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Nanostrukturen und Grenzflächen Poster: Do., 13:00–15:30 D-P271
Finite-size effects in the electrical resistance of single bismuth nanowires
electrochemically deposited in ion track-etched membranes
Thomas W. Cornelius 1 , M. Eugenia Toimil-Molares 1 , Shafqat Karim 2 , Reinhard
Neumann 1
1 Gesellschaft für Schwerionenforschung (GSI), Planckstr. 1, 64291 Darmstadt, Germany
– 2 Fachbereich Chemie, Marburg University, Hans-Meerwein-Str., 35032 Marburg,
Germany
In recent years, nanowires attracted enormous interest due to their possible future
applications. When the object size becomes comparable to intrinsic length scales -
electron mean free path and Fermi wavelength - classical and quantum size effects are
expected [1]. Both are large in bismuth compared to conventional metals, making it an
ideal material to study on the nanoscale. Polycarbonate foils were irradiated with single
swift heavy ions at the UNILAC linear accelerator of GSI and subsequently etched
in aqeuous sodium hydroxide. By this means, single-pore membranes were created in
which single bismuth nanowires were deposited electrochemically [2]. Thereafter, the
wires contacted electrically while left embedded in the template [3]. The mean size
of the grains building up the wires was varied systematically by employing different
deposition conditions. The specific electrical resistivity is a function of the wire crystallinity.
It increases for wires fabricated at lower temperatures and higher potentials,
i.e., consisting of smaller grains. These findings are in qualitative agreement with theoretical
models about electron scattering at grain boundaries [4]. The wire resistance as
a function of the temperature was recorded, revealing a non-monotonic behaviour. It
rises, exhibits a maximum, and declines when cooling down from room temperature to
20 K. The resistance maximum shifts to higher temperatures for diminishing diameter
and the maximum becomes the higher the smaller the mean grain size is. From the
electrical resistance, the carrier mobility was deduced. While the mobility increases
more than three orders of magnitude in bulk bismuth when cooling down from 300 to
4 K, it saturates for nanowires at low temperatures. Being a function of mean grain size
and wire diameter the mobility is one to two orders of magnitude smaller for nanowires
than for the bulk.
[1] V.B. Sandormirskii, Sov. Phys. JETP 25 (1967) 101
[2] T.W. Cornelius, et al., Nanotechnology 16 (2005) S246
[3] M.E. Toimil-Molares, et al., Nanotechnology 15 (2004) S201
[4] A.F. Mayadas, et al., Phys. Rev. B 1 (1970) 1382