STUDY OF THE LAYERS AND NANOPOWERS OF POROUS SILICON BASED ON X-RAY DIFFRACTION AND ULTRAVIOLET SPECTROSCOPY
Quite a number of studies today focus on the use of biocompatible and biodegradable nanostructures - such as silicon nanostructures and silicon nanopowders - as a practical tool for the diagnostics of various diseases and targeted delivery of drugs or dyes.
In order to further improve the technology for the preparation of nanostructured materials for medical applications it is necessary to address a number of problems. They include the peculiarities of the formation process of the samples and their structure, as well as the optical properties of nanostructured materials.
The aim of this paper is to study the way that electrochemical etching affects the crystal structure of porous silicon obtained using various techniques. We also focus on the optical absorption properties of the obtained samples and the changes that the optical properties of the samples undergo when the porous layer is ground up to powder.
Porous silicon samples were obtained by electrochemical etching of single-crystalline silicon KEF <100> with a resistivity of 0.2 Ohm·cm. The etching current density was j=25 mA/cm2. The etching was performed for 10 minutes in various solutions of fluoric acid. Porous silicon powder was obtained via mechanical separation of the porous layer from the Si substrate and its further fractionation in the ultrasonic bath. After that, the powder was separated into light and heavy fractions in a centrifuge.
Using the results of X-ray diffraction and the Scherrer equation, we calculated the size of the Si crystals of the porous layer. The lattice constant of these crystals coincided with the lattice constant of the crystalline silicon. In order to determine the mechanisms of optical absorption in the porous layers, the analysis of the absorption spectra of the samples was performed using the Beer–Lambert–Bouguer law.
Thus, using X-ray diffraction and UV-spectroscopy we studied two groups of porous silicon with different pore size, as well as the powders obtained from these samples. We found that the electrochemical formation of the porous layer resulted in the disorder of the crystals in the porous layer as compared to the initial substrate. We also determined the characteristic features of the optical absorption spectra of the porous layers and the nanopowders, and the difference between them.
The work on the development of the technology for obtaining highly functional epitaxial hetero-nanostructures on Si-wafers was supported by the Council for Grants of the President of the Russian Federation (grant no.MD-188.2017.2 and MK-4865.2016.2).
The work on determining the morphology, surface structure, and functional properties of silicon nanopowders was supported by the Russian Foundation for Basic Research (project No.17-32-50004 mol_nr).
All the experiments were conducted using the equipment of the Centre for Collective Use of Scientific Equipment of VSU.
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