Direct imaging of ultrafast lattice dynamics.

Area of Science:

• Materials Science
• Condensed Matter Physics
• High-Pressure Science

Background:

• Lattice dynamics under extreme conditions are complex and difficult to study.
• High-temperature, high-pressure loading induces challenging elastic-inelastic responses in materials.
• Experimental limitations hinder the measurement of dynamics at small spatial and temporal scales.

Purpose of the Study:

• To spatially resolve lattice dynamics of silicon under high-strain rate conditions.
• To investigate the elastic-inelastic responses of silicon under extreme environments.
• To characterize a newly observed intermediate elastic feature and its role in phase transformations.

Main Methods:

• Utilized an X-ray free-electron laser (XFEL) for simultaneous in situ direct imaging and X-ray diffraction.
• Employed ultrafast probe X-rays for time-resolved characterization of lattice dynamics.
• Applied high-temperature, high-pressure loading to silicon samples.

Main Results:

• Achieved the first imaging of a novel intermediate elastic feature in silicon.
• Identified the structure, compression, and density associated with observed waves.
• Constrained the kinetic inhibition of phase transformation using time-resolved data of the intermediate elastic feature (2-4 ns).

Conclusions:

• The study addresses fundamental questions regarding silicon's response to extreme conditions.
• Demonstrated the potential of ultrafast direct measurements for uncovering new lattice dynamics.
• Revealed a new intermediate elastic feature influencing compression and phase transformation kinetics.