Q. How to get 4dstem data on Velox?

[utkarshp1161]

4D STEM in Velox (Ceta Camera) - Check out this video by Thermofisher

1. Initial Setup

1. Open column valves and bring the microscope to your region of interest (ROI).
2. Insert fluorescent screen (SmartCam) → check diffraction pattern.
3. Align close to a zone axis using stage tilt if necessary.

2. Beam & Optics

4. Start in STEM mode with a reasonable probe current (e.g., ~100 pA).

5. Reduce diffraction disk overlap:

   • Switch from Nanoprobe → Microprobe mode.
   • Insert a smaller C2 aperture (e.g., 50 µm or 20 µm).
   • Result: convergence angle ~0.6–1.5 mrad (parallel beam).

6. Re-align beam center (use diffraction shift / reference circle).

3. Detector Setup

7. Insert Ceta camera in Velox → confirm it appears in the detector dropdown.

8. In Ceta settings:

   • Select binning / ROI for faster readout (start with 1/8 or 1/4 area).
   • Typical exposure: ~5–10 ms per pattern.
   • Ensure dark/gain correction enabled.

4. Virtual Detectors

9. In Velox → add virtual detectors (disks or rings) to highlight features:

   • Brightfield (central disk).
   • Darkfield disks for variant/superlattice reflections.

10. Make sure the central diffraction spot is correctly aligned.

5. Scan Settings

11. In Spectrum Imaging tab:

• Match dwell time to camera exposure (e.g., 5–10 ms).
• Choose scan size (e.g., 128×128 → 16,384 diffraction patterns).
• Reduce scan area to cover only the ROI.

12. Retract HAADF detector to avoid shadowing.

6. Acquisition

13. Confirm experiment duration in Velox SI window.
14. Hit Acquire.
15. During acquisition, Velox shows live:

• Real detectors (e.g., HAADF, BF).
• Virtual detectors (phase contrast separation).

7. Data Handling

16. Velox automatically saves 4D STEM data to the project offload folder.

• File format: .dm4 (Ceta) or .mrc depending on setup.

17. Open data in Velox, ImageJ, or Python tools (e.g., HyperSpy) for analysis.