Electron-beam induced damage process for Ca₂Na₂Nb₅O₁₆nanosheets

Area of Science:

• Materials Science
• Nanotechnology
• Solid State Chemistry

Background:

• Dielectric two-dimensional (2D) oxide nanosheets offer thermal stability and high-k properties, crucial for electronic applications.
• Characterizing the atomic structure of these materials is challenging due to their susceptibility to electron-beam degradation during analysis.
• Exfoliated Ca₂Na₂Nb₅O₁₆ (CNNO) nanosheets represent a class of materials with potential but limited structural understanding.

Purpose of the Study:

• To investigate the distinct electron-beam induced damage mechanisms in exfoliated CNNO nanosheets.
• To elucidate the roles of knock-on damage and radiolysis in structural degradation at varying electron beam energies.
• To establish optimal conditions for atomic-scale imaging of sensitive 2D oxide materials.

Main Methods:

• Utilized Cs-corrected scanning transmission electron microscopy (STEM) to analyze CNNO nanosheets.
• Investigated damage mechanisms at different accelerating voltages (high and low) to differentiate between knock-on and radiolysis effects.
• Employed a decreased beam current during imaging to minimize electron beam-induced damage.

Main Results:

• At high voltages, knock-on damage dominated, leading to short-range order and an amorphous structure.
• At low voltages, radiolysis, facilitated by dangling bonds in solution-processed CNNO, caused significant elemental loss and complete structural disorder.
• Radiolysis damage kinetics were faster and induced more extensive elemental loss than knock-on damage.
• Successful atomic-scale imaging of CNNO nanosheets was achieved at 300 keV with reduced beam current.

Conclusions:

• Electron beam damage in 2D oxide nanosheets occurs via distinct knock-on and radiolysis pathways, dependent on accelerating voltage.
• Radiolysis is a significant degradation pathway for insulating 2D oxides with dangling bonds, proceeding faster than knock-on damage.
• Understanding these damage mechanisms is critical for achieving high-resolution atomic imaging and accurate characterization of 2D materials using electron microscopy.