If I were to ion-irradiate a material that has regions of greater crystallinity, and more amorphous regions, in which region should I expect a more concentrated ion implantation and damage nearer to the surface?
I know this very well depends on the atomic density in the crystalline vs amorphous material; but say if you were to use SRIM to calculate DPA vs depth for a set stoichiometry and density, and the only difference in practice is bonding. SRIM doesn't take this into account, but how should this affect a material (specifically a ceramic material)?
If you know of any examples of measured DPA in amorphous VS crystalline ceramic, such as amorphous carbon vs graphite, I'd really appreciate it.
Dear Aimee Coleman ,
In general, crystalline materials are much more compact than amorphous ones. During an ion implantation process, I would expect more implantation in amorphous materials, without a doubt. However, the degree of implantation will also depend on the type of ion and the material...
Best,
Fran
Francisco Manuel Marquez
Dear Fran,
Thanks for your response. Maybe my question wording was poor; I am trying to ask that, if all parameters were similar (including atomic and material density), how could bonding/crystallinity affect the DPA vs penetration depth profile of the material. I would assume that there would not be significant increase or decrease in total number of ions implanted (i.e. that the number of ions reflected from the material does not change), but that the implantation would occur, on average, either closer to the surface, or further from (not that overall implantation number would change).
Can I take from your answer "I would expect more implantation in amorphous materials", that you mean the ions would be implanted closer to the surface? If so, why?
I might intuitively think of a crystal with elastic bonds being able to absorb a greater amount of energy from the incident ions, and so having the ions need fewer collision events on average before embedding into the material, thus the ion implantation should be closer to the surface for a crystalline material, and deeper in an amorphous one; I am not sure how true this is in reality, and want to check that there's not another explanation.
The other question is whether a greater overall DPA would be found in crystalline materials (which would make intuitive sense), but specifically whether the DPA-depth profile of a crystalline material peaks deeper into the material, or closer to the surface than an amorphous material. I can think of arguments for each scenario;
Former: The ion penetration depth into a crystlline material would be lower on average, so the peak DPA would be closer to the surface.
Latter: The bonding would allow the lower-energy collisions and grazing/shallow-angle collisions to be sustained without knocking a crystal atom out of place, and knock-on collisions account for a significant proportion of DPA.
I'm more convinced by the former, but again, I'm not sure of the reality of this scenario.
Apologies for the long-winded response.
Best wishes,
Aimee
Hi Aimee,
The key statement of Francisco is, "In general, crystalline materials are much more compact than amorphous ones." You may want to confirm this generalization for your system. The key point is crystalline materials are usually denser. And for two materials with the same chemistry, this statement is true:
"Former: The ion penetration depth into a crystlline material would be lower on average, so the peak DPA would be closer to the surface."
Just a consequence of greater density (with same elemental composition).
One exception to the above is if small ions are incident on your material in a specific crystallographic direction that is relatively open. See RBS channeling, in which He+ ions normally incident on a (100) oriented Si singly crystal will penetrate much deeper than when the ions are incident in a random crystallographic direction.
Dear Aimee,
I just saw your reply. I'm sorry for the delay...
Some time ago we were studying the ionic implantation of N+ on various substrates (amorphous TiO2, rutile TiO2 and TiO2 anatase). Implantation occurred in all three materials, however, the depth of implantation and the amount of nitrogen implanted (at the same dose and under the same conditions) were different. The substrate that had the highest incorporation of nitrogen was the amorphous one, with levels that could be detected at greater depths than in the crystalline substrates. In the case of crystalline substrates, the one with the highest implantation was anatase, and nitrogen penetration also occurred at a greater depth in anatase than in rutile. We justify these observations as due to the structure of the material. Crystalline compounds are less "reactive" to be implanted because incorporation of ions requires much more energy to "break" structures and incorporate. The difference between rutile (less reactive to N+) and anatase (more implanted material) is justified by the degree of compaction of the crystalline structure.
I hope that these results that we obtained years ago will be of some use to you.
Best,
Fran
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