Discoloration – autoclave
My previous discoloration post showed that chips in the Sepcon format discolored much slower than flat chips. A flat chip in the same well as a Sepcon chip seemed to accelerate discoloration. One thing about the Sepcon format that I hadn’t thought of earlier was that pnc-Si in Sepcons is autoclaved for sterility. So I autoclaved a chip and compared discoloration to a chip from the same wafer that hadn’t been autoclaved. (I used 0.5M NaCl and the oven to speed up discoloration – I know it’s not relevant to cell culture).
So, autoclaving appears to markedly delay discoloration. I think our autoclave works at 121C (at most it’s 134C), so this is surprising. Is this relatively low temperature high enough to slightly densify a native oxide layer?
The samples I am using in Sepcon format are not autoclaved, but aren’t discolored yet where as samples from the same wafer (and not in Sepcon) but in a different well did discolor.
i’ve seen the same thing
Yes. Boiling in water is known to produce a chemical oxide that is more stable than native oxide formed in air. If your autoclave runs at high temp, high pressure, and high humidity, I would not be surprised that the passivation is better. The effect is chemical, not physical densification.