Accurate Measurement of Electron Beam Induced Displacement Cross Sections for Single-Layer Graphene

Abstract

We present an accurate measurement and a quantitative analysis of electron-beam induced displacements of carbon atoms in single-layer graphene. We directly measure the atomic displacement ("knock-on") cross section by counting the lost atoms as a function of the electron beam energy and applied dose. Further, we separate knock-on damage (originating from the collision of the beam electrons with the nucleus of the target atom) from other radiation damage mechanisms (e.g. ionization damage or chemical etching) by the comparison of ordinary ( 12 C) and heavy ( 13 C) graphene. Our analysis shows that a static lattice approximation is not sufficient to describe knock-on damage in this material, while a very good agreement between calculated and experimental cross sections is obtained if lattice vibrations are taken into account.

Direct visualization of reversible dynamics in a Si6 cluster embedded in a graphene pore

“…Contrary to previously reported irreversible beam-induced dynamics [12][13][14][15][16][17][18][19][20][21][22] , here we report a beaminduced reversible conformational transformation of the trapped Si 6 cluster in a graphene nanopore. Density-functional calculations of an embedded Si 6 cluster are used to probe its bonding to the host graphene lattice and the energy barriers for the conformational transformation.…”

“…Figure 1 shows a sequential set of annular dark field (ADF) Z-contrast images of a single Si 6 cluster trapped in a graphene nanopore. Electron-beam-induced ejection of carbon atoms and defect creation/migration has been actively studied in graphene and carbon nanotubes [12][13][14][15][16][17][18][19][20][21][22] . Contrary to these irreversible dynamics, we find that an oscillatory motion occurs in the trapped Si 6 cluster: one of the Si atoms executes a back-and-forth motion corresponding to the reversible conformational change of the Si 6 cluster in the graphene pore.…”

Spatial control of defect creation in graphene at the nanoscale

“…Chemical etching by surface contamination can be eliminated as the cause of the reported defects, as it does not produce defects at defined locations in a clean area of graphene, as demonstrated by AC-STEM data showing holes opening in the graphene areas away from the focus point of irradiation but near sources of iron contamination (see Supplementary Methods). Furthermore, chemical etching typically produces holes rather than the defect structures observed here, with holes tending to appear for exposure times in excess of 120 s. Meyer et al 31 studied the electron beam dependent cross-section for sputtering in graphene using a BCD of at most 10 6 e − 1 nm − 2 s − 1 , and at 80 kV they did not observe a single defect for a total dose of up to 10 10 e − 1 nm − 2 . We measured a cross-section of 1.35×10 − 2 barn for a BCD ~10 8 e − 1 nm − 2 s − 1 , which is more than two orders of magnitude larger than the calculated value of 7×10 − 5 barn reported in ref.…”

Atomic scale study of the life cycle of a dislocation in graphene from birth to annihilation

“…In our experiment, we used an operating voltage of 80 kV, which is below the static sputtering threshold in graphene. However, thermal vibrations lead to non-zero displacement cross-section and therefore allow occasional sputtering 25 . As the structural changes were of specific interest in our experiment, we increased the temporal frequency of the transformation events by working at exceptionally high beam currents (up to 1 Â 10 8 e nm À 2 s À 1 , that is, one to two orders of magnitude higher than what is typically used for purely structural investigations).…”