Light Microscope

Once the separated graphite has been applied to the silicon chip, the chip is observed under a light microscope. The vast majority of the things seen on the chip were either remnants of the tape, air pollution, or graphite many layers thick. Because they are so thin, they are nearly indistinguishable from the background: we found only 2 monolayer, both of which were both found only because they were right next to a poly-layer sample of graphite which caused us to zoom in. An ideal sample would be large (8x10 mm), but these samples were too small and so close to other graphite residues that detailed and time intensive etching would be required to isolate the monolayer samples. Once we had learned the process, we used a sample of bilayer graphene found previously by a graduate student for the next step.

To the left can be seen one of the monolayer graphene samples we found, in the shape of a trapezoid, is shown surrounded by blue arrows. This image was taken through the 100x view on a light microscope. The ratio of the sample to background RBG value for the pixels was used to determine the atomic thickness: if the difference was less than 5%, it was monolayer, if it was between 5% and 10%, it was bilayer, and greater than 10% meant more than 2 layers.

Encapsulation with Boron-Nitride

To protect the quality of the graphene from air contaminants, the sample was encased on either side by a few nanometers of Boron-Nitride, an inert material. The result was a BN-graphene-BN array, which was mounted on the Silicon wafer and etched to create a 1-D exposure, which was used to create the contact with the gold wires made by electron beam lithography. The etching and electron beam lithography were performed by graduate students since Clean Room training was outside of the project's budget.