Bismuth nanowires with very low lattice thermal conductivity as revealed by the 3ω method.

Thermoelectric materials transform temperature gradients to voltages and vise versa. Despite their many advantages, devices based on thermoelectric materials are used today only in a few applications, due to their low efficiency, which is described by the figure of merit ZT. Theoretical studies predict that scaling down these materials to the nanometric scale should enhance their efficiency partially due to a decrease in their lattice thermal conductivity. In this work we determine for the first time the lattice thermal conductivity of 40 nm bismuth (Bi) nanowires (NWs), i.e. NWs with a diameter comparable to the Fermi wavelength of charge carriers in this material. We find a surprisingly low lattice thermal conductivity of 0.13 ± 0.05 W K(-1) m(-1) at 77 K. A quantitative argument, which takes into account several unique properties of Bi, is given to explain this unusual finding.

Segmented metal nanowires as nanoscale thermocouples.

Segmented Au-Ni nanowires are demonstrated to be highly effective thermocouples with a spatial resolution of a few nanometers and a temporal resolution in the microsecond range. The performance of the devices is characterized by a self-heating procedure in which an ac heating current with frequency ω is applied on the wires while monitoring the resulting thermoelectric voltage V(TH) at 2ω using a lock-in technique. An analytical model is developed that enables one to determine the time response of the thermocouples from plots of V(TH) as a function of ω.

Scanning electrochemical microscopy. Theory of the feedback mode for hemispherical ultramicroelectrodes: steady-state and transient behavior

This contribution represents the first comprehensive attempt to treat complex geometry configurations of the scanning electrochemical microscope (SECM) using the alternating direction implicit finite difference method (ADIFDM). Specifically, ADIFDM is used to simulate the steady-state as well as the transient (chronoamperometric) behavior of a hemispherical ultramicroelectrode (UME) tip of the SECM. The feedback effect in this configuration is less pronounced as compared with a disk-shaped UME system. The differences between the two systems are discussed. Analytical approximations for the steady-state behavior and for characteristic features of the transient behavior are suggested. Finally, experimental feedback currents measured above a conductor and an insulator are in excellent agreement with the theory.