Three-dimensional surface topography of graphene by divergent beam electron diffraction

摘要

There is only a handful of scanning techniques that can provide surfacetopography at nanometre resolution. At the same time, there are no methods thatare capable of non-invasive imaging of the three-dimensional surface topographyof a thin free-standing crystalline material. Here we propose a new technique -the divergent beam electron diffraction (DBED) and show that it can directlyimage the inhomogeneity in the atomic positions in a crystal. Suchinhomogeneities are directly transformed into the intensity contrast in thefirst order diffraction spots of DBED patterns and the intensity contrastlinearly depends on the wavelength of the employed probing electrons.Three-dimensional displacement of atoms as small as 1 angstrom can be detectedwhen imaged with low-energy electrons (50 - 250 eV). The main advantage of DBEDis that it allows visualisation of the three-dimensional surface topography andstrain distribution at the nanometre scale in non-scanning mode, from a singleshot diffraction experiment.