A short presentation of the Theory group at IEMN to download (pdf, 2.1M)
In our group we undertake atomic- and electronic-structure modelling of different kinds of nanostructures (semiconductor nanocrystals and nanowires) and oxides which are epitaxially grown on semiconductors.
We combine ab initio (Density Functional Theory, TD-DFT and GW approaches) and semi-empirical (Tight-Binding) approaches to simulate the properties of the matter at the nanoscale, working in close collaborations with experimentalists.
We are mostly interested in the study of the following properties:
- optical properties (absorption, photoluminescence)
- effects of Coulomb interactions (excitons, self-energy corrections, Coulomb charging and blockade)
- electron-phonon coupling (Raman, optically-assisted transitions, inelastic transport)
- dielectric properties
- transport properties (Landauer, diffusion)
- STM microscopy and spectroscopy
Nanocrystals and nanowires
Semiconductor nanocrystals are intensively studied for their peculiar physical properties and for their potential uses in microelectronics. Nanocrystals, with sizes below 10 nm, are characterized by a strong quantum confinement effect which considerably modifies the properties of the semiconductors. Applications of these objects are foreseen in the fields of opto-electronics (lasers, non-linear optics) and nano-electronics (single electron memories and transistors). Our group has an important activity in this field. Our main interest concerns silicon, III-V and II-VI semicondutor nanocrystals. We have developped original and efficient tools to calculate the electronic structure of semiconductor nanostructures for size between 1 nm and 15 nm. This is done at the microscopic scale which gives an accurate description of the electronic, optical and transport properties of these systems.
We use similar approaches to work on the physical properties of semiconductor nanowires. These systems grown for example by vapor-liquid-solid (VLS) approaches are actively studied because many applications are expected in the field of nanotechnologies. We presently study the electronic structure of the wires, and the effect of doping on the transport properties.
We also work on the simulation of the STM imaging and spectroscopy on surfaces, defects, and nanostructures. The optical properties of C and BN nanotubes, and of graphene sheets are predicted using ab initio approaches, including excitonic effects by solving Bethe-Salpeter equation.
Graphene, a single layer of graphite, is the 2-dimensional building block for 3-dimensional graphite and for 1-D nanotubes. Recently, it has been demonstrated that single layers of graphene can indeed be produced and can be used to build ambipolar transistors with a high charge carrier mobility. Furthermore, the linear dispersion around the K-point of the first Brillouin zone has interesting consequences for magneto-transport experiments such as a half-integer quantum-Hall effect. We are looking into the spectroscopic properties of graphene: calculation of the phonon dispersion (where standard DFT-methods failed to give accurate results) and the Raman-Spectra of single- and multi-layer graphene. Furthermore, we are investigating the effects of charging on the spectra.