  Usually, graphene is used in its horizontal directions to design novel
concept devices. Here, we report a single electron tunneling diode based on
quantum tunneling through a vertical graphene two-barrier junction. The
junction is formed by positioning a scanning tunnelling microscopy (STM) tip
above a graphene nanoribbon that was deposited on a graphite surface. Because
of the asymmetry of the two-barrier junction, the electrons can unidirectional
transfer from the tip to the graphene nanoribbon but not from the graphene to
the tip. This result opens intriguing opportunities for designing new type of
graphene transistors in its vertical direction.
