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L_Sim
Grenoble, France
CEA-Grenoble / DSM / INAC / SP2M / L_Sim

Logo Postdoc positions and PhD thesis

Every year several PhD and postdoctoral positions are proposed depending on obtained research project. Open positions are usually announced through the Psi-k network but anyone interested in theoretical or computational nanosciences and in developing numerical and computational methods should send an application to:
Thierry.Deutsch  @  cea.fr

Funding grants application forms should be done jointly with the lab (CEA-INSTN, UJF-Grenoble, RTRA).

Others PhD position are available at SP2M: SP2M booklet (french pdf file - 3,5 Mo) or at INAC: INAC booklet (french).

Currently opened positions:

«Theoretical study of epitaxial growth of graphene»

The objective of this PhD program is to study by means of ab initio calculations the CVD growth mechnisms as a function of the used metallic substrates (Cu, Ni, Ir). To achieve this the PhD candidate will use the ab initio based activation-relaxation technique we have just developed to understand diffusion and relaxation mechanisms associated with defect diffusion, growth processes, and catalysis as well.

« Theory and modelling of the transport properties of nanowires »

The characteristic dimensions of upcoming MOS transistors are entering the sub 20 nm range where quantum corrections due to confinement and tunnelling for example become increasingly important. This calls for the development of next generation modelling tools, that are able to cope with complex systems and to deal with atomic scale features. In this respect, the Non-Equilibrium Green's Functions (NEGF) method appears as one of the most versatile approach to quantum transport. It can account for both elastic (surface roughness, impurities, ...) and inelastic (phonons) scattering in a consistent framework. Combined with k.p and atomistic tight-binding methods for the electronic structure, it can address problems at various scales, from ultimate ~5 nm nanowires to thin-film SOI devices.

The aims of this postdoctoral position are i) to contribute to the development of these tools, and in particular to join the ongoing efforts on the advanced modeling of the electron-phonon interaction in an atomistic framework; ii) to use these tools to explore the physics of transport in nanostructures, such as the interaction between elastic and inelastic scattering, and to simulate the I(V) characteristics of realistic nanowire and FDSOI devices, in close connection with characterizations made at CEA-LETI.

« Theory and modelling of single impurity spectroscopy in nanowires and ultimate MOS devices »

The effect of single dopants on the electrical properties of short-channel devices is a major preoccupation of the microelectronics community. The fluctuations of the number and position of the dopants diffused from the source and drain contacts for example is one of the largest source of variability in ultimate MOS transistors. In addition, the electronic and transport properties of each individual dopant is expected to be dependent on its environment (dielectrics, neighbouring impurities, etc...). The low temperature I(V) characteristics of such transistors actually display well defined Coulomb blockade diamonds below the threshold voltage, which are the fingerprints of the tunnelling through one up to a few dopants in the channel. These outstanding experiments provide, in particular, a direct measure of the energy level structure of the neutral and charged impurities. While the data clearly show that the electronic properties of dopants are very different in such complex environments, a comprehensive analysis is still missing. Meanwhile, further experiments are carried out at CEA/INAC to make innovative devices (such as latch switches) based on single-electron (Coulomb correlated) transport through systems of few impurities.

The aims of this postdoctoral position are i) to model the electronic structure of neutral and charged dopants in realistic device geometries (including contacts, gate oxides and metals), in order to understand the experimental data and the physics of impurities in complex dielectric environments; and ii) to model the transport through few impurity devices in the Coulomb blockade regime, in order to assess the feasibility of such devices, and to help their design and characterization.

«Density Functional Theory for Material Design in the Field of Applications for Energy»

The recent oil crisis and the global necessity to find new green energy sources encourage the INAC institute to dedicate his research efforts in the direction of renewable energies. In the L_Sim lab, several efforts are ongoing to perform studies in this direction.BigFDT is a code with optimal features of reliability and precision, suitable to address different issues connected to material design for photovoltaic applications or energy storage applications.

