# Thickness map

You can produce a relative thickness map relatively easily in the EFTEM technique by acquiring an unfiltered and a 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

1. 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

1. SingleMap mode – Press the Select Thickness Map button

2. MultiMap mode – Specify via the MultiMap Configuration dialog

1. Window Settings – Set the energy loss (0 eV) and slit width for the filter

2. 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 for any spatial drift between the images

• Compute and display the thickness map

## References

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.