Abstract
Graphene provides a unique platform for the detailed study of its dopants at the atomic level. Previously, doped materials including Si, and 0D-1D carbon nanomaterials presented difficulties in the characterization of their dopants due to gradients in their dopant concentration and agglomeration of the material itself. Graphene’s two-dimensional nature allows for the detailed characterization of these dopants via spectroscopic and atomic resolution imaging techniques. Nitrogen doping of graphene has been well studied, providing insights into the dopant bonding structure, dopant-dopant interaction, and spatial segregation within a single crystal. Different configurations of nitrogen within the carbon lattice have different electronic and chemical properties, and by controlling these dopants it is possible to either n- or p-type dope graphene, grant half-metallicity, and alter nitrogen doped graphene’s (NG) catalytic and sensing properties. Thus, an understanding and the ability to control different types of nitrogen doping configurations allows for the fine tuning of NG’s properties. Here we review the synthesis, characterization, and properties of nitrogen dopants in NG beyond atomic dopant concentration.
Highlights
Doping has been used in silicon (Si)-based semiconductor technologies to alter the electronic properties of Si wafers by substitutionally incorporating non-isoelectronic heteroatoms
Micro- to millimeter large single crystals are available for the 2D carbon nanomaterial graphene, leading to a unique platform to investigate the fundamentals of single dopants
We provide an overview of its synthesis by categorizing in situ growth and post-growth treatments with aspects of dopant control
Summary
Doping has been used in silicon (Si)-based semiconductor technologies to alter the electronic properties (i.e., carrier density) of Si wafers by substitutionally incorporating non-isoelectronic heteroatoms. In NG, nitrogen is not observed only in a simple substitutional configuration (graphitic-N) but can be accompanied by a vacancy (pyridinic-N), form a five-membered ring (pyrrolic-N), triple bond to a carbon atom at a zigzag edge (nitrilic-N), and partially oxidize (oxidized-N) (Figure 1c) These different dopant configurations affect the local charge distribution and local density of states differently leading to different electronic, catalytic, and sensing properties [2,3]. A similar analysis was performed by Katoh et al [42]; the authors grew NG with four aromatic nitrogen-containing precursors, quinoline (C9H7N), pyridine (C5H5N), pyrrole (C4H5N), and pyrimidine (C4H4N2) on Pt(111) at a relatively low temperature of 500 ◦C They found that the aromatic molecules that had the highest activation energies for the breaking of the aromatic ring had the highest dopant concentration.
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