Аннотация:Due to its chemical and thermal inertness, refractoriness and accessible manufacturing technology, porous anodic aluminum oxide (PAAO) has found wide application in microelectronics and nanosensors. PAOA is characterized by a high degree of ordering: a small spread of pore diameters and a hexagonal-periodic arrangement of pores. By changing the technological parameters of anodic oxidation, it is possible to vary the size of pores and oxide cells of PAOA. It is possible to form porous aluminum oxide as both mesoporous (pore diameter from 2 to 50 nm) and microporous (pore diameter over 50 nm). In recent years, researchers have been attracted by the opportunity to study the optical properties of materials (analytes) deposited inside porous aluminum oxide in order to develop optical biosensors for diagnosing diseases at early stages, which allows for effective prediction, treatment and monitoring of their progress [3, 4]. Before introducing various analytes, it is necessary to obtain samples with reproducible geometric characteristics (length, pore diameter, porous cell diameter, porosity). The structural properties of porous aluminum oxide and the chemical composition of its surface can vary depending on the composition and concentration of the electrolyte in which it is formed, as well as the modes of its formation. Therefore, the aim of this work was to achieve control and reproducibility of the structural properties and chemical composition of PAOA.To obtain micrographs of the samples, Helios NanoLab 650 and Supra 40 scanning electron microscopes were used. Statistical analysis of SEM images was performed using the Fiji software package.The chemical composition was studied using a ZSX Rigaku Primus IV X-ray fluorescence spectrometer (Japan) with wavelength dispersion in vacuum. An RX40 diffraction crystal was used for the analysis of O, a PET crystal for Al, and a LiF200 crystal for Se. Analytical Kα lines were used for all elements. A PC detector was used to measure X-ray fluorescence radiation emitted by Al, O, and S.X-ray diffraction analysis was performed on a Rigaku MiniFlex 600 instrument (Rigaku Corporation, Tokyo, Japan) with a Cu Kα radiation source (λ = 1.54 Å).Let us discuss the effect of current density during sample formation on the geometric parameters of PAOA formed in H2SeO4 solutions. As an example, Fig.1 shows SEM images of the surface of PAOA formed at 5℃ in 1 M H2SeO4 and in 1.5 M H2SeO4 at different current densities.At low current density values (up to 5 mA/cm2), depending on the electrolyte concentration, two variants of the morphology of the porous structure are observed:1) many small pores in one porous cell. Most of these pores are practically spherical, i.e. they only originate on the surface, but do not develop into a cylindrical porous structure;2) one pore of large diameter, which indicates significant etching of the pore walls. If at low current densities the formation of large pores with thin walls was observed, then an increase in current density leads to an increase in the thickness of the walls and a decrease in the diameter of the pores. It is also possible to increase the number of pores in one porous cell, however, with a further increase in current density, the porous structure comes to a self-ordered state, in which one cell contains one pore, and the porous cells are smooth hexagons, the hexagonal symmetry of the porous structure has an extent of tens of cells. With a further increase in current density, defects in the formation of oxide "hot spots" are observed and the porous structure becomes non-uniform over the surface of the sample.The porosity of the oxide matrices obtained at 5°C varies from 1.5% to 25%. With increasing electrolyte temperature, the porosity increases significantly. When forming an oxide in 0.5 M H2SeO4, the porosity of the oxide increases from 1.6 to 16%. With increasing electrolyte concentration, the effect of increasing porosity (and therefore, enhancing chemical etching of the pore walls) increases significantly. The porosity changes from 1.7% to unmeasured values, since the porous structure in the upper part of the oxide is completely etched and the oxide disintegrates into fibers.The values of the intensity maxima of the main matrix of the substance (oxygen and aluminum) are almost identical, while the intensity of selenium decreases slightly with increasing concentration of H2SeO4. According to X-ray diffraction data, all obtained samples are amorphous.Thus, PAOA samples with controlled and reproducible structural parameters were synthesized. The obtained data are of great importance for practical applications of PAOA in various fields, including biomedicine.
