Detecting charge transfer at defects in 2D materials with electron ptychography.

Area of Science:

• Materials Science
• Condensed Matter Physics
• Atomic Scale Imaging

Background:

• Imaging electronic charge transfer at the atomic scale is crucial for understanding chemical bonding.
• Charge density is primarily determined by atomic nuclei, making subtle bonding perturbations difficult to detect.
• Existing imaging techniques lack the sensitivity to directly visualize charge transfer.

Purpose of the Study:

• To develop a highly sensitive method for imaging atomic-scale electronic charge transfer.
• To investigate charge transfer in pristine and defected monolayer tungsten disulfide (WS₂).
• To demonstrate the utility of electron ptychography for quantitative charge density mapping.

Main Methods:

• Utilized electron ptychography with high dose efficiency and aberration correction.
• Employed a focused-probe configuration to simultaneously collect annular dark-field (ADF) signals.
• Validated experimental results with first-principles simulations incorporating thermal diffuse scattering (TDS) via molecular dynamics (MD) based on density functional theory (DFT).

Main Results:

• Achieved unprecedented sensitivity to detect electronic charge transfer in monolayer WS₂.
• Demonstrated the ability to distinguish charge transfer in both pristine and defected samples.
• Obtained excellent agreement between experimental ptychographic reconstructions and theoretical simulations.
• Concurrently imaged atomic structure and chemical identity using ADF signals, independent of charge transfer.

Conclusions:

• Electron ptychography is a powerful tool for quantitative atomic-scale charge density imaging.
• Accurate first-principles simulations are essential for interpreting ptychographic data.
• This technique opens new avenues for studying chemical bonding and electronic properties at the atomic level.