«Theoretical study of SiC cage-like clusters stabilization»

The study of low-dimensionality compounds made of silicon and carbon presents a number of interests, both from a theoretical and applied viewpoint.The exceptional physical and mechanical properties of silicon carbide make this material one of the most promising for the emerging fields of micro-electronics and of catalysis, among the others.The goal of this study is to calculate the stability of SiC cage-like structures by means of ab initio calculations using the BigFDT package.

Recent history of proposed positions:

«Atomistic modelling of ZnO polar surface»

Ab initio simulation of systems in complex environments, like 2D slabs with a net charge dipole, is a challenging point which can efficiently be addressed only by flexible numerical treatments. BigFDT is a recently developed code, based on wavelets, whose features fit well with this task: the adaptivity of the description ease the treatment of particular environments like surface boundary conditions. ZnO is a frequently studied material in surface science for its wide range of technological applications in nanosciences (eg when doped with Co or Al). It crystallizes in the hexagonal wurtzite structure. One of the crystal termination of a ZnO surface exhibits a charge dipole. The mechanism of electronic stabilization of this polar surface is still theoretically unclear and object of debates. In this project, the trainee will use the BigDFT code for investigating some of the properties of the polar ZnO slab, like structural relaxation and the formation of defects . Besides the important studies of ZnO material preoperties, he will have the possibility to develop experience in ab initio simulations on massive parallel supercomputers, which is a powerful investigation tool widely used.

«Ab initio simulation of the point defects generation from a silicon surface »

L_Sim laboratory has been developing an electronic structure code ,BigFDT, based on wavelets. This powerful formalism has the capabilities to handle versatile boundary conditions as surfaces. Furthermore, this tool is adapted to massively parallel and hybrid architecture based on GPU (graphics processor units). The group of Prof. Stefan Goedecker from the University of Basel is a main contributor of our code and has been developing an original method called minima hopping» which can explore minima of the atomic configuration space in order to find the global minimum. This class of methods is used to simulate protein folding. L_Sim laboratory in collaboration with CEA-Leti is studying from many years the formation and activation energies of point defects in semi-conductors such as Si, Ge and SiGe. Stresses and charged defects in silicon are the actual research topics. The goal of this academic training is to use both ab initio and «minima hopping» methods to study the point defect generation initiated at the silicon surface in particular with oxygen adatoms.

«Atomistic simulation of GeMn magnetic semiconductors»

Spintronic is a very active field in condensed matter research. A new magnetic semiconductor GeMn has been recently grown by means of molecular beam epitaxy in the laboratory [Nature Materials, 5 653 (2006)]. It consists of Mn-rich nanocolumns embedded in an almost purely Ge diamond matrix. The structure and the good magnetic properties of these Mn-rich nanocolumns are still puzzling. Our recent Extended X-Ray Absorption Fine Structure study [Applied Physics Letters, Vol. 92 242510 (2008)] reveals that these nano-columns show a complex local structure that does not correspond to any known stable GeMn compound . Electronic structure calculations give information about the magnetic and structural properties of a possible Ge1-xMnx compound which may form inside the nano-columns. The goal of this thesis is to study the kinetics of the nanocolumns growth as well as their transformation into stable compound upon annealing. This will be done by means of Monte Carlo simulations for the MBE growth and of Molecular Dynamics for the nanocolumns annealing. Both simulations will be based on an energy model that will be derived from ab initio calculations on stable compounds that should also reproduce magnetic ordering whitin theses compounds.

Two postdoctoral positions in ab initio methods based on wavelets

Two postdoctoral positions based at the atomistic Simulation group (L_Sim, CEA-Grenoble) are available to carry out research on ab initio methods based on wavelet.

The first position is sponsorised by the ANR ProHMPT to exploit hybrid architectures (graphics processor units, GPU). The goal is to optimize and does some applications with the BigDFT code on hybrid architectures. A first preliminary version has a speedup of 7 between GPU and a traditional core of the whole code. Target applications will be in the field of growth and kinetics in semi-conductors.

