1,283 research outputs found
Plasmons in dimensionally mismatched Coulomb coupled graphene systems
We calculate the plasmon dispersion relation for Coulomb coupled metallic
armchair graphene nanoribbons and doped monolayer graphene. The crossing of the
plasmon curves, which occurs for uncoupled 1D and 2D systems, is split by the
interlayer Coulomb coupling into a lower and an upper plasmon branch. The upper
branch exhibits a highly unusual behavior with endpoints at finite .
Accordingly, the structure factor shows either a single or a double peak
behavior, depending on the plasmon wavelength. The new plasmon structure is
relevant to recent experiments, its properties can be controlled by varying the
system parameters, and be used in plasmonic applications.Comment: 5 pages, 3 figures; in press in Phys. Rev. Let
Graphene Helicoid: The Distinct Properties Promote Application of Graphene Related Materials in Thermal Management
The extremely high thermal conductivity of graphene has received great
attention both in experiments and calculations. Obviously, new feature in
thermal properties is of primary importance for application of graphene-based
materials in thermal management in nanoscale. Here, we studied the thermal
conductivity of graphene helicoid, a newly reported graphene-related
nanostructure, using molecular dynamics simulation. Interestingly, in contrast
to the converged cross-plane thermal conductivity in multi-layer graphene,
axial thermal conductivity of graphene helicoid keeps increasing with thickness
with a power law scaling relationship, which is a consequence of the divergent
in-plane thermal conductivity of two-dimensional graphene. Moreover, the large
overlap between adjacent layers in graphene helicoid also promotes higher
thermal conductivity than multi-layer graphene. Furthermore, in the small
strain regime (< 10%), compressive strain can effectively increase the thermal
conductivity of graphene helicoid, while in the ultra large strain regime
(~100% to 500%), tensile strain does not decrease the heat current, unlike that
in generic solid-state materials. Our results reveal that the divergence in
thermal conductivity, associated with the anomalous strain dependence and the
unique structural flexibility, make graphene helicoid a new platform for
studying fascinating phenomena of key relevance to the scientific understanding
and technological applications of graphene-related materials.Comment: 7 figure
Introduction to Graphene Electronics -- A New Era of Digital Transistors and Devices
The speed of silicon-based transistors has reached an impasse in the recent
decade, primarily due to scaling techniques and the short-channel effect.
Conversely, graphene (a revolutionary new material possessing an atomic
thickness) has been shown to exhibit a promising value for electrical
conductivity. Graphene would thus appear to alleviate some of the drawbacks
associated with silicon-based transistors. It is for this reason why such a
material is considered one of the most prominent candidates to replace silicon
within nano-scale transistors. The major crux here, is that graphene is
intrinsically gapless, and yet, transistors require a band-gap pertaining to a
well-defined ON/OFF logical state. Therefore, exactly as to how one would
create this band-gap in graphene allotropes is an intensive area of growing
research. Existing methods include nano-ribbons, bilayer and multi-layer
structures, carbon nanotubes, as well as the usage of the graphene substrates.
Graphene transistors can generally be classified according to two working
principles. The first is that a single graphene layer, nanoribbon or carbon
nanotube can act as a transistor channel, with current being transported along
the horizontal axis. The second mechanism is regarded as tunneling, whether
this be band-to-band on a single graphene layer, or vertically between adjacent
graphene layers. The high-frequency graphene amplifier is another talking point
in recent research, since it does not require a clear ON/OFF state, as with
logical electronics. This paper reviews both the physical properties and
manufacturing methodologies of graphene, as well as graphene-based electronic
devices, transistors, and high-frequency amplifiers from past to present
studies. Finally, we provide possible perspectives with regards to future
developments.Comment: This is an updated version of our review article, due to be published
in Contemporary Physics (Sept 2013). Included are updated references, along
with a few minor corrections. (45 pages, 19 figures
Modeling of Thermally Aware Carbon Nanotube and Graphene Based Post CMOS VLSI Interconnect
This work studies various emerging reduced dimensional materials for very large-scale integration (VLSI) interconnects. The prime motivation of this work is to find an alternative to the existing Cu-based interconnect for post-CMOS technology nodes with an emphasis on thermal stability. Starting from the material modeling, this work includes material characterization, exploration of electronic properties, vibrational properties and to analyze performance as a VLSI interconnect. Using state of the art density functional theories (DFT) one-dimensional and two-dimensional materials were designed for exploring their electronic structures, transport properties and their circuit behaviors. Primarily carbon nanotube (CNT), graphene and graphene/copper based interconnects were studied in this work.
Being reduced dimensional materials the charge carriers in CNT(1-D) and in graphene (2-D) are quantum mechanically confined as a result of this free electron approximation fails to explain their electronic properties. For same reason Drude theory of metals fails to explain electronic transport phenomena. In this work Landauer transport theories using non-equilibrium Green function (NEGF) formalism was used for carrier transport calculation. For phonon transport studies, phenomenological Fourier’s heat diffusion equation was used for longer interconnects. Semi-classical BTE and Landauer transport for phonons were used in cases of ballistic phonon transport regime. After obtaining self-consistent electronic and thermal transport coefficients, an equivalent circuit model is proposed to analyze interconnects’ electrical performances.
For material studies, CNTs of different variants were analyzed and compared with existing copper based interconnects and were found to be auspicious contenders with integrational challenges. Although, Cu based interconnect is still outperforming other emerging materials in terms of the energy-delay product (1.72 fJ-ps), considering the electromigration resistance graphene Cu hybrid interconnect proposed in this dissertation performs better. Ten times more electromigration resistance is achievable with the cost of only 30% increase in energy-delay product. This unique property of this proposed interconnect also outperforms other studied alternative materials such as multiwalled CNT, single walled CNT and their bundles
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