Anodic formation of microcrystals by electrolysis of KBr single crystals

Anodic deposition of ionic compound layers on insulator and metallic substrates by the combined action of ionic transport and a dc polarized plasma has been the subject of investigation in the last two decades. We now report on the growth of abundant ionic microcrystals on the anodic side of a solid electrolyte cell (W/KBr/stainless steel (ss)) formed by a KBr single crystal between a W plate anode and a stainless steel pointed cathode. KBr microcrystals are formed on the central zone of the W anodic plate. Prismatic and acicular microcrystals of some W–Br compounds are formed on the borders of the anodic plate and on the borders of the KBr anodic face. The observed crystallization can be qualitatively understood on the light of several phenomena: ionic electromigration along the axis of the KBr single crystal, existence of a dc plasma inside the small cavities between the W plate and the KBr crystal and a vapor deposition process induced by the Br2 provided by the KBr crystal. We finally consider the possibility of growing micro and smaller size crystals of different materials on controlled surfaces of small areas.