[NewCandle] Anodic glow discharge SEM images

[Keith Nagel]

Hey Nick,

You write:
>Now all of this begs the question, though, if color is
>tuned by pore size of the oxide, do we really know the
>mechanism by which the photons are generated?  Are we
>seeing visible vacuum modes?  I'm up for a review -
>what do we know about the presumed mechanism of this
>luminescence?

That's a tough question. When we last looked at this,
I did a literature review, and found to my surprise
that a great many people had looked into AGD over the
past 75 years, and a welter of (sometimes) conflicting
theories developed as to the how and why. The basics
of the oxide growth has been pretty well studied, and
with modern imaging techniques fairly well understood.
But why does it generate light? Is there a casual relationship
between the pore size and the color? I've been under
the impression from prior experiments ( mainly the
oxalic acid, it shows a range of color depending on
how you do it ) that it does. Can we measure the
pore size with any accuracy? And what role does
pore depth play? My oxalic experiments seemed to
indicate that it does affect color.  But is it fundamental, or
a side effect of the light filtering through
the overlying layer? I think the light itself is generated
at the surface of the aluminum metal where the oxidation
is taking place, so the layer would act as a filter.

I'll reread some of the old papers as time permits and
see if anything strikes me.

You mentioned cutting the sample; how big can a sample be
and still fit comfortably in the scope?

K.