212 research outputs found
Graphene Heat Spreaders and Interconnects for Advanced Electronic Applications
Graphene revealed a number of unique properties beneficial for electronics,
including exceptionally high electron mobility and widely tunable Fermi level.
However, graphene does not have an electron energy band gap, which presents a
serious hurdle for its applications in digital electronics. A possible route
for practical use of graphene in electronics is utilization of its
exceptionally high thermal conductivity and electron current conducting
properties. This invited review outlines the thermal properties of graphene and
describes prospective graphene technologies that are not affected by the
absence of the energy band gap. Specific examples include heat spreaders,
thermal coatings, high-current density electrodes and interconnects. Our
results suggest that thermal management of advanced electronic devices can
become the first industry-scale application of graphene.Comment: 6 pages; 3 figure
Review of the Low-Frequency 1/f Noise in Graphene Devices
Low-frequency noise with a spectral density that depends inversely on
frequency (f) has been observed in a wide variety of systems including current
fluctuations in resistors, intensity fluctuations in music and signals in human
cognition. In electronics, the phenomenon, which is known as 1/f noise, flicker
noise or excess noise, hampers the operation of numerous devices and circuits,
and can be a significant impediment to development of practical applications
from new materials. Graphene offers unique opportunities for studying 1/f noise
because of its 2D structure and carrier concentration tuneable over a wide
range. The creation of practical graphene-based devices will also depend on our
ability to understand and control the low-frequency 1/f noise in this material
system. Here, I review the characteristic features of 1/f noise in graphene and
few-layer graphene, and examine the implications of such noise for the
development of graphene-based electronics including high-frequency devices and
sensors.Comment: 25 manuscript pagers with 5 figure
Thermal Transport in Graphene and Graphene Multilayers
In this paper we review thermal properties of graphene and multilayer
graphene and discuss the optothermal technique developed for the thermal
conductivity measurements. We also outline different theoretical approaches
used for the description of phonon transport in graphene and provide comparison
with available experimental thermal conductivity data.Comment: 43 pages, 8 figures. arXiv admin note: substantial text overlap with
arXiv:1203.428
From Graphene to Bismuth Telluride: Mechanical Exfoliation of Quasi-2D Crystals for Applications in Thermoelectrics and Topological Insulators
Bismuth telluride (Bi2Te3) and its alloys are the best bulk thermoelectric
materials known today. The stacked quasi-two-dimensional (2D) layers of Bi2Te3
were also identified as topological insulators. In this paper we describe a
method for graphene-inspired exfoliation of crystalline bismuth telluride films
with a thickness of a few atoms. The atomically thin films were suspended
across trenches in Si/SiO2 substrates, and subjected to detail
characterization. The presence of the van der Waals gaps allowed us to
disassemble Bi2Te3 crystal into its quintuple building blocks - five
mono-atomic sheets consisting of Te(1)-Bi-Te(2)-Bi-Te(1). By altering the
thickness and sequence of atomic planes we were able to create designer
non-stoichiometric quasi-2D crystalline films, change their composition and
doping, as well as other properties. The exfoliated quintuples and ultra-thin
films have low thermal conductivity, high electrical conductivity and enhanced
thermoelectric properties. The obtained results pave the way for producing
stacks of crystalline bismuth telluride quantum wells with the strong spatial
confinement of charge carriers and acoustic phonons for thermoelectric devices.
The developed technology for producing free-standing quasi-2D layers of
Te(1)-Bi-Te(2)-Bi-Te(1) creates an impetus for investigation of the topological
insulators and their possible practical applications.Comment: 24 pages, 6 figure
Thermoelectric properties of electrically gated bismuth telluride nanowires
We theoretically studied the effect of the perpendicular electric field on
the thermoelectric properties of the intrinsic, n-type and p-type bismuth
telluride nanowires with the growth direction [110]. The electronic structure
and the wave functions were calculated by solving self-consistently the system
of the Schrodinger and Poisson equations using the spectral method. The Poisson
equation was solved in terms of the Newton - Raphson method within the
predictor-corrector approach. The electron - electron exchange - correlation
interactions were taken into account in our analysis. In the temperature range
from 77 to 500 K, the dependences of the Seebeck coefficient, thermal
conductivity, electron (hole) concentration, and thermoelectric figure of merit
on the nanowire thickness, gate voltage, and excess hole (electron)
concentration were investigated in the constant relaxation-time approximation.
