Voltage Dependence of Nanopattern Morphology and Size in Electropolished Monocrystalline Aluminum: An Experimental Study

The crystallographic orientation dependence of nanopattern morphology and size of electropolished Al at a fixed voltage (40 V) has been revealed and established. However, systematic experimental studies, with samples' crystallographic orientation exactly determined, on the effects of voltage on nanopattern morphology and size has been largely lacking. Here, miscut monocrystalline Al samples are electropolished in a common electrolyte at voltages 20-60 V. Various nanopatterns (pits, pits plus stripes, stripes, dots) with distinct morphologies emerge with increasing voltage. The findings that morphologies transform gradually with misorientation angle were explained from the perspective of surface structure sensitivity. Nanopattern sizes remain largely constant with misorientation angles but increase with voltages till about 40 V, level off and decrease at higher voltage. A reported model was reexamined to explain the observed voltage dependence of nanopattern size by considering the overlooked effects of voltage on dissolution and adsorption. These findings reveal the voltage and crystallographic orientation dependence of nanopattern morphology and size, and provide critical data for theoretical investigation into the nanopattern formation mechanism of electropolished Al.