Narrow Results

Ferroelectric Pb(ZrTi)O₃ (PZT) nanotubes were prepared by sol–gel method and porous anodic alumina (PAA) membrane using spin-coating technique. This method is based on filling-pyrolysis-filling process and the use of one-stage alumina membranes. One of the advantages of this method is its rapidity, which takes only 1 h time before the calcination step. The effect of repeated pores filling was investigated to get the required size of nanotubes. The field emission scanning electron microscope (FE-SEM) images were shown that the PZT nanotubes have inner diameters in the range of 65–90 nm and length of about 50–60 $\mu$m. This means that the samples have a significant aspect ratio (700–800). Also the FE-SEM image confirmed that the highly ordered, hexagonally distributed PAA membranes with the pore diameter about 140–150 nm were formed. The X-ray diffraction (XRD) results showed that the PZT nanotubes have a tetragonal structure. The metal oxide bands like ZrO₆ and TiO₆ of the final PZT nanotubes were detected by Fourier transform infrared (FT-IR) analysis and confirmed the formation of perovskite structure. By using FT-IR spectroscopy and Kramers–Kronig transformation method, the optical constants like real ${𝜀}_1$($\omega$) and imaginary ${𝜀}_2$($\omega$) parts of dielectric function, extinction coefficient k($\omega$) and refractive index n($\omega$) were determined. It was shown that the optical constants of PZT nanotubes are different from PZT nanoparticles.

Ordered large-scale alumina nanowire arrays on the surface of porous anodic alumina membranes (AAMs) have been synthesized by chemical etching. The analysis shows that amorphous alumina nanowires directly formed from AAMs have uniform size and shape. The mean length and mean diameter of alumina nanowires are about 6 μm and 24 nm, respectively. It is observed that chemical etching parameters affect the synthesis of alumina nanowires and preferable experimental conditions for the synthesis of alumina nanowire arrays. The intensity of photoluminescence excited from alumina nanowire is affected by post-annealing temperatures. The mechanisms for the synthesis and PL emission of alumina nanowires are discussed.

We have shown that the surface potential of anodic alumina films changes in time: immediately after the anodization process it was positively followed by the substantial decrease to negative values. Such variations of the surface potential can be associated with the negative built-in electric charge in alumina. The highest negative charge density occurs in the films formed in citric and phosphoric electrolytes.

The alumina thin films with brilliant structural colors have been fabricated by means of electrochemical oxidation in phosphoric electrolyte under the condition of room temperature. The relationship of the structural colors with the anodization time and the angle of incidence of illuminating light are discussed. The microstructures of the films have been characterized as well. The effective refractive index of film is calculated according to Maxwell-Garnett theory. The maximum reflection wavelength of films is calculated by Bragg's equation, and the generation mechanism structural color has also been discussed. In the end, organic-assist covering method has been applied to obtain the intricate multicolor pattern on the same alumina thin film. This thin film with brilliant colors may have potentials in color displays, decoration and anti-counterfeiting technology.