1,500 research outputs found
Graphene formation on SiC substrates
Graphene layers were created on both C and Si faces of semi-insulating,
on-axis, 4H- and 6H-SiC substrates. The process was performed under high vacuum
(<10-4 mbar) in a commercial chemical vapor deposition SiC reactor. A method
for H2 etching the on-axis sub-strates was developed to produce surface steps
with heights of 0.5 nm on the Si-face and 1.0 to 1.5 nm on the C-face for each
polytype. A process was developed to form graphene on the substrates
immediately after H2 etching and Raman spectroscopy of these samples confirmed
the formation of graphene. The morphology of the graphene is described. For
both faces, the underlying substrate morphology was significantly modified
during graphene formation; sur-face steps were up to 15 nm high and the uniform
step morphology was sometimes lost. Mo-bilities and sheet carrier
concentrations derived from Hall Effect measurements on large area (16 mm
square) and small area (2 and 10 um square) samples are presented and shown to
compare favorably to recent reports.Comment: European Conference on Silicon Carbide and Related Materials 2008
(ECSCRM '08), 4 pages, 4 figure
Arteriovenous fistulae complicating cardiac pacemaker lead extraction: Recognition, evaluation, and management
AbstractTransvenous pacemaker lead extraction has become a commonly performed procedure that is associated with a small but significant risk. We report two cases where lead extraction was complicated by arteriovenous fistulae between branches of the aortic arch and the left brachiocephalic vein. Presenting signs and symptoms included severe chest or back pain, persistent or copious bleeding from the venous puncture site, unexplained hypotension or anemia, superior vena cava syndrome, and signs of central venous hypertension or acute heart failure. One patient whose injury was not recognized immediately and who did not undergo repair died rapidly, whereas the other patient who was diagnosed quickly underwent successful repair. Immediate diagnosis with arteriography and rapid intervention with surgery or percutaneous techniques are indicated and may prevent mortality. (J Vasc Surg 2000;32:1225-8.
Improvement of Morphology and Free Carrier Mobility through Argon-Assisted Growth of Epitaxial Graphene on Silicon Carbide
Graphene was epitaxially grown on both the C- and Si-faces of 4H- and
6H-SiC(0001) under an argon atmosphere and under high vacuum conditions.
Following growth, samples were imaged with Nomarski interference contrast and
atomic force microscopies and it was found that growth under argon led to
improved morphologies on the C-face films but the Si-face films were not
significantly affected. Free carrier transport studies were conducted through
Hall effect measurements, and carrier mobilities were found to increase and
sheet carrier densities were found to decrease for those films grown under
argon as compared to high vacuum conditions. The improved mobilities and
concurrent decreases in sheet carrier densities suggest a decrease in
scattering in the films grown under argon.Comment: 215th Meeting of the Electrochemical Society (ECS 215), 14 pages, 6
figure
Hall Effect Mobility of Epitaxial Graphene Grown on Silicon Carbide
Epitaxial graphene films were grown in vacuo by silicon sublimation from the
(0001) and (000-1) faces of 4H- and 6H-SiC. Hall effect mobilities and sheet
carrier densities of the films were measured at 300 K and 77 K and the data
depended on the growth face. About 40% of the samples exhibited holes as the
dominant carrier, independent of face. Generally, mobilities increased with
decreasing carrier density, independent of carrier type and substrate polytype.
The contributions of scattering mechanisms to the conductivities of the films
are discussed. The results suggest that for near-intrinsic carrier densities at
300 K epitaxial graphene mobilities will be ~150,000 cm2V-1s-1 on the (000-1)
face and ~5,800 cm2V-1s-1 on the (0001) face.Comment: Accepted for publication in Applied Physics Letters, 10 pages, 2
figure
Morphology Characterization of Argon-Mediated Epitaxial Graphene on C-face SiC
Epitaxial graphene layers were grown on the C-face of 4H- and 6H-SiC using an
argon-mediated growth process. Variations in growth temperature and pressure
were found to dramatically affect the morphological properties of the layers.
The presence of argon during growth slowed the rate of graphene formation on
the C-face and led to the observation of islanding. The similarity in the
morphology of the islands and continuous films indicated that island nucleation
and coalescence is the growth mechanism for C-face graphene.Comment: 12 pages, 4 figure
Epitaxial Graphene Growth on SiC Wafers
An in vacuo thermal desorption process has been accomplished to form
epitaxial graphene (EG) on 4H- and 6H-SiC substrates using a commercial
chemical vapor deposition reactor. Correlation of growth conditions and the
morphology and electrical properties of EG are described. Raman spectra of EG
on Si-face samples were dominated by monolayer thickness. This approach was
used to grow EG on 50 mm SiC wafers that were subsequently fabricated into
field effect transistors with fmax of 14 GHz.Comment: 215th Meeting of the Electrochemical Society, 8 pages, 8 figure
Search for the Higgs boson in events with missing transverse energy and b quark jets produced in proton-antiproton collisions at s**(1/2)=1.96 TeV
We search for the standard model Higgs boson produced in association with an
electroweak vector boson in events with no identified charged leptons, large
imbalance in transverse momentum, and two jets where at least one contains a
secondary vertex consistent with the decay of b hadrons. We use ~1 fb-1
integrated luminosity of proton-antiproton collisions at s**(1/2)=1.96 TeV
recorded by the CDF II experiment at the Tevatron. We find 268 (16) single
(double) b-tagged candidate events, where 248 +/- 43 (14.4 +/- 2.7) are
expected from standard model background processes. We place 95% confidence
level upper limits on the Higgs boson production cross section for several
Higgs boson masses ranging from 110 GeV/c2 to 140 GeV/c2. For a mass of 115
GeV/c2 the observed (expected) limit is 20.4 (14.2) times the standard model
prediction.Comment: 8 pages, 2 figures, submitted to Phys. Rev. Let
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