The results of our calculations indicate that the external perpendicular
electric field can increase the Seebeck coefficient of the bismuth telluride
nanowires with thicknesses of 7 - 15 nm by nearly a factor of 2 and enhance ZT
by an order of magnitude. At room temperature, ZT can reach a value as high as
3.4 under the action of the external perpendicular electric field for realistic
widths of the nanowires. The obtain results may open up a completely new way
for a drastic enhancement of the thermoelectric figure of merit in a wide
temperature range.Comment: 19 pages, 12 figures, added references, added 2 tables, removed
figures 7,8,9, added new fig.
Phononics of Graphene and Graphene Composites
I present a concise account concerning the emergence of a research field,
which deals with the thermal properties of graphene, covering the refinement of
understanding of phonon transport in two-dimensional material systems. The
practical application of graphene and few-layer graphene in thermal interface
materials are also discussed.Comment: 6 pages; 3 figure
Specific Heat of Twisted Bilayer Graphene
We have studied the phonon specific heat in single-layer, bilayer and twisted
bilayer graphene. The calculations were performed using the Born-von Karman
model of lattice dynamics for intralayer atomic interactions and spherically
symmetric interatomic potential for interlayer interactions. We found that at
temperature T<15 K, specific heat varies with temperature as T^n, where n = 1
for graphene, n = 1.6 for bilayer graphene and n = 1.3 for the twisted bilayer
graphene. The phonon specific heat reveals an intriguing dependence on the
twist angle in bilayer graphene, which is particularly pronounced at low
temperature. The results suggest a possibility of phonon engineering of thermal
properties of layered materials by twisting the atomic planes.Comment: 15 pages, 3 figure
"Graphene-Like" Exfoliation of Atomically-Thin Bismuth Telluride Films
We report on graphene-like exfoliation of the large-area crystalline films
and ribbons of bismuth telluride with the thicknesses of a few atoms. It is
demonstrated that bismuth telluride, the most important material for
thermoelectric industry, can be mechanically separated into its building blocks
-[Te-Bi-Te-Bi-Te]- atomic five-folds with the thickness of ~1 nm and even
further - to subunits with smaller thicknesses. The atomically-thin crystals
can be structured into suspended crystalline ribbons providing quantum
confinement in two dimensions. The quasi two-dimensional (2-D) crystals of
bismuth telluride revealed high electrical conductivity. The proposed
atomic-layer engineering of bismuth telluride opens up a principally new route
for drastic enhancement of the thermoelectric figure of merit.Comment: 12 pages, 4 figures, to be presented at MRS Spring 201
Phonon Engineering of the Specific Heat of Twisted Bilayer Graphene: The Role of the Out-of-Plane Phonon Modes
We investigated theoretically the specific heat of graphene, bilayer graphene
and twisted bilayer graphene taking into account the exact phonon dispersion
and density of states for each polarization branch. It is shown that contrary
to a conventional believe the dispersion of the out-of-plane acoustic phonons -
referred to as ZA phonons - deviates strongly from a parabolic law starting
from the frequencies as low as ~100 1/cm. This leads to the frequency-dependent
ZA phonon density of states and the breakdown of the linear dependence of the
specific heat on temperature T. We established that ZA phonons determine the
specific heat for T<200 K while contributions from both in-plane and
out-of-plane acoustic phonons are dominant for 200 K < T < 500 K. In the
high-temperature limit, T>1000 K, the optical and acoustic phonons contribute
approximately equally to the specific heat. The Debye temperature for graphene
and twisted bilayer graphene was calculated to be around ~1861 - 1864 K. Our
results suggest that the thermodynamic properties of materials such as bilayer
graphene can be controlled at the atomic scale by rotation of the sp2-carbon
planes.Comment: 25 pages, 5 figure
Triple-Mode Single-Transistor Graphene Amplifier and Its Applications
In this article, we propose and experimentally demonstrate a triple-mode
single-transistor graphene amplifier utilizing a three-terminal back-gated
single-layer graphene transistor. The ambipolar nature of electronic transport
in graphene transistors leads to increased amplifier functionality as compared
to amplifiers built with unipolar semiconductor devices. The ambipolar graphene
transistors can be configured as n-type, p-type, or hybrid-type by changing the
gate bias. As a result, the single-transistor graphene amplifier can operate in
the common-source, common-drain, or frequency multiplication mode,
respectively. This in-field controllability of the single-transistor graphene
amplifier can be used to realize the modulation necessary for phase shift
keying and frequency shift keying, which are widely used in wireless
applications. It also offers new opportunities for designing analog circuits
with simpler structure and higher integration densities for communications
applications
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