Dear Basanta Kumar Parida,

In sputtering, the target is bombarded with ions. In your case you have Silicon and Cobalt as your target. and in general the ions are formed using noble gases of similar atomic mass as the target, like argon, krypton, and xenon.

As the Ar+, Xe+ or Kr+ ions recover there missing electron they emit a photon. In the case of the Argon the emission is violet, for krypton is whitish and for Xenon a blue colour.

Dear Olivera sir,

here I'm attaching the two different colors of plasma in Ar gas as sputter gas.I am asking about target Silicon and cobalt as in my case,anddifferent colors of plsmas.

in the same region.

Dear Basanta Kumar Parida,

Sorry, for the over simplification of the previous answer.

The plasma can have several sources:

- the sputter gas (Ar): It will dominate the plasma colour at low power

- impurities in the sputter gas and gas inside chamber (like O2, N2,CO2,...) : the electrons can also ionize these molecules and atoms making a contribution for the final plasma colour. In general this contribution is very small.

- ionization of sputtered atoms (Si, Co): As you increase the power the one ion of Ar will be able to 'generate' several Si or Co. Part will end up ionized and consequently changing the plasma colour.

To be sure about the contribution of each atom/ion for plasma colour would be necessary to measure the plasma spectrum.

Dear all

The light emitted by a plasma is caused by desexictation of atomic or ionic or even molecular species present in the vacuum chamber. This radiation coming from excited states are caused mainly by electron impact. therefore as soon as you have a given gas inside a plasma where electron and ions are present you get emission of light with various wavelengths which are the finger print of each atom or molecule. And the colors are due to the dominant wavelength of a given spectrum emitted by a given atom or molecule. In you case you wil see a given color for silicon and another one for cobalt and another one for Ar which are present as gases and therefore are subject to excitation by electron impact. 

Dr Mustapha,

Is this color due to transition from one level to another during excitation or de-excitation? 

Dear Basanta,

The color is always due to deexcitation where the excited states always tend to return to to its steady state or Librium. In case of excitation, the atoms needs energy to be excited. This energy will be taken from the collision of the accelerated with the the atoms or molecules.

So excitation is energy absorbing and de-excitation is energy desorbing.

Best wishes

The color of the plasma depends on the excited atoms and ionized species in the plasma.