Plasma component filtering through a hole using the sheath generated around the hole on surface modification by RF plasma

Glassy carbon (GC) surfaces were subjected to RF glow-discharged plasma treatment through a simple filter comprising of an aluminum plate with an aperture at the center. Surface properties were estimated by contact angle measurement and the atomic ratio O/C obtained from X-ray photoelectron spectroscopy (XPS). When the aperture was small enough (2 r < 1 mm), the properties of the GC surface did not alter with the Ar plasma treatment. Ar ions could not pass through the hole. The surface properties under the hole were changed when 2 r was 5 mm, suggesting the acceleration of the Ar ions to the GC surface as a result of the electric field in the sheath. There is a threshold value for aperture size above which the ions can pass through. On the other hand, the properties of the GC surface were changed almost uniformally after O 2 plasma treatment with a small aperture size (2 r < 1 mm). O 2 plasma components travelled to the interior of the sample. It is considered that the radicals mainly acted because they are neutral and uninfluenced by the electric field in the sheath. Radicals in the O 2 plasma moved by random walk and could reach the interior of the sample. With 2 r of 5 mm, the surface under the hole was mainly changed by ion-assisted reactions.