Dynamic lattice distortions driven by surface trapping in semiconductor nanocrystals

Area of Science:

• Materials Science
• Nanotechnology
• Physical Chemistry

Background:

• Nonradiative processes significantly hinder the optoelectronic functionality and device performance of nanocrystals.
• The dynamic structural origins of these nonradiative relaxations remain poorly understood at an atomic level.

Purpose of the Study:

• To investigate the transient structural dynamics underlying nonradiative electronic processes in colloidal semiconductor nanocrystals.
• To elucidate the role of excitation energy and carrier behavior in inducing lattice deformations.

Main Methods:

• Femtosecond electron diffraction measurements were employed to capture ultrafast structural changes.
• Atomistic simulations were used to corroborate experimental findings and provide detailed mechanistic insights.
• Core/shell nanocrystal systems were studied with varying excitation energies to probe different carrier dynamics.

Main Results:

• Transient lattice deformations were observed accompanying radiationless electronic processes.
• High-energy excitation (significantly above bandgap) induced surface structural distortions linked to trapped holes on picosecond timescales.
• Near-bandgap excitation resulted in lattice heating on a longer 200-picosecond timescale, dominated by Auger heating.

Conclusions:

• The study elucidates atomic-scale structural deformations associated with surface trapping of hot holes.
• These findings offer insights into mechanisms degrading optoelectronic performance in nanocrystal devices.
• Provides a potential pathway for minimizing performance losses in future nanocrystal-based technologies.