| 4D Scanning Transmission Electron Microscopy (4D STEM) is an advanced technique used in electron microscopy to provide detailed information about the structure, composition, and properties of materials at the nanoscale. The term "4D" refers to the four-dimensional data acquired during the experiment:
- Two spatial dimensions in the sample plane.
- Two dimensions in the diffraction space.
Here's what is typically included in 4D STEM:
- Probe Scanning: A focused electron beam (probe) is scanned across the sample in a raster pattern, creating a 2D grid of positions on the sample. At each point in this grid, a diffraction pattern is recorded, representing the scattering of electrons as they interact with the material.
- Diffraction Patterns: At each probe position, a 2D electron diffraction pattern is collected using a pixelated detector (such as a direct electron detector or a fast camera). This diffraction pattern provides information about the crystal structure, orientation, and other material properties.
- 4D Dataset: The combination of the 2D probe position grid and the 2D diffraction patterns at each position creates a 4D dataset. This dataset can be analyzed to extract various types of information, such as phase mapping, strain mapping, and more.
- Data Analysis: The 4D dataset can be processed and analyzed in numerous ways to extract quantitative information about the sample. For instance, you can map local variations in crystal orientation (orientation mapping), measure strain or deformation in the material (strain mapping), or analyze the distribution of phases or defects within the sample.
4D STEM is powerful because it captures a wealth of information in a single experiment, allowing for detailed analysis of complex materials, including their structural, electronic, and magnetic properties.
For instance, the phrase "STEM nano-beam diffraction (NBD) patterns can be captured at 10° intervals
at sample rotation around the θ-axis in Figure 0002a.
Figure 0002a. Schematic illustration of the rotation holder and pillar-shaped specimen in
the FIB (a) and in the STEM (b). The rotation holder allows 360° rotation of the
specimen (θ), while the microscope stage controls the sample tilt (α). [1, page0004] |
[1] Konrad Jarausch, Paul Thomas, Donovan N. Leonard, Ray Twesten, Christopher R. Booth, Four-dimensional STEM-EELS: Enabling nano-scale chemical tomography, Ultramicroscopy 109 (2009) 326–337.
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