Electrochemical Microstructuring of Columnar Cu2O Layers Through Preferential Grain Boundary Dissolution

Crystalline oxide microfeatures offer optical, electronic, catalytic, and interfacial functions, but their fabrication often requires templates, patterned scaffolds, or serial machining. A template-free route converted an electrodeposited Cu2O coating on Au(111)/Si into substrate-supported vertical microfeatures by anodization at a nominal cell voltage of 10 V in 0.002 mol L−1 Na2S2O8 at 277 K. FE-SEM showed progressive widening of the pre-existing intercolumnar network and narrowing of the retained features. This spatially non-uniform removal identifies preferential dissolution along the intercolumnar network as the principal removal pathway at the coating-morphology scale. From 1 to 8 min, the within-image mean and median feature widths decreased by 36.0% and 45.9%, respectively. The dominant out-of-plane Cu2O(111) diffraction signature was retained while mean visible reflectance decreased. The Cu-H2O potential-pH framework provides a qualitative thermodynamic guide to possible oxidative pathways that are evaluated against the experimental evidence. C 1s-referenced XPS provides direct ex situ evidence of an anodization-associated Cu(II)/CuO-like contribution at the outermost surface. Chopped photoelectrochemical measurements showed the largest condition-level light–dark current density contrast after short anodization, providing a secondary functional comparison of the completed coatings.