I performed some SIMS analyzes of 52Cr and 55Mn in c-Si (in profile mode). The sent findings showed zero concentrations.
Please, is it possible to get by SIMS a zero signal "zero counts per second" far below the detection limit of Cr and Mn?
Thank you in advance!
What concentrations were you expecting to observe? Are you seeing other constituents you would expect to see?
Thank you Boris . In fact, I expected concentrations equal or higher than detection limit (e. g. 1E14 - 1E15 cm-3). for exemple the analysis of phosphorus in boron-doped silicon matrix, gives a concentration around 1E17 cm-3 along the depth. this former concentration is the SIMS detection limit of phosphorus in silicon.
Dear Nabil,
I do not know how you introduced your dopants in silicon. However, It is so that the heavy metals diffuse fast in silicon such that their concentration in probed layer nearer to the surface may be below the detection limit. They normally have low maximum solid solubility . They tend also to cluster on crystallographic defects One has to take this fact into consideration when one doping silicon.
Best wishes
- Thanks Dr. Zekry. Yes exactly, in many cases the metals concentrations are below the detection limit of SIMS. And here my question; if the concentration of a given metal is below its detection limit, SIMS gives ''no signal'' or provides a constant profile around the detection limit value ?
" SIMS gives ''no signal'' or provides a constant profile around the detection limit value ? "
It depends, if detection limit comes from ionisation yield (zero signal) or background signal (constant profile). Backgrounds for metal signals come mostly from mass interference (overlapping).
Dear Rafal,
Thank you for your answer. for a better description of the problem, please you can analyze the SIMS profils illustrited in the attached Origin file. Profil of Cr(52) in red and that of Mn (55) in green showed zero concentration (results provided the engineer). In my mind, the species concentration cann't decrease to exceed the detection limit. SIMS says always "not detectable species" and never says "species not existe"... is it right ?
Best regards,
Nabil
Dear Nabil,
Yes You are right. SIMS can not say "species not exists" because then You would have to have detection limit 1 at/cm3 and it is impossible. When You have 0 c/s it is better treat it as 1 or 0,1 c/s (in log scale), and then You recalculate it to concentration e.g. 1e15 for Cr or 1e16 for Mn, then it is Your detection limit. Does mean that for Your current measurement conditions You can not ionise more then 1 atom/s of some element, but it corresponds to some concentration. I am not sure if it is clear so in case of any question please write more questions.
Regards
Rafal
Thank you Rafal for your valuable explanation.
Well, let me take this opportunity to ask you another question slightly different ; please, what is the best method (technical) to increase the resolution and , so, to separate the species having close mass ? i.e. separate 56Fe signal and that of 28Si-28Si in the silicon matrix.
Thank you in advance and best regards, - Nabil
Hello Nabil,
It is easy. Just take 54Fe signal for measurement.
Regards
Rafal
Thanks Rafal, Yes of course but my question was what is (briefly) the technical solution(s) to separate (56)Si2 and (56)Fe signals and avoid the interference between them ?
Best regards, -Nabil
Technically it is of course possible, but it depends which device You are equipped.
28Si-28Si has mass 55.95385
56Fe has mass 55.93494
so You need device with mass resolution R = M/deltaM = 56 / 0.02 = 2800 at least.
Technically it is done by:
- narrowing some slits (magnetic sector SIMS).
- decreasing of time of primary beam pulse (TOF SIMS).
Regards
Rafal
Very interesting. Thank you for your contribution and for all these explanations. Let's keep in touch!
Kindly, - Nabil
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