33 research outputs found
A Resonant Graphene NEMS Vibrometer
Measuring vibrations is essential to ensuring building structural safety and machine stability. Predictive maintenance is a central internet of things (IoT) application within the new industrial revolution, where sustainability and performance increase over time are going to be paramount. To reduce the footprint and cost of vibration sensors while improving their performance, new sensor concepts are needed. Here, double-layer graphene membranes are utilized with a suspended silicon proof demonstrating their operation as resonant vibration sensors that show outstanding performance for a given footprint and proof mass. The unveiled sensing effect is based on resonant transduction and has important implications for experimental studies involving thin nano and micro mechanical resonators that are excited by an external shaker
Heat to Electricity Conversion by a Graphene Stripe with Heavy Chiral Fermions
A conversion of thermal energy into electricity is considered in the
electrically polarized graphene stripes with zigzag edges where the heavy
chiral fermion (HCF) states are formed. The stripes are characterized by a high
electric conductance Ge and by a significant Seebeck coefficient S. The
electric current in the stripes is induced due to a non-equilibrium thermal
injection of "hot" electrons. This thermoelectric generation process might be
utilized for building of thermoelectric generators with an exceptionally high
figure of merit Z{\delta}T \simeq 100 >> 1 and with an appreciable electric
power densities \sim 1 MW/cm2.Comment: 8 pages, 3 figure
Mobility in Graphene Double Gate Field Effect Transistors
In this work, double-gated field effect transistors manufactured from
monolayer graphene are investigated. Conventional top-down CMOS-compatible
processes are applied except for graphene deposition by manual exfoliation.
Carrier mobilities in single- and double gated graphene field effect
transistors are compared. Even in double-gated graphene FETs, the carrier
mobility exceeds the universal mobility of silicon over nearly the entire
measured range. At comparable dimensions, reported mobilities for ultra thin
body silicon-on-insulator MOSFETs can not compete with graphene FET values.Comment: 7 pages, 9 figure
Thickness Estimation of Epitaxial Graphene on SiC using Attenuation of Substrate Raman Intensity
A simple, non-invasive method using Raman spectroscopy for the estimation of
the thickness of graphene layers grown epitaxially on silicon carbide (SiC) is
presented, enabling simultaneous determination of thickness, grain size and
disorder using the spectra. The attenuation of the substrate Raman signal due
to the graphene overlayer is found to be dependent on the graphene film
thickness deduced from X-ray photoelectron spectroscopy and transmission
electron microscopy of the surfaces. We explain this dependence using an
absorbing overlayer model. This method can be used for mapping graphene
thickness over a region and is capable of estimating thickness of multilayer
graphene films beyond that possible by XPS and Auger electron spectroscopy
(AES).Comment: 14 pages, 9 figure
Novel hysteresis effect in ultrathin epitaxial Gd₂O₃ high-k dielectric
Charge trapping in ultrathin high-k Gd₂O₃ dielectric leading to appearance of
hysteresis in C–V curves is studied by capacitance-voltage, conductance-frequency and
current-voltage techniques at different temperatures. It was shown that the large leakage
current at a negative gate voltage causes the reversible trapping of the positive charge in
the dielectric layer, without electrical degradation of the dielectric and dielectricsemiconductor
interface. The capture cross-sections of the hole traps are around 10⁻¹⁸ and
2 × 10⁻²⁰ cm²
. The respective shift of the C–V curve correlates with a “plateau” at the
capacitance corresponding to weak accumulation at the silicon interface
Klein tunneling in graphene: optics with massless electrons
This article provides a pedagogical review on Klein tunneling in graphene,
i.e. the peculiar tunneling properties of two-dimensional massless Dirac
electrons. We consider two simple situations in detail: a massless Dirac
electron incident either on a potential step or on a potential barrier and use
elementary quantum wave mechanics to obtain the transmission probability. We
emphasize the connection to related phenomena in optics, such as the
Snell-Descartes law of refraction, total internal reflection, Fabry-P\'erot
resonances, negative refraction index materials (the so called meta-materials),
etc. We also stress that Klein tunneling is not a genuine quantum tunneling
effect as it does not necessarily involve passing through a classically
forbidden region via evanescent waves. A crucial role in Klein tunneling is
played by the conservation of (sublattice) pseudo-spin, which is discussed in
detail. A major consequence is the absence of backscattering at normal
incidence, of which we give a new shorten proof. The current experimental
status is also thoroughly reviewed. The appendix contains the discussion of a
one-dimensional toy model that clearly illustrates the difference in Klein
tunneling between mono- and bi-layer graphene.Comment: short review article, 18 pages, 14 figures; v3: references added,
several figures slightly modifie
Mobility Extraction of UTB n-MOSFETs down to 0.9 nm SOI thickness
In this abstract, the impact of series resistance on mobility extraction in conventional and recessed-gate ultra thin body (UTB) n-MOSFETs is investigated. High series resistance leads to an overestimation of the internal source/drain voltage and influences the measurement of the gate to channel capacitance. A specific MOSFET design that includes additional channel contacts and recessed gate technology are used to successfully extract mobility down to 0.9 nm silicon film thickness (4 atomic layers). Quantum mechanical effects are found to shift the threshold voltage and degrade mobility at these extreme scaling limits
Gd silicate: A high-k dielectric compatible with high temperature annealing
The authors report on the investigation of amorphous Gd-based silicates as high- k dielectrics. Two different stacks of amorphous gadolinium oxide (Gd2 O3) and silicon oxide (Si O2) on silicon substrates are compared after annealing at temperatures up to 1000 \ub0C. Subsequently formed metal oxide semiconductor capacitors show a significant reduction in the capacitance equivalent thicknesses after annealing. Transmission electron microscopy, medium energy ion scattering, and x-ray diffraction analysis reveal distinct structural changes such as consumption of the Si O2 layer and formation of amorphous Gd silicate. The controlled formation of Gd silicates in this work indicates a route toward high- k dielectrics compatible with conventional, gate first complementary metal-oxide semiconductor integration schemes. \ua9 2009 American Vacuum Society