Institute of High Temperature Electrochemistry of the Ural Branch of the Russian Academy of Sciences, Ekaterinburg, Russia:

A. V. Isakov, Senior Researcher, e-mail: ihte_uran@mail.ru
Yu. P. Zaykov, Research Manager of Institute

Laboratory of Carbon Fiber and Functional Polymers of Ministry of Education, College of Materials Science and Engineering, Beijing University of Chemical Technology, Beijing, China.

X. Zhang, Professor
S. Jiang, Researcher

We studied the electrochemical reduction of silicon in the KF – KCl – KI – K₂SiF₆ melts and obtained the chronoamperometric dependences for estimation of the process times, at which the diffusion zones of silicon clusters overlap. The dependencies, described by the Cottrell equation, are indicative for the nucleation of silicon in the molten alkali metal halide. The constant values of the growth current for the new phase occur in the interval of 1.6–2.0 seconds. The processes of obtaining the thin-film silicon coatings were studied at the temperature of 993 K. The electron microscopy and micro-X-ray spectral analysis revealed that the thin films of the elemental silicon can be produced during galvanostatic electrolysis. The vibrational bands corresponding to the Si–Si bond vibrations were determined in the film study by Raman spectroscopy. The silicon film is formed from intergrown silicon clusters, which, in their turn are formed during the phase growth. At the same time, the film formation ultimately occurs due to the silicon clusters’ fusion. The clusters are the silicon formations of approximately the same size. We revealed the regularities of obtaining the continuous thin silicon films by molten salt electrolysis. The conditions for producing the silicon films in the KF – KCl – KI melts (28–75 mol.%) – K₂SiF₆ (0.1–0.4 wt.%) in the time interval of 60–4800 seconds and the cathode current density of 0.1–0.4 A/cm² were determined. The Submicron silicon films with a thickness of 450–800 nm of the large area were obtained. The change in the conditions results in the change of the morphological structure of the precipitate. Reduction of such parameters as the cathode current density or deposition time leads to the formation of an islet film. An increase in these parameters leads to the appearance of signs of a secondary crystallization, i. e. dendrite formation on the surface.
This research work was carried out with the financial support of the Russian Scientific Funds (agreement No. 16-13-00061).

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