The overall goal of this procedure is to obtain freestanding nano membranes of conjugated microporous polymers. This method can help to answer key questions in the field of conjugated microporous polymers, such as how to prepare thin films and freestanding membranes of usually insoluble materials. The main advantage of this technique is that it allows the production and the transfer of uniform membranes with ultra low and homogeneous thickness by performing a step by synthesis on al substrate.
Though this method can be applied for membrane separation, it can also be useful for other applications such as organic electronics or heterogeneous catalysis. Demonstrating the procedure will be yonic to line a technician from our lab. Prepare the apparatus for CMP fabrication.
Use a 500 milliliter one neck round bottom flask and add 300 milliliters of tetra nitrofuran or THF. Put a prepared substrate coated with alpine terminated, self-assembled monolayer or SAM in the sample compartment, use a sample holder so that the substrate is standing upright. Connect the apparatus to the schleck line via the junction on top of the reflux cooler.
Evacuate and ventilate the apparatus with inert gas three times. Then let THF out from the sample compartment over the outlet at the bottom of the sample compartment and close the outlet. Next, add one milliliter of a prepared TPM azi solution and 0.5 milliliters of a copper catalyst solution to the sample compartment via the screw cap with septum.
Use a syringe with a hollow needle to transfer the solutions sequentially from the flank flask to the reaction apparatus. After waiting approximately 30 minutes, let out the reaction solution over the outlet at the bottom of the sample compartment. Close the outlet and collect the condensed THF for rinsing the sample.
Wait approximately 30 minutes more, then let out the rinsing solution over the outlet at the bottom of the sample compartment and close the outlet. Give one milliliter of the prepared TPM Aine solution and 0.5 milliliters of the copper catalyst solution to the sample compartment via the screw cap with septum. Transfer the solution sequentially from thenk to the reaction apparatus using a syringe with a hollow needle.
After waiting approximately 30 minutes, let out the reaction solution over the outlet at the bottom of the sample compartment. Close the outlet and collect the condensed THF for rinsing the sample. After waiting for an additional 30 minutes, repeat the sequential addition until the desired amount of layers is reached, one layer is approximately one nanometer thick.
As a final step, take out the CMP coated mica substrate. Rinse it with THF and ethanol, and then dry it under a nitrogen stream. Set a spin coder to a ramp time of 10 seconds from zero to 4, 000 RPMA holding time of 40 seconds, and a ramp time of 10 seconds from 4, 000 to zero RPM.
Place the CMP coated MICA substrate on the spin coder and put A-P-M-M-A solution on the wafer until it is completely covered. Start the spin coder, cut off one millimeter from each edge of the coated mica substrate using a scissor to cut the edges. Then fill a 150 milliliter crystallizing dish with an iodine potassium iodide solution and fill a 100 milliliter crystallizing dish with a potassium iodide solution.
Put the PMMA coated CMP gold on the mica substrate with mica in contact with the solution on top of the iodine potassium iodide solution. Be careful that it does not sink. Wait at least five minutes, then transfer the PMMA coated CMP gold MICA substrate from the iodine potassium iodide solution to the top of the potassium iodide solution with MICA in contact with the solution.
Once again, be careful that it does not sink and wait at least five minutes. Next, fill a 250 milliliter crystallizing dish with distilled water. Strip off the P-M-M-A-C-M-P gold film from the MICA by slightly immersing the substrate beginning from one edge in distilled water.
Hold the substrate so that the MICA is pointing to the water dip coat the P-M-M-A-C-M-P gold on the silicon wafer by approaching the swimming P-M-M-A-C-M-P gold membrane. Slowly with the wafer until it touches the edge of the membrane, pull out the silicon wafer slowly. Once the silicon wafer is in contact with the P-M-M-A-C-M-P gold membrane, then strip the P-M-M-A-C-M-P gold film off of the silicon wafer by slightly immersing the substrate, beginning from one edge in the iodine potassium iodide solution, and waiting 15 minutes after the gold is completely etched.
Transfer the P-M-M-A-C-M-P membrane to water via the silicon wafer and wait an additional 15 minutes. Repeat this step three times to wash the membrane with water. Then transfer the washed P-M-M-A-C-M-P membrane to a gold coated silicon wafer.
As before, let the P-M-M-A-C-M-P substrate dry and air for at least two hours. To dissolve the PMMA. Put the P-M-M-A-C-M-P substrate in acetone and wait 30 minutes.
Take out the substrate and rinse it with acetone. After repeating this step three times, let the CMP substrate dry for at least two hours. The membranes are characterized by infrared reflection, absorption spectroscopy or ir.
RAS shown here is an IRRA spectrum from a CMP membrane transferred to a gold wafer. Typical bands from the vibrations of the aromatic backbone are at 1, 605 1, 515 and 1, 412 inverse centimeters. In case of residual unreactive, azide, or alkin groups characteristic bands at 2, 125 and 1, 227 inverse centimeters can be observed.
Shown here is a scanning electron microscopy image. The freestanding membrane is clearly visible Once mastered, this transfer technique can be done in less than one hour if it is performed properly. While attempting this procedure, it's important to remember to cut the edges of the micro substrate after spin coating Following this procedure.
Other methods like synthetic modification or photo patterning can be formed to optimize the purpose chemistry of the nan membrane for the desired applications After its development. This technique can help researchers in the field of congregated micro pros polymers to transfer the promising bulk properties into real devices.
