Dry exfoliation, or mechanical exfoliation, is a process by which a layered material like graphene is split into atomically thin sheets. The so-called “Scotch Tape method” was pioneered way back in 2004 at the University of Manchester, where researchers applied a strip of adhesive tape to graphite and then removed it, creating a single layer of the material. It’s a low-tech but effective method that’s still used today.
There are several different ways to get a single layer of graphene:
Micromechanical Cleavage separates layers of graphene from graphene, similar to the Scotch Tape method. The tape is carefully applied and then very carefully removed. The process is repeated until a single graphene layer remains.
Anodic Bonding produces graphene by pressing graphite onto a glass substrate, which is then jolted with electricity. Afterwards the glass is heated up, resulting in a few graphite layers stuck to the glass that can be removed.
Laser Ablation and Photoexfoliation use lasers to remove layers of material from a solid surface. So far, this method has only been used successfully in lab conditions or in a vacuum, so it’s still being perfected.
Dry Ball Milling shifts graphite layers by milling together a mixture of graphite and “chemically inert water-soluble inorganic salts”, producing graphene powder in the process.
Detonation is a particularly violent method for producing graphene that requires a powerful shockwave and thermal energy, such as the name suggests. As you’d expect, the method has not successfully yielded pristine graphene, although the process itself is more efficient than some other methods.