Sous la tutelle de :

Study of long-range interactions between proteins

Living cells harbor a complex network of biochemical reactions in which molecular actors seem to know where and when to go to their targets. These reactions could be accelerated by electrodynamic forces between biomolecular partners. We confirmed experimentally an essential prerequisite for this hypothesis: the activation of a collective vibration of a macromolecule under the influence of an external energy supply . Our experimental results are in agreement with the theory, which allows to identify a characteristic absorption (0.3 THz) corresponding to the collective oscillation of the molecule. Demonstrating the universal character of the existence of electrodynamic forces between biomolecular partners will make it possible to meet the remaining challenges in biology, medicine and pharmacy such as the understanding of the development processes of certain parasitic diseases and the development of associated therapies.

 Experimental setup of THz absorption near-field spectroscopy
(a) A drop of the biological sample placed under the near-fieldprobe, which is directly immersed in the solution.
(b) Picture of the near-field probe and its microwire.
(c) A drop of the biologicalsample placed above the near-field rectenna.
(d) Electron-beam microscopy picture of the bow-tie antenna with its integrated FET.

 

Differential transmission spectra of the microwire-based absorption
obtained with different excitation power ratings of the laser.
The labeled BSA concentration is kept fixed at 1 mg/mL.
The first three spectra are exactly superposed.

For more details, see our latest article about this topic: I. Nardecchia et al., Out-of-Equilibrium Collective Oscillation as Phonon Condensation in a Model Protein, in Physical Review X, 8, 031061, 2018.

 

Terahertz Detection and Imaging Using Graphene Ballistic Rectifiers

To detect THz waves, the performance of the components generally depends on the mobility of the electrons in the material. Thanks to the electronic structure that gives it the hexagonal arrangement of its carbon atoms, graphene offers precisely a very high mobility, provided to have a mono-atomic layer of very high crystallographic quality. We developed a new generation THz-wave-detector in the form of a bow-tie antenna a few millimeters long, installed on a graphene rectifier,of about thirty square microns. The antenna converts the electromagnetic THz-wave into alternating current, which the rectifier transforms into direct current. This component uses the quantization of the conduction channels, as formalized by Büttiker and Landauer, so as to produce a voltage between the source and drain contacts, thus creating an usable signal. Unlike components manufactured with conventional materials, this new detector works both at room temperature and without polarization, thus without loss of electrical energy. The detector achieves exceptional performance in terms of sensitivity and noise level, over a decade (from 0.07 to 0.7 THz). This work can be used to develop new spectrometry, potentially capable of detecting drugs and explosives remotely. They are also likely to interest wireless telecommunications, currently used in applications such as Wi-Fi and 5G.

 

Graphene Ballistic Rectifier GBR geometry and antenna structure:
(a) A schematic showing the central active region of the ballistic rectifier where the arrows indicate typical carrier trajectories; the inset shows the whole rectenna and the two input contacts connected to the antenna lobes have been labeled source (S) and drain (D) along with the gate (G), lower (L), and upper (U) contacts;
(b) An atomic-force micrograph showing the active region of the device with the GBR at its center where the same contacts have been labeled and a dotted line has been drawn around the edge of the localized gate as a guide for the eye;
(c) A 10× optical image of the device where the same contacts have been labeled.

For more details, see our latest article about this topic: G. Auton et al., Terahertz Detection and Imaging Using Graphene Ballistic Rectifiers, in NanoLetters, 17, 11, 7015-7020, 2017.

And for further information visit the following webpage : Terahertz Occitanie Platform

 

Modelling & THz Solid State Detectors

Our research team is also committed to modeling, trying to understand for instance plasma resonances in field effect transistors. Indeed, nanometric Field-Effect Transistors (FETs) present several potential applications at the THz frequencies specifically, in three domains: detectors, sources and amplifiers. Particularly, High-Electron Mobility Transistors (HEMTs) devices exhibit THz resonances in the small-signal admittance spectrum for short gate-length transistors.

In previous works, we obtained the elements of the admittance matrix and used them to calculate the voltage amplification of a FET loaded by a resistive component. We showed that the load had a significant influence on the THz dynamics behavior of the channel and consequently on the resonance frequencies. To model more efficiently an external circuit as, for instance a nano-antenna, these investigations are pursued by studying the influence of an arbitrary load.

Thus, we study here the small-signal response of a FET connected to a purely reactive load. In particular, this model, using the equivalent admittances approach, is applied to a transistor connected to an inductance L, a capacitance C and LC resonant and anti-resonant circuits. The influence of such frequency-dependent load on the dynamics of the transistor, dominated in the THz range by collective plasma behavior, is investigated. This leads to the possibilities of shifting, amplifying or softening resonances appearing in the voltage gain spectrum. The effect of a resistive part of the load is also estimated.

For the THz detection or antenna applications, we consider a FET whose source and drain terminals are connected to an external load of imaginary admittance Yc as presented below :

Equivalent circuit of the field-effect transistor and an imaginary admittance YC.

 

Some of the different gain spectra obtained are given here :

 

 

 

 

 

 

Voltage gain |G| as a function of the frequency, for different capacitance values C.

Voltage gain |G| calculated for the LC resonator tuned to :
asymmetric modes (a) and
symmetric modes (b)

Thus, the influence of the load on the frequency response and more particularly on the resonance frequencies associated with plasma modes clearly appears here. A high impedance load on the drain stimulates asymmetric plasma modes, while a low impedance stimulates symmetric modes - and obviously an overall reducing of the drain voltage. Connected to a load depending on the frequency, the FET can therefore presents some uncommon behaviors.

For further information, see for instance one of our latest articles: Terahertz response of a field-effect transistor loaded with a reactive component, A.M. Mammeri et al., Solid State Electronics, 145, 21-27, 2018.