High-density structures with well-ordered nanohole arrays have been obtained by the self-ordering growth of nanopores using 25–40 V anodization voltages in a sulfuric–oxalic acid mixture. In each anodization voltage, two types of electrolyte mixture were used with low and high sulfuric concentrations at a constant pH value. The ordering and regularity of a nanohole array was quantified by analysis of fast Fourier transformations of scanning electron and atomic force microscope images. The results show that the long range ordering of nanohole array is superior for high sulfuric concentration, while regularity is more pronounced for low sulfuric concentration. The interpore distance in the oxalic–sulfuric mixture is higher in the case of low sulfuric concentration. It is almost proportional to 2.6 nm V−1 and 2.5 nm V−1 for the electrolyte mixture with low and high sulfuric concentrations, respectively. While the porosity is nearly 10% for samples made in standard sulfuric and oxalic acid using 25 V and 40 V anodization voltage, respectively, it increases up to 50% for the sample made with 37.5 V in an oxalic–sulfuric mixture.

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The significant effect of anodization current on the morphology of nanopores encourages us to consider a novel method for engineering these nanostructures. In this paper we study a controlled anodization process using controlled electrolyte stirring. This is done using an electrical pump with variable speed for sprinkling an electrolyte on a membrane. The variable voltage applied to the pump can control the temperature gradient and diffusion of the ions which produce the anodization current. Here we show the significant role of pumping and how this effect can be used in the engineering of nanopores as a three-dimensional nanostructure. These experiments are carried out for a variety of anodization voltages and various electrolyte concentrations, and thus we investigate how these parameters in the vicinity of pumping can control the porosity of the template in three dimensions.

Piezoelectric poly(vinylidene fluoride) (PVDF) nanowires are of particular interest for energy harvesting as they are ultra‐sensitive to small vibrations. Here, a new, cost‐effective, and scalable approach to producing PVDF nanowires with strongly enhanced power output is presented. The method combines template‐wetting in cylindrical nano‐confinement with anisotropic solvent‐nonsolvent phase inversion to yield a fully novel nanowire morphology consisting of “sausage‐like” strings of nano‐domains. Dynamic numerical simulations of the phase inversion reveal the formation of these structures to be subject to a very rich and complex phenomenology. The simulated dependence of the feature size on the degree of confinement agrees with the experimentally observed trend. It is unambiguously demonstrated that the sausage‐like nano‐generators upsurge the power density to 280% compared to normal nanowires. Finite element modeling explains how the higher deformability of the sausage‐like nanostructures gives rise to this significant enhancement in piezoelectric performance.

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A hard anodization (HA) technique was employed using different mixtures of sulfuric/oxalic acid for fabrication of highly self-ordered alumina nanopore arrays. The sulfuric acid concentration was changed from 0.005 to 0.05 M and the anodization voltage was changed from 60 to 140 V. An optimum self-ordering was achieved in a wide range of interpore distances from 130 to 270 nm. For each mixture, there was a region of anodization voltage in which the self-ordering took place. The width of this region decreases with increasing sulfuric acid concentration. In these regions, the optimum voltages with the best self-ordering versus the sulfuric acid concentration follow a second order exponential decay function. Our investigations show that current–time characteristics at optimum anodization voltages were identical for all mixtures. For each electrolyte mixture, the interpore distance was dependent upon the anodization voltages with proportionality constants of 2.1 nm V−1 and 2.2 nm V−1 for high and low voltages, respectively. The porosity of the samples (about 3.5%) follows the porosity rule of HA.

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