Missions

The rapid electronic industry development with the device miniaturisation, the consequent high-power densification as well as the urgent energy transition, imposes challenges for both materials nanoengineering and energy management towards efficiently waste heat dissipation. To make feasible and reliable the densification of devices, smart and innovative solutions at the nanoscale are necessary. 2D materials continue to revolutionize the way we design high performance devices, particularly in the areas of sustainable energy conversion, storage, or remediation and sensing. Furthermore, 2D materials have been introduced as a solution for thermal management materials solving the issues of severe heat dissipation in both electronic and optoelectronic devices. Among the plethora of 2D materials, graphene and h-BN are distinguished due to their high thermal conductivity and their mechanical flexibility. Both materials mainly at their pristine form, have been studied quite extensively the last decades. It is nowadays possible to measure directly their thermal properties at the nanoscale. Here, we propose to focus on, develop, and enhance new functionalisation strategies and configurations to achieve preferential thermal dissipation direction with purpose to create building blocks for thermal management such as heat guides, lenses, spreaders, or thermal rectifiers.

Activités

The main strategy in our proposal to obtain smart thermal management, by breaking down Fourier's law is the controlled nanosized perforation, and the partial encapsulation or/and amorphisation of the 2D materials.
The originality of our project is to design the spatial organisation and density distribution of phonon scattering centers on the same scale as their wavelengths (a few tenths of a nm at 300K) from the theoretical aspect to measurements on the nanometric space and sub-picosecond time scales, with the aim of tailoring heat transport beyond the classical (diffusive) regime to the fields of ballistic and thermal hydrodynamics. To do so, we have chosen 2D materials, which are ideal platforms for this kind of fundamental studies, allowing the direct experimental probe of spatial temperature profiles and presenting entirely new thermal physics at length and time scales where the Fourier law is no longer valid.
Contactless measurement techniques are therefore critical to understand heat carrier behavior in the materials. The combination of time- and frequency-domain thermoreflectance techniques is a powerful contactless tool to characterize heat transport in 3D dimensions on small materials. This post-doctoral position will consist in using state- of-the-art thermoreflectance systems that constitute a unique ultra-broadband phonon spectrometer to measure both supported and suspended samples.
The candidat is expected to upgrade the experimental bench towards transmission measurements with respect to temperature from 77K to 900K. The wavelength of the current TDTR scheme will be adapted to 800 nm and 400 nm wavelengths for the probe and pump, respectively, which have been shown to give exploitable signal on graphene, but other wavelengths will be tested.
The measurements will start with point measurements on both supported and suspended samples. Suspended samples already used for Raman spectroscopy and thermometry can be used with the thermoreflectance systems. Temperature maps will be acquired to identify in-plane thermal properties with the help of inversion methods, such as the parabola method. To perform the acquisition, the system is equipped to move independently the sample and each laser.

Compétences

The candidate should have strong skills in femtosecond optics and instrumentation. He/she should be proficient in programming languages such as Matlab and Labview. Basic knowledge of solid state physics and thermics is expected. At least B2 level in English and French.

Contexte de travail

The LOMA laboratory at the University of Bordeaux specialises in ultra-fast energy transfer imaging and is currently the most advanced laboratory in the field of Heterodyne Time Domain Thermoreflectance (HeTDTR), which has been demonstrated in particular for the thermal and acoustic characterisation of nanostructured materials such as SOI substrates, superlattices and plasmonic devices. The supervisors are Stefan Dilhaire (Pr) and Stephane Grauby (Pr) at the University of Bordeaux.

Contraintes et risques

The risks are those associated with the use of class iv lasers.