Breathing delaminates nanomembrane tents
I have been having problems getting smoothed sheets of nanomembrane on my little oxide structures. I tried a number of different ways to delaminate the membrane, using tweezers to poke the membrane especially, but had little success getting smoothed sheets.
I tried compressing the two chips together using the burst pressure clamp, then poking it with tweezers. No success.
Then I accidentally breathed on the nanomembrane. And it came down beautifully.
I then wondered if it was the pressure from my breath or if it was the water vapor. I ran the assembly one more time, this time, blowing nitrogen at 15-20 psi on top of the punctured membrane. The nitrogen flow didn’t work, so I concluded it must be the water vapor.
In the video above, a porous nanomembrane is tented over some oxide posts, in a large sheet. Interesting wetting behaviour begins at about 1:20, where I breathed on the membrane again, and the membrane appears to “shrink wrap” to the posts. Once the membrane is down, it does not come up again. So these posts are obviously too far apart. It appears we need to reduce the pitch by half to get them truly tented.
This next video shows my repeated breathing and evaporation of some tented nanomembrane posts. Hopefully I will be able to apply an analysis that Kevin showed me to these events. More on this later.
Edit 5/28/15
There has been a lot of discussion about the wetting change in the end of the last video. Screenshot as below, showing rainbow wetting over the NPN tented material, but water balling up on the surface of the silicon nitride substrate. We believe this is due to the nanostructured surface of the NPN, as the chemistry of the two surfaces are identical.
The process seems very repeatable if you breathe on the nanomembrane, but there is no guarantee it won’t wet all the area under the tent and “shrink wrap” to your structures when dried out. There must be a happy optimum that I will find, either by controlling the device geometry (those rings are on the order of 1-2 um, with an oxide height of 200 nm) or water vapor concentration (likely reducing the chance for any particular nanocavity or tented structure to fill compared to the bulk areas).
But why?!? Are the membranes being pulled onto the target surface because vapor condenses between them, pulls them together via capillary forces, and then evaporates? Perhaps condensation is only occurring on the surface of the NPN and the evaporation forces cause it to collapse against the target?
It is now clear to me that the bulk of the color changes we see are from condensation onto and evaporation from the surface of the NPN. This makes me ask a bit more skeptically if we really know we are getting water between the tent and the target.
We need to come up with a “breath in a can” device. Coffee cup sleeve heater around a spritzer nozzle?
It’s very difficult to establish at which height above or below the membrane the water is at. We have some mild evidence that water can get through the nanomembrane tent from our earlier fluorescence experiments, as well as the videos of the holes ‘wetting’ and then evaporating. This is definitely still an outstanding question. However, I think we can redo the fluorescent experiments now that I can put down the tent effectively.
I think instead of a spritzer, I could throw the enclosed burst pressure setup with punctured nanomembrane into the freezer to see if it delaminates effectively. I am leaning toward the same ‘unzipping’ phenomena we have observed due to water gluing down the surface somehow. A little air vibration (or wind) should then be enough to tear the remnant, and then that piece gets glued and so on. It would explain the relatively flat membranes, with an occasional wrinkle that holds water. What if the those wrinkles are a result of too much water being put down, preventing the surfaces from coming into contact?