Re: RF Conductivity of thin Mo film

Peter Simon wrote:
>snip


, or
> amorphous.
>
> This deposition is going to occur in a vacuum, due to ion bombardment
> of a molybdenum surface, at temperatures that vary over the range of
> 90 to 400 K.
>
> I have found a paper (R. C. Hansen and W. T. Pawlewicz, "Effective
> conductivity and microwave reflectivity of thin metallic films," IEEE
> Trans. Antennas Propagat., vol 30, no 11, Nov 1982) that shows how to
> calculate the effective conductivity of a thin metallic layer given
> the bulk conductivity sigma_0 and the electron mean free path length L
> (in the bulk metal).  The calculation is based on earlier work by
> Fuchs, Sondheimer, and Campbell.  Hansen and Pawlewicz do not provide
> any comparison with measurements, but state that "this model fits
> polycrystalline films reasonably well" along with the claim that "most
> thin films will be polycrystalline."  They provide an example
> calculation for a gold (Au) film, using the values of sigma_0 = 4.1e7
> S/m and L = 570 Angstrom, which I assume are both valid at room
> temperature, approx. 300 K.
>
> My questions:
>
> 1. Should I expect the deposited Mo layer to be polycrystalline, so
> that the Hansen/Pawlewicz formulas are valid?  If not, how to proceed?


Look sputtering Mo and the deposit of it on a surface can lead to many 
different crystalline structures. These structures as you rightly point 
out depends on temperature, sputtering rates, co-sputtering of the film, 
  the kinetic energy of the clusters and ions hitting the film, the 
energy and type of ions used to sputter from the target, and the rate of 
sputtering. The best way I believe to get accurate estimates of the 
properties you desire is to just make the film in an environment as 
close as you can to the space environment and then measure the DC 
resistivity versus temperature and use that in your calculations. Also, 
remember Mo may oxide over long periods in space do to atomic oxygen. 
This will change the reflectivity of the film.

Measuring the DC resistivity only requires a closed cycle refrigerator,
a temperature controller, dc constant current source, a nanovoltmeter, 
some connectors, a Si-thermometer. If you want it automated then you 
need a 486 computer with an IEEE-488 card for controller and limited 
programming skills.


> Thanks very much,
>
> Peter Simon
> peter underscore simon at ieee dot org
> (return email address is a spam trap)