Nanomembrane transfer onto glass and SiN using vapor from tap and deionized water

Introduction: After meeting with Tucker, he showed me the experiment he conducted to induce membrane transfer to, supposedly, any kind of surface. The method he used was initially with breath, and then he passed on to deionized water vapor. The results were not satisfactory because of the wrinkles on the membrane and not much uniformity along its surface. My work was to modify his method so I could use a more controlled procedure and potentially get better results.

Objective: By using the basis of the previous method, perfect membrane transfer onto glass and SiN.

Methods: The nanomembrane transfer procedures were all done with the chip under pressure with a glass support, clamped to a metal structure. With that, most of them were exposed to vapor for transfer to occur and the vapor was created by heating water with a 1L becker in the microwave.

Experiment one

Sample: Three-slot chip with SiN membrane, 41nm.

For my first tries, I didn’t take any pictures of the results, but the conclusions that came from them were obvious in the way that either the transfer went correctly or it just did not occur.

A nitrogen jet was used for some trials as shown in the sketch. The becker was heated until the boiling point was reached and then put onto a heating plate to minimize heat loss. The water was initially at 80°C but fluctuated around 70°C and 80°C during the experiment.

Transfer Surface: Glass

Sketch:

Figure 1: First setup used for transfering membranes with vapor. — Figure 1: First setup used for transferring membranes with vapor.

Rotating the plate while applying one air spray, when it was in the position indicated above, there was transfer.
With the plate fixed to an oblique angle, after two air sprays there was transfer.
With the plate directly above the becker and with its plane perpendicular to the vapor flux there was transfer with no air spray.
With the plate fixed in a parallel position to the vapor flux (not above the becker), there was no transfer after one spray.
Using the chip from the previous trial, it was positioned directly above the vapor flux with the membrane’s major axis parallel to it. There was transfer.
The air spray was used directly on the plate, with no vapor and close to the chip, and it ruptured the membrane.
Same procedure as the fifth trial, but with membrane’s major axis perpendicular to the flux. There was transfer.
After every trial, I breathed on the membranes to see if wrinkles were formed, which they did, but all of them disappeared after the water droplets evaporated.

Results

The transfer presented a couple of cracks, but I assume it was from the removal of the chip.
Cleaner then the first trial, but with some defects on the sides.
One strip was uniform, but the other two presented a little crack in the middle.
No transfer.
It was a uniform transfer, with little defects on the tips
Membrane ruptured
Only more lateral imperfections than the fifth trial were noticed.

Conclusions for experiment 1

The different methods, for those that worked, presented little difference from each other, and compared to the results obtained by Tucker, no membrane had wrinkles. But what I concluded from the sprayed transfers is that vapor volume is not a contributing factor for a good transfer, although the whole area of the membrane must be exposed to vapor, little is actually needed. Also, the temperature of the vapor in the air current was lower, so it seems that high temperature is not a strong factor.

For the transfers without the air sprays, it seems that just by exposing the membrane to vapor in a large area will give out good results, but it was noticeable that the third and fifth trials were better than the others.

Experiment two

Sample: Three-slot chip with SiN membrane, 41nm.

The second experiment had the intention to evaluate how the transfer depends on the vapor flux.

A filter flask was used with water at 80°C to generate vapor and tubes were attached to it to conduct the vapor to a box with the chip plate. The box was sealed and connected to a vacuum tubing to force the vapor out of the flask. The vacuum line was opened for a few minutes.

Sketch:

Figure 2: Second setup used for transferring membranes with vapor.

Results

The first trial did not work due to bad sealing, but after the adjustments there was transfer. The resulting membrane had a few bubbles over it, and after breathing on it the formed wrinkles disappeared.

Conclusion for experiment 2

The vacuum was weak and there still was transfer, so it can be said that a strong flux is not needed and that heat is also not a necessity, since the vapor lost heat in the tubing and was cooled down even more by the acceleration from the vacuum.

Note: The chips I used for the following experiments were the ones that already had missing membranes. If one is missing, it’s because it was broken before I used it – unless stated otherwise.

Experiment three

Sample: Three-slot chip with SiN membrane, 41nm.

The first two experiments above served for me to learn how to manipulate the membranes, I was not entirely focused on the results.

For this set of experiments, several conditions were used, varying between angles, beckers and water. Each one is discussed in more detail separately with their respective photos taken with the microscope camera. The exposure of the membrane – under pressure using the plate – to vapor was done by positioning it directly above the beckers.

Transfer Surface: Glass

1. Erlenmeyer 125mL w/ deionized water.

Position of the chip plate: Normal of the plate’s plane parallel to the vapor flux.

2. Becker 1L w/ deionized water

Position of the chip plate: Normal of the plate’s plane parallel to the vapor flux.