I have optical glass substrates (LaSFN9) that have a 2nm Ti contact layer and 50nm Au layer, those need to be cleaned. The gold comes easily off with a solution of I2 and KI in water. The Ti is more persistent. Procedures such as aqua regia, hot conc. HCl, HF or oxalic acid would etch the expensive substrate. Are there less aggressive ways to dissolve titanium?
I would suggest selective etching of the Ti layer over a SCHOTT 'LASFN9' glass substrate by using conc. hot aq. sol. of KOH or NaOH (KOH being stronger), with relatively smaller contributions of added H2O2 (~30 wt%) and NH4OH aq. (≤ 35 wt% NH3). Strong acid etchants seem indeed not advisable, considering the approximate composition of the substrate glass, as taken from the following link:
http://www.schott.com/d/advanced_optics/2791b111-1bdd-4f94-b098-b9c5258c2164/LASFN9_SDS_EN_V5_201505.pdf?tenant=ao-cert
Thanks a lot for your suggestions. We have tried it but it does not completely remove the Ti. Eventually, we didn't couldn't find a way to quantitatively remove the Ti, so we moved on and use Chromium as a contact layer. It is much easier to remove than Ti.
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