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Colm Durkan's
Scanning probe microscopy and Nanoelectronics group


Scanning probe microscopy and nanoelectronics Group

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Nanoscience Centre  


Samsung LogoFunding awarded by SAMSUNG to develop next-generation memory cell  

  See our paper in PRL on the observation of a ferroelectric/ferroelastic vortex            PRL cover

Nanotechweb    See the article in Nanotechnology on nanotechweb on our paper on ferroelastic domain structures

   See our paper in ACS Nano on the decoupling of graphene layers in HOPG using the STM tip:

HOPG warps under the STM tip during scanning

    This can be done in a controlled way as shown below.  Here we have a region on a piece of graphite (HOPG) where there usual stacking of the graphene sheets has been disrupted, resulting in a slight rotational misorientation between the top few layers at the Basal plane.  This manifests itself as a superlattice , which is apparent on the right hand half of the images.  In the superlattice region, the average interlayer spacing is slightly larger than usual, resulting in a reduced electronic coupling.  In the image on the left, the typical atomic resolution image of HOPG is observed (displaying triangular symmetry, thus showing every second C-atom) everywhere.  In the image on the right, where we have brought the STM tip closer to the surface, we still observe the triangular lattice on the left half, but now obtain the true atomic lattice (honeycomb, hexagonal symmetry) on the right half.  Due to the reduced interlayer coupling on the right, the STM tip is able to lift the top layer there by a few tenths of a nanometre, enough to decouple it almost completely, so it appears like graphene.

           No decoupling: triangular lattice                              partial decoupling: trianglar lattice on left, honeycomb on right

Zoom-in on right-hand half of both images (image size ~ 0.8 nm x 0.8 nm):

  deouple              deouple
    Triangular lattice                      Hexagonal lattice
 We can also simulate these images using a simple model which we developed (see publications list):

deouple      deouple
   Triangular lattice                      Hexagonal lattice

Colm Durkan, University of Cambridge Engineering Department and Nanoscience centre, , 11 JJ Thomson Avenue, Cambridge, CB3 0FF, UK
Last updated July 2011.