Thickness Map

You can relatively easily produce a relative thickness map using the EFTEM technique by acquiring an unfiltered and zero-loss image from the same region under identical conditions. Once acquired, you can compute the relative thickness map when you utilize the Poisson statistics of inelastic scattering:

$t/\lambda = -ln (\frac{I_{o}}{I_{t}})$

where

• $I_{t}$ = Total intensity (unfiltered)
• $I_o$ = Zero-loss intensity (elastic or ZLP filtered)

1. To acquire a thickness map, specify the slit width for the zero-loss acquisition and the camera parameters to be used.
   • The same camera parameters will be applied for both the zero-loss and unfiltered image acquisition.
2. Access the Configure Thickness Map dialog will vary based on the mode you choose.
   • SingleMap mode – Press the Select Thickness Map button
   • MultiMap mode – Specify via the MultiMap Configuration dialog
     • Window Settings – Set the energy loss (0 eV) and slit width for the filter
     • Detector – Specify the detector settings you want to use
3. Click Capture.

The routine will

• Acquire an unfiltered image followed by a zero-loss (elastic) image
• Correct  any spatial drift between the images
• Compute and display the thickness map

Malis, T.; Cheng, S. C.; Egerton, R. F. EELS log ratio technique for specimen-thickness measurement in the TEM. J. Electron Microscope Technique. 8:193; 1988.