Kickshaws

A collection of linguistic kickshaws

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$_2$). 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 ($\varepsilon$) of few-layer graphene and MoS$_2$ is tunable by external electric fields ($E_{\rm ext}$). We show that at low fields ($E_{\rm ext}^{}<0.01$ V/\AA) $\varepsilon$ assumes a nearly constant value $\sim$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 $\varepsilon$ 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 $\varepsilon$ 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