3 research outputs found
Electronic Interaction between Nitrogen-Doped Graphene and Porphyrin Molecules
The chemical doping of graphene is a promising route to improve the performances of graphene-based devices through enhanced chemical reactivity, catalytic activity, or transport characteristics. Understanding the interaction of molecules with doped graphene at the atomic scale is therefore a leading challenge to be overcome for the development of graphene-based electronics and sensors. Here, we use scanning tunneling microscopy and spectroscopy to study the electronic interaction of pristine and nitrogen-doped graphene with self-assembled tetraphenylporphyrin molecules. We provide an extensive measurement of the electronic structure of single porphyrins on Au(111), thus revealing an electronic decoupling effect of the porphyrins adsorbed on graphene. A tip-induced switching of the inner hydrogen atoms of porphyrins, first identified on Au(111), is observed on graphene, allowing the identification of the molecular conformation of porphyrins in the self-assembled molecular layer. On nitrogen-doped graphene, a local modification of the charge transfer around the nitrogen sites is evidenced <i>via</i> a downshift of the energies of the molecular elecronic states. These data show how the presence of nitrogen atoms in the graphene network modifies the electronic interaction of organic molecules with graphene. These results provide a basic understanding for the exploitation of doped graphene in molecular sensors or nanoelectronics
Grain Boundaries in Graphene on SiC(0001̅) Substrate
Grain boundaries in epitaxial graphene
on the SiC(0001̅)
substrate are studied using scanning tunneling microscopy and spectroscopy.
All investigated small-angle grain boundaries show pronounced out-of-plane
buckling induced by the strain fields of constituent dislocations.
The ensemble of observations determines the critical misorientation
angle of buckling transition θ<sub>c</sub> = 19 ± 2°.
Periodic structures are found among the flat large-angle grain boundaries.
In particular, the observed θ = 33 ± 2° highly ordered
grain boundary is assigned to the previously proposed lowest formation
energy structural motif composed of a continuous chain of edge-sharing
alternating pentagons and heptagons. This periodic grain boundary
defect is predicted to exhibit strong valley filtering of charge carriers
thus promising the practical realization of all-electric valleytronic
devices
Identification of Nitrogen Dopants in Single-Walled Carbon Nanotubes by Scanning Tunneling Microscopy
Using scanning tunnelling microscopy and spectroscopy, we investigated the atomic and electronic structure of nitrogen-doped single walled carbon nanotubes synthesized by chemical vapor deposition. The insertion of nitrogen in the carbon lattice induces several types of point defects involving different atomic configurations. Spectroscopic measurements on semiconducting nanotubes reveal that these local structures can induce either extended shallow levels or more localized deep levels. In a metallic tube, a single doping site associated with a donor state was observed in the gap at an energy close to that of the first van Hove singularity. Density functional theory calculations reveal that this feature corresponds to a substitutional nitrogen atom in the carbon network