Benefits and Applications of Using Hybrid-Pixel Detectors for 4D-STEM Experiments

A 10-minute read

Discover how DECTRIS ARINA hybrid-pixel detectors enable 4D-STEM by providing for dose-efficient, detailed characterization of beam-sensitive materials, including organic thin films. This is crucial to the performance optimization of key applications, such as organic solar cells.

The field of Materials Science continuously seeks advanced techniques to improve the characterization of sensitive materials. A recent breakthrough comes from the use of fast hybrid-pixel detectors (HPDs) in Four-Dimensional Scanning Transmission Electron Microscopy (4D-STEM). This innovation enables the dose-efficient phase and orientation mapping of beam-sensitive organic molecular thin films, which are crucial to the properties of devices to the performance optimization of devices including organic solar cells. 

One such HPD is DECTRIS ARINA, which has shown remarkable performance in these applications by combining high sensitivity with exceptional speed.

4D-STEM and HPD Technology

4D-STEM is a powerful technique that involves scanning an electron beam over a sample while collecting diffraction patterns at each point. This generates a four-dimensional dataset containing detailed structural information. However, traditional detectors, such as scintillator-mediated Complementary Metal-Oxide-Semiconductor (CMOS) cameras, struggle with the speed and sensitivity that are required for effective 4D-STEM, especially when it comes to beam-sensitive materials.

HPDs address these challenges. HPDs are capable of extremely high frame rates and single-electron sensitivity, and this makes them ideal for capturing the intricate details of diffraction patterns with minimal beam damage to the sample.

Benefits of HPDs in 4D-STEM

• High Frame Rates: HPDs can operate at speeds significantly higher than those of traditional CMOS cameras, substantially reducing the time that is required for data acquisition. This provides flexibility in electron dose management, thus decreasing sample damage.

• Enhanced Sensitivity: The ability to detect individual electron events with high precision and minimal readout noise is crucial for recording electron scattering signals. This sensitivity enables better imaging of delicate samples such as organic thin films at moderate to low doses and fast frame rates.

• A High Dynamic Range: Localized intensities from intense bright field disks and weak diffraction spots can be handled without saturation or damage. In this application, moderate electron fluxes are used, but there is a significant difference -often 2-3 orders of magnitude- in counts between the bright field disk and the diffraction spots. Additionally, the signal localization to very few pixels, due to the confocal optics, requires a high dynamic range.

An Experimental Approach: An Application to Organic Solar Cell Thin Films

This study focused on bulk heterojunction (BHJ) thin films composed of DRCN5T small molecules blended in PC71BM, and processed through solvent vapor annealing. The material is beam-sensitive and can tolerate only accumulated doses on the order of 1 e⁻ / Ų. 

As the speed of CMOS detectors is slow, even low beam currents result in high accumulated doses, leading to sample damage. In contrast, HPDs demonstrated superior performance by:

• Allowing for easier alignment of the TEM optics at moderate to high beam currents. Experiments with DECTRIS ARINA used regular beam currents (30 pA), while CMOS detectors required very low beam currents (<1 pA).

• Detecting at the same time both faint diffraction signals that correspond to just a few electron events and the relatively intense bright field disk.

• Providing comprehensive orientation mapping of nano-crystallites with minimal sample damage over a large field of view for improved statistics.

4D-STEM experiments were conducted using two different setups. The first one, Nano-Beam Diffraction (NBD), was performed on a Thermo Fisher Scientific (TFS) Titan Themis microscope, equipped with the company’s CMOS Ceta 16M detector and operated at 300 kV. The second setup, 4D-Scanning Confocal Electron Diffraction (4D-SCED), utilized a TFS Spectra 200 microscope, equipped with both a CMOS TFS Ceta-S detector and a DECTRIS ARINA HPD detector, and operated at 200 kV. 

Results showed that while both NBD and 4D-SCED setups could detect edge-on π-stacking nano-crystallites, the 4D-SCED setup with the DECTRIS ARINA HPD provided clearer and more detailed diffraction patterns with less sample damage, as compared to the CMOS detectors. This improvement is attributed to the higher frame rates and sensitivity of the HPD, which allowed for better detection of weak signals and reduced beam-induced damage. Additionally, the ARINA HPD enabled the coverage of larger sample areas in a shorter time, enhancing throughput and providing for more significant statistical analysis.

Conclusion

The implementation of fast HPDs in 4D-STEM represents a significant advancement in the characterization of beam-sensitive organic molecular thin films. By providing for high-speed, high-sensitivity imaging with minimal sample damage, HPDs open new possibilities for studying complex nanostructures in Materials Science. This includes advanced phase and orientation mapping of materials, which is crucial for detailed structural analysis and devices performance optimization. 

As the technology evolves, it promises to enhance the scope of 4D-STEM applications, extending beyond traditional materials to include various soft-matter and organic structures.

References

The data, findings, and images discussed and shown in this blog post are based on a study by Mingjian Wu et al., published in the Journal of Physics: Materials. For more details, please refer to the original publication: 

Wu, M., Stroppa, D. G., Pelz, P., & Spiecker, E. (2023). Using a fast hybrid-pixel detector for dose-efficient diffraction imaging of beam-sensitive organic molecular thin films. Journal of Physics: Materials, 6, 045008. https://doi.org/10.1088/2515-7639/acf524. 

Have questions about our ARINA detector or 4D-STEM? Contact our expert!

Dr. Daniel Stroppa
Senior Application Scientist for EM
Email: daniel.stroppa@dectris.com