Animation of graphite surface erosion

K. Nordlund

Accelerator Laboratory, University of Helsinki, P.O. BOX 43, FIN-00014 Helsinki, Finland

It is well known from scanning tunneling microscopy (STM) experiments that low-dose ion irradiation of (1000) graphite results in the production of isolated defects on the graphite surface [1]. These defects typically appear as small hillocks comprising of a few tens of atoms in the STM measurements. We have studied the formation mechanisms of such hillocks using molecular dynamics simulations of collision cascades [2,3]. Postscript preprints of our papers are available here

Based on molecular dynamics and ab initio calculations, we have identified several defect structures which correspond to the experimentally seen defects. On this WWW page, we demonstrate the formation of the perhaps most interesting defect, in which an extra atom has entered the graphite surface layer, forming a double 7-atom ringstructure, where the top three atoms form an almost equilateral triangel. The figures below and this MPEG animation (7.2 Mb) demonstrate how it can be formed by a 50 eV secondary recoil. We have seen that the defect type can form under many different implantation conditions, with a probability of a few % in typical cases.


Fig. 1. Top view of the D3 defect (click on the figure for a larger view).


Fig 2. Snapshots of the evolution of the cascade. See also the MPEG animation (7.2 Mb)

References

[1] @Article{Rei95,
  author = 	 "K. P. Reimann and W. Bolse and U. Geyer and
		  K. P. Lieb",
  title = 	 "Atomically Resolved Imaging of the Defect Structure
		  on Graphite After Oblique Single-Ion Impact",
  journal =	 "Europhys Lett.",
  year =	 1994,
  volume =	 30,
  number =	 8,
  pages =	 463,
}


[2] @Article{Nor96,
  author = 	 "K. Nordlund and J. Keinonen and T. Mattila",
  title = 	 "Formation of ion irradiation-induced
                  small-scale defects on graphite surfaces",
  year =	 1996,
  journal =      "Phys. Rev. Lett.",
  volume =       "77",
  number =       "4",
  year =         "1996",
  pages =        "699"
}

@Article{Nor96b,
  author =       "K. Nordlund and T. Mattila",
  title =        "Hillock formation on ion-irradiated graphite surfaces",
  year =         1996,
  note =         "submitted for publication in Rad. Eff. \& Def. in
                  Sol."
}