Mechanical Exfoliation to Make Graphene and Visualization Instructor Preparation and Discussion Authors: Angela Jones, Ph.D. 1, 2 and Nathaniel Safron 2, 3 1 Institute for Chemical Education, 2 Nanoscale Science and Engineering Center, 3 Department of Materials Science and Engineering University of Wisconsin – Madison Age: This activity is most appropriate for a high school science class rather than a take home project. Background: In 2004, Andre Geim and Konstantin Novoselov of University of Manchester, UK won a Nobel Prize in Physics for isolating 1-carbon atom thick graphene sheets. To separate the graphene sheets from graphite flakes they used Scotch Tape. To visualize the graphene, they stuck the tape on a silicon wafer and examined the wafer under an optical microscope. Thin films of graphene are transparent to the naked eye which is why it is believed they will play an important role in the next generation of extremely thin electronics. However, when stuck to the wafer, the added graphene layers interfere with the light causing a shift in colors that allow you to distinguish wafer from graphene, and few-layer graphene from multi-layer graphene. In this activity students use natural graphite to duplicate the mechanical exfoliation technique used to separate graphene sheets from graphite. Ideally this would coincide with a trip to an electron microscope facility. Instructor Notes: Preparation for the experiment will take approximately 30 minutes of instructor time. You’ll want to prepare the graphite flakes adhered to the tape and cleave the silicon wafer into ~1 cm 2 pieces, once piece for each student. Handle the wafers using wafer tweezers as fingerprints will be clearly visible on the wafer when examined using the microscope. Instruct your students to not touch the wafer surface as well. That being said, examining fingerprints on wafers using an electron microscope is pretty interesting! Safety: Graphite flakes are small and could easily form dust when first adhering to the Scotch Tape. It is best if you provide the students with graphite flakes already on the tape prepared in advance. This will also reduce the waste that could result from spilling the graphite flakes. Supplies • Scotch tape • Natural graphite flakes (Sigma Aldrich, 332461-2.5KG) • SiO 2 /Si wafers , 90 nm oxide thickness, N type/Antimony dopant, <100> orientation, SSP finish (Addison Engineering, (408) 956-5127) • Diamond scribe • Wafer tweezers • Ziploc bags • Access to an SEM and/or an optical microscope with at least 100X objective. Preparing graphite flake and tape: 1. Gently tap your bottle of graphite flakes on the end quarter of a 2 inch piece of Scotch tape. You’ll want approximately 10-15 flakes for each sample. 2. Take another piece of tape, and stick it on top of the graphite flakes, perpendicular to the initial piece of tape. The sticky-sides of both pieces of tape are now together at a 90 degree angle. It might be best to fold over the remaining exposed tape to prevent the samples from adhering to each other and to provide a nice tab for the students to hold.