Removal of Surface Layers - Sample Preparation for SEM and TEM

Application Note for Leica EM RES102 - Material Research, Industrial Manufacturing, Natural Resources

January 11, 2017

Sometimes it is necessary to remove surface layers to gain access to the real surface structure. That can be a native oxide, or layers coming from the preparation process itself, like re-deposition. Depending on the layers thickness and the energy used for the cleaning process, it takes between a few seconds and half an hour. The energy depends on the milling rate of the material.

Application Examples shown here:
Reducing the thickness of a Pt Coating
Removing re-deposition from a TEM sample surface

Reducing the Thickness of a Pt Coating

The coating of the oil shale sample shown in the images below was too thick (Fig.1) The sample looks "foggy".
The real structure is not clearly visible.
A short los energy milling solved the problem.

Preparation conditions

Acceleration voltage: 2 kV
Gun current:1.5 mA
Milling time:2 min

After milling the oils shale structure is clearly visible (Fig.2).

Cleaning of a Contaminated TEM Sample

The reason for contamination of TEM samples glued on a Cu ring was single sided ion milling. Because the rear side can have material re-deposited from the Cu ring (Fig.3)

Preparation Parameters

Acceleration voltage:2 kV
Gun current:1.5 mA
Sample movement:Rotation
Milling angle:10°
Milling time:25 min.


As shown in the image the re-deposition is completely removed after the cleaning procedure. The grain structure is clearly visible (Fig.4).

Fig.1: Oil shale sample with too thick Pt coating
Fig.2: after reducing the thickness with ion milling
Fig.3: TEM image of a contaminated ceramic sample
Fig.4: TEM image of the sample holder after additional ion beam milling at lower ion energy