Embedded Files
Logic
Logic
The final design utilizes an Arduino to control all other components. The code is organized into stages.
Etching: starts after the user pours in ammonium persulfate and lasts for a parametrically-set amount of time.
Draining: triggers the solenoid to open and drain for 3 minutes and then close
Filling: the pumps are powered until the water level reaches the level switch
Cleaning: the graphene floats in deionized water for 5 minutes while conductivity is monitored
Drying: The system is essentially turned off
After each clean, the stage is reset back to draining. If the conductivity at the end of a cleaning cycle is below the set threshold of 50 μS/cm, steps 3 and 4 are skipped and the sample is left to dry.
The Arduino connects with USB to an already existing desktop computer in the lab. The user interfaces with the graphene transfer device by using a serial terminal, like PuTTY. The Arduino constantly provides current conductivity data, tagged with the current stage. By logging all serial output, the data of each transfer process is saved for further analysis by the lab.
Basket
Basket
Consistent final rotation of graphene
The basket went through the most iterations of any component in the project. The geometry and materials were constantly tweaked to ensure proper graphene alignment. Resin printing became the first choice of manufacturing method due to its high resolution. A test was conducted leaving the resin basket in a bath of persulfate for over a week. The plastic showed no signs of deteriorating.
Early geometries utilized holes in the walls to allow liquid in and out during the draining and filling processes. However, the graphene appeared to get stuck in the ridges on the edge of the resin print, preventing them from settling onto the basket.
It was also noted that graphene, when put into large baskets, appeared to center itself but consistently settled into an orientation 45° rotated from the substrate. It is hypothesized this is because surface tension increases the water level in the corners of the basket. These raised corners rotate the graphene so it rests at a level of lower potential energy. Alternate baskets were printed where the basket is rotated with respect to the substrate slot, with the goal of straightening the graphene.
Conductivity Probe
Conductivity Probe
An initial concept of the project involved using the conductivity probe to detect the end of the etching process. Theoretically, the conductivity should change throughout the etching process and when copper ions stop dissolving into the solution, the value steadies out. However, as shown in the graph, the conductivity reached a steady-state value at a time irrelevant to when the copper actually finished dissolving. Time-based etching was sufficient for the final product.
Important considerations for choosing the probe included:
Range: Etching and cleansing processes occur at extremes of the conductivity threshold, from 5 to 70,000 μS/cm
Interface: Output data in a way that can be read by the Arduino
Results
Results
Professor Mena states that, by visual criteria, the automated transfer matches the quality of the transfers performed by his best-trained lab students, with no creases, folds, tears, cracks, bends, or ripples.
Out of 6 transfers performed by the group, 100% of the stacks which were cut symmetrically successfully transferred to the substrate.
A lab student was able to test a sample produced by the device and reported that the graphene adhered to the substrate successfully. They were looking for linearity in the line on the graph shown to the right.
Current vs voltage test of graphene
Miscellaneous
Miscellaneous
All waste fluid is conveniently routed through PVC piping into a chemical waste container under the desk. Lab students will need to periodically dispose of waste fluid appropriately.
Towards the end of the project, the Professor requested a new feature which would stop the drain before it fully emptied, and refill to a different level. Implementing the feature was simple, despite it requiring two more level switches, showing the effectiveness of the modular design chosen for this device. All mounts can be resized or repositioned as necessary for new requirements that may arise after the term of 156B.
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