Diversifying the sample environment in the toroidal DAC for ultrahigh pressure and temperature studies

The toroidal diamond-anvil cell (tDAC) can routinely achieve pressures under static compression above 300 GPa, pressures relevant to the center of Earth and the deep interiors of multi-Earth mass exoplanets. Building intricate sample environments for high-quality equations of state (EoS), phase relations, and melting studies of planetary and other condensed-matter materials remains difficult in the tDAC. The small tDAC sample chamber (~4 – 6 µm diameter) presents a great challenge for embedding micron-sized samples in soft media for measuring the room-temperature EoS and in insulating media for exploring high-temperature properties. Here we will discuss our recent advancements in microfabricating a tDAC sample environment where we test refractory Mo and Ta fully encapsulated in a copper or bismuth medium. We demonstrate that compressing samples in a softer metal in the tDAC improves the compression environment and results in measured sample volumes comparable to those collected in noble-gas media at multi-megabar conditions. To target high-temperature studies, we further develop a large-volume toroidal design capable of reaching pressures >4 Mbar while accommodating a sample compartment as large as a typical laser-heating spot size (~30 um). This larger-volume configuration also offers ample space to insulate the sample under high temperature conditions. The tDAC sample packages developed through this work expand capabilities to obtain high-quality pressure-volume-temperature data for planetary and other condensed matter studies at multi-megabar conditions.