mardi 20 mars à 17h45 – ISEN Lille

Séverine Gomès
CNRS researcher, Micro and Nanoscale Heat Transfer group at the Centre for Energy and Thermal SciencesLyon University

Abstract: The control of heat flow is central to all technologies. According to the first law of thermodynamics, heat is the universal consequence of physical activity. At the same time modern material science and technology is increasingly devoted to the control of matter on the nanoscale and miniaturization of device elements well below 100 nm. By nano-structuring materials their physical properties may be engineered to achieve optimal performance. Examples include materials used in renewable energy generation (thermoelectric, photovoltaics) and structural composites. Thermal control is the dominant problem in many of these fields. For example, the continuous linear scaling of clock frequency in silicon device technology has been suspended for the last ten years as a direct consequence of the decreasing element size and increasing power density in VLSI systems. This is the first aspect of Moore's law to fail and it has failed directly because of thermal management problems at the nanoscale.

The flow of heat at the nanoscale is completely different from that experienced in macroscopic systems. The dominant phonon wavelengths at room temperature are of order a nanometer with ballistic mean-free path extending from tens of nanometers (in copper) to hundreds of nanometers in Si. Accordingly, at the nanoscale heat flow in solids ceases to be entirely diffusive and may, indeed, be quantized. Convection is suppressed. Radiative transport, where significant, takes place in the near field, since the wavelength of thermal photons is approximately 10 µm at room temperature. Accordingly, the normal methods of modelling and design used for macroscopic thermal work are completely inappropriate.

Effective tools for thermal measurement at the nanoscale are limited. The highest spatial resolution systems which are used for quantitative thermal measurement are based on optical effects, such as IR thermal emission, Raman spectroscopy or photo-reflectance. The spatial resolution of all of these methods is limited to 500 nm or greater. The key technique for thermal measurement at the nanoscale is Scanning Thermal Microscopy (SThM), but this remains highly non-quantitative in normal use. The need is for a complete thermal measurement and modelling technology for use at the nanoscale.

In this talk I will outline our efforts in better understanding the heat transfer and measuring thermal properties at the micro and nanoscales. I will give my feedback after four years as scientific coordinator of a European large scale- NMP Project QUANTIHEAT that was centered around the SThM technique to solve the problem of thermal metrology at the nano-scale and delivering validated standards, methods and modelling tools for nano-thermal design and measurement and gathered 21 strategic partners in Europe.

Organic shorts:
Dr Séverine Gomès received her European PhD in Physics at the University of Reims, France in 1999.
She is a permanent CNRS researcher, head of the Micro and Nanoscale Heat Transfer group at the Centre for Energy and Thermal Sciences (CETHIL), a common centre of the National Institute of Applied Sciences in Lyon, CNRS and the University Claude-Bernard of Lyon.
She was recruited in 2001 by CNRS in the area of Scanning Thermal Microscopy (SThM), a scanning probe microscopy method with which she worked during her PhD in collaboration with the group of Hubert Pollock and Azzedine Hammiche at Lancaster University (ULANC, UK). She was awarded the CNRS Bronze Medal in 2005 for her pioneering works on SThM.
Her main research interests deal with the development and the application of SThM and electrical methods with the goals of studying heat generation and transport at micro and nanoscales and measuring thermal properties of nanostructured materials and local temperature. During 8 years (2007-2014) she was co-responsible along with Prof. O. Kolosov (ULANC), for the 'Local Probes' group in the 'Advanced Metrology' axis of the CNRS-sponsored European Research Network: 'Thermal NanoSciences and NanoEngineering'. From dec. 2013 to nov. 2017, she was the scientific coordinator of the European large scale- NMP Project QUANTIHEAT.

Contact:
Séverine Gomes - CETHIL UMR 5008
Mail : Severine.gomes@insa-lyon.fr
Phone : 04 72 43 64 28