(k F R)=1.56. (k F R)=1.2. (k F R)=1.11. Shell Effects in Gold Nanowires at Room Temperature. A.I. Hulea, A.F. Otte, R.H.M. Smit, J.M. van Ruitenbeek Kamerlingh Onnes Laboratorium, Leiden University, The Netherlands.
Shell Effects in Gold Nanowires at Room Temperature
A.I. Hulea, A.F. Otte, R.H.M. Smit, J.M. van RuitenbeekKamerlingh Onnes Laboratorium, Leiden University, The Netherlands
Recently Yanson et al.,Nature 400, 144 (1999) discovered that the formation of alkali nanowires presents periodic spectrum of exceptionally stable diameters. This has been identified as a shell effect that is governing also the stability of atoms, nuclei and metallic clusters. Similar to clusters, metallic nanowires present two magical series of stable diameters given by electronic and atomic shell effects. We extended the studies of shell filling effects to gold nanowires obtained by a new mechanically controllable break junction technique (MCBJ) in ultra high vacuum (UHV) at room temperature.
The UHV-MCBJ technique:
A notched wire is clamped between two bendable substrates and stretched in a controlled way by the piezoelement
Simultaneously the conductance of the constriction is monitored.
Stable diameters occurs for complete atomic layers –periodicity (kFR)~0.48
This shell structure occurs at large radius of the nanowires
Atomic shell effect
Electronic shell effect
The periodicity of the stable diameters of the nanowire is related to the periodic orbits of a particle inside a cylinder
Observation of shell effects in gold nanowires at T=300K
We have used a histogram method that is averaging over many conductance curvesStable nanowire diameters correspond to peaks in the conductance histogram
Two sets of periodic oscillations:-electronic (kFR) =1.12-atomic: (kFR) =0.44 Crossover at G~15 G0
Periodicity (kFR)=1.18 related to electronic shell filing effect
We have obtained evidence for two sets of magic numbers in gold nanowires: electronic and atomic. The former is related to closing of electronic shells while the latter is due to the surface energy, dominating at large diameters.
The electronic shell effect does not appear to be affected by non-spherical features of the gold Fermi surface.
The periodicities of the peaks in the gold conductance histogram are similar to the ones obtained for alkaline nanowires (kFR)= 1.18 for electronic and (kFR)=0.44 for atomic shell effect), although often somewhat smaller. We propose that the smaller slopes can be attributed to defect scattering.