In low Frequency plasma, and IN CCP in perticular, the ions gain large
energy from the applied AC field and as a consequence of this there are two
effects that take place.

1. Ions gain large energy and sputtering of material increases and as a
result, there will be plasma of not only argon but also material sputtered.

2. As ions have higher energies, they create more excited states of other
neutrals of mixed plasma

So depending on the frequency applied power and target material, the colour
changes.

In case of higher frequency, mostly color remains same (mostly true after
few 10s of MHz till GHz (as it happens in ECR Ion sources)
Here ions do not gain much energy as they are too slow to respond to these
frequencies. But electrons gain large energy as they mostly fall in
synchronization with applied freqncies. So, you will find dense plasma with
more light output from higher frequencies than that of lower frequency
plasma.

In summary, even if you keep all the parameters same, different frequencies
generate different color plasma, so far the ions respond to applied electric
field. Once they become slow as compared to the applied frequencies, colour
more or less remains same if the plasma is pure.

There are many phenomena and it is very complex.

Hope this explains some of the queries.

Nabhiraj P Y
Variable Energy Cyclotron Centre,
Kolkata, India



On Fri, Sep 10, 2010 at 10:47 AM, DEBASHIS MAJI wrote:

> Dear All,
>
> Thanks everyone for your help and comments. I hope it helps me with my
> work.
> Please let me know if anybody comes along any such similar observations.
> Thanks once again.
>
> Regards,
> Debashis Maji