High-precision atomic-scale strain mapping of nanoparticles from STEM images

Area of Science:

• Materials Science
• Nanotechnology
• Physics

Background:

• Nanoparticle strain significantly impacts their physicochemical properties and performance.
• Accurate strain measurement is vital for understanding nanoparticle mechanisms.
• Existing strain analysis methods include diffraction-based and imaging-based techniques in scanning transmission electron microscopy (STEM).

Purpose of the Study:

• To develop and validate a methodology for quantifying atomic-scale deformation in nanoparticles using STEM.
• To explore the suitability of various deformation parameters for atomic-scale analysis.
• To apply the developed method to a bimetallic nanoparticle (PtCo3).

Main Methods:

• Utilized image simulation techniques to assess the accuracy of 2D displacements from annular dark field (ADF) STEM images as a projection of 3D displacements.
• Developed a deformation analysis methodology based on atomic column detection in real-space, atomic-resolution STEM images.
• Investigated the appropriateness of continuum-based deformation parameters for atomic-scale investigations.

Main Results:

• Measured 2D displacements from ADF STEM images approximate 3D displacements.
• Local lattice parameter and principal strain components are the most physically meaningful parameters for material distortion.
• Other deformation parameters (normal strains, shear strains, displacements) are dependent on the reference lattice choice, with different reference grids introducing uniform offsets.

Conclusions:

• The presented methodology effectively quantifies deformation behavior at the atomic scale in nanoparticles.
• Local lattice parameter and principal strain components offer robust metrics for material distortion.
• The approach was successfully applied to a PtCo3 bimetallic nanoparticle.