[Spm] three postdoctoral positions at LNE (French National Institute of Metrology)

Tue Apr 29 04:59:56 EDT 2008

Postdoctoral position (12 months) at LNE

Metrology for nanomagnetism : development of a nanosized Hall probe microscope

In the framework of a European research project on nanomagnetism, the French National Institute of Metrology LNE (Laboratoire National de Métrologie et d'Essais) proposes an 12 months postdoctoral position in its research team in fundamental metrology
Description
With the development of magnetic recording technology or magneto-electronic devices utilizing GMR, for example, the industry needs high resolution tools for imaging and characterizing nanostructured magnetic layers. Indeed, the high level of miniaturization makes difficult the characterization of these novel systems. However, investigating precisely their structure is necessary to improve their reliability. In this context, the LNE wants to develop a scanning Hall probe microscope (SHPM) operating at room temperature and a metrology dedicated to magnetism at nanometer scale. This project is in two parts : 
·	The first work package consists in making the probe. This probe is a Hall cross made from GaAs/AlGaAs or InGaAs/AlInAs two-dimensional electron gas (2DEG) heterostructures. As a first step, the specific dimensions will have to be within 500 nm x 500 nm. Therefore, the e-beam lithography and chemical etching will be used and this stage will be carried out at LPN (Laboratoire Photonique et nanostructures, CNRS, Marcoussis). This laboratory of nanofabrication has an internationally recognized experience in this field. Afterwards, the postdoctoral fellow will have to characterize the metrological properties of the device within quantum metrology team of the LNE which is equipped with the instrumentation necessary for calibration purposes (measuring bridge, standard magnet...). A preliminary objective would be to achieve a roughly 500 nm magnetic spatial resolution and a few << Objet OLE: Microsoft Éditeur d'équations 3.0>>noise level with a high carrier mobility at room temperature. Several heterostructure compositions will be tested and the sensor design will have to be optimised.
Hall probes have the metrological advantage of being direct magnetic field sensors, because the measured Hall voltage is directly proportional to the perpendicular magnetic field averaged over the Hall cross area. Furthermore the SHPM is a non-invasive technique owing to a low self-field. It can provide quantitative information about local fields and the measured quantity can be directly linked to SI units. Note that at LNE as in most of national metrology institutes, the Quantum Hall Effect (QHE) is already used and allows to realise a highly reproducible resistance standard.
·	In a second part, our prototype sensor will be integrated either at the end of a cantilever or on a tuning fork and then mounted on a SPM (scanning probe microscope). This work will be performed in collaboration with the nano-dimensional metrology team. This question has to be discussed. Then, this sensor will be driven in order to map the stray magnetic field issued from a reference magnetic thin layer or from nanoparticles distributed on this layer.
As a conclusion, the postdoctoral fellow will work in collaboration with both the dimensional nanometrology team and the quantum metrology team. The fabrication part will take place in another laboratory (LPN) located near Trappes. We are looking for a PhD or a Research Engineer with two or three years of experience in experimental physics and nano-fabrication in clean room. A good understanding of magnetism is required. A first experience on AFM measurement and elementary knowledge in metrology will be appreciated.

The position is available immediately.

Contacts :
Dominique GIRBAL, dominique.girbal at lne.fr <mailto:dominique.girbal at lne.fr>, tel +33 1 30 69 12 47
François PIQUEMAL, francois.piquemal at lne.fr <mailto:francois.piquemal at lne.fr>, tel +33 1 30 69 21 73

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Postdoctoral position (12 months) at LNE.

Development of an AC quantum voltage standard

In the framework of the european project JoSy (Next generation of quantum voltage systems for wide range applications), the French National Institute of Metrology LNE (Laboratoire National de Métrologie et d'Essais) proposes a 12 months postdoctoral position in its research team in quantum electrical metrology.

Description

The quantum electrical metrology revolves around three quantum phenomena: the Josephson Effect, the Quantum Hall Effect, and the Single-electron-tunnel, that link the electrical units to fundamental constants.<http://www.lne.fr/fr/r_et_d/metrologie_electrique/metrologie-electrique-quantique-recherche.asp>.

In recent years the LNE has been engaged in the study and implementation of programmable Josephson junctions arrays (PJJA), the principle of which is based on a series arrangement of overdamped Josephson junctions divided in binary sequences. These arrays can be used as multibit digital-to-analog converter and can generate high accuracy staircase-approximated ac waveforms that are ideally suited for applications at relatively low frequency.

