Re: RF Conductivity of thin Mo film

Mark Fergerson <[EMAIL PROTECTED]> wrote in message news:<[EMAIL PROTECTED]>...

> 
>    Are you writing a proposal, or doing design work? I ask 
> because if the former, you have a lot of paper to plow 
> through to find such arcane data. If the latter, you can do 
> some preliminary labwork to narrow things down.
> 
Design work.  We are planning on measuring the plane wave return loss
and insertion loss of some test pieces, but I would like to obtain
analytic predictions first.

> 
>    Elsewhere I suggested you provide a cold finger to 
> collect the Mo before it contaminates your radome; why is 
> that unacceptable?
> 
I apologize.  I have never before heard of a "cold finger" and thought
that your answer was some kind of jest or sarcastic comment.  Could
you please enlighten me on this subject?

> > I have found a paper (R. C. Hansen and W. T. Pawlewicz, "Effective
> > conductivity and microwave reflectivity of thin metallic films," IEEE

> <some possible answers interspersed>
> 
> > 1. Should I expect the deposited Mo layer to be polycrystalline, so
> > that the Hansen/Pawlewicz formulas are valid?  If not, how to proceed?
> 
>    There doesn't seem to be a lot of info about pure Mo 
> films. But
> 

http://msewww.engin.umich.edu/research/groups/yalisove/publications/impurities_in_Mo/sct132124
 
>    and similar papers suggest film structure (both 
> mechanical and chemical) is strongly influenced by substrate 
> temperature, trace gas(es) present, and so on, implying the 
> film structure will change as it deposits unless your radome 
> is a very precisely controlled environment.
> 
>    You may have to build it and collect some data.

Thanks for the reference.  I fear that duplicating the space
environment, with its hard vacuum, diurnal temperature variations, and
very intermittent firing of the plasma thruster for short bursts over
several years, may be very difficult to replicate in the lab.  But we
will do the best we can here.
> 
> > 2. What is the electron mean free path length for Mo?  Does this
> > depend on temperature?
> 
> http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1975PhLA...54..229A
> 

Great reference! Thanks!  How'd you find it?

> > 3. Is it true that the bulk conductivity of metals is inversely
> > proportional to temperature over my working range (90K to 400K)?
> 
>    Got a CRC? Plot some graphs.
I only have a very old CRC (1978) here at home, and it doesn't seem to
have anything relevant, at least that I can find (it lacks a detailed
table of contents <amazing!>)

[snip] 
>  Why not prevent 
> the deposition in the first place?

I agree.  My job is to help convince the configuration people that the
electrical performance of the radome is going to be unacceptably
degraded and that they need to do something to remove the source of
the contamination.  I look forward to your reply with more details
about the "cold finger" approach.

--Peter