2 research outputs found
The structure of suspended graphene sheets
The recent discovery of graphene has sparked significant interest, which has
so far been focused on the peculiar electronic structure of this material, in
which charge carriers mimic massless relativistic particle. However, the
structure of graphene - a single layer of carbon atoms densely packed in a
honeycomb crystal lattice - is also puzzling. On the one hand, graphene appears
to be a strictly two-dimensional (2D) material and exhibits such a high crystal
quality that electrons can travel submicron distances without scattering. On
the other hand, perfect 2D crystals cannot exist in the free state, according
to both theory and experiment. This is often reconciled by the fact that all
graphene structures studied so far were an integral part of larger 3D
structures, either supported by a bulk substrate or embedded in a 3D matrix.
Here we report individual graphene sheets freely suspended on a microfabricated
scaffold in vacuum or air. These membranes are only one atom thick and still
display a long-range crystalline order. However, our studies by transmission
electron microscopy (TEM) have revealed that suspended graphene sheets are not
perfectly flat but exhibit intrinsic microscopic roughening such that the
surface normal varies by several degrees and out-of-plane deformations reach 1
nm. The atomically-thin single-crystal membranes offer an ample scope for
fundamental research and new technologies whereas the observed corrugations in
the third dimension may shed light on subtle reasons behind the stability of 2D
crystals.Comment: 14 pages, includes supplementary informatio
Electronic structure and the minimum conductance of a graphene layer on SiO2 from density-functional methods.
The effect of the SiO substrate on a graphene film is investigated using
realistic but computationally convenient energy-optimized models of the
substrate supporting a layer of graphene. The electronic bands are calculated
using density-functional methods for several model substrates. This provides an
estimate of the substrate-charge effects on the behaviour of the bands near
, as well as a variation of the equilibrium distance of the graphene
sheet. A model of a wavy graphene layer is examined as a possible candidate for
understanding the nature of the minimally conducting states in graphene.Comment: 6 pages, 5 figure