79 research outputs found
Modification of Graphene Properties due to Electron-Beam Irradiation
The authors report micro-Raman investigation of changes in the single and
bilayer graphene crystal lattice induced by the low and medium energy
electron-beam irradiation (5 and 20 keV). It was found that the radiation
exposures results in appearance of the strong disorder D band around 1345 1/cm
indicating damage to the lattice. The D and G peak evolution with the
increasing radiation dose follows the amorphization trajectory, which suggests
graphene's transformation to the nanocrystalline, and then to amorphous form.
The results have important implications for graphene characterization and
device fabrication, which rely on the electron microscopy and focused ion beam
processing.Comment: 13 pages and 4 figure
Crystal Symmetry Breaking in Few-Quintuple Bismuth Telluride Films: Applications in Nanometrology of Topological Insulators
We report results of micro-Raman spectroscopy investigation of the
"graphene-like" mechanically exfoliated single-crystal bismuth telluride films
with the thickness ranging from a few-nm-range to bulk limit. It is found that
the optical phonon mode A1u, which is not-Raman active in bulk bismuth
telluride crystals, appears in the atomically-thin films due to
crystal-symmetry breaking. The intensity ratios of the out-of-plane A1u and A1g
modes to the in-plane Eg mode grow with decreasing film thickness. The
evolution of Raman signatures with the film thickness can be used for
identification of bismuth telluride crystals with the thickness of
few-quintuple layers, which are important for topological insulator and
thermoelectric applications.Comment: 13 pages, 2 tables, 3 figures; to be presented at MRS Spring Meeting,
201
Flicker Noise in Bilayer Graphene Transistors
We present the results of the experimental investigation of the low -
frequency noise in bilayer graphene transistors. The back - gated devices were
fabricated using the electron beam lithography and evaporation. The charge
neutrality point for the fabricated transistors was around 10 V. The noise
spectra at frequencies above 10 - 100 Hz were of the 1/f - type with the
spectral density on the order of 10E-23 - 10E-22 A2/Hz at the frequency of 1
kHz. The deviation from the 1/f spectrum at the frequencies below 10 -100 Hz
indicates that the noise is of the carrier - number fluctuation origin due to
the carrier trapping by defects. The Hooge parameter of 10E-4 was extracted for
this type of devices. The gate dependence of the noise spectral density
suggests that the noise is dominated by the contributions from the ungated part
of the device channel and by the contacts. The obtained results are important
for graphene electronic applications
Tuning of Graphene Properties via Controlled Exposure to Electron Beams
Controlled modification of graphene properties is essential for its proposed
electronic applications. Here we describe a possibility of tuning electrical
properties of graphene via electron beam irradiation. We show that by
controlling the irradiation dose one can change the carrier mobility and
increase the resistance at the minimum conduction point in the single layer
graphene. The bilayer graphene is less susceptible to the electron beam
irradiation. The modification of graphene properties via irradiation can be
monitored and quantified by the changes in the disorder D peak in Raman
spectrum of graphene. The obtained results may lead to a new method of defect
engineering of graphene physical properties, and to the procedure of "writing"
graphene circuits via e-beam irradiation. The results also have implications
for fabrication of graphene nanodevices, which involve scanning electron
microscopy and electron beam lithography
Anomalous Electron Transport in Field-Effect Transistors with Titanium Ditelluride Semimetal Thin-Film Channels
We report on "graphene-like" mechanical exfoliation of thin films of titanium
ditelluride and investigation of their electronic properties. The exfoliated
crystalline TiTe2 films were used as the channel layers in the back-gated
field-effect transistors fabricated with Ti/Al/Au metal contacts on SiO2/Si
substrates. The room-temperature current-voltage characteristics revealed
strongly non-linear behavior with signatures of the source-drain threshold
voltage similar to those observed in the charge-density-wave devices. The
drain-current showed an unusual non-monotonic dependence on the gate bias
characterized by the presence of multiple peaks. The obtained results can be
potentially used for implementation of the non-Boolean logic gates.Comment: 11 pages, 4 figure
Effect of oxygen plasma etching on graphene studied with Raman spectroscopy and electronic transport
We report a study of graphene and graphene field effect devices after
exposure to a series of short pulses of oxygen plasma. We present data from
Raman spectroscopy, back-gated field-effect and magneto-transport measurements.
The intensity ratio between Raman "D" and "G" peaks, I(D)/I(G) (commonly used
to characterize disorder in graphene) is observed to increase approximately
linearly with the number (N(e)) of plasma etching pulses initially, but then
decreases at higher Ne. We also discuss implications of our data for extracting
graphene crystalline domain sizes from I(D)/I(G). At the highest Ne measured,
the "2D" peak is found to be nearly suppressed while the "D" peak is still
prominent. Electronic transport measurements in plasma-etched graphene show an
up-shifting of the Dirac point, indicating hole doping. We also characterize
mobility, quantum Hall states, weak localization and various scattering lengths
in a moderately etched sample. Our findings are valuable for understanding the
effects of plasma etching on graphene and the physics of disordered graphene
through artificially generated defects.Comment: 10 pages, 5 figure
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