Evolution of structural and chemical properties of CoAl-based layered double hydroxides grown on silicon substrate

We report on the evolution of the characteristics of CoAl-based layered double hydroxide (LDH) nanostructures on a rigid substrate using various source concentrations in a solution-based growth method. As the source concentration in the solution increases, the morphologies of the CoAl-LDHs become denser and more closely packed, while the thickness of each LDH plate is maintained. Structural and chemical investigations revealed that mixed phases of CoO and CoAl-LDH formed at lower source concentrations, while Co²⁺Al³⁺- and Co²⁺Co³⁺-LDHs formed as the concentration increased. The optical band gap energy and abnormal electronic transition in the CoAl-based LDH were determined for the first time. The band gap energy decreased when increasing the Co³⁺ ion content in the LDHs in the range of 2.64–3.06 eV. Based on structural and chemical investigations, a morphological evolution mechanism is suggested for the formation of Co²⁺Al³⁺- and Co²⁺Co³⁺-LDH with variation of the solution concentration.