Collaborative: EAGER: Demonstration that Thin Film Phase Transformations Can Be Monitored at High-Temperature and High-Pressure in a Diamond Anvil Cell

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Phase transitions and the associated volume changes strongly influence materials’ properties. When occurring in minerals in subduction zones - where one tectonic plate dives underneath another - they may cause earthquakes. Preliminary observations suggest that phase boundaries (where transitions occurred) are influenced by changes in mineral grain size and stress state. However, such effects are still poorly understood because of experimental limitations. Indeed, it is challenging to tune minerals’ grain size and stress state at the extreme pressures and temperatures prevailing in subduction zones. Here, the researchers explore the capabilities of a new experimental approach which allows such tuning. They produce thin films of mineral with controlled grain size and stress state using state-of-the-art deposition techniques. They then probe the mineral stability at the extreme conditions of the deep Earth using high-pressure devices. This work fosters technological transfers between Materials Science and Mineral Physics. Its outcomes have broad implications, notably regarding the stability of thin films for incorporation into everyday devices. The project also provides support for a graduate student trained in a multidisciplinary environment.Here, silica (SiO2) thin films with variable crystallite sizes and biaxial stress states are fabricated via Pulsed Laser Deposition by modulating the growth conditions and choice of substrate. These thin films are then placed within the independently modulated hydrostatic stress field of a diamond anvil cell. This high-pressure device can produce very high pressures at the tips of two opposing diamonds. The films’ properties are probed in situ with visible light and/or x-rays at various pressures and temperatures. The goal is to map out how given SiO2 crystallite size and/or biaxial stress state changes the pressure and temperature conditions of silica phase boundaries. More generally, the team explores whether Pulsed Laser Deposition can produce geologically relevant thin films with tunable stress states, crystallite sizes and orientations. Such a novel tool could be transformative for the study of phase transformations - as well as other processes related to transport properties and chemical reactions - occurring in the deep Earth.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.