Our study is devoted to sheath structures emerging in Ar/O-2 plasma. By means of two dimensional PIC/MCC computer model two configurations were investigated - sheath structure in the vicinity of a cylindrical Langmuir probe for two different biases and changes of the sheath structure when a cylindrical probe passes into a semi-planar probe.
It was shown that O+ ions play important role in shielding out negative bias of a solid immersed in Ar/O-2 plasma and edge effects of a semi-planar probe on its sheath structure were evaluated.