Tungsten thinned upto 20 micron need to be Ar ion milling for tem observation.
I want to do ion milling at 3KeV and 5o angle.
The time taken for tungsten to be electron transparency is ?
A lot. A matter of days actually. Try to diple it down to 5-7 um at least... I etched quite a few samples on different ion mills, and they really make a difference (regarding diameter of the ion-beam)... what's your setup? And watch out for re-sputtering of W back onto the sample... otherwise you'll discover nano-W in TEM :-)
It is hard to analytically to tell the time because the W is a refractory/hard material. The experience of running the Ar ion milling on the W will only tell when the W becomes transparent for the TEM examination. I have run Ar ion milling on of several Fe-B-Si metallic glasses with an average thickness of 20 um in my previous investigation. It took from a half day to one day to make the samples transparent for the TEM observation.
Impossible, I think. Usually I thined the tungsten foil by FIB to 300 nm and then use Ar to remove the FIB damage.
20 micron is too thick. and it will bend the tungsten foil after long time irradiation
You can get some idea about W sputtering rate reading attached paper.
http://www.sciencedirect.com/science/article/pii/S0168583X08011877?np=y
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