Thermal transport and amorphous/crystalline switching in nanostructures – TACOS

The TACOS project aims at quantifying the thermal properties (conductivities and interface conductances) of nanofilms made of amorphous/crystal phase change materials. To this end, atomic models based on machine-learning interatomic potentials as well as measurements targeted to low thermal conductors will be conducted in parallel. Our systems of choice will be Ge2Sb2Te5 and Sb2S3, two phase change materials used for neuromorphic and photonic devices. Nanofilms with thicknesses smaller than 200 nm will be fabricated using the technology of the INL nanofabrication platform. Their thermal properties will be determined by photothermal radiometry at ITheMM. On the modelling side, carried out in Strasbourg (ICube and IPCMS), ab-initio molecular dynamics, based on density functional theory (DFT), will serve as a data base for the construction of machine learning (MLIP) interatomic potentials. The use of MLIP will allow tackling systems containing hundreds of thousands of atoms by retaining the predictivity of ab-initio calculations. Thermal conductivities and interface conductances will be calculated by simulating heat transients, according to the Approach-to-Equilibrium Molecular Dynamics (AEMD) method. Thus, it will thus be possible to extend atomic calculations to thicknesses up to about 100 nm, thereby taking advantage of a joint effort featuring measurements and calculations to firmly elucidate and quantify the existence of nanometric effects in the thermal properties of phase change materials. This knowledge will be used to optimize the thermal operation of reconfigurable photonic devices in development at the INL, and allow heat to be efficiently transported or evacuated during amorphous/crystal and reverse switching.