Kevin, thanks for the tips and for pointing me back to that old e-mail
(that I in fact started)!

I was thinking of the Bosch DRIE type chems for the plasma chamber method,
wikipedia says Octafluorocyclobutane

I'll give the vacuum dessicator protocol a try


On Mon, Nov 19, 2012 at 6:39 AM, Kevin Nichols  wrote:

> Nathan,
>
> Pasted below is the protocol for this in gas phase from an older email
> from this list about the topic. Note that you don't need a plasma
> cleaner as it look like your email implies, a cheap vacuum desiccator
> with a roughing pump will work fine to do this in gas phase.
>
> However, if you really want to use a liquid phase, FDTS is soluble in
> most alcohols. Dissolve the liquid FDTS in methanol, and you can get
> it to work (though I don't have a protocol for that handy). After
> contacting, rinse off the unbound FDTS with another shot of pure
> alcohol (whatever one you're using) and bake as below. Keep in mind
> that you should store anything with an exposed silane in nitrogen or
> argon when not in use.
>
> Also, note that the purpose of the FDTS is not bonding to the PDMS.
> PDMS will adhere (and bond under the right conditions) to an exposed
> oxide. The FTDS blocks the oxide with a long fluorocarbon chain (the
> silane bonds to the oxide, and the FC chain sticks up from the
> surface).
>
> - Kevin
>
> ---------- Forwarded message ----------
> From: Kevin Paul Nichols 
> Date: Sat, Mar 27, 2010 at 11:22 AM
> Subject: Re: [mems-talk] Best way to spin PDMS for making sheets?
> To: General MEMS discussion 
>
>
> Nathan,
>
> To get PDMS to come off, you don't need a very well controlled
> hydrophobic layer. Just use perfluorodecyltrichlorosilane (FDTS)
> applied in a vacuum desiccator, and then baked at ~110. You can find
> FDTS suppliers here: http://www.chemexper.com/
>
> 1) Place your Si wafers (with no PDMS on them, this is just so you end
> up with a long fluorinated molecule sticking up from the surface so
> the PDMS will peel off easily later) in a vacuum desiccator connected
> to house vacuum (do a google image search for vacuum desiccator to see
> what these look like). 2) Place 10-20 uL of FDTS in a small container
> (the top of an eppendorf tube works well) in the bottom of the chamber
> (location doesn't matter much). 3) Pull house vacuum, and leave them
> for ~2 hours (exact time will be more or less depending on the vacuum
> strength and container size). 4) Bake the wafers at 110 for ~2 hours.
>
> There are lots of methods out there to get higher contact angles, but
> that will be good enough.
>
> If you have a goniometer, measure the static contact angle and check
> that it's at least 90 with DI water. If you don't have a goniometer
> handy, just pipette (or somehow dispense) a few microliters of DI
> water on the surface, and make sure that it forms tight balls that
> roll around easily.
>
> Also, keep in mind that most people use PDMS precisely because you
> don't need to ablate, etch, or otherwise chemically attack it. You can
> just use "soft lithography" which uses a stamp to mold the PDMS as it
> cures. Si molds are common, but glass and metal (even CNC machined
> brass molds are good enough for some microfluidic applications). There
> are hundreds of papers out there describing it, if you're interested.
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--
-Nathan
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