N-Doping of Graphene Through Electrothermal Reactions with Ammonia

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Science  08 May 2009:
Vol. 324, Issue 5928, pp. 768-771
DOI: 10.1126/science.1170335

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Negatively Doped Graphene Nanoribbons

The potential applications in electronic devices of graphene (single atom, thick layers of graphite) would be even greater if it can be accessed in both p- and n-doped forms. Graphene nanoribbons (long strips only tens of nanometers in width) are readily p-doped by adsorbates from the ambient atmosphere. Wang et al. (p. 768) show that when graphene nano-ribbons are electrically heated in an ammonia atmosphere, nitrogen is incorporated mainly at the edges of the ribbon and creates an n-type material. Field-effect transistors that operate at room temperature can be made from this material.


Graphene is readily p-doped by adsorbates, but for device applications, it would be useful to access the n-doped material. Individual graphene nanoribbons were covalently functionalized by nitrogen species through high-power electrical joule heating in ammonia gas, leading to n-type electronic doping consistent with theory. The formation of the carbon-nitrogen bond should occur mostly at the edges of graphene where chemical reactivity is high. X-ray photoelectron spectroscopy and nanometer-scale secondary ion mass spectroscopy confirm the carbon-nitrogen species in graphene thermally annealed in ammonia. We fabricated an n-type graphene field-effect transistor that operates at room temperature.

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