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.

Monolayer molybdenum disulfide (MoS(2)), unlike its bulk form, is a direct band gap semiconductor with a band gap of 1.8 eV. Recently, field-effect transistors have been demonstrated experimentally using a mechanically exfoliated MoS(2) monolayer, showing promising potential for next generation electronics. Here we project the ultimate performance limit of MoS(2) transistors by using nonequilibrium Green's function based quantum transport simulations. Our simulation results show that the strength of MoS(2) transistors lies in large ON-OFF current ratio (>10(10)), immunity to short channel effects (drain-induced barrier lowering ∼10 mV/V), and abrupt switching (subthreshold swing as low as 60 mV/decade). Our comparison of monolayer MoS(2) transistors to the state-of-the-art III-V materials based transistors, reveals that while MoS(2) transistors may not be ideal for high-performance applications due to heavier electron effective mass (m = 0.45 m(0)) and a lower mobility, they can be an attractive alternative for low power applications thanks to the large band gap and the excellent electrostatic integrity inherent in a two-dimensional system.

In contrast to typical metals, carbon nanotubes are shown to form a unique Schottky barrier contact with semiconductors wherein a gate field can modulate not only the band bending in the semiconductor but also the height of the barrier. These phenomena are exploited to enable two new device architectures: a vertical field‐effect transistor (figure) and a vertical light‐emitting transistor.

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Capacitance-voltage (C-V) characteristics are important for understanding fundamental electronic structures and device applications of nanomaterials. The C-V characteristics of graphene nanoribbons (GNRs) are examined using self-consistent atomistic simulations. The results indicate strong dependence of the GNR C-V characteristics on the edge shape. For zigzag edge GNRs, highly non-uniform charge distribution in the transverse direction due to edge states lowers the gate capacitance considerably, and the self-consistent electrostatic potential significantly alters the band structure and carrier velocity. For an armchair edge GNR, the quantum capacitance is a factor of 2 smaller than its corresponding zigzag carbon nanotube, and a multiple gate geometry is less beneficial for transistor applications. Magnetic field results in pronounced oscillations on C-V characteristics.