Continuous-feed nanocasting process for the synthesis of bismuth nanowire composites

We present a novel, continuous-feed nanocasting procedure for the synthesis of bismuth nanowire structures embedded in the pores of a mesoporous silica template. The immobilization of a bismuth salt inside the silica template from a diluted metal salt solution yields a sufficiently high loading to obtain electrically conducting bulk nanowire composite samples after reduction and sintering the nanocomposite powders. Electrical resistivity measurements of sintered bismuth nanowires embedded in the silica template reveal size-quantization effects

Effects of hole self-trapping by polarons on transport and negative bias illumination stress in amorphous-IGZO

The effects of hole injection in amorphous-IGZO is analyzed by means of first-principles calculations. The injection of holes in the valence band tail states leads to their capture as a polaron, with high self-trapping energies (from 0.44 to 1.15 eV). Once formed, they mediate the formation of peroxides and remain localized close to the hole injection source due to the presence of a large diffusion energy barrier (of at least 0.6eV). Their diffusion mechanism can be mediated by the presence of hydrogen. The capture of these holes is correlated with the low off-current observed for a-IGZO transistors, as well as, with the difficulty to obtain a p-type conductivity. The results further support the formation of peroxides as being the root cause of Negative bias illumination stress (NBIS). The strong self-trapping substantially reduces the injection of holes from the contact and limits the creation of peroxides from a direct hole injection. In presence of light, the concentration of holes substantially rises and mediates the creation of peroxides, responsible for NBIS.Comment: 8 pages, 8 figures, to be published in Journal of Applied Physic

Phonon driven spin distribution due to the spin-Seebeck effect

Here we report on measurements of the spin-Seebeck effect of GaMnAs over an extended temperature range alongside the thermal conductivity, specific heat, magnetization, and thermoelectric power. The amplitude of the spin-Seebeck effect in GaMnAs scales with the thermal conductivity of the GaAs substrate and the phonon-drag contribution to the thermoelectric power of the GaMnAs, demonstrating that phonons drive the spin redistribution. A phenomenological model involving phonon-magnon drag explains the spatial and temperature dependence of the measured spin distribution.Comment: 12 pages, 3 figure

Thermoelectricity in Nanowires: A Generic Model

By employing a Boltzmann transport equation and using an energy and size dependent relaxation time ($\tau$) approximation (RTA), we evaluate self-consistently the thermoelectric figure-of-merit $ZT$ of a quantum wire with rectangular cross-section. The inferred $ZT$ shows abrupt enhancement in comparison to its counterparts in bulk systems. Still, the estimated $ZT$ for the representative Bi$_2$Te$_3$ nanowires and its dependence on wire parameters deviate considerably from those predicted by the existing RTA models with a constant $\tau$. In addition, we address contribution of the higher energy subbands to the transport phenomena, the effect of chemical potential tuning on $ZT$, and correlation of $ZT$ with quantum size effects (QSEs). The obtained results are of general validity for a wide class of systems and may prove useful in the ongoing development of the modern thermoelectric applications.Comment: 15 pages, 6 figures; Dedicated to the memory of Amirkhan Qezell

Atomic layer deposition of titanium nitride for quantum circuits

Superconducting thin films with high intrinsic kinetic inductance are of great importance for photon detectors, achieving strong coupling in hybrid systems, and protected qubits. We report on the performance of titanium nitride resonators, patterned on thin films (9-110 nm) grown by atomic layer deposition, with sheet inductances of up to 234 pH/square. For films thicker than 14 nm, quality factors measured in the quantum regime range from 0.4 to 1.0 million and are likely limited by dielectric two-level systems. Additionally, we show characteristic impedances up to 28 kOhm, with no significant degradation of the internal quality factor as the impedance increases. These high impedances correspond to an increased single photon coupling strength of 24 times compared to a 50 Ohm resonator, transformative for hybrid quantum systems and quantum sensing.Comment: 10 pages, 8 figures including supplemental material

Magnon-drag thermopower and Nernst coefficient in Fe, Co, and Ni

Magnon-drag is shown to dominate the thermopower of elemental Fe from 2 to 80 K and of elemental Co from 150 to 600 K; it is also shown to contribute to the thermopower of elemental Ni from 50 to 500 K. Two theoretical models are presented for magnon-drag thermopower. One is a hydrodynamic theory based purely on non-relativistic, Galilean, spin-preserving electron-magnon scattering. The second is based on spin-motive forces, where the thermopower results from the electric current pumped by the dynamic magnetization associated with a magnon heat flux. In spite of their very different microscopic origins, the two give similar predictions for pure metals at low temperature, allowing us to semi-quantitatively explain the observed thermopower of elemental Fe and Co without adjustable parameters. We also find that magnon-drag may contribute to the thermopower of Ni. A spin-mixing model is presented that describes the magnon-drag contribution to the Anomalous Nernst Effect in Fe, again enabling a semi-quantitative match to the experimental data without fitting parameters. Our work suggests that particle non-conserving processes may play an important role in other types of drag phenomena, and also gives a predicative theory for improving metals as thermoelectric materials.Comment: main text plus 7 figures; accepted in PRB September 201

Evolution of structural and electronic properties of highly mismatched InSb films

We have investigated the evolution of structural and electronic properties of highly mismatched InSb films, with thicknesses ranging from 0.1 to 1.5 μm. Atomic force microscopy, cross-sectional transmission electron microscopy, and high-resolution x-ray diffraction show that the 0.1 μm films are nearly fully relaxed and consist of partially coalesced islands, which apparently contain threading dislocations at their boundaries. As the film thickness increases beyond 0.2 μm, the island coalescence is complete and the residual strain is reduced. Although the epilayers have relaxed equally in the 〈110〉 in-plane directions, the epilayer rotation about an in-plane axis (epilayer tilt) is not equal in both 〈110〉 in-plane directions. Interestingly, the island-like surface features tend to be preferentially elongated along the axis of epilayer tilt. Furthermore, epilayer tilt which increases the substrate offcut (reverse tilt) is evident in the [110] direction. High-resolution transmission electron microscopy indicates that both pure-edge and 60° misfit dislocations contribute to the relaxation of strain. In addition, as the film thickness increases, the threading dislocation density decreases, while the corresponding room-temperature electron mobility increases. The other structural features, including the residual strain, and the surface and interface roughness, do not appear to impact the electron mobility in these InSb films. Together, these results suggest that free-carrier scattering from the threading dislocations is the primary room-temperature mobility-limiting mechanism in highly mismatched InSb films. Finally, we show quantitatively that free-carrier scattering from the lattice dilation associated with threading dislocations, rather than scattering from a depletion potential surrounding the dislocations, is the dominant factor limiting the electron mobility. © 2000 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70332/2/JAPIAU-88-11-6276-1.pd