Nanomoulding of Functional Materials, a Versatile Complementary Pattern Replication Method to Nanoimprinting

The overall aim of this procedure is to transfer a pattern from an arbitrary master structure to a functional material. This video illustrates the procedure using zinc oxide as a functional material pattern transfer is accomplished by first fabricating a negative mold from the master structure. The second step is to create the zinc oxide replica by first adding an antis stick layer onto the mold, followed by zinc oxide deposition, the zinc oxide is then anchored to the final glass substrate using a UV cured resin and finally released from its mold.

Ultimately, multiple functional replicas can be prepared from a single master mold using this technique While another printing serves traditionally to pattern a UV or thermally curable resin. Nano molding offers the potential to be generalized to many other functional materials, material stacks, and even complete devices, provided that the mold material is chosen compatible with the material deposition process. We first had the idea for this method when we tried to find a way to obtain a transparent conductive nano imprinted electrode as commercially available Nano printing resins are insulating.

We had to find another way and that's why we developed nano molding. Generally, individuals knew to this method with struggle because the anion properties should be adjusted carefully Begin by preparing a master carrying the nanoscale pattern to be transferred. Shown here a three prefabricated master structures.

On the left is a plastic foil with line grating made using interference lithography. In the middle is a textured aluminum plate made using anodic oxidation and subsequent etch off of the aluminum oxide layer. And on the right is a textured zinc oxide layer on glass grown by chemical vapor deposition.

The zinc oxide sample will be used in this demonstration in preparation for the anti aian layer. First coat the textured master with a spotter coat of chromium, five to 10 nanometers thick to promote the adhesion of the anti aian agent. Next, apply a small drop of anti aian agent onto a glass slide.

Transfer the glass slide together with the master into a vacuum chamber and pump down. A light vacuum is sufficient for the anti aian agent to evaporate and deposit onto the master. Then remove the master from the vacuum chamber and place in an oven at 80 degrees Celsius for one to two hours for the anti aian coating to Aneel.

The single most difficult aspect of this procedure is adjusting the anti aian layer properties to prevent spontaneous spilling while guaranteeing that control peeling remains possible. In order to achieve this, the properties of the anti edition layer are adjusted empirically. Next, prepare the mold by cleaning a polyethylene naft, alate or pen sheet in an ultrasonic acetone bath for two minutes, followed by an ultrasonic isopropanol bath.

For two more minutes, remove the sheet from the bath and rinse once more with fresh isopropanol before drying with nitrogen. Then place the pen sheet into the spotter coter and apply a five to 10 nanometer chromium aian layer on the pen sheet. Next, transfer the pen sheet into the spin coter and add one to two milliliters of mosa, a UV curable resin onto the pen sheet spin coat at 5, 000 RPM.

To get uniform coverage, pre-bake the freshly coated pen sheet on a hot plate at 80 degrees Celsius for five minutes. To evaporate the solvent, improve film uniformity and improve the resin addition to the pen sheet. Then place the pen sheet inside the nano imprinter with the UV curable resin pointing up and the master upside down on the holder arms.

Replace the cover of the nano imprinting setup and evacuate the vacuum chamber by turning on the pump. Pull back the holder arms to drop the master onto the UV curable resin. On the pen sheet, apply pressure onto the flexible silicone membrane that bisects the vacuum chamber by venting the upper compartment while maintaining the vacuum on the lower chamber.

This pushes the flexible membrane towards the bottom of the setup, providing the stamping pressure while maintaining the pressure on the membrane. Expose the UV curable resin through the pen sheet side to LED UV light for 15 to 20 minutes to provoke the cross-linking reaction. Next, vent the lower part of the vacuum chamber to release the pressure on the silicone membrane and remove the sample.

Carefully grip the mold and slowly peel it off the master structure. Then place the mold into an oven and bake it 150 degrees Celsius for three to five hours to improve thermal stability of the resin. Finally, after applying anion layer to the mold as previously shown, the sample is ready for zinc oxide deposition to begin chemical vapor deposition of zinc oxide.

First place the prepared pen mold onto a glass slide. Place the metal frame on top of the mold to avoid bending it during the chemical vapor deposition. Next, place the mold onto the hot plate of the chemical vapor deposition reactor held at 155 degrees Celsius while the mold is heating up.

Close the reactor pump down to below 10 to the minus three millibar and allow for thermalization. Then admit the precursor gases of water and ethal zinc along with a small amount of di boran diluted in argon for doping for 10 minutes. At a process pressure of 0.4 millibars creating a zinc oxide layer that is two microns thick.

Following deposition, remove the mold carefully to avoid excessive bending of the newly deposited layer, which may result in spontaneous peeling. To begin layer transfer, first prepare glass slides for spin coating by washing them with acetone followed by isopropanol. Then dry the slides with a stream of nitrogen.

Next spin coat, one to two milliliters of UV curable resin on the glass slide at 5, 000 RPM, anchor the mold carrying the deposited layers onto the final substrate using the nano imprinter as was previously shown during mold fabrication. However, in place of the master, the mold is set into the holder arms and lowered onto the resin coated glass substrate before being cured with UV light. Finally, complete the transfer by manually peeling the mold off the glass slide carrying the transferred zinc oxide layer.

Nano molding reproduces nanoscale features such as the pyramid texture of the zinc oxide layer shown here in the scanning electron microscope image on the left. The right image shows the nano molded replica atomic force microscopy or a FM is used to image the surface shown here in varying intensities of orange that represents surface height. This information is used to measure the height and angle differences between the mold shown in black and the replica in red.

For the zinc oxide layer, there was very little variation between the mold and replica demonstrating the high fidelity of the nano molding process. The individual lines of the grating produced by interference lithography shown on the left are also well produced in the replica shown on the right. The heightened angle histograms that correspond with this pattern also exhibit very similar shape.

However, there is a slight shift towards lower angles in the replica shown in red on the bottom right on the left are the unique features of a dimple array obtained by the antic oxidization of aluminum and the matching replica on the right. A slight smoothing of the features are found when using this pattern. This is exhibited by a slight shift towards lower angles for the replica in the angle histogram shown on the bottom right One's.

Master of anom molding can be done in a few hours if performed properly. So nano molding paved the way for researchers in the field of photovoltaics to explore new nano photonic structures in solar cells. Following these procedures, other functional materials can be patented, opening the door to wide range of application.

Don't forget that working with chemicals, gases, uv, radiation sources and vacuum equipment can be hazardous and precautions such as appropriate personal protective equipment should be worn at all times, and proper installation of the equipment should be verified before performing this procedure.