Influence of Dimensionality on Thermoelectric Device Performance

The role of dimensionality on the electronic performance of thermoelectric devices is clarified using the Landauer formalism, which shows that the thermoelectric coefficients are related to the transmission, T(E), and how the conducing channels, M(E), are distributed in energy. The Landauer formalism applies from the ballistic to diffusive limits and provides a clear way to compare performance in different dimensions. It also provides a physical interpretation of the "transport distribution," a quantity that arises in the Boltzmann transport equation approach. Quantitative comparison of thermoelectric coefficients in one, two, and three dimension shows that the channels may be utilized more effectively in lower-dimensions. To realize the advantage of lower dimensionality, however, the packing density must be very high, so the thicknesses of the quantum wells or wires must be small. The potential benefits of engineering M(E) into a delta-function are also investigated. When compared to a bulk semiconductor, we find the potential for ~50 % improvement in performance. The shape of M(E) improves as dimensionality decreases, but lower dimensionality itself does not guarantee better performance because it is controlled by both the shape and the magnitude of M(E). The benefits of engineering the shape of M(E) appear to be modest, but approaches to increase the magnitude of M(E) could pay large dividends.Comment: 23 pages, 5 figure

A theory for molecular transport phenomena through thin membranes

Theory for molecular transport phenomena through thin membrane

Inclusive growth analytics : framework and application

This paper argues that inclusive growth analytics has a distinct character focusing on both the pace and pattern of growth. Traditionally, applied country-specific poverty and growth analyses have been done separately. This paper describes the conceptual elements for an analytical strategy aimed to integrate these two strands of analyses, and to identify and prioritize country-specific constraints to sustained and inclusive growth. The authors apply the framework to the case of Zambia. The analysis suggests that income growth in Zambia is constrained by poor access to domestic and international markets, inputs, extension services, and information. High indirect costs - mostly attributable to infrastructure service-related inputs in production including energy, transport, telecom, water, but also insurance, marketing, and professional services - undermine Zambia's competitiveness, limit job creation, and therefore serve as a major constraint to inclusive growth. Improving the quality and access to secondary and tertiary education is essential if the poor are to benefit from future growth of the non-farm economy. Weak governance and, in particular, poor government effectiveness are factors behind the market coordination failures and the identified government failures, and are as such major obstacles to inclusive growth in Zambia.Rural Poverty Reduction,Achieving Shared Growth,,Access to Finance,Economic Theory&Research

Oxygen in the Galactic thin and thick disks

First results from a study into the abundance trends of oxygen in the Galactic thin and thick disks are presented. Oxygen abundances for 21 thick disk and 42 thin disk F and G dwarf stars based on very high resolution spectra (R\sim 215000) and high signal-to-noise (S/N>400) of the faint forbidden oxygen line at 6300 A have been determined. We find that [O/Fe] for the thick disk stars show a turn-down, i.e. the ``knee'', at [Fe/H] between -0.4 and -0.3 dex indicating the onset of SNe type Ia. The thin disk stars on the other hand show a shallow decrease going from [Fe/H] \sim -0.7 to the highest metallicities with no apparent ``knee'' present indicating a slower star formation history.Comment: To be published in "CNO in the Universe", ASP Conference Series, C. Charbonnel, D. Schaerer & G. Meynet (eds.

A Numerical Study of Scaling Issues for Schottky Barrier Carbon Nanotube Transistors

We performed a comprehensive scaling study of Schottky barrier carbon nanotube transistors using self-consistent, atomistic scale simulations. We restrict our attention to Schottky barrier carbon nanotube FETs whose metal source/drain is attached to an intrinsic carbon nanotube channel. Ambipolar conduction is found to be an important factor that must be carefully considered in device design, especially when the gate oxide is thin. The channel length scaling limit imposed by source-drain tunneling is found to be between 5nm and 10nm, depending on the off-current specification. Using a large diameter tube increases the on-current, but it also increases the leakage current. Our study of gate dielectric scaling shows that the charge on the nanotube can play an important role above threshold.Comment: 26 pages, 8 figure