Femtosecond electron diffraction: 'making the molecular movie'

Area of Science:

• Materials Science
• Physical Chemistry
• Condensed Matter Physics

Background:

• Femtosecond electron diffraction (FED) offers potential for observing transition states.
• Ultrafast motions relevant to barrier-crossing events occur on femtosecond timescales.
• Advances in high-flux electron sources enable capturing these dynamics at atomic resolution.

Purpose of the Study:

• To describe advances in FED for observing atomic-level structural dynamics.
• To investigate phase transitions in Al and Au using FED.
• To introduce new methods for pulse characterization and time-zero determination.

Main Methods:

• Utilizing high-flux femtosecond electron pulses for diffraction.
• Studying the ordered-to-disordered phase transition in Al and Au.
• Applying electron-electron correlation for pulse characterization and time-zero determination.
• Investigating laser-based methods for enhanced time resolution and electron acceleration.

Main Results:

• FED successfully captured atomic-level structural dynamics during phase transitions.
• Melting dynamics in Au showed distinct timescales for lattice heating and disordering.
• Superheated FCC metals were observed to melt via homogeneous nucleation.
• Electron-electron correlation provided precise t=0 determination (<100 fs).

Conclusions:

• FED is a powerful tool for visualizing chemical events in real-time.
• The study elucidated melting mechanisms in metals at the nanoscale.
• Advanced pulse characterization techniques improve temporal accuracy in FED experiments.