Advanced Neutron Scattering Techniques for Operando Characterization of Phase Change Materials

The reversible amorphous to crystalline phase transition in Ge-Se glasses has led to their critical use in applications ranging from heat sensors for real time temperature monitoring to optical media storage. Despite these important applications, our understanding of the dynamical changes occurring across this phase transition remains incomplete. This work describes the development of an operando inelastic neutron scattering technique as an advanced thermal and material characterization tool to study the phase transition in bulk Ge-Se glasses. The operando inelastic neutron scattering technique produces time-resolved information about the phonon vibrational dynamics in these materials transition from amorphous solid to undercooled liquid and crystalline solid. This new technique allows us to capture a phonon density of states in as little as 90 seconds, providing real-time quantitative evaluation of the vibrational entropy in the glass, liquid, and crystalline phases. Aspects of operando neutron scattering data collection and analysis will be discussed alongside new insights into the vibrational dynamics in Ge-Se glasses. Potential for application of this technique to additional phase change materials will also be discussed.