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

Abstract

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.