1,238 research outputs found
Realistic large-scale modeling of Rashba and induced spin-orbit effects in graphene/high-Z-metal systems
Graphene, as a material with a small intrinsic spin-orbit interaction of
approximately 1 eV, has a limited application in spintronics. Adsorption
of graphene on the surfaces of heavy-metals was proposed to induce the strong
spin-splitting of the graphene -bands either via Rashba effect or due to
the induced spin-orbit effects via hybridization of the valence band states of
graphene and metal. The spin-resolved photoelectron spectroscopy experiments
performed on graphene adsorbed on the substrates containing heavy elements
demonstrate the "giant" spin-splitting of the states of the order of 100
meV in the vicinity of the Fermi level () and the K point. However, the
recent scanning tunneling spectroscopy experiments did not confirm these
findings, leaving the fact of the observation of the "giant" Rashba effect or
induced spin-orbit interaction in graphene still open. Thus, a detailed
understanding of the physics in such systems is indispensable. From a theory
side this requires, first of all, correct modeling of the graphene/metal
interfaces under study. Here we present realistic super-cell density-functional
theory calculations, including dispersion interaction and spin-orbit
interaction, for several graphene/high-Z-metal interfaces. While correctly
reproduce the spin-splitting features of the metallic surfaces, their
modifications under graphene adsorption and doping level of graphene, our
studies reveal that neither "giant" Rashba- nor spin-orbit induced splitting of
the graphene pi states around take place.Comment: accepted for publicatio
Playing graphene nanodrums: force spectroscopy of graphene on Ru(0001)
Graphene, a thinnest material in the world, can form moire structures on
different substrates, including graphite, h-BN, or metal surfaces. In such
systems the structure of graphene, i. e. its corrugation, as well as its
electronic and elastic properties are defined by the combination of the system
geometry and local interaction strength at the interface. The corrugation in
such structures on metals is heavily extracted from diffraction or local probe
microscopy experiments and can be obtained only via comparison with theoretical
data, which usually simulate the experimental findings. Here we show that
graphene corrugation on metals can be measured directly employing atomic force
spectroscopy and obtained value coincides with state-of-the-art theoretical
results. We also address the elastic reaction of the formed graphene nanodoms
on the indentation process by the scanning tip that is important for the
modeling and fabrication of graphene-based nanoresonators on the nanoscale.Comment: manuscript and supplementary materia
First multi-reference correlation treatment of bulk metals
Existence of the sp-d hybridization of the valence band states of the fcc Ca
and Sr in the vicinity of the Fermi level indicates that their electronic wave
function can have a multi-reference (MR) character. We performed a wave
function-based correlation treatment for these materials by means of the method
of increments. As oppose to the single-reference correlation treatment (here:
coupled cluster), which fails to describe cohesive properties in both cases,
employing the MR averaged coupled pair functional one can achieve almost 100 %
of the experimental correlation energy.Comment: 16 pages, 8 figures, 3 table
Graphene growth and properties on metal substrates
Graphene-metal interface as one of the interesting graphene-based objects
attracts much attention from both application and fundamental science points of
view. This paper gives a timely review of the recent experimental works on the
growth and the electronic properties of the graphene-metal interfaces. This
work makes a link between huge amount of experimental and theoretical data
allowing one to understand the influence of the metallic substrate on the
electronic properties of a graphene overlayer and how its properties can be
modified in a controllable way. The further directions of studies and
applications of the graphene-metal interfaces are discussed.Comment: 30 pages, 18 figure
Comment on "Spin-Orbit Coupling Induced Gap in Graphene on Pt(111) with Intercalated Pb Monolayer"
Recently a paper of Klimovskikh et al. was published presenting experimental
and theoretical analysis of the graphene/Pb/Pt(111) system. The authors
investigate the crystallographic and electronic structure of this
graphene-based system by means of LEED, ARPES, and spin-resolved PES of the
graphene states in the vicinity of the Dirac point of graphene. The
authors of this paper demonstrate that an energy gap of approx. 200 meV is
opened in the spectral function of graphene directly at the Dirac point of
graphene and spin-splitting of 100 meV is detected for the upper part of the
Dirac cone. On the basis of the spin-resolved photoelectron spectroscopy
measurements of the region around the gap the authors claim that these
splittings are of a spin-orbit nature and that the observed spin structure
