Graphene Width Research Articles

Fabrication of Carbon Nanoscrolls from Monolayer Graphene Controlled by P-Doped Silicon Nanowires: A MD Simulation Study

It is demonstrated using molecular dynamics (MD) simulations that P-doped silicon nanowires (Si NWs) can activate graphenes self-scrolling onto Si NWs and thus produce new kinds of graphene nanoscroll (NS)/Si core/shell heterojunctions. The simulations show that graphene sheets can fully self-scroll onto Si NWs when the Si NW radius is larger than a threshold of about 5 Å, forming a stable core/shell structure. It is the van der Waals force that plays a primary role in the self-scrolling process. The configuration of the graphene–Si heterojunction depends significantly on the diameter of the Si NWs. The final NS becomes multiwalled with increasing graphene length when the diameter of the Si NWs is larger than a threshold of about 6 Å. The zigzag NS is proved to be the most stable, while the chiral NSs are unstable and tend to evolve into zigzag NS and a model is set up to interpret the tendency from the standpoint of bond. It is demonstrated that the graphene width has no influence on the self-scrolling process at all. Compared with the conventional fabricating method, the new self-assembling one occurs at room temperature and the thickness of the NSs can be controlled accurately. Besides, the unique structure of the graphene/Si core/shell heterojunctions will significantly enhance their applications in nanoelectronic devices, hydrogen storage, solar cells, chemical or biological sensors, and energy storage in supercapacitors or batteries.

Lateral confinement effects on the structural properties of surfactant aggregates: SDS on graphene

The structure of aqueous sodium dodecyl sulfate (SDS) surfactant aggregates formed on small graphene sheets and graphene nanoribbons has been studied using all-atom molecular dynamics simulations. Because the edges of the carbonaceous supports confine laterally the surfactant aggregates, by changing the size of the support (diameter of graphene sheets and width of graphene nanoribbons) it is possible to investigate lateral confinement effects on the aggregate morphology. The results are compared to those available on graphite, with no lateral confinement. Aqueous SDS aggregates were studied on 2.0 nm, 5.0 nm, and 10.0 nm circular graphene sheets and on 2.0 and 5.0 nm wide graphene nanoribbons. For the first time our results show that, because of lateral confinement provided by the graphene edges, SDS yields multiple layers, hemispheres, hemicylinders or multiple hemispheres depending on the graphene size and shape. Results are quantified in terms of morphology of the surfactant aggregates, order parameter of the adsorbed surfactant aggregates, and number of water molecules at contact with the carbonaceous support.

Alignment of graphene nanoribbons by an electric field

In this paper, we develop an analytical approach to predict the field-induced alignment of cantilevered graphene nanoribbons. This approach is validated through molecular simulations using a constitutive atomic electrostatic model. Our results reveal that graphene’s field-oriented bending angle is roughly proportional to the square of field strength or to the graphene length for small deformations, while is roughly independent of graphene width. The effective bending stiffness and the longitudinal polarizability are found to be approximately proportional to the square of graphene length. Compared with carbon nanotubes, graphene nanoribbons are found to be more mechanically sensitive to an external electric field.

Electronic structure of gated graphene and graphene ribbons

We study the electronic structure of gated graphene sheets. We consider both infinite graphene and finite width ribbons. The effect of Coulomb interactions between the electrically injected carriers and the coupling to the external gate are computed self-consistently in the Hartree approximation. We compute the average density of extra carriers n2D, the number of occupied subbands, and the density profiles as a function of the gate potential Vg. We discuss quantum corrections to the classical capacitance and we calculate the threshold Vg above which semiconducting armchair ribbons conduct. We find that the ideal conductance of perfectly transmitting wide ribbons is proportional to the square root of the gate voltage.

Pseudodiffusive conduction at the Dirac point of a normal-superconductor junction in graphene

A ballistic strip of graphene (width $W⪢\text{length}$ $L$) connecting two normal metal contacts is known to have a minimum conductivity of $4{e}^{2}∕\ensuremath{\pi}h$ at the Dirac point of charge neutrality. We calculate what happens if one of the two contacts becomes superconducting. While the ballistic conductance away from the Dirac point is increased by Andreev reflection at the normal-superconductor (NS) interface, we find that the minimum conductivity stays the same. This is explained as a manifestation of pseudodiffusive conduction at the Dirac point. As a generalization of our results for a ballistic system, we provide a relation between the conductance ${G}_{\mathrm{NS}}$ of an arbitrarily disordered normal-superconductor junction in graphene and its value ${G}_{\mathrm{N}}$ when both contacts are in the normal state.