| Chronology | Current Month | Current Thread | Current Date |
| [Year List] [Month List (current year)] | [Date Index] [Thread Index] | [Thread Prev] [Thread Next] | [Date Prev] [Date Next] |
I only skimmed JD's reference, so I may be repeating that an early FE
microscope was the first to directly* reveal crystal structure with a
W tip.
* as opposed to electron and neutron diffraction. W, probably the
easiest to make a very sharp tip.
bc remembers photos if W in Sci. Am. and possibly even Life.
On 2009, Mar 27, , at 08:04, Joseph Bellina wrote:
Just a few comments.
You are correct, if the electric field between the plates is high
enough, little fingers of metal normally lying in the plane of the
surface can be drawn up off the plane. Now the region is no longer
planar, but rather a metal piece with a small radius of curvature
where the electric field near the surface goes roughly as the inverse
of the radius of curvature. As a result, there is the possibility of
quantum tunnelling of electrons out of the metal, and as Dan pointed
out the electron current density will depend on the strenght of the
electric field, and work function of the metal, more work function
less current. If the current is high enough, the sliver of metal can
become hot from ohmic heating, creating the possibility for
thermionic emission, that is electrons in the metal no longer need to
tunnel through the barrier, but can go over it. That means even more
current flows, things get hotter, the metal vaporizes and you have a
small arc or spark at the surface.
As C O rightly points out, how this goes depends on the real
properties of the plates. On the other hand the analogy with metal
grinding I don't think is a good one.
cheers,
joe
Joseph J. Bellina, Jr. Ph.D.
Professor of Physics
Saint Mary's College
Notre Dame, IN 46556