confirms the observation of the quantum spin Hall state in graphene, proposed
in earlier theoretical works. Here we will show that careful systematic
analysis of the experimental data presented in this manuscript is needed and
their interpretation require more critical consideration for making such
conclusions. Our analysis demonstrates that the proposed effects and
interpretations are questionable and require further more careful experiments.Comment: submitted: 02.02.2017; accepted: 09.03.201
Multichannel scanning probe microscopy and spectroscopy of graphene moire structures
The graphene moire structures on metals, as they demonstrate both long
(moire) and short (atomic) scale ordered structures, are the ideal systems for
the application of scanning probe methods. Here we present the complex studies
of the graphene/Ir(111) system by means of 3D scanning tunnelling and atomic
force microscopy/spectroscopy as well as Kelvin-probe force microscopy. All
results clearly demonstrate a variation of the moire and atomic scale contrasts
as a function of the bias voltage as well as the distance between the scanning
probe and the sample, allowing to discriminate between topographic and
electronic contributions in the imaging of a graphene layer on metals. The
presented results are accompanied by the state-of-the-art density functional
theory calculations demonstrating the excellent agreement between theoretical
and experimental data.Comment: 30 pages, 13 figures, submitted on 20.09.201
Restoring a free-standing character of graphene on Ru(0001)
Realization of a free-standing graphene is always a demanding task. Here we
use scanning probe microscopy and spectroscopy to study the crystallographic
structure and electronic properties of the uniform free-standing graphene
layers obtained by intercalation of oxygen monolayer in the "strongly" bonded
graphene/Ru(0001) interface. Spectroscopic data show that such graphene layer
is heavily p-doped with the Dirac point located at 552 meV above the Fermi
level. Experimental data are understood within DFT and the observed effects are
in good agreement with the theoretical data.Comment: manuscript and supplementary materia
Scanning probe microscopy and spectroscopy of graphene on metals
Graphene, a two-dimensional (2D) material with unique electronic properties,
appears to be an ideal object for the application of surface-science methods.
Among them, a family of scanning probe microscopy methods (STM, AFM, KPFM) and
the corresponding spectroscopy add-ons provide information about the structure
and electronic properties of graphene on the local scale (from inline imagem to
atoms). This review focuses on the recent applications of these
microscopic/spectroscopic methods for the investigation of graphene on metals
(interfaces, intercalation-like systems, graphene nanoribbons, and quantum
dots, etc.). It is shown that very important information about interaction
strength at the graphene/metal interfaces as well as about modification of the
electronic spectrum of graphene at the Fermi level can be obtained on the local
scale. The combination of these results with those obtained by other methods
and comparison with recent theoretical data demonstrate the power of this
approach for the investigation of the graphene-based systems.Comment: Feature Article in pss (b
General approach to the understanding the electronic structure of graphene on metals
This manuscript presents the general approach to the understanding of the
connection between bonding mechanism and electronic structure of graphene on
metals. To demonstrate its validity, two limiting cases of the "weakly" and
"strongly" bonded graphene on Al(111) and Ni(111) are considered, where the
Dirac cone is preserved or fully destroyed, respectively. Furthermore, the
electronic structure, i. e. doping level, hybridization effects, as well as a
gap formation at the Dirac point of the intermediate system, graphene/Cu(111),
is fully understood in the framework of the proposed approach. This work
summarises the long-term debates regarding connection of the bonding strength
and the valence band modification in the graphene/metal systems and paves a way
for the effective control of the electronic states of graphene in the vicinity
of the Fermi level.Comment: manuscript and supplementary materia
Adsorption of NO2 on WSe2: DFT and photoelectron spectroscopy studies
The electronic structure modifications of WSe2 upon NO2-adsorption at room
and low temperatures were studied by means of photoelectron spectroscopy. We
found only moderate changes in the electronic structure, which are manifested
as an upward shift of the WSe2-related bands to the smaller binding energies.
The observed effects are modelled within the density functional theory
approach, where a weak adsorption energy of gas molecules on the surface of
WSe2 was deduced. The obtained experimental data are explained as a valence
bands polarisation effect, which causes their energy shift depending on the
adsorption geometry and the formed dipole moment.Comment: manuscript and supplementary materia
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