Surface Charge Driven Growth of Eight-Branched Cu2O Crystals

Cu2O crystals are synthesized hydrothermally with an eight-branched morphology, which can undergo a transition to a cubic shape by increasing the reaction time. The rapid branch formation of these structures is studied over time using scanning electron microscopy, transmission electron microscopy, selected area electron diffraction, powder X-ray diffraction, and thermogravimetric analysis. The formation of Cu2+/polyvinylpyrrolidone soft matter clusters is shown to play a key role in the reduction of Cu2+, the nucleation of Cu2O crystals, and the rapid growth of branches along all eight equivalent <111> directions of the cubic Cu2O structure, due to the presence of negatively charged hydroxyl sites on the {111} surfaces. This nonclassical crystal growth mechanism, which relies on aggregation of the precursor on the crystal surface, may help us to understand the formation of many abnormal crystal morphologies.