Self-organized hexagonal pore arrays with a 50–420 nm interpore distance in anodic alumina have been obtained by anodizing aluminum in oxalic, sulfuric, and phosphoric acid solutions. Hexagonally ordered pore arrays with distances as large as 420 nm were obtained under a constant anodic potential in phosphoric acid. By comparison of the ordered pore formation in the three types of electrolyte, it was found that the ordered pore arrays show a polycrystalline structure of a few micrometers in size. The interpore distance increases linearly with anodic potential, and the relationship obtained from disordered porous anodic alumina also fits for periodic pore arrangements. The best ordered periodic arrangements are observed when the volume expansion of the aluminum during oxidation is about 1.4 which is independent of the electrolyte. The formation mechanism of ordered arrays is consistent with a previously proposed mechanical stress model, i.e., the repulsive forces between neighboring pores at the metal/oxide interface promote the formation of hexagonally ordered pores during the oxidation process.

Crystallographic and magnetic identification of secondary phase in orientated Bi5Fe0.5Co0.5Ti3O15 ceramics J. Appl. Phys. 112, 073919 (2012) Fabrication and performance optimization of the magneto-optical (Tb1−xRx)3Al5O12 (R=Y, Ce) transparent ceramics Appl. Phys. Lett. 101, 131908 (2012) Domain evolution in lead-free thin film piezoelectric ceramics J. Appl. Phys. 112, 052014 (2012) Ferroelectric domain morphology and structure in Li-doped (K,Na)NbO3 ceramics J. Appl. Phys. 112, 052005 (2012) Room temperature ferroelectric and magnetic investigations and detailed phase analysis of Aurivillius phase Bi5Ti3Fe0.7Co0.3O15 thin films

Ordered arrays of nickel nanowires have been prepared using pulsed electrodeposition. Two self‐patterning anodization processes were used to fabricate alumina pore matrices into which nickel was deposited from a Watts bath: two short millisecond deposition pulses followed by a long delay yielded almost 100 % filled pores (see Figure). Nanowire arrays are expected to have important applications as magnetic memories.

The brownian motion of mesoscopic particles is ubiquitous and usually random. But in systems with periodic asymmetric barriers to movement, directed or 'rectified' motion can arise and may even modulate some biological processes. In man-made devices, brownian ratchets and variants based on optical or quantum effects have been exploited to induce directed motion, and the dependence of the amplitude of motion on particle size has led to the size-dependent separation of biomolecules. Here we demonstrate that the one-dimensional pores of a macroporous silicon membrane, etched to exhibit a periodic asymmetric variation in pore diameter, can act as massively parallel and multiply stacked brownian ratchets that are potentially suitable for large-scale particle separations. We show that applying a periodic pressure profile with a mean value of zero to a basin separated by such a membrane induces a periodic flow of water and suspended particles through the pores, resulting in a net motion of the particles from one side of the membrane to the other without moving the liquid itself. We find that the experimentally observed pressure dependence of the particle transport, including an inversion of the transport direction, agrees with calculations of the transport properties in the type of ratchet devices used here.

The morphology and formation conditions of ordered hexagonal pore arrays in anodic alumina are discussed. The ordered arrangement of pores is shown to form by a self-organized process starting from randomly distributed pore positions at the surface of the alumina. The influence of the pretreatment of the aluminum substrate and the anodizing conditions on the growth kinetics and the tendency to form hexagonal pore structures were investigated. Homogeneous etching conditions are required in order to obtain regular pore arrays. This observation corresponds to the finding that hexagonal pore arrays are related to a smooth etching front and a homogeneous depth of neighboring pores.