A.I. Hulea, A.F. Otte, R.H.M. Smit, J.M. van Ruitenbeek Kamerlingh Onnes Laboratorium, Leiden University, The Netherlands

1
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.

• Advantages
• Free choice of sample material
• Optimum for study of shell effects in different
  metals wide range of temperatures achievable
  70K-500K
• UHV conditions maintain a clean surface

The UHV-MCBJ technique A notched wire is clamped
between two bendable substrates and stretched in
a controlled way by the piezoelement Simultaneousl
y 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
Electronic shell effect
Atomic 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
T300K
We have used a histogram method that is averaging
over many conductance curvesStable nanowire
diameters correspond to peaks in the conductance
histogram
The wire radius is obtained from the conductance
as RG1/2. A periodic shell structure can be
demonstrated as a constant slope ? (G1/2) vs.
peak index
Two sets of periodic oscillations-electronic
?(kFR) 1.12-atomic ?(kFR) 0.44 Crossover at
G15 G0
Periodicity ?(kFR)1.18 related to electronic
shell filing effect
Conclusions
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.