I want to make a micro pillar out of the a metallic sample by using focused ion beam milling method. I wonder if the platinum coated on the surface of the specimen is needed or just optional before commence ion beam milling (annular milling procedure)?
It is not needed. If you have a metallic sample, it is conductive without any coating.
Good luck!
The platinum is de factor only applied in order to protect the original surface. It has been developed for TEM sample preparation. In many cases scientists want to see the microstructure below a certain defect visible at the surface or the change of the microstructure below the surface. In such cases you want to see your original surface still after preparation. On the other hand, if you do NOT use Pt as protection layer, each scan with ions will remove the layer you just imaged, i.e. this what you've just seen does not exist anymore. In so far, I am not sure whether for your application you can simply abandon the Pt.
Sorry for the simplification. As Dr. Nolze said, Pt coating can be important as a surface protection for precise HR-TEM sample preparation. But if one won't use ions (or just decrease the current) for visualization after milling, all will be good without Pt.
For the micro-pillars fabrication with FIB you do not need coating, as you are probably primarily interested in mechanical properties of your pillars. From this perspective, additional Pt layer can even affect your results in e.g. compression tests. Therefore, if you don't have a problem with charging, do not complicate :-)
Janez Zavašnik : Is it possible to "mask" the micro pillars (as for chemical etching) and remove Pt in a later step? Or is this simply too much additional work?
I wonder, how the quite strong ion beam affects the remaining microstructure (from ion implantation up to microstructure transformation)...or do you use a weak beam in a last polishing step? To use ion beam in order to get the shape is certainly useful as long as you do not change the material to be tested...
Gert Nolze exactly, ewe should be interested in measuring the real properties, not the artifacts. I'm not sure about the masking, but the literature on the fib-induced damage during micro-pillars fabrication is quite extensive. Rule of the thumb is - fib will produce a damaged layer, and the effect is more pronounced in smaller diameter pillars (since the damaged layer takes quite a big percentage of the whole volume).
This two articles are directly researching the FIB effect on some of the measured properties: Article Effects of Focused Ion Beam Induced Damage on the Plasticity...
http://matrix.seas.ucla.edu/papers/2005/ElAwadyEffects%20of%20focused%20ion%20beam%20induced%20damage%20on%20the%20plasticity%20of%20micropillars.pdf
While this text is more general (primarly for the OP):
http://www.eu-f-n.org/cms/wp-content/uploads/2017/07/tutorial_joakimreuteler_fib-artifacts-and-how-to-overcome-them_2017-05-24.pdf
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