The objective of the proposed position is to work on the design and the development of a quantum voltage synthesizer based on PJJA for frequencies up to 1 kHz with uncertainties of 10-7 in order to increase the precision of primary standards for the ac electrical metrology.
To achieve this ambitious objective, at LNE, we are developing a 4-terminal digital Josephson synthesizer (2 terminals for the ac Josephson voltage output and 2 for supplying the current demanded by the load). We have already performed direct RMS measurements against thermal converters, that have given promising results (10-6 at few hundred hertz), but these measurements also revealed significant uncertainty contributions due to the transitions between the quantized Josephson voltage levels. One important task of the hired postdoc will be to contribute understanding the limiting factors, modelling precisely the system, improving the system software. Another important task of the hired post-doc will be to contribute to the instrumental developments required to reach these goals. The work will include aspects from analogue and digital electronics for high frequencies, superconductivity and measurement techniques for ac signals.
The postdoc will benefit of the long experience of the group and its specific equipments and facilities for the implementation of the Josephson Effect for metrology : labs with controlled environment (temperature regulated within 0.1°C, humidity within 5%, electromagnetic shielding, anti-vibrating installations...), low noise instrumentation, top of the range instruments, low temperatures (4 K).
Strong collaborations with other national laboratories will be developed during the European project, and short stays abroad are possible.

The applicant will have a PhD (or to be graduated) in condensed matter physics with a great experience in the measurement, instrumentation, and electronics or in instrumentation/metrology. Experience in one or more of the following fields: superconductivity, low temperature Physics, High frequency electronics, precision measurements will be appreciated.

Duration: 12 months
Start date: Available now

Contacts :
Dominique GIRBAL, dominique.girbal at lne.fr <mailto:dominique.girbal at lne.fr>, tel +33 1 30 69 12 47
François PIQUEMAL, francois.piquemal at lne.fr <mailto:francois.piquemal at lne.fr>, tel +33 1 30 69 21 73

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Postdoctoral position

Quantum Hall Effect for Metrology

Quantum Metrology Group - Laboratoire National de Métrologie et d'Essais (LNE) Trappes - France

Framework/Funding: European Commission/IMERA+Project: ULQHE "Enabling ultimate metrological quantum Hall effect devices"
Duration: 13 months
Location: LNE Trappes (78) - France
Start date: September 2008 (or to be discussed)

The position proposed is in the context of the realization of Quantum Hall Effect (QHE) universality
tests. These quantization tests of the Hall resistance in the integer QHE regime consist in high-accuracy
comparison (<10-10 in relative value) of quantized Hall resistances implemented in 2 dimensional electrons
systems of different natures (Si-Mosfet, III-V and II-VI semiconductor heterostructures, and mainly
graphene). The objective is to demonstrate the QHE universality with an uncertainty more than one order
of magnitude smaller than the uncertainty of the previous tests, that is to say smaller than some parts in
1011.

To achieve this ambitious objective, at LNE, we have developed an original technique, the socalled
quantum Wheatstone bridge which has already given promising results (rel. uncertainty of 3x10-11 in
the comparison of 4 GaAs/AlGaAs Hall bars). One important task of the hired postdoc will be also to
contribute to the instrumental developments required to reach theses goals (fitting of a 3He fridge and a
18-20T superconducting magnet, fabrication of a cryogenic current comparator (CCC) equipped with a DC
SQUID).

The results obtained concerning the QHE universality will be of crucial importance in the
redefinition of the Système International of units (SI) based on fundamental physical constants. Those
concerning graphene will have, moreover, a great impact on the whole Physics community.
The postdoc will benefit of the long experience of the group and its specific equipments and
facilities for the implementation of the QHE for metrology (realization of primary electrical resistance
standards and more fundamental issues requiring high resolution measurement of the effect...): labs with
controlled environment (temperature regulated within 0.1°C, humidity within 5%, electromagnetic
shielding, anti-vibrating installations...), ultra low noise instrumentation for high resolution electronic
transport measurement, high magnetic fields (soon up to 20T), low temperatures (T<300mK)...
The applicant will be PhD (or to be graduated) either in condensed matter physics (mesophysics
and nanophysics for instance) with a great experience in the measurement and instrumentation or in
instrumentation/metrology but with tastes for more fundamental issues.

Contacts:
Félicien Schopfer +33 1 30 69 21 69
Wilfrid Poirier +33 1 30 69 21 74

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Sébastien Ducourtieux

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Laboratoire national de métrologie et d'essais 

CSMI 338 - Unité Nanometrologie Dimensionnelle
Z.A. de Trappes-Elancourt
29, avenue Roger Hennequin
78197 Trappes Cedex
http://www.lne.fr

tel : 33 1 30 69 21 84
fax : 33 1 30 16 28 41
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Sébastien Ducourtieux

***********************************************************************
Laboratoire national de métrologie et d'essais 

CSMI 338 - Unité Nanometrologie Dimensionnelle
Z.A. de Trappes-Elancourt
29, avenue Roger Hennequin
78197 Trappes Cedex
http://www.lne.fr

tel : 33 1 30 69 21 84
fax : 33 1 30 16 28 41
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