity in their determined properties. In rare cases
however, the Universe offers a helping hand: to date a few SNe Ia have been
observed that have had their luminosities magnified by intervening galaxies and
galaxy clusters acting as gravitational lenses. In this paper we present
long-slit spectroscopy of the lensed SNe Ia 2016geu, which occurred at a
redshift of z=0.409, and was magnified by a factor of ~55 by a galaxy located
at z=0.216. We compared our spectra, which were obtained a couple weeks to a
couple months past peak light, with the spectroscopic properties of
well-observed, nearby SNe Ia, finding that SN 2016geu's properties are
commensurate with those of SNe Ia in the local universe. Based primarily on the
velocity and strength of the Si II 6355 absorption feature, we find that SN
2016geu can be classified as a high-velocity, high-velocity gradient and
"core-normal" SN Ia. The strength of various features (measured though their
pseudo-equivalent widths) argue against SN 2016geu being a faint, broad-lined,
cool or shallow-silicon SN Ia. We conclude that the spectroscopic properties of
SN 2016geu imply that it is a normal SN Ia, and when taking previous results by
other authors into consideration, there is very little, if any, evolution in
the observational properties of SNe Ia up to z~0.4. [Abridged]Comment: 12 pages, 5 figures, 4 tables. Submitted to MNRAS. Comments welcome
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