Thermodynamics and Biophysics of small systems

Goals

Our research is based on the fundamental hypothesis that the activity and the exchange of energy  or entropy at small scales control the physics of many systems which could appear very different at first glance. The team focuses on systems from room temperature such as mesoscopic living system or biopolymer self-assembly to nanoscopic system at very low temperatures where quantum effects emerge. This research leans on the development of electrical or thermal sensors of unprecedented sensitivity. They are applied to neuron and DNA auto-assembly, nanophononics, shape memory alloys, and nanocalorimetry for the study of phase transition in 2D systems to name few examples.

Nanophononics - Phonon thermal transport at the nanoscale

The mechanisms responsible for phonon thermal transport at the nanoscale are studied via 3 omega measurements of thermal conductance of nanowire and membrane (0.3K-300K). These measurements illustrate the importance of various characteristic lengths: phonon mean free path, dominant phonon wave length, surface roughness. The general objective rely on heat manipulation at the nanoscale knowing that understanding phonon transport at the nanoscale is one of the most difficult experimental challenges of current mesoscopic physics. The thermal conductance of suspended silicon nanowire and silicon nitride membranes is measured from low temperature to high temperature. Since 2009, we have demonstrated that the thermal transport is dominated by phonon scattering on the surface. We used the presence of ballistic phonon transport at low temperature to reduce thermal conductance by doing nano-engineering of the phonon conductor. This reduction of thermal transport is of high interest for the increasing of the thermoelectric efficiency in nanostructured materials, as described below.

• 
• Serpentine section in a silicon nanowire (left). Thermal conductances (right) show reduced thermal conductance in serpentine nanowires, illustrating blocking of heat transfer.

More details here (pdf)

C. Blanc, A. Rajabpour, S. Volz, T. Fournier, and O. Bourgeois « Phonon Heat Conduction in Corrugated Silicon Nanowires Below the Casimir Limit », Appl. Phys. Lett. 103, 043109 (2013). (pdf)

J-S. Heron, C. Bera, T. Fournier, N. Mingo, and O. Bourgeois « Blocking phonons via nanoscale geometrical design », Phys. Rev. B 82, 155458 (2010). (Virtual Journal of Nanoscale Science and Technology, 22, 20, November 8, 2010). (link)

J.-S. Heron, T. Fournier, N. Mingo and O. Bourgeois « Mesoscopic surface effects on the phonon transport in silicon nanowire », Nano Letters 9, 1861 (2009). (link)

Biophysics - Nano-Neuroelectronics

We develop ultra-sensitive nano-sensors and their instrumentation to follow spikes propagation along the cells and their networks. Because nanoscale field effect transistors are able to overcome size limitation of conventional capacitive sensors (conventional commercial micro-electrodes), we are integrating silicon nanowires and graphene based FET arrays for multisite recording and stimulation of designable neurons networks. Such highly bio-compatible and highly sensitive bioelectronics appear also suitable for enhancing the time-stability of the current Brain Interfaces.

PhD theses :
– Interfacing neurons with nanoelectronics: form silicon nanowires to carbon devices, F. Veliev, thesis dissertation 2016 pdf
– Graphene bioelectronics for long term neuronal interfacing, A. Bourrier, thesis dissertation 2017 pdf

Articles :
– Sensing ion channels in neuronal networks with graphene transistors, F.Veliev et al pdf
– Recording spikes activity in cultured hippocampal neurons using flexible or transparent graphene transistors, F.Veliev et al pdf

Biophysics - Neural Affinity of Pristine Graphene

Graphene monolayers have shown unique feature for neural interfaces by providing direct and highly adhesive contacts to neurons. Being crucial for extracellular detection of neural spikes, the tunable affinity of graphene with neurons appears also useful for achieving long lasting designable neuronal circuits.

Veliev, F., Briançon-Marjollet, A., Bouchiat, V., & Delacour, C. (2016). Impact of crystalline quality on neuronal affinity of pristine graphene. Biomaterials, 86, 33-41. PDF

Biophysics - DNA origami

DNA is the molecule storing the genetic code of all living organisms on earth. Its double helical structure as well as the complementary interactions between nucleobases gives to the molecule a setable double stranded structure that is controlled by the sequence of the single strands. The various genome projects lead the biotech industry to the developement of high efficiency sequencer and synthetizers, hence the cost of the materials have been greatly reduced. As a result DNA is becoming a generic material for programmable self assembly at the nanoscale. Our researchs are motivated by the understanding of the assembly pathways and their optimization in order to design functional nanomaterial with a natural interface with living systems.

DNA origami: the structure spontaneously self-assemble upon annealing of a mix of long genomic DNA taken out of plasmid and about 200 different shorter oligonucleotides

PhD Thesis of Clothilde Coilhac

Functional material - Shape Memory Alloys

Spin-off compagny - Modulo