659 research outputs found
Kohn anomaly and interplay of electron-electron and electron-phonon interactions in epitaxial graphene
The interplay of electron-phonon (el-ph) and electron-electron (el-el)
interactions in epitaxial graphene is studied by directly probing its
electronic structure. We found a strong coupling of electrons to the soft part
of the A1g phonon evident by a kink at 150+/-15 meV, while the coupling of
electrons to another expected phonon E2g at 195 meV can only be barely
detected. The possible role of the el-el interaction to account for the
enhanced coupling of electrons to the A1g phonon, and the contribution of el-ph
interaction to the linear imaginary part of the self energy at high binding
energy are also discussed. Our results reveal the dominant role of the A1g
phonon in the el-ph interaction in graphene, and highlight the important
interplay of el-el and el-ph interactions in the self energy of graphene.Comment: accepted to Phys. Rev.
Argumentative Competence in Friend and Stranger Dyadic Exchanges
This is a post-peer-review, pre-copyedit version of an article published in Argumentation. The final version is available online at: https://doi.org/10.1007/s10503-019-09487-x .This manuscript investigates the role of argumentative competence in interpersonal dyadic exchanges. Specifically, this study examined the two sub-dimensions of competence, argumentative effectiveness and appropriateness, and their connections with argumentative traits, situational features, and argument satisfaction. In addition, self-perceived versus observed argumentative competence were compared. Participants in the study (N = 282, 141 dyads) completed measures before and after a face-to-face argumentative discussion with another person about one of two possible topics (student athlete pay and texting while driving). Results revealed that argumentation traits had little effect on argumentative competence, but competence was predicted by one’s knowledge about the topic. Argument satisfaction depended only on arguers’ own competence, not their partners’. Finally, a perceptual bias existed regarding argument effectiveness (but not appropriateness) in that participants rated themselves higher than did observers
Persistence of metabolic monitoring for psychiatry inpatients treated with second‐generation antipsychotics utilizing a computer‐based intervention
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/135222/1/jcpt12368.pd
Penetration of alkali atoms throughout graphene membrane: theoretical modeling
Theoretical studies of penetration of various alkali atoms (Li, Na, Rb, Cs)
throughout graphene membrane grown on silicon carbide substrate are reported
and compared with recent experimental results. Results of first principles
modeling demonstrate rather low (about 0.8 eV) energy barrier for the formation
of temporary defects in carbon layer required for the penetration of Li at high
concentration of adatoms, higher (about 2 eV) barrier for Na, and barriers
above 4 eV for Rb and Cs. Experiments prove migration of lithium adatoms from
graphene surface to the buffer layer and SiC substrate at room temperature,
sodium at 100{\deg}C and impenetrability of graphene membrane for Rb and Cs.
Differences between epitaxial and free standing graphene for the penetration of
alkali ions are also discussed.Comment: 16 pages, 3 figure, accepted to Nanoscal
Scanning tunneling spectroscopy of inhomogeneous electronic structure in monolayer and bilayer graphene on SiC
We present a scanning tunneling spectroscopy (STS) study of the local
electronic structure of single and bilayer graphene grown epitaxially on a
SiC(0001) surface. Low voltage topographic images reveal fine, atomic-scale
carbon networks, whereas higher bias images are dominated by emergent spatially
inhomogeneous large-scale structure similar to a carbon-rich reconstruction of
SiC(0001). STS spectroscopy shows a ~100meV gap-like feature around zero bias
for both monolayer and bilayer graphene/SiC, as well as significant spatial
inhomogeneity in electronic structure above the gap edge. Nanoscale structure
at the SiC/graphene interface is seen to correlate with observed electronic
spatial inhomogeneity. These results are important for potential devices
involving electronic transport or tunneling in graphene/SiC.Comment: Acknowledgment added. 11 pages, 3 figure
Electric Field Effects on Graphene Materials
Understanding the effect of electric fields on the physical and chemical
properties of two-dimensional (2D) nanostructures is instrumental in the design
of novel electronic and optoelectronic devices. Several of those properties are
characterized in terms of the dielectric constant which play an important role
on capacitance, conductivity, screening, dielectric losses and refractive
index. Here we review our recent theoretical studies using density functional
calculations including van der Waals interactions on two types of layered
materials of similar two-dimensional molecular geometry but remarkably
different electronic structures, that is, graphene and molybdenum disulphide
(MoS). We focus on such two-dimensional crystals because of they
complementary physical and chemical properties, and the appealing interest to
incorporate them in the next generation of electronic and optoelectronic
devices. We predict that the effective dielectric constant () of
few-layer graphene and MoS is tunable by external electric fields (). We show that at low fields ( V/\AA)
assumes a nearly constant value 4 for both materials, but increases at
higher fields to values that depend on the layer thickness. The thicker the
structure the stronger is the modulation of with the electric
field. Increasing of the external field perpendicular to the layer surface
above a critical value can drive the systems to an unstable state where the
layers are weakly coupled and can be easily separated. The observed dependence
of on the external field is due to charge polarization driven by
the bias, which show several similar characteristics despite of the layer
considered.Comment: Invited book chapter on Exotic Properties of Carbon Nanomatter:
Advances in Physics and Chemistry, Springer Series on Carbon Materials.
Editors: Mihai V. Putz and Ottorino Ori (11 pages, 4 figures, 30 references
Atomic Hole Doping of Graphene
Graphene is an excellent candidate for the next generation of electronic
materials due to the strict two-dimensionality of its electronic structure as
well as the extremely high carrier mobility. A prerequisite for the development
of graphene based electronics is the reliable control of the type and density
of the charge carriers by external (gate) and internal (doping) means. While
gating has been successfully demonstrated for graphene flakes and epitaxial
graphene on silicon carbide, the development of reliable chemical doping
methods turns out to be a real challenge. In particular hole doping is an
unsolved issue. So far it has only been achieved with reactive molecular
adsorbates, which are largely incompatible with any device technology. Here we
show by angle-resolved photoemission spectroscopy that atomic doping of an
epitaxial graphene layer on a silicon carbide substrate with bismuth, antimony
or gold presents effective means of p-type doping. Not only is the atomic
doping the method of choice for the internal control of the carrier density. In
combination with the intrinsic n-type character of epitaxial graphene on SiC,
the charge carriers can be tuned from electrons to holes, without affecting the
conical band structure
Graphene for spintronics: giant Rashba splitting due to hybridization with Au
Graphene in spintronics has so far primarily meant spin current leads of high
performance because the intrinsic spin-orbit coupling of its pi-electrons is
very weak. If a large spin-orbit coupling could be created by a proximity
effect, the material could also form active elements of a spintronic device
such as the Das-Datta spin field-effect transistor, however, metal interfaces
often compromise the band dispersion of massless Dirac fermions. Our
measurements show that Au intercalation at the graphene-Ni interface creates a
giant spin-orbit splitting (~100 meV) in the graphene Dirac cone up to the
Fermi energy. Photoelectron spectroscopy reveals hybridization with Au-5d
states as the source for the giant spin-orbit splitting. An ab initio model of
the system shows a Rashba-split dispersion with the analytically predicted
gapless band topology around the Dirac point of graphene and indicates that a
sharp graphene-Au interface at equilibrium distance will account for only ~10
meV spin-orbit splitting. The ab initio calculations suggest an enhancement due
to Au atoms that get closer to the graphene and do not violate the sublattice
symmetry.Comment: 16 pages (3 figures) + supplementary information 16 pages (14
figures
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