Hole-doped Graphene Research Articles

Graphene Gate Electrode for MOS Structure-Based Electronic Devices

We demonstrate that the use of a monolayer graphene as a gate electrode on top of a high-κ gate dielectric eliminates mechanical-stress-induced-gate dielectric degradation, resulting in a quantum leap of gate dielectric reliability. The high work function of hole-doped graphene also helps reduce the quantum mechanical tunneling current from the gate electrode. This concept is applied to nonvolatile Flash memory devices, whose performance is critically affected by the quality of the gate dielectric. Charge-trap flash (CTF) memory with a graphene gate electrode shows superior data retention and program/erase performance that current CTF devices cannot achieve. The findings of this study can lead to new applications of graphene, not only for Flash memory devices but also for other high-performance and mass-producible electronic devices based on MOS structure which is the mainstream of the electronic device industry.

The diffusion of hydrogen monomers on hole-doped graphitic lattices: over-barrier transition and quantum tunneling

The diffusion of hydrogen and deuterium monomers on hole-doped graphene (a planar graphitic lattice), the outside wall and the inside wall of hole-doped (6, 0) single-walled carbon nanotubes (a curved graphitic lattice) was investigated using density functional theory and density functional perturbation theory. The jump frequencies for the over-barrier transition and phonon-assisted quantum tunneling were calculated by transition state theory and small-polaron theory, respectively. The effects of the local curvature of the surface and the hole doping on the thermodynamic and kinetic properties of a hydrogen monomer on these graphitic lattices are discussed. Our results demonstrate that it is sufficient to judge the diffusional mobility of a hydrogen monomer on graphitic lattices from just the over-barrier transition, no matter how much it is curved and hole doped, while the quantum tunneling can be safely neglected because it is significantly suppressed by the covalent bonding of hydrogen with the graphitic lattice.

Hybrid Graphene/Titania Nanocomposite: Interface Charge Transfer, Hole Doping, and Sensitization for Visible Light Response.

We demonstrated for the first time by large-scale ab initio calculations that a graphene/titania interface in the ground electronic state forms a charge-transfer complex due to the large difference of work functions between graphene and titania, leading to substantial hole doping in graphene. Interestingly, electrons in the upper valence band can be directly excited from graphene to the conduction band, that is, the 3d orbitals of titania, under visible light irradiation. This should yield well-separated electron-hole pairs, with potentially high photocatalytic or photovoltaic performance in hybrid graphene and titania nanocomposites. Experimental wavelength-dependent photocurrent generation of the graphene/titania photoanode demonstrated noticeable visible light response and evidently verified our ab initio prediction.

Supermetallic conductivity in bromine-intercalated graphite

Exposure of highly oriented pyrolytic graphite to bromine vapor gives rise to in-plane charge conductivities which increase monotonically with intercalation time toward values (for $\ensuremath{\sim}6\text{ }\text{at}\text{ }\mathrm{%}$ Br) that are significantly higher than Cu at temperatures down to 5 K. Magnetotransport, optical reflectivity and magnetic susceptibility measurements confirm that the Br dopes the graphene sheets with holes while simultaneously increasing the interplanar separation. The high-room-temperature mobility $(\ensuremath{\sim}5\ifmmode\times\else\texttimes\fi{}{10}^{4}\text{ }{\text{cm}}^{2}/\text{V}\ensuremath{\cdot}\text{s})$ and resistance anisotropy together with the reduced diamagnetic susceptibility of the intercalated samples suggests that the observed supermetallic conductivity derives from a parallel combination of weakly coupled hole-doped graphene sheets.

Effect of a gap opening on the conductance of graphene superlattices

The electronic transmission and conductance of a gapped graphene superlattice were calculated by means of the transfer-matrix method. The system that we study consists of a sequence of electron-doped graphene as wells and hole-doped graphene as barriers. We show that the transmission probability approaches unity at some critical value of the gap. We also find that there is a domain around the critical gap value for which the conductance of the system attains its maximum value.