Domains of doping in graphene on polycrystalline gold: first-principles and scanning tunneling spectroscopy studies

We have studied the graphene/gold interface by means of density functional theory (DFT) and scanning tunneling spectroscopy (STS). Weak interaction between graphene and the underlying gold surface leaves unperturbed Dirac cones in the band-structure, but they can be shifted with respect to the Fermi level of the whole system, which results in effective doping of graphene. DFT calculations revealed that the interface is extremely sensitive to the adsorption distance and to the structure of metal's surface, in particular strong variation in doping can be attributed to the specific rearrangements of substrate's atoms, such as the change in the crystallographic orientation, relaxation or other modifications of the surface. On the other hand, STS experiments have shown the presence of energetic heterogeneity in terms of the changes in the local density of states (LDOS) measured at different places on the sample. Randomly repeated regions of zero-doping and p-type doping have been identified from parabolic shape characteristics and from well defined Dirac points, respectively. The doping domains of graphene on gold seem to be related to the presence of various types of the surface structure across the sample. DFT simulations for graphene interacting with Au have shown large differences in doping induced by considered structures of substrate, in agreement with experimental findings. All these results demonstrate the possibility of engineering the electronic properties of graphene, especially tuning the doping across one flake which can be useful for applications of graphene in electronic devices

Reversible modifications of linear dispersion - graphene between boron nitride monolayers

Electronic properties of the graphene layer sandwiched between two hexagonal boron nitride sheets have been studied using the first-principles calculations and the minimal tight-binding model. It is shown that for the ABC-stacked structure in the absence of external field the bands are linear in the vicinity of the Dirac points as in the case of single-layer graphene. For certain atomic configuration, the electric field effect allows opening of a band gap of over 230 meV. We believe that this mechanism of energy gap tuning could significantly improve the characteristics of graphene-based field-effect transistors and pave the way for future electronic applications.Comment: 5 pages, v2 with slightly modified introduction and summar

Energy gap tuning in graphene on hexagonal boron nitride bilayer system

We use a tight binding approach and density functional theory calculations to study the band structure of graphene/hexagonal boron nitride bilayer system in the most stable configuration. We show that an electric field applied in the direction perpendicular to the layers significantly modifies the electronic structure of the whole system, including shifts, anticrossing and other deformations of bands, which can allow to control the value of the energy gap. It is shown that band structure of biased system may be tailored for specific requirements of nanoelectronics applications. The carriers' mobilities are expected to be higher than in the bilayer graphene devices.Comment: 10 pages, 7 figures, submitted to Physical Review

Defective transport properties of three-terminal carbon nanotube junctions

We investigate the transport properties of three terminal carbon based nanojunctions within the scattering matrix approach. The stability of such junctions is subordinated to the presence of nonhexagonal arrangements in the molecular network. Such "defective" arrangements do influence the resulting quantum transport observables, as a consequence of the possibility of acting as pinning centers of the correspondent wavefunction. By investigating a fairly wide class of junctions we have found regular mutual dependencies between such localized states at the carbon network and a strikingly behavior of the conductance. In particular, we have shown that Fano resonances emerge as a natural result of the interference between defective states and the extended continuum background. As a consequence, the currents through the junctions hitting these resonant states might experience variations on a relevant scale with current modulations of up to 75%.Comment: 8 pages, 8 figure

Insulator-metal transition on heavily reduced TiO 2 (1 1 0) surface studied by high temperature-scanning tunnelling spectroscopy (HT-STS)

Abstract Scanning tunnelling microscopy (STM) and scanning tunnelling spectroscopy (STS) were used to study the electronic structure of the reduced TiO 2 (1 1 0) surface. At the occupied part of the spectra some states at energies of about 1.1 and 0.6 eV below the Fermi level were found. At the unoccupied part of the spectra, the presence of a surface state at an energy of about 0.6 eV above the Fermi level was observed. Their presence has been ascribed to the appearance of Ti 2 O 3 regions on the TiO 2 (1 1 0) surface. High temperature spectroscopy measurements indicated smooth insulator-metal transition (I-M) caused by bands overlap in Ti 2 O 3 , which takes place at elevated temperatures.

Nanoscale studies of the oxidation and hydrogenation of graphite surface

Abstract Nanoscale studies of the thermal oxidation and hydrogenation of graphite surfaces have been investigated using scanning tunnelling microscopy and scanning tunnelling spectroscopy. ðp à Þ, IS and negative differential resistance electronic states recorded over islands of such treated graphite. However, these states vanish on various regions on the thermally oxidized graphite islands. This is ascribed to the disappearance of p=p à bands when the graphite surface oxidizes and indicates the presence of oxygenated groups on the graphite surface

Self-reduction of the native TiO2(110) surface during cooling after thermal annealing - in-operando investigations

We investigate the thermal reduction of TiO2 in ultra-high vacuum. Contrary to what is usually assumed, we observe that the maximal surface reduction occurs not during the heating, but during the cooling of the sample back to room temperature. We describe the self-reduction, which occurs as a result of differences in the energies of defect formation in the bulk and surface regions. The findings presented are based on X-ray photoelectron spectroscopy carried out in-operando during the heating and cooling steps. The presented conclusions, concerning the course of redox processes, are especially important when considering oxides for resistive switching and neuromorphic applications and also when describing the mechanisms related to the basics of operation of solid oxide fuel cells