Speed bumps less important than potholes for graphene. Comparison of an STM topographic image of a section of graphene sheet (top left) with spectroscopy images of electron interference at three different energies shows strong interference patterns generated by atomic scale defects in the graphene crystal (red arrows) but only modest disturbances caused by larger scale bumps in the sheet (blue arrows.) Analysis of the ripples shows that the electron energy in graphene is inversely proportional to its wavelength, just like light waves. The area imaged is approximately 40 nanometers square. Graphene is an allotrope of carbon in the form of a two-dimensional, atomic-scale, hexagonal lattice in which one atom forms each vertex. It is the basic structural element of other allotropes, including graphite, charcoal, carbon nanotubes and fullerenes. Graphene is about 100 times stronger than steel by weight, conducts heat and electricity with great efficiency and is nearly transparent.