Large enhancement of the thermoelectric power factor in disordered materials through resonant scattering

In the search for more efficient thermoelectric materials, scientists have placed high hopes in the possibility of enhancing the power factor using resonant states. In this study, we investigate theoretically the effects of randomly distributed resonant impurities on the power factor. Using the Chebyshev Polynomial Green's Function method, we compute the electron transport properties for very large systems (10 million atoms) with an exact treatment of disorder. The introduction of resonant defects can lead to a large enhancement of the power factor together with a sign inversion in the Seebeck coefficient. This boost depends crucially on the position of the resonant peak, and on the interplay between elastic impurity scattering and inelastic processes. Strong electron-phonon or electron-electron scattering are found detrimental. Finally, the robustness of our results is examined in the case of anisotropic orbitals and two-dimensional confinement. Our findings are promising for the prospect of thermoelectric power generation.Comment: To appear in Phys. Rev.

Investigating the high-temperature thermoelectric properties of n-type rutile TiO2_2

Transition metal oxides are considered promising thermoelectric materials for harvesting high-temperature waste heat due to their stability, abundance and low toxicity. Despite their typically strong ionic character, they can exhibit surprisingly high power factors $\sigma S^2$, as in n-type SrTiO$_3$ for instance. Thus, it is worth examining other transition metal oxides that might surpass the performances of SrTiO$_3$. This theoretical paper investigates the thermoelectric properties of n-type rutile TiO$_2$, which is the most stable phase of titanium oxide up to 2000 K. The electronic structure is obtained through ab initio calculations, while the prominent features of strong electron-phonon interaction and defects states are modelled using a small number of parameters. The theoretical results are compared with a wealth of experimental data from the literature, yielding very good agreements over a wide range of carrier concentrations. This validates the hypothesis of band conduction in rutile TiO$_2$ and allows the prediction of the high-temperature thermoelectric properties

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Surface Segregation and Backscattering in Doped Silicon Nanowires

By means of ab initio simulations, we investigate the structural, electronic, and transport properties of boron and phosphorus doped silicon nanowires. We find that impurities always segregate at the surface of unpassivated wires, reducing dramatically the conductance of the surface states. Upon passivation, we show that for wires as large as a few nanometers in diameter, a large proportion of dopants will be trapped and electrically neutralized at surface dangling bond defects, significantly reducing the density of carriers. Important differences between p- and n-type doping are observed. Our results rationalize several experimental observations

Ring patterns in high-current field emission from carbon nanotubes

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Influence of Disorder on DNA Conductance

Disorder along a DNA strand due to non uniformity associated with the counter ion type and location, and in rise and twist are investigated using density functional theory. We then model the conductance through a poly(G) DNA strand by including the influence of disorder. We show that the conductance drops by a few orders of magnitude between typical lengths of 10 and 100 nm. Such a decrease occurs with on-site potential disorder that is larger than 100 meV

Multiscale simulation of carbon nanotube devices

International audienceIn recent years, the understanding and accurate simulation of carbon nanotube-based devices has become very challenging. Conventional simulation tools of microelectronics are necessary to envisage the performance and use of nanotube transistors and circuits, but the models need to be refined to properly describe the full complexity of such novel type of devices at the nanoscale. Indeed, many issues such as contact resistance, low dimensional electrostatics and screening effects, as well as nanotube doping or functionalization, demand for more accurate quantum approaches. In this article, we review our recent progress on multiscale simulations which aim at bridging first principles calculations with compact modelling, including the comparison between semiclassical Monte Carlo and quantum transport approaches