No abstract

No abstract

Knowledge of the carrier type (p- or n-type) and the carrier density of carbon nanotubes is critical in semiconductor applications such as thermoelectric power generation and Peltier cooling. In this paper, an experimental procedure for electrochemically characterizing multiwalled carbon nanotubes (MWCNTs) doped with boron or nitrogen has been presented. The carrier type and carrier density of the doped MWCNTs were determined by generating Mott–Schottky plots. The boron-doped nanotubes were synthesized using the substitution reaction method and the nitrogen-doped MWCNTs were synthesized using the continuous-feed chemical vapor deposition (CVD) method using pyridine or acetonitrile as the carbon precursor and ferrocene as the metal catalyst particle precursor. The nitrogen-doped nanotubes were synthesized at different CVD reaction temperatures: 650, 700, 800, and 900°C , and the effect of reaction temperature on the carrier densities of the carbon nanotubes was examined. Thermoelectric devices were constructed using pyridine nanotubes synthesized at different synthesis temperatures, and it was found that with any change (increase/decrease) in the carrier densities reflected a corresponding change in the thermoelectric power of the nanotubes.

Alternative discretization and solution procedures are developed for the 1-D dual phase-lag (DPL) equation, a partial differential equation for very short time, microscale heat transfer obtained from a delay partial differential equation that is transformed to the usual non-delay form via Taylor expansions with respect to each of the two time delays. Then in contrast to the usual practice of decomposing this equation into a system of two equations, we utilize this formulation directly. Truncation error analysis is performed to show consistency and first-order temporal accuracy of the discretized 1-D DPL equation, and it is shown by von Neumann stability analysis and numerical results that the proposed numerical technique is unconditionally stable. The overall approach is then extended to three dimensions via Douglas-Gunn time-splitting, and a simple argument for stability is given for the time-split formulation. Based on a straightforward arithmetic operation count, qualitative comparisons are made with explicit and iterative methods with the expected result that the current approach is generally significantly more efficient, and this is demonstrated with CPU-time results. Application of Richardson extrapolation in time is then investigated to improve the first-order temporal accuracy, and finally, it is shown that numerical predictions agree with available experimental data during sub-picosecond laser heating of a thin film.

No abstract