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CNRS 
Study of the physical mechanisms leading to compositional biases in Atom Probe Tomography of semiconductors
Université de Rouen, St Etienne du Rouvray
Gruope de Physique des Matériaux
Condensed Matter Physics Materials Science Physical Chemistry 
Full Description:

Laser-assisted Atom Probe Tomography (La-APT) is a technique developed at the Groupe de Physique des Matériaux in Rouen, France. It is based on field emission of ions from a sample tip, allowing for the reconstruction in 3D of the chemical composition of nanoscale objects (1) (2) (3). This technique is nowadays more and more applied in the domain of materials sciences and nanosciences.

During the last few yers, several exploratory studies demonstrated that the chemical composition of binary (GaN , MgO ZnO ) or ternary  (InGaN , ZnO :Tb ) semiconductors and dielectrics measured by La-APT may depend on the experimental parameters of the measurement (sample surface field, laser intensity, sample temperature) (4). This is a major problem if such measurements as that of the x alloy fraction in ternary compounds (AxB1-xC) or that of the doping density in a binary semiconductor are considered.

The experimental results obtained up to now showed that the surface electric field is the main parameter determining the deviation of the measured composition from the real stoichiometry in a set of wide bandgap semiconductors (GaN, AlN, ZnO, MgO) . However, it has still not been established what are the physical mechanisms leading to a measurement rich in group III (II) elements at low field and rich in N (O) at high field.

The main objective of this thesis is a systematic study of semiconductors of high technological interest in order to (i) obtain a coherent description of the compositional biases in APT (ii) identify the physical mechanisms leading to these biases (iii) assess the experimental conditions for which the compositional analysis is reliable. In particular, it should be answered to the following questions:

-         Can surface diffusion in an electric field explain – at least in part – the observed deviation from the real composition?

-         Is there a field emission of neutral molecules, which could not be detected by the
system? (O2, N2, for instance – this hypothesis has been formulated, but never demonstrated)

-         What is the impact of the dissociation during the flight of emitted molecular species?
 

This Ph.D. work should not only yield a deeper insight into the fundamental mechanisms of field ion emission in compound semiconductors, but also an important feedback for the community
working with APT on materials for micro- and nano-electronics.

The candidate will take advantage of the cutting-edge experimental facilities at GPM (atom probes, field ion microscopy, focused ion beam), of the expertise of the supervisors and of their teams in
atom probe and materials science, and of a starting collaboration with a theoretical team at CIMAP (Caen, France) specialized in molecular dynamics calculations. He/She should have excellent bases and excellent records in solide state physics and/or physical chemistry.

Start: September 2015. Contacts (before March 2015):
didier.blavette@univ-rouen.fr , lorenzo.rigutti@univ-rouen.fr

 

REFERENCES

(1) Groupe de Physique des Matériaux. Principes de fonctionnement de
la Sonde Atomique. http://gpm.labos.univ-rouen.fr/spip.php?article170. (in French)
(2) Blavette, D.; Bostel, A.; Sarrau, J. M.; Deconihout, B.; Menand,
A. An atom probe for three-dimensional tomography. Nature 1993, 363, 432-435.
(3) Cameca, Inc. Principles of Atom Probe Tomography. http://www.cameca.com/instruments-for-research/atom-probe.aspx.
(4) Mancini, L.; Amirifar, N.; Shinde, D.; Blum, I.; Gilbert, M.; Vella, A.;.; Rigutti, L. Composition of
Wide Bandgap Semiconductor Materials and Nanostructures Measured by Atom Probe Tomography and Its Dependence on the Surface Electric Field. Journal of Physical Chemistry C 2014, 118
(41), 24136-24151 (And References Therein).

 

 



Posted on: 16 February 2015Deadline to apply: 20 March 2015Start Date: 01 September 2015 Duration: 36 months
The Fund category is Not Defined and the salary is Not Specified
in the Haute-Normandie Region.

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