I am going to study a hydrogen distribution in complex materials. I should firstly prepare samples: to cut, to polish, and to fix small pieces in “resin” o “epoxy”. The principal limitation is: this "resin" should not contain hydrogen! Another limitation is: the embedding materials would be used under UHV conditions.
Let me understand why you need to embed your material. Is not indispensible for ToF SIMS this kind of preparation.... A simpler deposit on a metallic substrate i.e. gold or indium (depending if you start from a solution of from a powder) is not feasible?
Hello Matteo,
I am going to measure hydrogem distribution in minerals. A polished "slice" of a mineral is embedded into epoxy to make EDX or SIMS measurement. This is a typical manner.
But any epoxy has a lot of hydrogen and I cannot be sure about hydrogen especially at the interface: epoxy-sample. This is my problem.
One more thing: I cannot heat the analyzed sample, so I cannot use Sn based alloy to fix it. The maximum temperature I can suppose is less than 80oC
I'm not an expert of these samples and this kind of sample preparation but I've found this paper ("Hydrogen concentration analyses using SIMS and FTIR: Comparison and calibration for nominally anhydrous minerals" Geochemistry Geophysics Geosystems Volume 4, Number 2 20 February 2003 1019; doi:10.1029/2002GC000378).
They say " .....(Sample preparation) is achieved by attaching the samples to aluminum disks with a small amount of superglue, or pressing the samples into holes filled with indium metal. Epoxy is to be avoided at all costs, as numerous measurements of the hydrogen detection limit suggest that epoxy forms a hydrogen-bearing gaseous boundary layer at the surface of a degassing sample, which contributes to the hydrogen background although it may not degrade the overall vacuum pressure."
So I gues you could try to cut your mineral and put/press mechanically on top of a metallic substrate (Al or In).
Thanks Matteo,
I use In in my practice for small samples mounting, but this is another case: my samples are relatively big and I have no enough In to use this technique for a tens samples I need to measure. And I cannot press my samples in Al: they are quite brittle.
There are plenty of low-temp metal alloys, though varieties containing Cadmium must be avoided as it would sublimate in vacuum.
Could like Roto136F/58C (Bismuth, Tin, Led, Indium) be suitable?
https://rotometals.com/low-melt-fusible-alloys/
I avoided any Epoxi resin when I did imaging of hydrides in Zirconium.
For ToF-SIMS measurements, pressing metal at the same level than the polished surface is an option...but I would decrease the extractor voltage (500V) and adjust the reflectron parameters, because a small step/edge will have an effect on the transmission of your secondary ions (inhomogeneous electric field lines can lead to shadows in your SI image function of the analysis area). Something to care for.
When you characterize samples with sharp edges, the extraction voltage can be a problem.
Further, For hydrogen measurements, a lower extraction voltage and a bias at the extraction (during sputtering time in interlaced or non interlaced) could lower the "memory effect". It's worth giving it a try.
It was an old question but the tips are still valid.
Nicolas,
Thanks a lot.
I'll play with bias and extraction potential. The problem is I analyse hydrogen in glasses, so there are two ion beams and electron beam co-located, and still I need play with TOF voltages to compensate surface charge...
I really liked these papers by Joanna Lee about the extraction:
https://www.researchgate.net/publication/230421979_Topography_and_field_effects_in_secondary_ion_mass_spectrometry_Part_II_Insulating_samples
https://www.researchgate.net/publication/51667639_Topography_and_Field_Effects_in_Secondary_Ion_Mass_Spectrometry_-_Part_I_Conducting_Samples
Article Topography and field effects in secondary ion mass spectrome...
Article Topography and Field Effects in Secondary Ion Mass Spectrome...
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