Photoluminescent Semiconducting Graphene Nanoribbons via Longitudinally Unzipping Single-Walled Carbon Nanotubes.

The lack of a sizeable band gap has so far prevented graphene from building effective electronic and optoelectronic devices despite its numerous exceptional properties. Intensive theoretical research reveals that a band gap larger than 1 eV can only be achieved in sub-3 nm wide graphene nanoribbons (GNRs), but real fabrication of such ultranarrow GNRs still remains a critical challenge. Herein, we demonstrate an approach for the synthesis of ultranarrow and photoluminescent semiconducting GNRs by longitudinally unzipping single-walled carbon nanotubes. Atomic force microscopy reveals the unzipping process, and the resulting 2.2 nm wide GNRs are found to emit strong and sharp photoluminescence at ∼685 nm, demonstrating a very desirable semiconducting nature. This band gap of 1.8 eV is further confirmed by follow-up photoconductivity measurements, where a considerable photocurrent is generated, as the excitation wavelength becomes shorter than 700 nm. More importantly, our fabricated GNR field-effect transistors (FETs), by employing the hexagonal boron nitride-encapsulated heterostructure to achieve edge-bonded contacts, demonstrate a high current on/off ratio beyond 105 and carrier mobility of 840 cm2/V s, approaching the theoretical scattering limit in semiconducting GNRs at room temperature. Especially, highly aligned GNR bundles with lengths up to a millimeter are also achieved by prepatterning a template, and the fabricated GNR bundle FETs show a high on/off ratio reaching 105, well-defined saturation currents, and strong light-emitting properties. Therefore, GNRs produced by this method open a door for promising applications in graphene-based electronics and optoelectronics.

Graphene bridge rectifier based on self-switching diode arrays.

Here, we present theory and measurements for a bridge rectifier formed from arrays of graphene self-switching diodes (GSSDs). Despite graphene's lack of a bandgap and high carrier concentration causing a reduced rectification ratio, the extremely high carrier mobility will allow GSSDs to work at frequencies well into the THz region. Compared with a single SSD array, the bridge rectifier structure allows for full-wave rectification of an AC signal. Here we derive an equation for the voltage output of a bridge rectifier formed from GSSDs, which predicts a quadratic relationship between output voltage and input current. This relationship is confirmed using AC and DC measurements. The fabricated rectifier is found to have a high room temperature intrinsic responsivity of [Formula: see text] at low frequency and a low noise equivalent power of [Formula: see text].