3,305 research outputs found
An Evaluation of the Optical Maser Photon Rate Gyroscope
Mathematical development of resonant frequencies of electromagnetic cavity - Evaluation of optical maser photon rate gyroscop
Optical Maser Photon Rate Gyroscope
Resonant frequency equations for optical maser photon rate gyroscope desig
Finite element formulation for linear thermoviscoelastic materials
Report presents the finite difference equations in time and finite element matrix equations in space for general linear thermovisoelastic problems. The equations are derived for a general three-dimensional body but are applicable to one- and two-dimensional configurations with minor changes
Pressure seal Patent
Pressure seals suitable for use in environmental test chamber
Landau level spectroscopy of ultrathin graphite layers
Far infrared transmission experiments are performed on ultrathin epitaxial
graphite samples in a magnetic field. The observed cyclotron resonance-like and
electron-positron-like transitions are in excellent agreement with the
expectations of a single-particle model of Dirac fermions in graphene, with an
effective velocity of c* = 1.03 x 10^6 m/s.Comment: 4 pages 4 figures Slight revisions following referees' comments. One
figure modifie
Few layer graphene on SiC, pyrolitic graphite and graphene: a Raman scattering study
The results of micro-Raman scattering measurements performed on three
different ``graphitic'' materials: micro-structured disks of highly oriented
pyrolytic graphite, graphene multi-layers thermally decomposed from carbon
terminated surface of 4H-SiC and an exfoliated graphene monolayer are
presented. Despite its multi-layer character, most parts of the surface of the
graphitized SiC substrates shows a single-component, Lorentzian shape, double
resonance Raman feature in striking similarity to the case of a single graphene
monolayer. Our observation suggests a very weak electronic coupling between
graphitic layers on the SiC surface, which therefore can be considered to be
graphene multi-layers with a simple (Dirac-like) band structure.Comment: 4 pages, 3 Figures Structure of the paper strongly modified, small
changes in Fig 2 and 3. Same interpretation and same result
Experimental observation of nanoscale radiative heat flow due to surface plasmons in graphene and doped silicon
Owing to its two dimensional electronic structure, graphene exhibits many
unique properties. One of them is a wave vector and temperature dependent
plasmon in the infrared range. Theory predicts that due to these plasmons,
graphene can be used as a universal material to enhance nanoscale radiative
heat exchange for any dielectric substrate. Here we report on radiative heat
transfer experiments between SiC and a SiO2 sphere which have non matching
phonon polariton frequencies, and thus only weakly exchange heat in near field.
We observed that the heat flux contribution of graphene epitaxially grown on
SiC dominates at short distances. The influence of plasmons on radiative heat
transfer is further supported with measurements for doped silicon. These
results highlight graphenes strong potential in photonic nearfield and energy
conversion devices.Comment: 4 pages, 3 figure
Weak antilocalization in epitaxial graphene: evidence for chiral electrons
Transport in ultrathin graphite grown on silicon carbide is dominated by the
electron-doped epitaxial layer at the interface. Weak anti-localization in 2D
samples manifests itself as a broad cusp-like depression in the longitudinal
resistance for magnetic fields 10 mT 5 T. An extremely sharp
weak-localization resistance peak at B=0 is also observed. These features
quantitatively agree with graphene weak-(anti)localization theory implying the
chiral electronic character of the samples. Scattering contributions from the
trapped charges in the substrate and from trigonal warping due to the graphite
layer on top are tentatively identified. The Shubnikov-de Haas oscillations are
remarkably small and show an anomalous Berry's phase.Comment: 5 pages, 4 figures. Minor change
Tuning the electron-phonon coupling in multilayer graphene with magnetic fields
Magneto Raman scattering study of the E optical phonons in multi-layer
epitaxial graphene grown on a carbon face of SiC are presented. At 4.2K in
magnetic field up to 33 T, we observe a series of well pronounced avoided
crossings each time the optically active inter Landau level transition is tuned
in resonance with the E phonon excitation (at 196 meV). The width of the
phonon Raman scattering response also shows pronounced variations and is
enhanced in conditions of resonance. The experimental results are well
reproduced by a model that gives directly the strength of the electron-phonon
interaction.Comment: 4 pages, 3 figure
Microscopic correlation between chemical and electronic states in epitaxial graphene on SiC(000-1)
We present energy filtered electron emission spectromicroscopy with spatial
and wave-vector resolution on few layer epitaxial graphene on SiC$(000-1) grown
by furnace annealing. Low energy electron microscopy shows that more than 80%
of the sample is covered by 2-3 graphene layers. C1s spectromicroscopy provides
an independent measurement of the graphene thickness distribution map. The work
function, measured by photoelectron emission microscopy (PEEM), varies across
the surface from 4.34 to 4.50eV according to both the graphene thickness and
the graphene-SiC interface chemical state. At least two SiC surface chemical
states (i.e., two different SiC surface structures) are present at the
graphene/SiC interface. Charge transfer occurs at each graphene/SiC interface.
K-space PEEM gives 3D maps of the k_|| pi - pi* band dispersion in micron scale
regions show that the Dirac point shifts as a function of graphene thickness.
Novel Bragg diffraction of the Dirac cones via the superlattice formed by the
commensurately rotated graphene sheets is observed. The experiments underline
the importance of lateral and spectroscopic resolution on the scale of future
electronic devices in order to precisely characterize the transport properties
and band alignments
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