Growth of cubic crystals of cobalt-hexacyanoferrate under the octadecyl amine monolayer

Abstract

Highly oriented cubic crystals of Cobalt (II)-hexacyanoferrate (III) (Co-hcf) are formed at the air–water interface under the compressed Langmuir monolayer of octadecyl amine (ODA) when we react K 3Fe(CN) 6 solution with cobalt (II) chloride solution in the sub-phase, while no crystals are formed at the air–water interface without the ODA monolayer. X-ray diffraction and electron diffraction studies indicate that these Co-hcf crystals are oriented with their {1 0 0} plane parallel to the monolayer. Transmission electron microscopy and atomic force microscopy reveal that cubic crystals with sides of 50–300 nm are initially formed, which grow further with time and coalesce to form a thin film. Cyclic voltammetry on those Co-hcf films, transferred on gold coated glass, indicates the presence of a surface couple corresponding to Fe(CN) 6 3−/Fe(CN) 6 4− system. Present study gives an insight into the in situ growth behaviour of crystals and has implications in the design and development of advanced materials for devices.