Calculation of the hole conduction mass reduction
due to a longitudinal compressive stress along the
 direction. In contrast, the transverse mass
almost keeps its unstrained value.
Contact: Mireille Mouis
An analytical model of electron and hole mobility in strained silicon is being developed in order to describe low field transport along any channel orientation with an arbitrary stress configuration (arbitrary stress tensor). The model, which runs in a few seconds on a standard PC, is based on an exact solution of the 6x6 k.p Hamiltonian coupled with a Kubo-Greenwood approach for mobility calculation. It can be used to support the interpretation of experimental results in terms of strain induced mobility variations or to find channel orientations and stress configurations that optimize carrier transport.
Top: A methyl group grafted on the graphene surface. Bottom: Transmission coefficient, averaged over 50 disorder realizations, as a function of the electron energy for a 10 nm wide armchair ribbon with a density n = 0.1 % of methyl-group adsorbates and for different lengths of the functionalized region from 0 to 1 ?m.
The absence of band gap is a major issue for the use of graphene in logic devices, whose on/off current ratio turns out to be very poor. Graphene chemical modification is a perspective tool to open a transport gap and design efficient carbon-based logic transistors. Starting from ab initio calibrated tight-binding models, we simulate transport in nanoribbons in the presence, for example, of methyl group functionalization or boron substitutional doping. Varying the density of adsorbates and the system size and geometry allows us to engineer the transport gap. The simulation of a complete boron-doped graphene-based transistor shows that actually screening can partially reduce the expected high on/off current ratio, thus indicating the necessity for a further optimisation (in terms of doping and electrostatics) and to explore the use of different types of dopants
Contact: Alessandro Cresti
• A. Cresti, Scaling properties of diffusive electronic transport in graphene nanoribbons functionalized with methyl-groups, J. Comput. Electron. 12, 94 (2013)
• P. Marconcini, A. Cresti, F. Triozon, G. Fiori, B. Biel, Y.-M. Niquet, M. Macucci and S. Roche, Atomistic boron-doped Graphene Field-Effect Transistors: A Route toward Unipolar Characteristics, ACS Nano 6, 7942 (2012)
• S. Roche, B. Biel, A. Cresti and F. Triozon, Chemically enriched graphene-based switching devices: A novel principle driven by impurity-induced quasibond states and quantum coherence, Physica E 44, 960 (2012).
• A. Cresti, A. Lopez-Bezanilla, P. Ordejón and S. Roche, Oxygen surface functionalization of graphene nanoribbons for transport gap engineering, ACS Nano 5, 9271 (2011).
Density plot of the current injected into the superconducting lead IS in an interacting double dot system as a function of the detuning ?=2?+U, being ? the dot level and U the Coulomb interaction, and of the chemical potential µ of the normal leads for degenerate dots’ levels ??=0.
We develop a real-time diagrammatic technique to describe non-equilibrium transport through interacting quantum dots connected to normal and superconducting leads. We compute the Josephson current given by the transport of Cooper pairs between the two superconductors and the Andreev current in normal leads. Normal contacts allow us to control the level population and to bring the dot out of equilibrium.
Contact: Marco Pala
• A. Braggio, M.G. Pala, M. Governale, J. König, Superconducting proximity effect in interacting quantum dots revealed by shot noise, Solid-State Communications 151, 155, (2011).
• D. J. Eldridge, M.G. Pala, M. Governale, J. König, Superconducting proximity effect in interacting double-dot systems, Physical Review B 82, 184507 (2010).
• D. Futterer, M. Governale, M.G. Pala, and J. König, Nonlocal Andreev transport through an interacting quantum dot, Physical Review B 79, 054505 (2009).
• M. Governale, M.G. Pala, and J. König, Real-time diagrammatic approach to transport through interacting quantum dots with normal and superconducting leads, Physical Review B 78, 069902 (2008).
• M.G. Pala, M. Governale, and J. König, Non-Equilibrium Josephson and Andreev Current through Interacting Quantum Dots, New Journal of Physics 9, 278 (2007).
The increasing need for autonomous applications demands the development of efficient energy harvesting techniques, mainly based on thermoelectricity, piezoelectricity or photovoltaic effect. In the last decade, material nanostructuration has allowed a significant increase of the thermoelectric ZT factor of merit thanks to the combined effect of thermal conductivity decrease and moderate impact on the electron conductivity. In our group, we focus on semiconductor nanowires, which have been experimentally seen to be very promising in this respect. We describe the interatomic coupling by a valence force model, which is able to account for experimentally relevant sources of disorder such as roughness, and estimate the thermal conductivity by the Green’s function approach. The combination with electronic transport simulation, for the calculation of conductivity, Seebeck coefficient and electronic thermal conductivity, allows us to estimate the ZT factor and to explore new possible roots for its engineering. lead.
Contact: Alessandro Cresti , Marco Pala
See for instance: G. Ardila, A. Kaminski-Cachopo, M. Pala, A. Cresti, L. Montes, R. Hinchet, J. Michallon, M. Daanoune, M. Mouis, Towards self-powered systems: using nanostructures to harvest ambient energy, 2nd Ukrainian-French Seminar, April 8-11 2013, Kiev, Ukraine
Date of update October 15, 2020