Activity Report 2010 - CNRS

SCIENTIFIC REPORT
FURTHER READING
Nature 464, 1174-1177 (2010)
Substrate-enhanced supercooling in
AuSi eutectic droplets
Astronomy and Astrophysics, 521, id.
A29 (2010)
NIKA: A millimeter-wave kinetic
inductance camera
In situ X-ray investigation
of growing semiconductor
nanowires
“New comers” Project 2007: Tobias
SCHÜLLI (ESRF & French CRG)
Post-doctoral Fellow: Valentina CANTELLI
Supercooled liquids are trapped in a
metastable state even well below their
freezing point, which can only be
achieved in liquids that do not contain
seeds that may trigger crystallization. It
was during their studies, focused on the
growth of semiconducting nanowires,
that T. Schülli et al. discovered the
unusual properties of a gold-silicon alloy,
in contact with silicon (111) surface.
(Fig.2)
As they were observing the first stage of
growth of nanowires, they saw that the
metal-semiconductor alloy they used
remained liquid at a much lower
temperature than its crystallization point.
The team studied what happened to the
liquid in contact with a five-fold
coordinated surface and then performed
the control experiment with the same
liquid exposed to three-fold and four-fold
coordinated surfaces, which reduced the
supercooling effect dramatically. This
constituted the first experimental proof
that pentagonal order is at the origin of
supercooling.
the solid–liquid interaction for the
structure of the adjacent liquid layers.
Such processes are crucial for present
and future technologies, as fluidity and
crystallization play a key part in soldering
and casting, as well as in processing and
controlling chemical reactions for
microfluidic devices or during the
vapour–liquid–solid growth of
semiconductor nanowires.
New generation of nanodetectors
for astrophysics
“New comers” Project 2007: Alessandro
MONFARDINI (Institut Néel)
Post-doctoral Fellow: Loren SWENSON
The Néel IRAM KIDs Arrays (NIKA)
project was kicked off in November 2008
to develop a large mm-wave resident
instrument at the 30-m IRAM
radiotelescope on the Pico Veleta, near
Granada (Spain). The main competitor to
achieve this goal at IRAM is the GISMO
collaboration led by the NASA Goddard
Space Flight Center, focusing on
superconducting TES (Transition Edge
Sensors).
An excellent post-doc (Loren SWENSON)
was hired in July 2008 coming from Dr.
Cleland’s famous group at the University
of California Santa Barbara. A new
dilution cryostat was developed, adapted
for KIDs testing, when also started the
designing/fabricating/testing of the first
NbN resonators in collaboration with
INAC (J.C. Villegier) and Olivier Buisson
at the Institut Néel.
In 2009, beginned the investigation of a
particular KID concept known as LEKID
(Lumped Element KID), allowing a purely
planar design and a good optical
coupling. Totally unexplored at that time,
the potential of this new configuration for
future large instruments operating in the
mm-wave range was well appreciated.
24
Fig. 2: Droplet of a gold-silicon liquid alloy on
a silicon (111) surface. Pentagonal clusters
formed at the interface exhibit a denser
structure compared to solid gold and prevent
the liquid from crystallization at temperatures
as low as 300 Kelvin below the solidification
temperature. Graphics: M. Collignon
It was therefore revealed that pentagonal
atomic arrangements of Au atoms at this
interface favour a lateral-ordering
stabilization process of the liquid phase.
This interface-enhanced stabilization of
the liquid state shows the importance of
Thanks to the rapid development of the
project, a request for one week technical
time at the 30-m telescope was made in
September 2009. (To better understand
the amplitude of the project, the
approximate cost of one single hour time
at Pico Veleta is estimated 1 k€.)
The first run took place in October 2009,
with very encouraging results. One could
observe, for example, a number of faint
galactic and extra-galactic sources.
This LEKID array, used at the telescope,
had been fabricated at the PTA-Grenoble
platform.
After the first light, and despite the small
number of pixels (30-40) NIKA was
already exhibiting better performances