Boundary/materials setting in eigenmode for Qu calculation

Dear all,

I am confused by the "subtract" command in hfss.
I simulate my cavity in eigenmode to obtain the Qu. In my project, the inner conductor and the shield are silver-plated, and the cavity is filled with air. Such as, the out shield has material of "air" and the inner conductor has material of "silver".

i) Do I need to "subtract" the inner conductors from the out shield? If so, after the operation of "subtract", which materials do the inner surface of the cavity have?

ii) Do I need to handly set each surface of the shield as silver boundary? If so,is there any convenient way to do it?

need help.

Thanks