Jhao-Wun Huang

Aryl functionalization as a route to band gap engineering in single layer graphene devices.

Chemical functionalization is a promising route to band gap engineering of graphene. We chemically grafted nitrophenyl groups onto exfoliated single-layer graphene sheets in the form of substrate-supported or free-standing films. Our transport measurements demonstrate that nonsuspended functionalized graphene behaves as a granular metal, with variable range hopping transport and a mobility gap ∼0.1 eV at low temperature. For suspended graphene that allows functionalization on both surfaces, we demonstrate tuning of its electronic properties from a granular metal to a semiconductor in which transport occurs via thermal activation over a transport gap ∼80 meV from 4 to 300 K. This noninvasive and scalable functionalization technique paves the way for CMOS-compatible band gap engineering of graphene electronic devices.

Organometallic hexahapto functionalization of single layer graphene as a route to high mobility graphene devices.

Organometallic hexahapto chromium metal complexation of single layer graphene, which involves constructive rehybridization of the graphene pi-system with the vacant chromium d orbital, leads to field effect devices which retain a high degree of the mobility with enhanced on-off ratio. This hexahapto mode of bonding between metal and graphene is quite distinct from the modification in electronic structure induced by conventional covalent sigma-bond formation with creation of sp3 carbon centers in graphene lattice and this chemistry is reversible.

Visualizing electrical breakdown and ON/OFF states in electrically switchable suspended graphene break junctions.

Narrow gaps are formed in suspended single- to few-layer graphene devices using a pulsed electrical breakdown technique. The conductance of the resulting devices can be programmed by the application of voltage pulses, with voltages of 2.5 to ~4.5 V, corresponding to an ON pulse, and ~8 V, corresponding to an OFF pulse. Electron microscope imaging of the devices shows that the graphene sheets typically remain suspended and that the device conductance tends to zero when the observed gap is large. The switching rate is strongly temperature dependent, which rules out a purely electromechanical switching mechanism. This observed switching in suspended graphene devices strongly suggests a switching mechanism via atomic movement and/or chemical rearrangement and underscores the potential of all-carbon devices for integration with graphene electronics.

Superior Current Carrying Capacity of Boron Nitride Encapsulated Carbon Nanotubes with Zero-Dimensional Contacts.

We report fabrication and characterization of hexagonal boron nitride (hBN)-encapsulated carbon nanotube (CNT) field effect transistors, which are coupled to electrical leads via zero-dimensional contacts. Device quality is attested by the ohmic contacts and observation of Coulomb blockade with a single periodicity in small bandgap semiconducing nanotubes. Surprisingly, hBN-encapsulated CNT devices demonstrate significantly enhanced current carrying capacity; a single-walled CNT can sustain >180 μA current or, equivalently, a current density of ∼2 × 10(10) A/cm(2), which is a factor of 6-7 higher than devices supported on SiO2 substrates. Such dramatic enhancement of current carrying capacity arises from the high thermal conductivity of hBN and lower hBN-CNT interfacial thermal resistance and has implications for carbon electronic applications.