10 research outputs found
Enhancing thermoelectric properties of graphene quantum rings
We study the thermoelectric properties of rectangular graphene rings
connected symmetrically or asymmetrically to the leads. A side-gate voltage
applied across the ring allows for the precise control of the electric current
flowing through the system. The transmission coefficient of the rings manifests
Breit-Wigner line-shapes and/or Fano line-shapes, depending on the connection
configuration, the width of nanoribbons forming the ring and the side-gate
voltage. We find that the thermopower and the figure of merit are greatly
enhanced when the chemical potential is tuned close to resonances. Such
enhancement is even more pronounced in the vicinity of Fano like
anti-resonances which can be induced by a side-gate voltage independently of
the geometry. This opens a possibility to use the proposed device as a tunable
thermoelectric generator.Comment: 6 pages, 5 figures, accepted for publication in Physical Review
Quantum nanoconstrictions fabricated by cryo-etching in encapsulated graphene
More than a decade after the discovery of graphene, ballistic transport in
nanostructures based on this intriguing material still represents a challenging
field of research in two-dimensional electronics. The presence of rough edges
in nanostructures based on this material prevents the appearance of truly
ballistic electron transport as theo\-re\-tically predicted and, therefore, not
well-developed plateaus of conductance have been revealed to date. In this work
we report on a novel implementation of the cryo-etching method, which enabled
us to fabricate graphene nanoconstrictions encapsulated between hexagonal boron
nitride thin films with unprecedented control of the structure edges. High
quality smooth nanometer-rough edges are characterized by atomic force
microscopy and a clear correlation between low roughness and the existence of
well-developed quantized conductance steps with the concomitant occurrence of
ballistic transport is found at low temperature. In par\-ti\-cu\-lar, we come
upon exact 2 quantization steps of conductance at zero magnetic field
due to size quantization, as it has been theoretically predicted for truly
ballistic electron transport through graphene nanoconstrictions
Tuning the thermoelectric response of silicene nanoribbons with vacancies
In this work, we present a thorough study of the thermoelectric properties of silicene nanoribbons in the presence of a random distribution of atomic vacancies. By using a linear approach within the Landauer formalism, we calculate phonon and electron thermal conductances, the electric conductance, the Seebeck coefficient and the figure of merit of the nanoribbons. We found a sizable reduction of the phonon thermal conductance as a function of the vacancy concentration over a wide range of temperature. At the same time, the electric properties are not severely deteriorated, leading to an overall remarkable thermoelectric efficiency. We conclude that the incorporation of vacancies paves the way for designing better and more efficient nanoscale thermoelectric devices