We report electronic structure and electric field modulation calculations in the width direction for armchair graphene nanoribbons (acGNRs) using a semi-empirical extended Hückel theory. Important band structure parameters are computed, e.g. effectives masses, velocities and bandgaps. For the three types of acGNRs, the pz orbital tight-binding parameters are extracted if feasible. Furthermore, the effect of electric field in the width direction on acGNRs dispersion is explored. It is shown that for the two types of semiconducting acGNRs, an external electric field can reduce the bandgap to a few meV with different quantitative behavior.

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The dispersion relations for plasmons in intrinsic and extrinsic semimetallic armchair graphene nanoribbons (acGNR) are calculated in the random phase approximation using the orthogonal pz-orbital tight binding method. Our model predicts new plasmons for acGNR of odd atomic widths N = 5, 11, 17, . . . Our model further predicts plasmons in acGNR of even atomic width N = 2, 8, 14, . . . related to those found using a Dirac continuum model, but with different quantitative dispersion characteristics. We find that the dispersion of all plasmons in semimetallic acGNR depends strongly on the localization of the pz electronic wavefunctions. We also find that overlap integrals for acGNR behave in a more complex way than predicted by the Dirac continuum model, suggesting that these plasmons will experience a small damping for all q = 0. Plasmons in extrinsic semimetallic acGNR with the chemical potential in the lowest (highest) conduction (valence) band are found to have dispersion characteristics nearly identical to their intrinsic counterparts, with negligible differencs in dispersion arising from the slight differences in overlap integrals for the interband and intraband transitions.

Abstract-Self-assembled monolayers (SAMs) of either ferrocenecarboxylic acid or 5-(4-Carboxyphenyl)-10,15,20-triphenylporphyrin-Co(II) (CoP) with a high-κ dielectric were integrated into the Flash memory gate stack. The molecular reductionoxidation (redox) states are used as charge storage nodes to reduce charging energy and memory window variations. Through the program/erase operations over tunneling barriers, the device structure also provides a unique capability to measure the redox energy without strong orbital hybridization of metal electrodes in direct contact. Asymmetric charge injection behavior was observed, which can be attributed to the Fermi-level pinning between the molecules and the high-κ dielectric. With increasing redox molecule density in the SAM, the memory window exhibits a saturation trend. Three programmable molecular orbital states, i.e., CoP 0 , CoP 1− , and CoP 2− , can be experimentally observed through a charge-based nonvolatile memory structure at room temperature. The electrostatics is determined by the alignment between the highest occupied or the lowest unoccupied molecular orbital (HOMO or LUMO, respectively) energy levels and the charge neutrality level of the surrounding dielectric. Engineering the HOMO-LUMO gap with different redox molecules can potentially realize a multibit memory cell with less variation. Index Terms-Coulomb blockade effect, high-κ dielectric, nonvolatile memory devices, reduction-oxidation (redox)-active molecules, self-assembled monolayer (SAM).

We theoretically study the effect of a localized unpaired dangling bond (DB) on occupied molecular orbital conduction through a styrene molecule bonded to a n ++ H:Si(001)-(2×1) surface. For molecules relatively far from the DB, we find good agreement with the reported experiment using a model that accounts for the electrostatic contribution of the DB, provided we include some dephasing due to low lying phonon modes. However, for molecules within 10Å to the DB, we have to include electronic contribution as well along with higher dephasing to explain the transport features.

We report a uniform and low-defect synthesis of bilayer graphene on evaporated polycrystalline nickel films. We used atmospheric pressure chemical vapor deposition with ultra-fast substrate cooling after exposure to methane at 1,000°C. The optimized process parameters, i.e., growth time, annealing profile and flow rates of various gases, are reported. By using Raman spectroscopy mapping, the ratio of 2D to G peak intensities (I2D/IG) is in the range of 0.9 to 1.6 over 96% of the 200 μm × 200 μm area. Moreover, the average ratio of D to G peak intensities (ID/IG) is about 0.1.

We theoretically study the electronic band structure of isolated unpaired and paired dangling bonds (DB), DB wires and DB clusters on H:Si(100)-(2×1) surface using Extended Hückel Theory (EHT) and report their effect on the Si band gap. An isolated unpaired DB introduces a near-midgap state, whereas a paired DB leads to π and π * states, similar to those introduced by an unpassivated asymmetric dimer (AD) Si( 100)-(2×1) surface. Such induced states have very small dispersion due to their isolation from the other states, which reside in conduction and valence band. On the other hand, the surface state induced due to an unpaired DB wire in the direction along the dimer row (referred to as [110]), has large dispersion due to the strong coupling between the adjacent DBs, being 3.84 Å apart. However, in the direction perpendicular to the dimer row (referred to as [110]), due to the reduced coupling between the DBs being 7.68 Å apart, the dispersion in the surface state is similar to that of an isolated unpaired DB. Apart from this, a paired DB wire in [110] direction introduces π and π * states similar to those of an AD surface and a paired DB wire in [110] direction exhibits surface states similar to those of an isolated paired DB, as expected. Besides this, we report the electronic structure of different DB clusters, which exhibit states inside the band gap that can be interpreted as superpositions of states due to unpaired and paired DBs.

An atomistic model based on the spin-restricted extended Hückel theory (EHT) is presented for simulating electronic structure and I-V characteristics of graphene devices. The model is applied to zigzag and armchair graphene nano-ribbons (GNR) with and without hydrogen passivation, as well as for bilayer graphene. Further calculations are presented for electric fields in the nano-ribbon width direction and in the bilayer direction to show electronic structure modification. Finally, the EHT Hamiltonian and NEGF (Nonequilibrium Green's function) formalism are used for a paramagnetic zigzag GNR to show 2e 2 /h quantum conductance.