The second position is sponsorised by the ANR SAMSON to use adaptive methods with order N in the BigDFT code. The goal is to re-use previous ab initio calculations when a small displacement is applied to the system. Target applications are to study kinetics of materials or macro-molecules.

«Atomistic modeling of the transport properties of semiconductor nanowires»

Semiconductor nanowires are attracting much attention due to their promising properties and due to their possible applications in opto- and nano-electronics. The diameter of these nanowires ranges from a few to a few ten of nanometers, while their length can reach microns. These nanostructures provide many opportunities: For example, it is possible to vary the composition of the wires along their axis to introduce quantum dots or tunnel barriers whose width and position are well controlled. These nanowire heterostructures can then be connected to electrodes for charge transport measurements. Many such original experiments are being performed today to explore the potential of semiconductor nanowires for nano-electronics. The physics of semiconductor nanowires is complex and not yet fully understood. In this context, theory and modeling can bring valuable insights into the properties of these structures. The L_Sim laboratory is actively developing tools for the atomistic modeling of the electronic, optical and transport properties of semiconductor nanowires for a few years now (see web page below). We are now seeking a candidate for a PhD thesis on the modeling of the transport properties of semiconductor nanowires, using non-equilibrium Green function methods in an atomistic tight-binding framework. Various aspects such as the electron-phonon coupling, the treatment of contacts and open boundaries conditions, or charged defects might be explored during the thesis. These calculations will help achieving a better understanding of the physics of the nanowires and refining the interpretation of the experiments.

«Theory & modelling of charge transport in semiconducting nanowires­based devices»

A postdoctoral position (2 years, starting early 2009) is opened at CEA/INAC (Grenoble, France) to work on the theory and simulation of charge transport in semiconducting nanowires (SC-NWs) based materials and devices (field effect transistors).

«Numerical simulation of magnetisation dynamics in ferromagnet/antiferromagnet multilayers»

This work will take place at CEA-Grenoble within the fundamental research department. An active collaboration is expected between the Nanostructures and Magnetim laboratory (NM), the atomistic simulation laboratory (L_Sim) , the SpinTec laboratory working in applied areas of spin electronics, and the Micro-Nano Magnetism team from the neighbouring Néel Institute (CNRS).

The position is for one year, renewable upon mutual agreement to a second year.

Applications are being considered now. The applicant must have strong skills in magnetic physics as well as a profound knowledge of computer environments and numerical simulation methods. The combination of both would be highly valued, as previous experience with ferro-antiferro biased materials and/or radiofrequencies.

«Multiscale simulation of diffusion in SiGe»

The subject of this postdoctoral study is to understand the diffusion processes in SiGe using an atomistic multilevel approach, combining ab initio and kinetic Monte Carlo calculations. This work will take place in CEA-Grenoble within the simulation laboratory of the fundamental research department. The funding is provide by the French National Research Agency (ANR) through the OSiGe_Sim project. This project brings together three academic laboratories, as well as an applied-research and an industrial modeling groups.

The position is for one year, renewable upon mutual agreement to a second year. The start date is between March 2006 and June 2006.

Applications are being considered now. The applicant must have strong skills in quantum physics, atomistic simulations and solid state physics, licensed by a PhD in the domain. A good knowledge of computer programming and environment is essential.

«Wavelets and order N methods (BigDFT)»

One postdoctoral position based at the atomistic Simulation group (L_Sim, CEA-Grenoble) is available to carry out research in electronic structure calculations. This position is funded by the European project BigDFT.

The subject is to apply wavelet techniques within linear scaling electronic structure calculations. The work involves implementing new methodologies to use wavelet functions in the ABINIT program.

Applicants are expected to have a strong background in electronic structure calculations, as well as a programming experience (Fortran 95). A background in mathematics (wavelet) would be appreciated.

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