Quantifying nanoscale order in amorphous materials via scattering covariance in fluctuation electron microscopy

Area of Science:

• Materials Science
• Condensed Matter Physics
• Electron Microscopy

Background:

• Fluctuation Transmission Electron Microscopy (FTEM) probes nanoscale topological order (1-3 nm) in amorphous materials.
• Quantifying this order in diffraction amorphous materials using FTEM has been a significant challenge.
• Existing methods often require material-specific atomistic models, limiting general applicability.

Purpose of the Study:

• To develop a quantitative method for describing nanoscale topological order in amorphous materials using FTEM.
• To establish a general analysis framework applicable across different amorphous systems.
• To differentiate between various regimes of order based on size and volume fraction.

Main Methods:

• Computed the FTEM covariance at two non-degenerate Bragg reflections.
• Employed a Monte-Carlo approach to simulate covariance regimes based on Bragg reflection excitation probabilities.
• Analyzed sputtered amorphous thin films: a-Si, nitrogen-alloyed GeTe, and Ge₂Sb₂Te₅.

Main Results:

• The FTEM covariance successfully distinguished between different regimes of nanoscale topological order.
• The covariance analysis proved general, not requiring material-specific atomistic models.
• Experimental data from diverse amorphous thin films aligned with simulated covariance regimes.

Conclusions:

• FTEM covariance analysis provides a robust, model-independent method for quantifying topological order in amorphous materials.
• This approach enables the characterization of nanoscale order across various amorphous systems.
• The findings open new avenues for understanding structure-property relationships in amorphous materials.