Compositionally bilayered feature of interfacial voids in a porous anodic alumina template directly formed on Si

Preparation of a porous anodic alumina (PAA) template, directly formed on Si, is known to form the nanosized interfacial voids between the alumina film and Si substrate. The presence of interfacial voids, however, complicates the organization of reliable contacts between the nanopores (or nanowires) and substrate. In this paper, a process of void formation according to the inversion behavior of the barrier layers is described experimentally. Interestingly, the compositional morphology which surrounded the voids reflected a bilayered feature that consisted of thin (1–5 nm) Al-rich and thick (∼20 nm) Al-poor regions, implying that these voids were formed physically, rather than chemically.