Quantitative chemical evaluation of dilute GaNAs using ADF STEM: avoiding surface strain induced artifacts

Area of Science:

• Materials Science
• Solid State Physics
• Nanotechnology

Background:

• High-angle annular dark-field (HAADF) scanning transmission electron microscopy (STEM) is crucial for chemical composition analysis.
• Quantitative analysis of dilute GaNAs quantum wells is complicated by strain fields that obscure chemical contrast.
• Distinguishing strain contrast from chemical contrast is essential for accurate HAADF intensity evaluation.

Purpose of the Study:

• To develop a method for quantitative 2D compositional mapping of GaNAs/GaAs quantum well systems.
• To overcome the limitations of HAADF intensity analysis caused by strain fields.
• To enable precise chemical composition evaluation in dilute nitride quantum wells.

Main Methods:

• Utilizing high-angle annular dark-field (HAADF) intensity in scanning transmission electron microscopy (STEM).
• Comparing experimental HAADF intensities with simulated intensities for quantitative evaluation.
• Employing information from two different camera lengths to differentiate strain and chemical contrast.
• Achieving full 2D compositional mapping of GaNAs/GaAs quantum wells.

Main Results:

• Successfully demonstrated a method for quantitative 2D HAADF STEM compositional mapping.
• Enabled the distinction between strain contrast and chemical contrast in GaNAs/GaAs systems.
• Provided a reliable approach for evaluating chemical composition in dilute GaNAs quantum wells.

Conclusions:

• The presented method allows for accurate quantitative chemical composition mapping of GaNAs/GaAs quantum wells.
• This technique overcomes the challenge of strain-induced contrast in HAADF STEM analysis.
• The findings are significant for the characterization and development of dilute nitride quantum well materials.