[NewCandle] Anodic glow discharge SEM images

[Nick Reiter]

Hi Keith and all,

Got delayed a bit, but just sent some oxalic acid
generated oxide pore photos to you, Keith.  Very
subjectively, I would say the pores in the oxalic
generated layer look like they are maybe half the size
or less than the pores of the phosphoric generated.

If the pores act as a band pass filter, then what
parameters would determine the basic spectrum of the
aluminum surface oxidizing?  hm.  Now I suppose if I
could try this with Zr foil instead of Al, and
determine if the light color coming off at similar
conditions was similar in hue, then it might add more
weight to some mechanism based on cavities rather than
emission from the metal surface...  whatda think?

You asked about SEM sample size - the microscope I
have access to is not a real big one... I can have
pretty much free roaming distance over about a 1.5" by
1.5" area.  So call it roughly 4cm x 4cm x 2cm high, I
would say.

N


> 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.
> 
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