ARTICLE IN PRESS
Physica B 403 (2008) 1542–1543
Superconducting proximity effect in single-crystal Sn nanowires
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Haidong Liua, Zuxin Yea, Hong Zhanga, Wenhao Wua, , Zhiping Luob,
K.D.D. Rathnayakaa, D.G. Nauglea
aDepartment of Physics, Texas A&M University, College Station, TX 77843, USA
bMicroscopy and Imaging Center, Texas A&M University, College Station, TX 77843, USA
Abstract
An in situ template-based electrochemical method was used to fabricate single-crystal Sn nanowires, of 6 mm in length and 30–200 nm
in diameter, in contact with two bulk film electrodes of Au, Sn, or Pb. Superconductivity in these Sn nanowires was found to depend
strongly on the electrode materials.
r 2007 Elsevier B.V. All rights reserved.
Keywords: Superconductivity; Proximity effect; Nanowires
While earlier studies of the proximity effect were focused
on layered superconducting/normal systems, recent experi-
ments have found interesting proximity effects in nanosized
structures. Of particular interest is the induced super-
conductivity in carbon nanotubes [1] and semiconductor
nanowires [2] when they are in good contact with super-
conducting electrodes. In addition, the suppression of
superconductivity on the nanoscale is of current interest
[3]. Here, we report a long-range proximity effect on a
length scale of at least 6 mm in single-crystal Sn nanowires
whose ends were in contact with bulk film electrodes that
were either superconducting (Sn or Pb) or normal (Au). We
did not observe superconductivity in the Sn nanowires
down to 1.8 K when they were in contact with Au
electrodes. When they were in contact with Pb electrodes,
they were superconducting below the transition tempera-
ture Tc of bulk Pb, ꢀ7.2 K.
Films of Au, Sn, or Pb, 100–300 nm in thickness, were pre-
evaporated on both surfaces of the membranes to form the
cathodes and the front electrodes as described [4,5]. During
electroplating, Sn nanowires grew from the cathode. When
the first nanowire filled a pore and made a contact with the
front electrode, electroplating was terminated, producing a
single Sn nanowire whose two ends were in good contact
with the cathode and the front electrode [4,5]. For
structural analysis, Sn nanowires were extracted in a
centrifuge after the membranes were dissolved in dichlor-
omethane. Fig. 1 shows an image of two Sn nanowires and
selected-area electron diffraction patterns taken by a JOEL
2010 transmission electron microscope. The diffraction
patterns were identical along the length of a nanowire,
indicating that the nanowires were single crystalline. They
had a tetragonal lattice structure and a growth direction
along [0 0 1]. The ring structure in the diffraction patterns
was consistent with a thin oxide layer on the Sn nanowires
rather than the presence of an amorphous phase. Energy
dispersion spectroscopy (not shown here) demonstrated
that the nanowires were indeed Sn, without any observable
trace of mixing of the electrode materials.
Sn nanowires were electroplated into porous polycarbo-
nate membranes of 6 mm in thickness and pore diameters
30–200 nm, purchased from Whatman Co. and SPI
Supplies Inc. The electrolyte was prepared by mixing
16.72 g of a Sn(BF4)2 solution at 50 wt% with 200 ml of
water. A Pt anode was used and the reducing potential
was 0.4–0.5 V relative to an Ag/AgCl reference electrode.
Fig. 2 shows the resistance R versus the temperature T
for Sn nanowires of various diameters in contact with Au
(Fig. 2(a)), Sn (Fig. 2(b)), and Pb (Fig. 2(c)) bulk film
electrodes. We have found that Sn nanowires in contact
with two Au electrodes do not show any signature of
Ã
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0921-4526/$ - see front matter r 2007 Elsevier B.V. All rights reserved.