Broad Ion Beam (BIB) milling is a versatile method for obtaining high quality surface finish, that is mostly required for high precision EBSD and analytical microscopy research work.
There are, however, a number of parameters that affect the final polishing result, such as gun angle, milling voltage, milling time, modulation, temperature, etc.
Besides, each sample, depending on the chemical composition and existing phases, behaves different under the ion beam. In this regard, selective etching limits the application of this method to some extend.
Given all these complications, is there any reference or database that has gathered "optimized" ion milling parameters for various metals and alloys?
interesting question. The german company Roth&Rau is selling those 'ion polisher'.
TRIM used to be the base for ion sputtering. Multi-elemental targets can be simulated today I believe.
Now may be some extensions are available for roughness evolution?
looking forward to see more informations
We used the PECS for several years. Finally I have to summarize that ion bombardmend is for (at least metallic like Fe) materials a quite rough technique. It implements surface near lattice defects which especially affect surface sensitive techniques like EBSD. Mechanically polished surfaces gave better patterns than subsequently ion-polished. In those days we expected an even improved pattern quality but observed the opposite.
We used 70 degrees tilt and 1.5kV accelleration voltage (Ar) on a rotating sample.
We just got PECS II, which is relatively a new product of Gatan.
By 70 degrees tilt you mean the sample tilt right? because guns can be tilted up to 18 degree max. at least in our instrument.
So what you recommend generally: Mechanical polishing and then a gentle ion polishing. right?
Hi Ehsan, as mentioned, we never combined both techniques. Only when we could not prepare our samples manually (brass containing lead drops, gold, lead-free solders etc...) we use PECS. The tilt means the sample tilt. You are right. The old PECS does not allow to tilt the guns (presently I do not get it for what this should be beneficial, but this is certainly my missing knowledge).
The problem is actually quite clear: Kikuchi patterns (background processed BSE signal) only display the effect of the surface-near depth, which is Z-and kV-dependent, and is usually estimated as 10 to a few tens (20kV) microns. In this depth you certainly generate interstitials, i.e. Ar is entering this small layer. With EDS you shouldn't see this, and also in TEM it is not clear what happens with this layer if you investigate it as cross section lamella. It wouldn't surprise me that the relaxation of the microstructure would cause a migration of Ar atoms to the huge and near surface so that you cannot see these effects in TEM as well (maybe also triggered by the electron interaction, local heating etc). Therefore we were really surprized that after polishing a steel metallographicalle and a subsequent gentle ion polishing (1.5kV) the pattern quality became worse in comparison to the mechanically polishing before. That clearly indicates (from my point of view) that ion polishing generates defects which causes a blurring of Kikuchi patterns. I have no idea how ceramics are concerned. Maybe less since the lattice distortions are perhaps not that big since the unit cell dimensions are commonly bigger and therefore the relative change of the lattice.
Thanks Gert. Interesting evidence!
Probably changing the gun angle, which is possible in the new product, could help in resolving the mentioned issue. I can let you know within a few months ;)
But as mentioned, there are a lot of parameters that can change the final result, and I am looking for a database to use a base for my studies....
I hardly assume that GATAN is collecting these data since they need them for application ans sales. You should ask them.
I have asked them. But it seems there is no database and they do not show any interest on a collaboration for making a database!!!
Well, then you perhaps bought the wrong system :-|. I would ask here in Researchgate again, who is operating an GATAN PECS? Maybe you will find some people who use it? If I remember correctly, I've seen some kind of presentation showing many different materials. GATAN definitely knows about it. Did you contact GATAN US? In case not, write them a kind letter. I strongly assume that they won't neglect you. Good luck!