Cleaning of Smeared Sample Surfaces - Sample Preparation for SEM

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

September 02, 2016

Problem
Mechanical polishing of soft materials or hard / soft material combinations is tricky. The mechanical polishing process leads very often to smearing of the soft material. The smeared material covers the surface and fills small pores or holes. Grain structures, interfaces and other structural details can be masked. An additional ion milling step with milling angles between 10° C and 15° C with respect to the sample surface can remove or reduce the contamination.

Preparation Conditions


1. Step (Cleaning):

Acceleration voltage:4 kV
Gun current:2 mA
Sample movement:70° Oscillation
Milling angle:10°
Milling Time:10 min

 

2. Step (Polishing):

Acceleration voltage:6 kV
Gun current:2.5 mA
Sample movement:Rotation
Milling angle
Milling Time:20 min
Fig.1: Surface of Ag SnIn after mechanical polishing
Fig.2: Surface of Ag SnIn after mechanical polishing and additional ion milling
Fig.3: Surface cleaning of a cross-section of Ag SnIn–oxide with additional structure information
Fig.4: Surface cleaning of a cross-section of Ag SnIn–oxide with additional structure information

 

(Images: FEM Schwäbisch Gmünd)

Results
Fig. 1 shows the sample surface after mechanical polishing. One can see some scratches. The information concerning the grain structure is very weak. There are just some grains visible. The surface looks ”foggy”. The sample surface looks much better after ion milling. The real grain structure and structural details are clearly visible now. The milling procedure could remove the smeared material that covered the real sample structure. The cleaning step was followed by an additional polishing step to remove possible surface roughness.

 

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