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Electron microscopy, simulations provide atom-by-atom knowledge of doped graphene

Thu, 10/18/2012 - 8:31am

A thread of research pursued in a pan-European collaboration lead by Aalto University Department of Applied Physics scientists has yielded prominent results for the electron microscopy of nitrogen-doped graphene and carbon nanotubes.

A paper published in ACS Nano provides a detailed atomistic description of the electron-beam-induced damage in these important structures by combining advanced computational methods with electron microscopy.

Toma Susi, postdoctoral researcher in Aalto University Department of Applied Physics, began studying the system in 2010 together with current University of Vienna researcher Jani Kotakoski.

"Our work began as a chance meeting during a workshop poster session. I had questions that Jani could answer by computational modeling. The collaboration eventually grew to include 11 authors from five European countries," recounts Susi.

Susi and his colleagues investigated how the energetic electron beams used in transmission electron microscopes affect carbon-based nanomaterials doped with nitrogen atoms.

The microscopes basically operate by the same principle as optical microscopes, but they use electron waves instead of light for the imaging. The materials are interesting because they have exciting prospects for nanoelectronics, metal-free electrocatalysis, and gas sensing.

The exact atomic bonding of the dopants greatly affects the resulting modification of host properties. Recent developments in instrumentation have enabled atom-by-atom analysis and even direct imaging of nitrogen sites in graphene. However, since electrons carry momentum, inelastic collisions can lead to the ejection of atoms from the target material, potentially leading to misidentification of the unmodified dopant structures.

"Most excitingly, we could directly image the ejection of carbon atoms next to the dopants and never the dopants themselves—exactly as the simulations predicted," explains Susi.

Besides providing an improved understanding of the irradiation stability of these structures, the results show that structural changes cannot be neglected in characterization using high-energy electrons. This notion will increase in importance as the devices become more powerful.

Source: Aalto University

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