Topic 1 GeTe amorphous and crystalline films have been prepared. Films of Ge0.15Te0.85, which is a good glass-former, have also been prepared to contrast the case of PCMs, which by definition are bad glass-formers instead. The amorphous films have then been characterized in terms of thermodynamic properties via fast-scanning calorimetry, and structural properties, via X-ray diffraction. Molecular dynamics simulations with machine learning potentials fitted on ab initio forces are being carried out to help in the analysis of the experimental data and shed light on the connection between the distribution of local structures and the protocol used to prepare the amorphous films.
Topic 2 Pump-probe experiments on GeTe and Ge0.15Te0.85 films have been carried out to study the transient amorphous states during and after the non-thermal melting transition. The experiments probed both the structure, via X-ray diffuse scattering, and the dynamics, via X-ray photon correlation spectroscopy. Moreover, a computational scheme to describe via DFT, molecular dynamics and machine learning techniques this transition has been set up and simulations are being carried out to help interpret the experimental results. The data analysis is in progress.
Topic 3 Fast calorimetry experiments on GeTe amorphous films are being performed to measure both the relaxation time around the glass-transition temperature and the crystal growth rate. These measurements also provide information on the fragility of the glass, which is a long-standing open issue for GeTe. Since the GeTe amorphous films are prone to crystallize even before reaching the glass transition temperature, specific thermal protocols (ageing) have been tested to associate the out-of-equilibrium state to the propensity of crystallization.