Re: IONS on metals/dielectrics

[jmclean@chem.ucsd.edu (James Mclean)]

Bob Sciamanda wrote:
> 1) If the deposited charge is made up of electrons, then the states
> available to them are described by the band structure of the electron
> states of that solid.
>    a) If the receiving solid is a metal there will be conduction states
> available to them,and they (and the native electrons) will redistribute;
>    b) if an insulator there will be no conduction states available and
> the imposed charge distribution is maintained.

This kind of begs the question.  In the band structure picture, insulators
do have a conduction band.  But because it is so much higher in energy than
the valence band, virtually no electrons are normally in the conduction
band.  The reason that the electrons in the valence band can't carry
current is because the band is completely full.

But, since the valence band is full, that means that any extra electrons
(such as from charging) *must* go into the conduction band!

The only way I can see out of this is that the band structure model must
break down somehow.  It does assume that the electronic states are extended
throughout the material.  Pretty clearly the electronic states in an
insulator are localized, so that local spots can get charged.

-- 
--James McLean
jmclean@chem.ucsd.edu
post doc
UC San Diego, Chemistry