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 K₃Fe(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.