An improved electrode useful for modifying a substrate using corona discharge dielectric barrier discharge or glow discharge plasma treatment or coating a substrate using plasma enhanced chemical vapor deposition under atmospheric or near atmospheric pressure conditions, the electrode having a body defining a cavity therein, the body having at least one inlet passageway there through in gaseous communication with the cavity so that a gas mixture can be flowed into the cavity by way of the at least one inlet passageway, the electrode having at least one outlet passageway there through in gaseous communication with the cavity so that a gas that is flowed into the cavity can flow out of the cavity by way of the at least one outlet passageway, the at least one outlet passageway being a slot. The improvement is to position a porous body in the cavity sealed to the wall of the cavity adjacent to the outlet passageway so that a gas that is flowed into the cavity will pass through the porous body before flowing through the outlet passageway.