Alexandra Fursina

Kinetics of Diazonium Functionalization of Chemically Converted Graphene Nanoribbons

We demonstrate that graphene nanoribbons (GNRs) produced by the oxidative unzipping of carbon nanotubes can be chemically functionalized by diazonium salts. We show that functional groups form a thin layer on a GNR and modify its electrical properties. The kinetics of the functionalization can be monitored by probing the electrical properties of GNRs, either in vacuum after the grafting, or in situ in the solution. We derive a simple kinetics model that describes the change in the electrical properties of GNRs. The reaction of GNRs with 4-nitrobenzene diazonium tetrafluoroborate is reasonably fast, such that >60% of the maximum change in the electrical properties is observed after less than 5 min of grafting at room temperature.

Electronic transport in monolayer graphene nanoribbons produced by chemical unzipping of carbon nanotubes

We report on the structural and electrical properties of graphene nanoribbons (GNRs) produced by the oxidative unzipping of carbon nanotubes. GNRs were reduced by hydrazine at 95 °C and further annealed in Ar/H2 at 900 °C; monolayer ribbons were selected for the fabrication of electronic devices. GNR devices on Si/SiO2 substrates exhibit an ambipolar electric field effect typical for graphene. The conductivity of monolayer GNRs (∼35 S/cm) and mobility of charge carriers (0.5–3 cm2/V s) are less than the conductivity and mobility of pristine graphene, which could be explained by oxidative damage caused by the harsh H2SO4/KMnO4 used to make GNRs. The resistance of GNR devices increases by about three orders of magnitude upon cooling from 300 to 20 K. The resistance/temperature data is consistent with the variable range hopping mechanism, which, along with the microscopy data, suggests that the GNRs have a nonuniform structure.

Nanogaps with very large aspect ratios for electrical measurements

For nanoscale electrical characterization and device fabrication, it is often desirable to fabricate planar metal electrodes separated by large aspect ratio gaps with interelectrode distances well below 100nm. We demonstrate a self-aligned process to accomplish this goal using a thin Cr film as a sacrificial etch layer. The resulting gaps can be as small as 10nm and have aspect ratios exceeding 1000, with excellent interelectrode isolation. Such Ti∕Au electrodes are demonstrated on Si substrates and are used to examine a voltage-driven transition in magnetite nanostructures. This shows the utility of this fabrication approach even with relatively reactive substrates.

Sequential Electron Transport and Vibrational Excitations in an Organic Molecule Coupled to Few-Layer Graphene Electrodes

Graphene electrodes are promising candidates to improve reproducibility and stability in molecular electronics through new electrode-molecule anchoring strategies. Here we report sequential electron transport in few-layer graphene transistors containing individual curcuminoid-based molecules anchored to the electrodes via π-π orbital bonding. We show the coexistence of inelastic co-tunneling excitations with single-electron transport physics due to an intermediate molecule-electrode coupling; we argue that an intermediate electron-phonon coupling is the origin of these vibrational-assisted excitations. These experimental observations are complemented with density functional theory calculations to model electron transport and the interaction between electrons and vibrational modes of the curcuminoid molecule. We find that the calculated vibrational modes of the molecule are in agreement with the experimentally observed excitations.

Interplay of bulk and interface effects in the electric-field-driven transition in magnetite

Contact effects in devices incorporating strongly-correlated electronic materials are comparatively unexplored. We have investigated the electrically-driven phase transition in magnetite (100) thin films by four-terminal methods. In the lateral configuration, the channel length is less than 2

Coplanar switching of polarization in thin films of vinylidene fluoride oligomers

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Electrically driven phase transition in magnetite nanostructures

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Origin of hysteresis in resistive switching in magnetite is Joule heating

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Polarization-Dependent Electronic Transport in Graphene/Pb(Zr,Ti)O3 Ferroelectric Field-Effect Transistors

100 nm in width are directly patterned within the channel. Multilead measurements quantitatively separate the contributions of each electrode interface and the magnetite channel. We demonstrate that on the onset of the transition contact resistances at both source and drain electrodes and the resistance of magnetite channel decrease abruptly. Temperature dependent electrical measurements below the Verwey temperature indicate thermally activated transport over the charge gap. The behavior of the magnetite system at a transition point is consistent with a theoretically predicted transition mechanism of charge gap closure by electric field.

Electropolymerization of Poly(phenylene oxide) on Graphene as a Top-Gate Dielectric

Switching characteristics of vinylidene fluoride oligomer thin films with molecular chains aligned normal to the substrate and exhibiting a preferential in-plane polarization have been investigated using coplanar geometry of inter-digital electrodes via high-resolution piezoresponse force microscopy. It has been shown that in-plane switching proceeds via non-180° rotation of dipoles mediated by non-stochastic nucleation, expansion, and coalescence of domains. As-grown multidomain configuration is found to be strongly pinned aided by charged domain walls, and the electrically induced (in-plane) mono-domain states relax to the as-grown state. The observed coercive field (approximately 0.6 MV/m) is two to three orders of magnitude smaller than that for the oligomer films with out-of-plane polarization. It is suggested that the low steric hindrance to the rotation of molecular dipoles gives rise to the observed low coercive field.