Role of silicon dangling bonds in the electronic properties of epitaxial graphene on silicon carbide

In this paper, we study the electronic properties of epitaxial graphene (EG) on silicon carbide by means of ab initio calculations based on the local spin density approximation + U method taking into account the Coulomb interaction between Si localized electrons. We show that this interaction is not completely suppressed but is screened by carbon layers grown on-top of silicon carbide. This finding leads to a good qualitative understanding of the experimental results reported on EG on silicon carbide. Our results highlight the presence of the Si localized states and might explain the anomalous Hanle curve and the high values of spin relaxation time in EG

Optimization of an extrusion die for polymer flow

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Dependence of hole effective mass on nitrogen concentration in W-type strained InAs(N)/GaSb/InAs(N) quantum well lasers

We have investigated the effects of nitrogen N concentration on the properties of hole subbands and effective mass in dilute-nitride type-II InAsN/GaSb laser diodes on InAs substrate with “W” design. Using a 5-bands k·p model, we obtained interesting numerical results for the heavy-hole (hh) and the light-hole (lh) subbands. The hole effective masses were found to be very sensitive to the nitrogen concentration and to the differences in the Luttinger parameters between the well and the barrier. In addition, the hole effective masses are found to be strongly affected by band-anticrossing (BAC) model

Enhanced sensitivity of epitaxial graphene to NO2 by water coadsorption

Abstract Image Epitaxial graphene has shown a high sensitivity to NO2 down to ppb-level. However, the surrounding environment can strongly influence its sensing capability. Since water is naturally present in the atmosphere, understanding the effect of humidity on the gas sensitivity of epitaxial graphene is of paramount interest for creating novel gas sensors. Here, we show experimentally that epitaxial graphene exhibits an enhanced electrical response of a factor more than two for NO2 under humid condition compared to dry condition due to a strong enhancement of the hole doping of the graphene layer. Using electronic structure calculations, we explain the sensitivity enhancement by a water dipole screening of the graphene-NO2 dipole causing an increase of the charge transfer and consequently of the hole doping of the graphene layer

From nanographene to monolayer graphene on 6H-SiC(0001) substrate

International audienceGraphene quantum dots, nanoribbons, and nanographene are great promising in various applications owing to the quantum confinement and edge effects. Here we evidence the presence of epitaxial nanographene on SiC. Morphology and electronic structure of the graphene layers have been analyzed by SPELEEM. Using Scanning Tunneling Microscopy, we show that the increase of relative number of clusters carbon enabled the observation of nanographene, the diameter of which was around 20 nm. This nanographene shows a honeycomb structure at atomic level. The local chemical and electronic properties of the sample have been determined by photoelectron spectroscopy using synchrotron radiation

Control of the degree of surface graphitization on 3C-SiC(100)/Si(100)

International audienceThe current method of growing graphene by thermal decomposition of 3C-SiC(100) on silicon substrates is technologically attractive. Here, we investigate the evolution of the surface graphitization as a function of the synthesis temperature. We establish that the carbon enrichment of the surface is characterized by a clear modulation of the surface potential and structuration. The structural properties analysis of the graphene layers by low energy electron diffraction and micro-Raman spectroscopy demonstrate a graphitization of the surfac

THEORETICAL COMPARISON OF DILUTE-NITRIDE "W" AND "M" InAsN / GaSb MID-INFRARED LASER DIODES

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