159 research outputs found
Stacking-dependent electronic structure of trilayer graphene resolved by nanospot angle-resolved photoemission spectroscopy
The crystallographic stacking order in multilayer graphene plays an important
role in determining its electronic structure. In trilayer graphene,
rhombohedral stacking (ABC) is particularly intriguing, exhibiting a flat band
with an electric-field tunable band gap. Such electronic structure is distinct
from simple hexagonal stacking (AAA) or typical Bernal stacking (ABA), and is
promising for nanoscale electronics, optoelectronics applications. So far clean
experimental electronic spectra on the first two stackings are missing because
the samples are usually too small in size (um or nm scale) to be resolved by
conventional angle-resolved photoemission spectroscopy (ARPES). Here by using
ARPES with nanospot beam size (NanoARPES), we provide direct experimental
evidence for the coexistence of three different stackings of trilayer graphene
and reveal their distinctive electronic structures directly. By fitting the
experimental data, we provide important experimental band parameters for
describing the electronic structure of trilayer graphene with different
stackings
A chemical imaging and Nano-ARPES study of well-ordered thermally reduced SrTiO3(100)
The structural and electronic properties of thermally reduced SrTiO3(100)
single crystals have been investigated using a probe with real- and
reciprocal-space sensitivity: a synchrotron radiation microsopic setup which
offers the possibility of Scanning Photoemission Microscopy and Angle Resolved
Photoelectron Spectroscopy (ARPES) down to the nanometric scale. We have
spectroscopically imaged the chemical composition of samples which present
reproducible and suitable low-energy electron diffraction patterns after
following well-established thermal reduction protocols. At the micrometric
scale, Ca-rich areas have been directly imaged using high-energy resolution
core level photoemission. Moreover, we have monitored the effect of Ca
segregation on different features of the SrTiO3(100) electronic band structure,
measuring ARPES inside, outside and at the interface of surface inhomogeneities
with the identified Ca-rich areas. In particular, the interaction of Ca with
the well-known intragap localized state, previously attributed to oxygen
vacancies, has been investigated. Moreover, the combination of direct imaging
and spectroscopic techniques with high spatial resolution has clarified the
long-standing dilemma related to the bulk or surface character of Ca
segregation in SrTiO3. Our results present solid evidence that the penetration
depth of Ca segregation is very small. In contrast to what has been previously
proposed, the origin of long-range surface reconstructions can unlikely be
associated to Ca due to strong local variations of its surface concentration.Comment: 7 pages, 6 figure
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Large-area epitaxial growth of curvature-stabilized ABC trilayer graphene.
The properties of van der Waals (vdW) materials often vary dramatically with the atomic stacking order between layers, but this order can be difficult to control. Trilayer graphene (TLG) stacks in either a semimetallic ABA or a semiconducting ABC configuration with a gate-tunable band gap, but the latter has only been produced by exfoliation. Here we present a chemical vapor deposition approach to TLG growth that yields greatly enhanced fraction and size of ABC domains. The key insight is that substrate curvature can stabilize ABC domains. Controllable ABC yields ~59% were achieved by tailoring substrate curvature levels. ABC fractions remained high after transfer to device substrates, as confirmed by transport measurements revealing the expected tunable ABC band gap. Substrate topography engineering provides a path to large-scale synthesis of epitaxial ABC-TLG and other vdW materials
Flat Electronic Bands in Long Sequences of Rhombohedral-stacked Multilayer Graphene
The crystallographic stacking order in multilayer graphene plays an important
role in determining its electronic properties. It has been predicted that a
rhombohedral (ABC) stacking displays a conducting surface state with flat
electronic dispersion. In such a flat band, the role of electron-electron
correlation is enhanced possibly resulting in high Tc superconductivity, charge
density wave or magnetic orders. Clean experimental band structure measurements
of ABC stacked specimens are missing because the samples are usually too small
in size. Here, we directly image the band structure of large multilayer
graphene flake containing approximately 14 consecutive ABC layers.
Angle-resolved photoemission spectroscopy experiments reveal the flat
electronic bands near the K point extends by 0.13 {\AA}-1 at the Fermi level at
liquid nitrogen temperature. First-principle calculations identify the
electronic ground state as an antiferromagnetic state with a band gap of about
40 meV
Diamond-like carbon coating under oleic acid lubrication: Evidence for graphene oxide formation in superlow friction
International audienceThe achievement of the superlubricity regime, with a friction coefficient below 0.01, is the Holy Grail of many tribological applications, with the potential to have a remarkable impact on economic and environmental issues. Based on a combined high-resolution photoemission and soft X-ray absorption study, we report that superlubricity can be realized for engineering applications in bearing steel coated with ultra-smooth tetrahedral amorphous carbon (ta-C) under oleic acid lubrication. The results show that tribochemical reactions promoted by the oil lubrication generate strong structural changes in the carbon hybridization of the ta-C hydrogen-free carbon, with initially high sp 3 content. Interestingly, the macroscopic superlow friction regime of moving mechanical assemblies coated with ta-C can be attributed to a few partially oxidized graphene-like sheets, with a thickness of not more than 1 nm, formed at the surface inside the wear scar. The sp 2 planar carbon and oxygen-derived species are the hallmark of these mesoscopic surface structures created on top of colliding asperities as a result of the tribochemical reactions induced by the oleic acid lubrication. Atomistic simulations elucidate the tribo-formation of such graphene-like structures, providing the link between the overall atomistic mechanism and the macroscopic experimental observations of green superlubricity in the investigated ta-C/oleic acid tribological systems
Graphene ribbon growth on structured silicon carbide
Structured Silicon Carbide was proposed to be an ideal template for the production of arrays of edge specific graphene nanoribbons (GNRs), which could be used as a base material for graphene transistors. We prepared periodic arrays of nanoscaled stripe-mesas on SiC surfaces using electron beam lithography and reactive ion etching. Subsequent epitaxial graphene growth by annealing is differentiated between the basal-plane mesas and the faceting stripe walls as monitored by means of atomic force microscopy (AFM). Microscopic low energy electron diffraction (ÎĽ-LEED) revealed that the graphene ribbons on the facetted mesa side walls grow in epitaxial relation to the basal-plane graphene with an armchair orientation at the facet edges. The ÂĽ- band system of the ribbons exhibits linear bands with a Dirac like shape corresponding to monolayer graphene as identified by angle-resolved photoemission spectroscopy (ARPES)
Influence of the adherence to the Mediterranean diet on the effect of smoking on genomewide methylation among subjects with metabolic syndrome
Pòster presentat al congrés " Epigenetics: Playing with the Gameof Life" celebrat al University Hospital Halle (Saale) entre els dies 13-15 de 2019.Tobacco smoking is an important risk factor for lung cancer, respiratory diseases and cardiovascular diseases, among others. Moreover, smoking can speed up the normal aging process of several tissues increasing the biological age. Changes in methylation due to smoking have been demonstrated at several loci across the genome, particularly in long-term smokers (Figure 1). The most consistent association reported in different populations has been decreased methylation in smokers in comparison with non-smokers at the CpG cg05575921, located in the gene for the aryl hydrocarbon receptor repressor (AHRR) located in chromosome 5
The Gln241His polymorphism in the carbohydrate response element binding protein (MLXIPL) gene
Comunicació presentada com a pòster a European Association of Human Genetics Conference, May 23-26, 2009, Vien
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