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Re: IONS on metals/dielectrics



Hi James!
Your point is well taken. It seems that the added electrons must, at
least locally, alter the band structure. Texts seem to indicate that, at
least in the case of the doping of semi-conductors, the added electrons
enter states somewhere within the forbidden gap. In an insulator this
must still be well out of reach of the conduction band.

I think that much of this surface physics is still a black art (I am
certainly a laymen here) and has only been vigorously explored in the
course of developing applications to semi-conductor device manufacturing.

If you, or anyone, can shed light, please emit!

Bob Sciamanda
Physics, Edinboro Univ of PA (ret)
trebor@velocity.net
http://www.velocity.net/~trebor
-----Original Message-----
From: James Mclean <jmclean@chem.ucsd.edu>
To: phys-l@atlantis.uwf.edu <phys-l@atlantis.uwf.edu>
Date: Friday, October 02, 1998 4:51 PM
Subject: Re: IONS on metals/dielectrics


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