Search

We demonstrate field emission from an integrated three-terminal device using a suspended planar graphene edge as the source of vacuum electrons. Energy spectra of the emitted electrons confirm the field-emission mechanism. The energy spectra produced by graphene grown by chemical vapor deposition and reduced graphene oxide are compared. The drain-source voltage required to produce a given drain current increases when negative voltages are applied to the gate, confirming field-effect transistor operation. The emission current rises exponentially with inverse voltage over the measured current range from 1 pA to 10 nA. The current-voltage characteristics are consistent with tunneling through barrier potentials calculated numerically from the device geometry. [ABSTRACT FROM AUTHOR]

The properties of reduced graphene oxide (GO) are reported from a non-chemical reduction method. Ultra-high vacuum annealing of GO films in the thickness of 1-80 nm was studied by XPS, AFM, UV-Vis-NIR, Raman and TEM to observe the controlled removal of oxygen. We observed the loss of hydroxyl (C-OH) at low temperatures (<600 °C) followed by the complete loss of carbonyls (C=O) and epoxy (C-O-C) species by 1200 °C. As oxygen was removed, we observed a decrease in the layer spacing between the GO sheets and a concurrent decrease in the film resistance. While the Raman spectroscopy showed no change with reduction, indicating no change in the overall defect density or the general structure of the GO, the transmission spectra showed a shift in the transmission minimum from 245 nm to 260 nm and a total decrease in transmission above 800 nm occurs as the films visibly darken. TEM indicated that there is turbostratic stacking of the graphene layers as the reduction occurs, leading us to conclude that at a certain threshold of reduction the film properties are similar to epitaxial graphene growth on the C-face of SiC, but that a reduction gone too far results in a layer spacing equivalent to graphite. [ABSTRACT FROM AUTHOR]

Tunnel barriers are key elements for both charge-and spin-based electronics, offering devices with reduced power consumption and new paradigms for information processing. Such devices require mating dissimilar materials, raising issues of heteroepitaxy, interface stability, and electronic states that severely complicate fabrication and compromise performance. Graphene is the perfect tunnel barrier. It is an insulator out-of-plane, possesses a defect-free, linear habit, and is impervious to interdiffusion. Nonetheless, true tunneling between two stacked graphene layers is not possible in environmental conditions usable for electronics applications. However, two stacked graphene layers can be decoupled using chemical functionalization. Here, we demonstrate that hydrogenation or fluorination of graphene can be used to create a tunnel barrier. We demonstrate successful tunneling by measuring non-linear IV curves and a weakly temperature dependent zero-bias resistance. We demonstrate lateral transport of spin currents in non-local spin-valve structures, and determine spin lifetimes with the non-local Hanle effect. We compare the results for hydrogenated and fluorinated tunnel and we discuss the possibility that ferromagnetic moments in the hydrogenated graphene tunnel barrier affect the spin transport of our devices. [ABSTRACT FROM AUTHOR]

Single-layer graphene derived from chemical vapor deposition (CVD) holds promise for scalable radio frequency (RF) electronic applications. However, prevalent low-frequency flicker noise (1/f noise) in CVD graphene field-effect transistors is often up-converted to higher frequencies, thus limiting RF device performance. Here, we achieve an order of magnitude reduction in 1/f noise in fieldeffect transistors based on CVD graphene transferred onto silicon oxide substrates by utilizing a processing protocol that avoids aqueous chemistry after graphene transfer. Correspondingly, the normalized noise spectral density (10-7-10-8 µm² Hz-1) and noise amplitude (4 × 10-8-10-7) in these devices are comparable to those of exfoliated and suspended graphene. We attribute the reduction in 1/f noise to a decrease in the contribution of fluctuations in the scattering cross-sections of carriers arising from dynamic redistribution of interfacial disorder. [ABSTRACT FROM AUTHOR]

We demonstrate the use of a unique plasma source to controllably functionalize graphene with nitrogen and primary amines, thereby tuning the chemical, structural, and electrical properties. Critically, even highly aminated graphene remains electronically conductive, making it an ideal transduction material for biosensing. Proof-of-concept testing of aminated graphene as a bio-attachment platform in a biologically active field-effect transistor used for DNA detection is demonstrated. [ABSTRACT FROM AUTHOR]

We report gate tunable linear magnetoresistances (MRs) of ∼600% at 12 T in metal-shunted devices fabricated on chemical vapor deposition (CVD) grown graphene. The effect occurs due to decreasing conduction through the shunt as the magnetic field increases (known as the extraordinary magnetoresistance effect) and yields an MR that is at least an order-of-magnitude higher than in un-shunted graphene devices. [ABSTRACT FROM AUTHOR]

Graphene grown by chemical vapor deposition and supported on SiO2 and sapphire substrates was studied following the controlled introduction of defects induced by 35 keV carbon ion irradiation. Changes in Raman spectra for fluences ranging from 1012 to 1015 cm-2 indicate that the structure of graphene evolves from a highly ordered layer, to a patchwork of disordered domains, to an essentially amorphous film. These structural changes result in a dramatic decrease in the Hall mobility by orders of magnitude while, remarkably, the Hall concentration remains almost unchanged, suggesting that the Fermi level is pinned at a hole concentration near 1×1013 cm-2. A model for scattering by resonant scatterers is in good agreement with mobility measurements up to an ion fluence of 1×1014 cm-2. [ABSTRACT FROM AUTHOR]

A novel method for creating bilayer graphene is described where single-layer CVD graphene grown on Cu is bonded to single-layer epitaxial graphene grown on Si-face SiC. Raman microscopy and x ray photoelectron spectroscopy demonstrate the uniqueness of this bilayer, as compared to a naturally formed bilayer, in that a Bernal stack is not formed with each layer being strained differently yet being closely coupled. Electrical characterization of Hall devices fabricated on the unusual bilayer show higher mobilities, and lower carrier concentrations, than the individual CVD graphene or epitaxial graphene layers. [ABSTRACT FROM AUTHOR]