We report the atomic-scale imaging with concurrent transport measurements of the breakdown of individual multiwall carbon nanotubes inside a transmission electron microscope equipped with a piezomanipulator. We found unexpectedly three distinct breakdown sequences: namely, from the outermost wall inward, from the innermost wall outward, and alternatively between the innermost and the outmost walls. Remarkably, a significant amount of current drop was observed when an innermost wall is broken, proving unambiguously that every wall is conducting. Moreover, the breakdown of each wall in any sequence initiates in the middle of the nanotube, not at the contact, proving that the transport is not ballistic.

We report that kink motion is a universal plastic deformation mode in all carbon nanotubes when being tensile loaded at high temperatures. The kink motion, observed inside a high-resolution transmission electron microscope, is reminiscent of dislocation motion in crystalline materials: namely, it dissociates and multiplies. The kinks are nucleated from vacancy creation and aggregation, and propagate in either a longitudinal or a spiral path along the nanotube walls. The kink motion is related to dislocation glide and climb influenced by external stress and high temperatures in carbon nanotubes.

The thermoelectric performance of materials relies substantially on the band structures that determine the electronic and phononic transports, while the transport behaviors compete and counter-act for the power factor PF and figure-of-merit ZT. These issues make a full-scale computation of the whole set of thermoelectric parameters particularly attractive, while a calculation scheme of the electronic and phononic contributions to thermal conductivity remains yet challenging. In this work, we present a full-scale computation scheme based on the first-principles calculations by choosing a set of doped half-Heusler compounds as examples for illustration. The electronic structure is computed using the WIEN2k code and the carrier relaxation times for electrons and holes are calculated using the Bardeen and Shockley’s deformation potential (DP) theory. The finite-temperature electronic transport is evaluated within the framework of Boltzmann transport theory. In sequence, the density functional perturbation combined with the quasi-harmonic approximation and the Klemens’ equation is implemented for calculating the lattice thermal conductivity of carrier-doped thermoelectric materials such as Ti-doped NbFeSb compounds without losing a generality. The calculated results show good agreement with experimental data. The present methodology represents an effective and powerful approach to calculate the whole set of thermoelectric properties for thermoelectric materials.

Experimental test of the interlayer pairing models for high-Tc superconductors using grazing-incidence infrared reflectometry Schuetzmann, J.; Somal, H.S.; Tsvetkov, A.A.; van der Marel, D.; Koops, G.E.J.; Koleshnikov, N.; Ren, Z.F.; Wang, J.H.; Bruck, E.H.; Menovsky, A.A.

The microscopic mechanisms for higher thermoelectric performance of cost competitive rock salt compound Bi 2 SeS 2 were investigated. A low doping of Cu as an n-type dopant was conducted in order to optimize the band structure and improve the electrical conductivity. It was revealed that this compound exhibits a Seebeck coefficient higher than 300 μV K À 1 , which sustains above 100 μV K À 1 even with Cu doping, leading to a higher power factor. The microstructural characterizations revealed nano-scale Bi 2 S 3 precipitates in the Cu x Bi 2 SeS 2 matrix, beneficial to the lower lattice thermal conductivity that is insensitive to the Cu doping. A thermoelectric figure-of-merit factor ZT of $0.7 at 450 1C in accompanying with the power factor of $ 5.36 μW cm À 1 K À 2 was obtained under the optimized doping level, enabling this environmentally friendly compound interesting for thermoelectric power generation applications.