Graphene is a honeycomb like planar thin film formed by sp2 hybridization of carbon atoms. It is a quasi two-dimensional material with only one atomic layer thickness, hence also known as single atomic layer graphite. Its thickness is approximately 0.335nm, and there are different undulations depending on the preparation method. It usually has a height of about 1nm in the vertical direction and a width of about 10nm to 25nm in the horizontal direction. It is the basic structural unit of all carbon crystals (zero dimensional fullerene, one-dimensional carbon nanotube, three-dimensional oriented graphite) except for diamond.