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IONS on metals/dielectrics



Ludwig,
I have pondered and searched about your question re: the
motion/non-motion of a charge deposited on the surface of a solid
conductor/insulator. The model which currently persuades me is this:

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.

2) If the deposited charge consists of ionized atoms, they will be
trapped where deposited (ignoring long-term, temperature dependent
diffusion of the ions - as is encouraged in semi-conductor "doping").
a) If the receiving solid is a metal, the free electrons in the metal
will move (not the deposited ions) to achieve the final equilibrium
charge distribution.
b) If an insulator, its electrons cannot move, and the imposed charge
distribution is maintained (ignoring long-term leakage/diffusion).

The only support I could find (indeed the only words saying anything
directly applicable) is a model of the coating of a thermionic tungsten
filament with thorium:

"The work function is likely to be altered if a foreign atom, ion or
molecule is adsorbed at the surface of a metal. In the case . . . of
thorium on tungsten, atoms striking the surface lose an electron to the
metal, because their ionization energy is less than the work function of
tungsten. The positive ions so formed are tightly bound to the metal
surface and induce a dipole layer with its positive charge outwards.
This lowers the energy which the electrons require to escape." (by
thermionic emission, as in vacuum tube filaments)

Semi-Conductors, D.A. Wright, ppg 16,17, Methuen & Co, London UK,1950,
1966.

The process is surely electrodynamics, but quantum mechanical - not
Maxwellian. Eg. the Pauli principle is operative. This is not a
separate force but a general constraint on all forces/system states.
(It's effect has been referred to as the "exchange force" because of its
root in particle statistics.)

In classical mechanics, Newton's third law plays an analogous role as an
over-riding constraint on all (two-body) forces.

Bob Sciamanda
Physics, Edinboro Univ of PA (ret)
trebor@velocity.net
http://www.velocity.net/~trebor