Single crystals of NiO, CoO, FeO, Co(3)O(4), and Fe(3)O(4) have been epitaxially deposited on MgO single-crystal substrates by the hydrolysis of anhydrous metal bromides in the gaseous phase. All of the crystals were grown at temperatures below 700 degrees C and at a total pressure of less than 25 torr. The deposition was usually complete after approximately 30 min, and the crystals were of uniform thickness with a glassy-clear, smooth surface. Depending on the number of depositions, these crystals can be formed in various thicknesses ranging from approximately 5 mu m to 1 mm. The crystals were found to deposit in parallel alignment with the (100) cleavage plane of MgO. A substantial increase in chemical purity is observed, and only 10(3) a to 10(5) dislocations/cm(2) were observed in all NiO crystals. A reaction mechanism is proposed which involves: (i) the formation of a hydroxybromide transport phase with fluid properties; (ii) adsorption of the transport phase on the MgO substrate; followed by (iii), the chemical disproportionation-crystallisation of the intermediate phase to the oriented, solid oxide phase.
