Atom-by-atom structural and chemical analysis by annular dark-field electron microscopy.

Area of Science:

• Materials Science
• Nanotechnology
• Analytical Chemistry

Background:

• Transmission electron microscopy (TEM) has long been envisioned for atomic-level imaging.
• Aberration-corrected optics have significantly advanced TEM capabilities.
• Resolving and identifying all atoms in non-periodic, multi-element materials remains a challenge.

Purpose of the Study:

• To demonstrate atom-by-atom imaging and chemical identification in ultra-thin materials.
• To analyze substitutional defects in monolayer hexagonal boron nitride (h-BN).
• To achieve direct resolution of atomic-scale structural distortions.

Main Methods:

• Utilized aberration-corrected scanning transmission electron microscopy (STEM) with annular dark-field (ADF) imaging.
• Operated the STEM at low voltage for enhanced sensitivity.
• Employed density functional theory (DFT) calculations for verification.

Main Results:

• Successfully resolved and identified the chemical type of every atom in monolayer h-BN.
• Detected and characterized three types of substitutional defects: C on B, C on N, and O on N sites.
• Directly observed in-plane distortions of approximately 0.1 Å caused by substitutions.

Conclusions:

• Atom-by-atom structural and chemical analysis is now possible for radiation-damage-resistant atoms in ultra-thin sheets.
• This technique provides unprecedented insight into atomic-scale defects and their impact on material structure.
• The findings pave the way for advanced characterization of 2D materials and nanostructures.