Author Correction: Impact of pore anisotropy on the thermal conductivity of porous Si nanowires.

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Impact of pore anisotropy on the thermal conductivity of porous Si nanowires.

Porous materials display enhanced scattering mechanisms that greatly influence their transport properties. Metal-assisted chemical etching (MACE) enables fabrication of porous silicon nanowires starting from a doped Si wafer by using a metal template that catalyzes the etching process. Here, we report on the low thermal conductivity (κ) of individual porous Si nanowires (NWs) prepared from MACE, with values as low as 0.87 W·m-1·K-1 for 90 nm diameter wires with 35-40% porosity. Despite the strong suppression of long mean free path phonons in porous materials, we find a linear correlation of κ with the NW diameter. We ascribe this dependence to the anisotropic porous structure that arises during chemical etching and modifies the phonon percolation pathway in the center and outer regions of the nanowire. The inner microstructure of the NWs is visualized by means of electron tomography. In addition, we have used molecular dynamics simulations to provide guidance for how a porosity gradient influences phonon transport along the axis of the NW. Our findings are important towards the rational design of porous materials with tailored thermal and electronic properties for improved thermoelectric devices.

Thermal conductivity of Bi2Te3 nanowires: how size affects phonon scattering.

This work provides an in-depth study of how the thermal conductivity of stoichiometric [110] Bi2Te3 nanowires becomes affected when reducing its diameter from an experimental and theoretical point of view. The thermal conductivity was observed to decrease more than 70% (from 1.78 ± 0.46 W K-1 m-1 to 0.52 ± 0.35 W K-1 m-1) when the diameter of the nanowire was reduced one order of magnitude (from 300 nm to 25 nm). The Kinetic-Collective model was used to understand such a reduction, which can be explained by the impact that surface scattering has in acoustic phonons. The smaller the diameter of the nanowires is, the larger the alteration in the mean free path of the low-frequency phonons is. The model agrees well with the experimental data, and the reduction in the thermal conductivity of the nanowires can be explained in terms of an increment of phonon scattering.

Computation of many-particle quantum trajectories with exchange interaction: application to the simulation of nanoelectronic devices.

Following Oriols (2007 Phys. Rev. Lett. 98 066803), an algorithm to deal with the exchange interaction in non-separable quantum systems is presented. The algorithm can be applied to fermions or bosons and, by construction, it exactly ensures that any observable is totally independent of the interchange of particles. It is based on the use of conditional Bohmian wave functions which are solutions of single-particle pseudo-Schrödinger equations. The exchange symmetry is directly defined by demanding symmetry properties of the quantum trajectories in the configuration space with a universal algorithm, rather than through a particular exchange-correlation functional introduced into the single-particle pseudo-Schrödinger equation. It requires the computation of N(2) conditional wave functions to deal with N identical particles. For separable Hamiltonians, the algorithm reduces to the standard Slater determinant for fermions (or permanent for bosons). A numerical test for a two-particle system, where exact solutions for non-separable Hamiltonians are computationally accessible, is presented. The numerical viability of the algorithm for quantum electron transport (in a far-from-equilibrium time-dependent open system) is demonstrated by computing the current and fluctuations in a nano-resistor, with exchange and Coulomb interactions among electrons.

The BN-pair impurity in carbon nanotubes and the possibility for disorder-induced frustration of gap formation.

We study the BN-pair impurity complex inside a metallic and a semiconducting single-walled carbon nanotube host. For the single impurity in the semiconducting tube, we find that no electron or hole bound states can be sustained because the distance between the B and the N is less than the effective Fermi-Teller radius for that system. If the BN pairs are incorporated at stoichiometric concentrations (BC(10)N nanotubes), achievable for example with a borabenzene-pyridine adduct C(10)H(10)BN precursor, the metallic tube becomes semiconducting for an ordered arrangement of the impurities, but the introduction of disorder restores a finite density of states at the Fermi level. Thus, in the mechanism presented here, disorder effectively restores the symmetry of the nanotube, returning the nanotube to its original metallic character.