19 research outputs found
Edge Saturation effects on the magnetism and band gaps in multilayer graphene ribbons and flakes
Using a density functional theory based electronic structure method and
semi-local density approximation, we study the interplay of geometric
confinement, magnetism and external electric fields on the electronic structure
and the resulting band gaps of multilayer graphene ribbons whose edges are
saturated with molecular hydrogen (H) or hydroxyl (OH) groups. We discuss
the similarities and differences of computed features in comparison with the
atomic hydrogen (or H-) saturated ribbons and flakes. For H
edge-saturation, we find \emph{shifted} labeling of three armchair ribbon
classes and magnetic to non-magnetic transition in narrow zigzag ribbons whose
critical width changes with the number of layers. Other computed
characteristics, such as the existence of a critical gap and external electric
field behavior, layer dependent electronic structure, stacking-dependent band
gap induction and the length confinement effects remain qualitatively same with
those of H-saturated ribbons.Comment: 9 pages, 10 figures, submitte
Tuning the electronic structure of graphene by ion irradiation
Mechanically exfoliated graphene layers deposited on SiO2 substrate were
irradiated with Ar+ ions in order to experimentally study the effect of atomic
scale defects and disorder on the low-energy electronic structure of graphene.
The irradiated samples were investigated by scanning tunneling microscopy and
spectroscopy measurements, which reveal that defect sites, besides acting as
scattering centers for electrons through local modification of the on-site
potential, also induce disorder in the hopping amplitudes. The most important
consequence of the induced disorder is the substantial reduction in the Fermi
velocity, revealed by bias-dependent imaging of electron-density oscillations
observed near defect sites
Different sensing mechanisms in single wire and mat carbon nanotubes chemical sensors
Chemical sensing properties of single wire and mat form sensor structures
fabricated from the same carbon nanotube (CNT) materials have been compared.
Sensing properties of CNT sensors were evaluated upon electrical response in
the presence of five vapours as acetone, acetic acid, ethanol, toluene, and
water. Diverse behaviour of single wire CNT sensors was found, while the mat
structures showed similar response for all the applied vapours. This indicates
that the sensing mechanism of random CNT networks cannot be interpreted as a
simple summation of the constituting individual CNT effects, but is associated
to another robust phenomenon, localized presumably at CNT-CNT junctions, must
be supposed.Comment: 12 pages, 5 figures,Applied Physics A: Materials Science and
Processing 201
Graphene nanoribbons with zigzag and armchair edges prepared by scanning tunneling microscope lithography on gold substrates
The properties of graphene nanoribbons are dependent on both the nanoribbon width and the crystallographic orientation of the edges. Scanning tunneling microscope lithography is a method which is able to create graphene nanoribbons with well defined edge orientation, having a width of a few nanometers. However, it has only been demonstrated on the top layer of graphite. In order to allow practical applications of this powerful lithography technique, it needs to be implemented on single layer graphene. We demonstrate the preparation of graphene nanoribbons with well defined crystallographic orientation on top of gold substrates. Our transfer and lithography approach brings one step closer the preparation of well defined graphene nanoribbons on arbitrary substrates for nanoelectronic applications
Spontaneous doping of the basal plane of MoS2 single layers through oxygen substitution under ambient conditions
The chemical inertness of the defect-free basal plane confers environmental
stability to MoS2 single-layers, but it also limits their chemical versatility
and catalytic activity. The stability of the pristine MoS2 basal plane against
oxidation under ambient conditions is a widely accepted assumption in the
interpretation of various studies and applications. However, single-atom level
structural investigations reported here reveal that oxygen atoms spontaneously
incorporate into the basal plane of MoS2 single layers during ambient exposure.
Our scanning tunneling microscopy investigations reveal a slow oxygen
substitution reaction, upon which individual sulfur atoms are one by one
replaced by oxygen, giving rise to solid solution type 2D MoS2-xOx crystals. O
substitution sites present all over the basal plane act as single-atomic active
reaction centers, substantially increasing the catalytic activity of the entire
MoS2 basal plane for the electrochemical H2 evolution reaction.Comment: 6 pages, 5 figure
Tailoring the atomic structure of graphene nanoribbons by scanning tunnelling microscope lithography
Dominantly epitaxial growth of graphene on Ni (1 1 1) substrate
Graphene was grown on a Ni (1 1 1) thin layer, used as a substrate. The Ni layer itself was grown on singlecrystal sapphire (0 0 0 1). Carbon was deposited by chemical vapor deposition using a mixture of methane,argon and hydrogen at atmospheric pressure implementing a constant gas flow (4.8–5 l/min) varying boththe gas composition and the deposition temperature (900–980◦C) and cooling rate (8–16◦C/min) in thedifferent experiments. Formation of uninterruptedly grown epitaxial single layer graphene was observedover the Ni (1 1 1) thin film substrate. Epitaxial growth was proven through STM measurements. Electrondiffraction studies, also confirmed by STM, demonstrated that only one dominant orientation exists inthe graphene, both results providing evidence of the epitaxial growth. On top of the, continuous, largearea graphene flakes were also observed with sizes varying between 10 nm and 10 m. Most of the topflakes are turbostratically related to the continuous underlying epitaxial graphene layer. The formation ofthe graphene layer with constant dominant orientation was observed over millimeter wide areas. Largeareas (≈20–40 m in diameter) of continuous, epitaxial graphene, free of additional deposits and flakeswere obtained for the best set of growth parameters.16101sciescopu