Can you share some information on that, like how he setup should be? What should be the voltage and current range should be used. Is there any requirement of vacuum in the chamber?
Actually, making electrets with the triode Corona discharge is very easy. You just have to put a needle at a high voltage (10kV) and a grid at the voltage you want to charge the electret.
For the sample to charge, you can use Teflon metallized on the rear face. You can find more information here: Cantilever-based electret energy harvesters, Smart Materials and Structures, 2011.