I need to coat only one side of a substrate (Palladium) with a self assembled monolayer SAM (alkanethiol) solution. All the methods in literature coat both sides of the substrate with the SAM by dipping the substrate into the solution or by physical vapour deposition etc. I tried using a setup which sandwiches my substrate and has the capacity to expose only one side to the solution but the O-ring which is an integral part of the setup expanded when it came in contact with ethanol/Tetrahydrofuran solvent and left an imprint (mechanical deformation) on my thin Palladium substrate (25 micron). Can anyone suggest me a way to go about doing this without mechanically deforming my substrate?
Thank you.
You can just coat the surface by any gum or chemically inactive material with thiol to that side, you don't need to form SAM.
Dear Dr. Dey, thank you for your answer. To clarify, you are asking me to coat the side I don't want to form any SAM by a chemically inactive material such as gum ? Do you have a reference for this kind of an approach ? How does one remove the gum afterwards ? My sample is really thin 25 micron and I am wondering if this will work without leaving a mechanical deformation during the whole process.
I immediately though "Scotch tape", but then I saw how thin your sample was.
There are a few things you could try.
1. Putting your coating solution in a watch glass, and floating the Pd foil on top. The effectiveness of that would depend a lot on the surface tension and wettability, but it might work.
2. Depending on how SAM-free you need the other surface, you could take a flat surface, such as a glass slide, wet with with pure THF/ethanol and stick your Pd foil to that (make sure to flatten it, leaving as little solvent between the Pd and the glass). Then treat it. With any luck, you will not have liftoff from the glass, and any alkanethiol on the back side will be only diffuse a little bit past the edge, if at all.
3. Place your Pd onto a solid flat surface, and put the O-ring on top. Fill it with SAM solution like a kiddie pool. Even if the O-ring deforms, it shouldn't damage your sample. It could leak though.
So, a few thoughts here.
Coat both sides of the substrate by submersion in solution. Then remove the SAM on one side by exposure to strong UV light. I dont know how inert palladium is, UV exposure might form an oxide layer?
I wouldn't try something too difficult like forming a protective layer on one side or coating on both side and then removing one side, Simple is the best, like some of the previous suggestion why not physical block one side ? you can put an adhesive easy to remove type on one side and immerse it in your solution (if it is not containing ethanol you should be fine). another why is that there are electrochemical cells or flow cells that allow you the connect surfaces that only one side is exposed and then you add your solution so only one side will be covered by SAMs. last idea which is a little more tricky is cover both sides and then polish one side....
Thank you all for your kind comments/suggestions. I will try out all the suggested methods and get back to you on which worked the best. Thanks again !
One other possibility would be to coat both sides of the thin substrate, then remove SAM from one side with a plasma ext (Ar). By weighting down the edges of the sample on a slide, the plasma and UV from the plasma should not materilly affect the masked side's SAM.
If your SAM material is soluble in N-methyl pyrrolidone you can use a surface tension trick to coat only one side. Follow the second (2) procedure suggested by Mardilovich on a glass slide placed in the bottom of a Petri dish. Very carefully deposit the thiol dissolved in NMP onto the surface to be coated. Done right, the solution will form a domed layer held in place by surface tension. Cover the dish and let sit overnight. The NMP will not evaporate and the thiol will adsorb to the surface without leaking over the edge.
more detail: use a Pipetman type pipetter to deposit solution, squeezing it out slowly onto the center of the surface and allowing the solution to spread to the edges. Should probably practice with pure NMP to determine the optimal volume of solution that will form a droplet covering the surface and held in place by surface tension. Thiols take from a few hours, to overnight, to 36-48 hours to adsorb onto a metal surface and form a good SAM, depending on the structure of the linker. After allowing adsorption to take place, the foil can be lifted with a forceps and the coated surface, held at an angle, can washed in a stream of ethanol using a Pasteur pipet. The thiol should remain adsorbed.
Maybe you can use micro-contact printing method there you can even make microscopic pattern and so on plane surface.
Best regards
Christian
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