Substrate-Induced Anisotropic Growth of CuAlO₂ Platelets in a Liquid-Solid Reaction

This study reports a simplified method to grow CuAlO₂ crystals of submillimeter sizes with a highly anisotropic shape of a platelet. The solid-state reaction of forming CuAlO₂ at ca. 1373 K in the first stage of the conventional flux method is no longer required. The CuAlO₂ platelets nucleated directly onto the (0001)_sapphire surface in a melt of Cu₂O saturated with Al₂O₃ at 1473 K. The excess flux was mostly removed by the capped alumina plate on cooling with a limited amount of residue which can be leached afterward. The CuAlO₂ platelets all have a 3R crystal structure with no line and planar defects observed by TEM. The CuAlO₂ crystals emit a luminescence at 3.49 eV associated with resonant Raman effect resulted from a band-to-band transition in room-temperature PL measurement. The facile fabrication method for growing highly anisotropic CuAlO₂ crystals paves the way for their practical application in photoelectrochemical devices.