Mapping structure and morphology of amorphous organic thin films by 4D-STEM pair distribution function analysis

Area of Science:

• Materials Science
• Nanotechnology
• Analytical Chemistry

Background:

• Imaging nanoscale phase distribution and local atomic structure in organic materials is challenging.
• Existing methods often struggle with unstained or amorphous/partially crystalline samples.

Purpose of the Study:

• To develop and validate a novel approach for nanoscale phase imaging and local structure analysis of organic materials.
• To demonstrate the capability of 4D-STEM-PDF for characterizing short- and medium-range order in organic molecules.

Main Methods:

• Utilizing scanning transmission electron diffraction (4D-STEM) combined with pair distribution function analysis (PDF).
• Applying the method to organic semiconductor blends like PC61BM and P3HT.
• Comparing results with virtual dark-field analysis and validating with electron energy loss spectroscopy.

Main Results:

• 4D-STEM-PDF successfully characterizes short- and medium-range order in aperiodically packed organic molecules.
• The method achieves local structural information with a few nanometers resolution.
• Distinct, thickness-independent phase contrast images were generated for organic composites.

Conclusions:

• 4D-STEM-PDF is a powerful tool for imaging phase distribution and local structure in organic materials, especially unstained composites.
• The technique offers high dose efficiency and is suitable for materials lacking distinct valence states for EELS.
• This approach advances the analysis of complex organic materials for applications like organic solar cells.