Thursday, September 30, 2010

Giant Thermoelectric Effect from Transmission Supernodes

We are presently mastering the art of fabricating devices at the molecular level and using the fine detail to produce useful effects.  Here we are converting heat into electricity and from the description they are beginning to see astounding efficiencies.  

Obviously, there is no end of applications when one understands that just about everything we do produces thermal energy or more correctly, it wastes thermal energy.

This makes an energy future with even zero wastage at least a talking point and progressively more practical.  As costs drop more waste energy will be captured and used.

We have already made the point many times that our gasoline engines are struggling to capture as little as twenty five percent of the available energy.  From so low a conversion base, a modest improvement provides huge energy.  This is why I have posted often on energy efficiency issues when discussing limits in fuel supplies.

The easiest fix for strained supplies happens to be getting all that is actually been already used.  This technology shows us that it may even be possible.

SEPTEMBER 26, 2010

University of Arizona researchers predict an enormous order-dependent quantum enhancement of thermoelectric effects in the vicinity of a higher-order ‘supernode’ in the transmission spectrum of a nanoscale junction. Single molecule junctions based on 3,3’-biphenyl and polyphenyl ether (PPE) are investigated in detail.

If a TE material were found exhibiting ZT over 4 it would constitute a commercially viable solution for many heating and cooling problems at both the macro- and nanoscales, with no operational carbon footprint. Currently, the best TE materials available in the laboratory exhibit ZT about 3, whereas for commercially available TE devices ZT are 1, owing to various packaging and fabrication challenges.

The predicted peak ZT could be 50 if the many body theoretical work is accurate for 30 phenyl groups. If there were 100 phenyl groups then the ZT would be 100.

Thermoelectric devices based on individual single-molecule junctions (SMJs) are ideally suited for local cooling in integrated nanoscale circuit architectures. Supernode-based devices have allow transmission probability and thus a large electrical impedance capable of withstanding voltage surges. Moreover, high-power macroscopic devices could be constructed by growing layers of densely packed molecules. For example, a self-assembled monolayer with a surface density of 4×10^15molecules/cm2 would give 352kW/cm2 at peak efficiency for a meta-benzene film. The efficiency of PPE-based devices increases with ring number and is only limited by the electronic coherence length, suggesting that highly efficient molecular-based thermoelectric devices may soon be realized.

Getting better than ZT of 5 is better than any small engine or generator using smaller temperature differentials.

Getting better than ZT of 20 is better than almost any existing engine or generator that we have now.

Getting to ZT of 50 or 100 and the actual energy efficiency of the conversion of heat to electricity would be very close to Carnot efficiency. There would be very little practical difference in the percentage of conversion that was not being captured.

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