JEOL IT800SHL - Reduced Charging Imaging Modes

Techniques to reduce charging during your imaging session.

The first and easiest method is to deposit a thin layer of Au/Pd onto your sample, and use clips to provide a path to ground from the sample surface, as described here:

• Hummer SEM Sample Coater - thin Au/Pd coating to reduce charging in SEMs

Samples accumulating electric charge during imaging is a common issue in the SEM. This typically manifests as the image drifting/shifting (blurring the image during slow photo acquisitions), astigmatism needing constant re-correction, and generally inability to get sharp images no matter the imaging conditions.

Imaging conditions for reduced charging

Here are some settings to reduce charging:

• Beam Voltage (in databar on bottom of screen): 1kV
• Set "P.C." (Probe Current, in databar) to: HD/High Definition mode, and then 75% current.
  • HD mode increases resolution (smaller beam) but is lower current (higher noise), so sliding up to 75% increases SNR back to original levels.

• Adjust Wobble first. Ok to do at lower magnifications. Use X/Y knobs to make image not shift laterally when defocused.
  • Use "Lens Clear" function beforehand (right-click image and choose "Lens Clear")
  • Use "ABA" (Auto Beam Alignment) - faster than manual for low beam voltages
• Adjust Astigmatism "Stig": see this video for tips: Optimizing Astigmatism (CalTech Nanoscience Institute)
  • Adjust stig while observing an object with many angles (eg. dust/dirt) - avoid adjusting stig on an object with flat lines (eg. cleaved edge) or you will skew the image along that edge.
• Switch to [CF1] or [CF2] acquisition modes for final image (next to Scan1/Scan2 etc) - "Charge Free" mode.
  • Fast scans to reduce charging, but re-scans each line multiple times to reduce noise.

During imaging

• Right-click the image and click "Lens Clear" - this removes residual magnetism in the lens and can help remove distortion, or make stig correction work better. Especially if you have trouble getting Wobble and Stig to align.
• If you have set Wobble and Stigmator to "no man's land" (you're "lost"), reset it with: Alignment > OL Stigmator > [Reset All]

• Use "RDC" for optimizing image on a small, fast scan area before acquiring entire image.
• Right-Click > [Find Focus] to auto-focus on a particular feature/location on the image.

Written by Demis D. John, 2024-11-02.