12 research outputs found
Intraband electron focusing in bilayer graphene
We propose an implementation of a valley selective electronic Veselago lens
in bilayer graphene. We demonstrate that in the presence of an appropriately
oriented potential step, low-energy electrons radiating from a point source can
be re-focused coherently within the same band. The phenomenon is due to the
trigonal warping of the band structure that leads to a negative refraction
index. We show that the interference pattern can be controlled by an external
mechanical strain.Comment: 14 pages, 8 figure
Thermoelectric Performance of various Benzo-difuran Wires
Using a first principles approach to electron transport, we calculate the
electrical and thermoelectrical transport properties of a series of molecular
wires containing benzo-difuran subunits. We demonstrate that the side groups
introduce Fano resonances, the energy of which is changing with the
electronegativity of selected atoms in it. We also study the relative effect of
single, double or triple bonds along the molecular backbone and find that
single bonds yield the highest thermopower, approximately 22V/K at room
temperature, which is comparable with the highest measured values for
single-molecule thermopower reported to date.Comment: 7 pages, 8 figure
Quantum-interference-enhanced thermoelectricity in single molecules and molecular films
We provide a brief overview of recent measurements and predictions of thermoelectric properties of single-molecules and porous nanoribbons and discuss some principles underpinning strategies for enhancing their thermoelectric performance. The latter include (a) taking advantage of steep slopes in the electron transmission coefficient T(E)T(E), (b) creating structures with delta-function-like transmission coefficients and (c) utilising step-like features in T(E)T(E). To achieve high performance, we suggest that the latter may be the most fruitful, since it is less susceptible to inhomogeneous broadening. For the purpose of extrapolating thermoelectric properties of single or few molecules to monolayer molecular films, we also discuss the relevance of the conductance-weighted average Seebeck coefficient
Suppression of single-molecule conductance fluctuations using extended anchor groups on graphene and carbon-nanotube electrodes
Devices formed from single molecules attached to noble-metal electrodes exhibit large conductance fluctuations, which inhibit their development as reproducible functional units. We demonstrate that single molecules with planar anchor groups attached to carbon-based electrodes are more resilient to atomic-scale variation in the contacts and exhibit significantly lower conductance fluctuations. We examine the conductance of a 2,6-dibenzylamino core-substituted naphthalenediimide chromophore attached to carbon electrodes by either phenanthrene anchors or more extended anchor groups, which include oligophenylene ethynylene spacers. We demonstrate that for the more spatially extended anchor groups conductance fluctuations are significantly reduced. The current-voltage characteristic arising from long-range tunneling is found to be strongly nonlinear with pronounced conductance suppression below a threshold voltage of approximately 2.5 V