Subject: Power in single molecules

From: Jorge Seminario <[email-masked]>
Date: Thu, 22 Jan 1998 19:22:46 -0500 (EST)

Dear All,
There is a class of experiments on nanotechnology that I would like
to ask you for help in order to understand them better so I can
have also a better way to interpret our ab initio calculations.
The experiment consist of measurements of current-voltage (IV) on single
molecules or even atoms.

    GoldLead----Molecule----GoldLead

a DC voltage (V) is applied between the two leads and a current (I)
circulates through the molecule.
Assuming perfect contacts and perfect voltage source,
the voltage drop in the molecule is also V and therefore the power
dissipated in the molecule is P=VI (perhaps naively speaking).

Several experiments report currents in the order of 1 uA (microamper)
and voltages in the order of 1 volt. This implies that the power-
supply is sending 1 uW (microwatt) of power to the Au-M-Au system which
will be dissipated in the single molecule.  This certainly means a huge
amount of energy to be dissipated in the single molecule.  The explanation
given to me is that this energy will be transfered to the leads where is
finally dissipated. This seems reasonable; however I would like to know
your views.

Other explanation that I got is that the
product V*I does not make sense for mesoscopic systems; however I can
not find a good justification.

One more explanation is that the voltage drop is in the contacts only
and practically zero in the molecule, so the power in the molecule is
also close to zero.

If you have any thoughts about this, another possibility, or any idea of
what could be happening on the system above, I would be very interested to
share your views whether through this media or to any of my coordinates
below.

Thanks so much in advance for your cooperation.
Cordially
Jorge
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Jorge M. Seminario
Department of Chemistry and Biochemistry
University of South Carolina
Columbia, South Carolina 29208
Tel: 803-777-9567
Fax: 803-777-9521
email: [email-masked]
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