16 research outputs found
Zr-metal adhesion on graphenic nanostructures
3 pages, 3 figures.-- PACS nrs.: 68.35.Np, 61.46.Fg, 61.46.Df.Our high resolution transmission electronic microscopy studies of multiwall carbon nanotubes show, after the growth of zirconia nanoparticles by a hydrothermal route, the presence of surface Zr, forming an atomically thin layer. Using first-principles calculations we investigate the nature of the Zr–C interaction, which is neither ionic nor covalent, and the optimal coverage for the Zr metal in a graphene flake. This preferred coverage is in agreement with that deduced from electron energy loss spectra experiments. We show also that the amount of charge transferred to the C layer saturates as the Zr coverage increases and the Zr–C bond becomes weaker.We want to acknowledge the support by the ETORTEK (NANOMAT) program of the Basque government, the Intramural Special Project (Reference No. 2006601242), the Spanish Ministerio de Ciencia y Tecnología (MCyT) of
Spain (Grant No. Fis 2007-66711-C02-C01), and the European Network of Excellence NANOQUANTA (NM4-CT-2004-500198). Y.S.P. gratefully acknowledges his DIPC grant.Peer reviewe
Chemical Bonding of Transition-metal Co Clusters with Graphene
We carried out density functional calculation to study Co clusters on
graphene. We deposit several free isomers in different disposition respect to
hexagonal lattice nodes, studying even the isomer recently obtained
as the most stable one. Surprisingly, Co clusters bonded to graphene
prefer structures where the low lying isomer is much
distorted, because it is linked with more bonds than in previous works. For any
isomer the most stable position binds to graphene by the Co atoms that can lose
electrons. We find that the charge transfers between graphene and clusters are
small enough to conclude that the Co-graphene binding is not ionic-like but
chemical. Besides, the same order of stability among the different isomers on
doped graphene is well kept. These findings could also be of interest for
magnetic clusters on graphenic nanostructures such as ribbons and nanotubes.Comment: 12 pages, 6 figure
Properties of Graphene: A Theoretical Perspective
In this review, we provide an in-depth description of the physics of
monolayer and bilayer graphene from a theorist's perspective. We discuss the
physical properties of graphene in an external magnetic field, reflecting the
chiral nature of the quasiparticles near the Dirac point with a Landau level at
zero energy. We address the unique integer quantum Hall effects, the role of
electron correlations, and the recent observation of the fractional quantum
Hall effect in the monolayer graphene. The quantum Hall effect in bilayer
graphene is fundamentally different from that of a monolayer, reflecting the
unique band structure of this system. The theory of transport in the absence of
an external magnetic field is discussed in detail, along with the role of
disorder studied in various theoretical models. We highlight the differences
and similarities between monolayer and bilayer graphene, and focus on
thermodynamic properties such as the compressibility, the plasmon spectra, the
weak localization correction, quantum Hall effect, and optical properties.
Confinement of electrons in graphene is nontrivial due to Klein tunneling. We
review various theoretical and experimental studies of quantum confined
structures made from graphene. The band structure of graphene nanoribbons and
the role of the sublattice symmetry, edge geometry and the size of the
nanoribbon on the electronic and magnetic properties are very active areas of
research, and a detailed review of these topics is presented. Also, the effects
of substrate interactions, adsorbed atoms, lattice defects and doping on the
band structure of finite-sized graphene systems are discussed. We also include
a brief description of graphane -- gapped material obtained from graphene by
attaching hydrogen atoms to each carbon atom in the lattice.Comment: 189 pages. submitted in Advances in Physic
Magnetic Properties of Single Transition-Metal Atom Absorbed Graphdiyne and Graphyne Sheet
The electronic and magnetic properties of single 3d transition-metal(TM) atom
(V, Cr, Mn, Fe, Co, and Ni) adsorbed graphdiyne (GDY) and graphyne (GY) are
systematically studied using first-principles calculations within the density
functional framework. We find that the adsorption of TM atom not only
efficiently modulates the electronic structures of GDY/GY system, but also
introduces excellent magnetic properties, such as half-metal and spin-select
half-semiconductor. Such modulation originates from the charge transfer between
TM adatom and the GDY/GY sheet as well as the electron redistribution of the TM
intra-atomic s, p, and d orbitals. Our results indicate that the TM adsorbed
GDY/GY are excellent candidates for spintronics.Comment: 8 pages, 7 figure
sp-Electron Magnetic Clusters with a Large Spin in Graphene
Motivated by recent experimental data (Sepioni, M. et al. Phys. Rev. Lett.
2010, 105, 207205), we have studied the possibility of forming magnetic
clusters with spin S> 1/2 on graphene by adsorption of hydrogen atoms or
hydroxyl groups. Migration of hydrogen atoms and hydroxyl groups on the surface
of graphene during the delamination of HOPG led to the formation of seven-atom
or seven-OH-group clusters with S=5/2 that were of a special interest. The
coincidence of symmetry of the clusters with the graphene lattice strengthens
the stability of the cluster. For (OH)7 clusters that were situated greater
than 3 nm from one another, the reconstruction barrier to a nonmagnetic
configuration was approximately 0.4 eV, whereas for H7 clusters, there was no
barrier and the high-spin state was unstable. Stability of the high-spin
clusters increased if they were formed on top of ripples. Exchange interactions
between the clusters were studied and we have shown that the ferromagnetic
state is improbable. The role of the chemical composition of the solvent used
for the delamination of graphite is discussed.Comment: 22 pages, 1 table, 4 figures. Minor changes, few refs added. Accepted
to ACS Nan
Do Cement Nanotubes exist?
Using atomistic simulations, this work indicates that cement nanotubes can exist. The chemically compatible nanotubes are constructed from the two main minerals in ordinary Portland cement pastes, namely calcium hydroxide and a calcium silicate hydrate called tobermorite. These results show that such nanotubes are stable and have outstanding mechanical properties, unique characteristics that make them ideally suitable for nanoscale reinforcements of cements.Peer reviewe