Re: News: Molecular transistor discovery




Hi, Tim and Fred,


> Some more details:
> http://www.science.ualberta.ca/nav02.cfm?nav02=36033&nav01=11471


If you hurry, the full text of the paper may be downloaded for free
from the Nature site, www.nature.com. That's Piva et al., Nature 435
(2005) 658.

Although Wolkow claims it's a nanotransistor, it looks far further from
a real technology than the nanotube transistor does. Nanotube
transistors just lack the technology for producing large ordered arrays
of the things. Wolkow's transistors lack a lot more.

> I wonder if they observed quantized conductance.

See for yourself, the answer is no. And why would you expect
conductance to be quantized in a transistor? Conductance quantization
occurs in nanowires, meaning nanostructures with a metallic
bandstructure, i.e. a nonzero density of propagating modes at the Fermi
level. The integer "quantum number" is the number of propagating modes
in the energy range between the Fermi levels of the electrodes on
either side. The assumption underlying Landauer's prediction of
quantization is that these modes show 100% transmission, with zero
coefficient of electron reflection at the interfaces with the two
electrodes.

Transistors are made from semiconductors. Their whole point is the
possibility of control of current flow, and this can only be achieved
if the coefficient of transmission of a given mode may vary. This is
achieved by arranging for the modes to be evanescent under some bias
conditions.

Cheers,

Zigoteau.


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