# Methanol vs Ethanol Substrate cleaning

We have to clean substrates, often made of STO or MgO, before PLD for thin film growth. Previously we would use ethanol for sonication to clean the substrates. We recently ran out of ethanol but have a lot a methanol. In looking on the web I have only found conflicting viewpoints on which to use, or how corrosive methanol is. Are the two interchangeable for cleaning substrates? From where do you know?

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• What is STO (strontium titanate?) and PLD? What kind of films are you growing on the substrates? – airhuff Jun 8 '17 at 19:29
• Yes strontium titantate. Pulsed Laser Deposition to grow doped STO or ScF3. – bryan dunn Jun 8 '17 at 19:39

Both $\ce{SrTiO3}$ and $\ce{MgO}$ can safely be washed with methanol. These compounds are insoluble in most any solvent other than certain acids. I suspect that any online reference you've found saying methanol is corrosive is with respect to organic compounds, nothing like the composition of your substrates.

One (somewhat handwaving) way to convince yourself that this is the case is that we know the compounds are insoluble in water (see their Wikipedia and PubChem pages) and ethanol (from your experience, also confirmed for $\ce{MgO}$ in it's Wikipedia and PubChem pages). In terms of solvent polarity, methanol lies between water and ethanol. It would be extremely unlikely for an ionic solid to be completely insoluble in water and ethanol yet have some significant solubility in methanol.

Although we can be confident that the substrate materials will not be destroyed by methanol, only trial will let you know how effective it is for cleaning whatever contamination may be present in your situation. Methanol is fairly, though not completely, similar to ethanol in it's solvent properties, and there is a good chance that it will be as effective as ethanol. Again though, only trial will verify this in your situation.

• Generally in semiconductor and thin film work, the preferred final rinse before drying is methanol, not ethanol (although much has to do with how much easier it is in the US to have reagent grade methanol in the lab vs ethanol). – Jon Custer Jun 9 '17 at 0:44
• Upvoted. Seems to be no theoretical reason for it not to work, just test it and see. The only drawback is while ethanol can be safely added to a coffee cup to make the laboratory day go a bit faster and smoother, methanol must not. ;-) – Stian Yttervik Jun 9 '17 at 7:37