We are using a Silicon crystal for our ATR-FTIR measurements. For cleaning the crystal we use isopropanol and medical wipes. The cleaning is not very satisfactory, if I wipe the crystal gently there is often some sample left on the crystal. If I wipe more intensely pieces of the medical wipe get detached and contaminate the sample. Are there any suggestions how to clean the crystal efficiently without contaminating the sample?
For clarification: the crystal is placed onto the sample from above
I have experience in cleaning Si wafers in Semiconductor processing - used this in my Grad School days. Never touch the Si crystal with wipes or bare/gloved hands - always handle with a tweezer. Hope the same applies to your "crystal". Rinse Si crystal in a mix of H2SO4(7parts)+H2O2(3parts) for 10 min and rinse thoroughly with DI water. This will remove any organic contamination on the crystal. Then blow dry the crystal with pressured clean dry air or N2. This may not be necessary for you - but If you wnat to remove any native oxide that is grown on the Si crystal - dip it in Water (10parts)+HF(1part) for 10sec and rinse with DI water and blow dry with N2 or CDA - this may remove about 50A of native SiO2 that grows on Si in ambient which is a self-limiting process. I think the key for you NEVER touch it with a wipe - ALWAYS blow dry. Hope this helps.
In our lab we used to clean with ethanol (99%), before and after measuring the samples...
I hope it will help u .....
Rajan Beera Thanks for your immediate answer, it's very much appreciated.
The ATR crystal at our FTIR microscope is attached to a stamp that presses down onto the sample. I'm not sure how the Si crystal is attached to the stamp but I suspect that there might be some glue or similar involved. I don't dare to use such a harsh mixture like H2SO4/H2O2. I'm actually looking for a combination of mechanical/mild chemical cleaning. For the mechanical cleaning it would be good to have some type of brush or similar.
Naveen Kumar Reddy Bogireddy Thank you for your answer!
Do you use any tissue to apply the EtOH?
If you use IPA or Ethanol and that is serving your "cleanliness" requirements - here is what I suggest - stay with IPA, use a very soft electric toothbrush for gentle , which doesn't shed any particulates and use blow dry. I suspect your contamination issues are coming from using wipes - blow dry should take care of it. Good luck.
@Evelyne Hamacher-Barth, yes we use soft tissue paper to clean...
For diamond or germanium crystal:
Hold folded piece of optical quality lens paper (lint free) wetted with 'spectrophotometric grade' or spectra quality methanol or ethanol with tweezers, never fingers. The oils from your fingers show up in FTIR spectra if there is contamination. The trace containants in your solvent can also.
Swipe gently with the surface (not the edge) of the paper. Don't soak, or the crystal might come loose. Don't press hard, it's easy to scratch and damage ATR cystals. The tension from the fold in the paper is often enough. Don't rewipe with the part of the paper that is soiled from wiping. Don't use kimwipes. Don't use plastic squirt bottle ethanol. Don't use fingers. Don't wipe optics with dry paper.
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