Epitaxial single crystal and boron-doped diamond layers were exposed to reactive ion etching in Ar/O2 plasma (rf power of 25 W and self-bias of 100 V); and the electrical, structural, and electrochemical characteristics of the exposed surface were investigated. Angle-resolved x-ray photoemission spectroscopy (XPS) measurements revealed a nonuniform layer of amorphous carbon at the exposed surface with an average thickness of approximately 4 nm, as confirmed also by atomic force microscopy profiling of selectively etched areas. On highly boron-doped diamond, the plasma-induced damages resulted also in a nonconductive surface layer. This damaged and insulating surface layer remained resistant to graphite-etching chemicals and to rf oxygen plasma but it was removed completely in microwave hydrogen plasma at 700 °C. The surface characteristics after the H-plasma process followed by wet chemical oxidation were restored back to the initial state, as confirmed by XPS. Such “recovery” treatment had been applied to an all-diamond submicrometer electrode array initially patterned by an Ar/O2 plasma etching. The electrochemical characteristics of this electrode array were improved by more than two orders of magnitude, approaching theoretical limit for the given geometrical configuration.