Graphite Step Edges Research Articles

Synthesis with Single Macromolecules: Covalent Connection between a Neutral Dendronized Polymer and Polyelectrolyte Chains as well as Graphene Edges

Single chains of a neutral, dendronized polymer with peripheral azide groups (PG3A) are co-deposited onto molecularly modified graphite substrates with a positively charged dendronized polymer (PG2) as well as with negatively charged plasmid dsDNA. PG3A is also prepared near graphite step-edges. Single PG3A chains are moved with a scanning force microscope tip, into close contact with either of the two polyelectrolytes, as well as the step-edge at predetermined positions. Treating these structures in situ with UV light leads to photochemically induced cross-linking between the PG3A chains carrying azide groups and PG2, dsDNA, and graphite step-edges, respectively, which is proven by mechanically challenging the "welding" points by pulling on the molecules with the SFM-tip.

Anisotropic corner crossing barriers in nanorod growth

The growth of quasi 1-dimensional bismuth rods from graphite step edges is modeled using kinetic Monte Carlo simulations. An anisotropic growth model is developed and tested against experimentally observed behaviour. The model incorporates adatom deposition, diffusion, and irreversible attachment of material to the aggregate. It is found that the best agreement between experiments and simulations occurs when anisotropic corner crossing barriers are introduced to the model.

Growth of oriented Bi nanorods at graphite step-edges

We report on the growth of ordered arrays of bismuth nanorods, extending outward from highly oriented pyrolitic-graphite (HOPG) step--edges. The rods grow via adatom diffusion in a multilayer two-dimensional growth mode, with ${{01\overline{1}2}}_{\mathrm{Bi}}$ planes parallel to the basal plane of the substrate, and in-plane orientations aligned with the high symmetry directions of the substrate such that ${⟨11\overline{2}0⟩}_{\mathrm{Bi}}\ensuremath{\parallel}{⟨10\overline{1}0⟩}_{\mathrm{HOPG}}$. The morphologies are characterized with varying particle flux and coverage. It is shown that bismuth aggregates become elongated when the particle flux is reduced. When coupled with an anisotropic diffusion field surrounding step-edge structures, this results in the manifestation of rods in a low flux growth environment. The rods are only $\ensuremath{\sim}2\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ tall and can extend up to several microns in length.

Scanning tunneling microscopy and spectroscopy studies of graphite edges

We studied experimentally and theoretically the electronic local density of states (LDOS) near single-step edges at the surface of exfoliated graphite. In scanning tunneling microscopy measurements, we observed the ( 3 × 3 ) R 30 ° and honeycomb superstructures extending over 3–4 nm both from the zigzag and armchair edges. Calculations based on a density-functional-derived non-orthogonal tight-binding model show that these superstructures can coexist if the two types of edges admix each other in real graphite step edges. Scanning tunneling spectroscopy measurements near the zigzag edge reveal a clear peak in the LDOS at an energy below the Fermi energy by 20 meV. No such a peak was observed near the armchair edge. We concluded that this peak corresponds to the “edge state” theoretically predicted for graphene ribbons, since a similar prominent LDOS peak due to the edge state is obtained by the first principles calculations.