Early-Stage Growth Mechanism and Synthesis Conditions-Dependent Morphology of Nanocrystalline Bi Films Electrodeposited from Perchlorate Electrolyte

Bi nanocrystalline films were formed from perchlorate electrolyte (PE) on Cu substrate via electrochemical deposition with different duration and current densities. The microstructural, morphological properties, and elemental composition were studied using scanning electron microscopy (SEM), atomic force microscopy (AFM), and energy-dispersive X-ray microanalysis (EDX). The optimal range of current densities for Bi electrodeposition in PE using polarization measurements was demonstrated. For the first time, it was shown and explained why, with a deposition duration of 1 s, co-deposition of Pb and Bi occurs. The correlation between synthesis conditions and chemical composition and microstructure for Bi films was discussed. The analysis of the microstructure evolution revealed the changing mechanism of the films’ growth from pillar-like (for Pb-rich phase) to layered granular form (for Bi) with deposition duration rising. This abnormal behavior is explained by the appearance of a strong Bi growth texture and coalescence effects. The investigations of porosity showed that Bi films have a closely-packed microstructure. The main stages and the growth mechanism of Bi films in the galvanostatic regime in PE with a deposition duration of 1–30 s are proposed.

Overpotential controls a morphology of electrolytically produced copper dendritic forms

The morphologies of copper dendritic forms obtained in both potentiostatic and galvanostatic regimes of electrolysis with various amounts of the electricity were analyzed by the scanning electron microscopy (SEM) technique. Irrespective of amount of passed electricity, 3D (three dimensional) pine-like dendrites with sharp tips were formed in the potentiostatic regime of electrolysis. On the other hand, the amount of passed electricity had a strong effect on the shape of the 3D pine-like dendrites formed in the galvanostatic regime of electrolysis. Dendrites with sharp tips were formed with smaller amount of passed electricity, while dendrites with globular tips were formed with larger amounts. The change in the shape of the galvanostatically synthesized 3D pine-like dendrites was explained by comparison with copper deposits obtained potentiostatically at overpotentials that corresponded to the final overpotentials during galvanostatic regime of electrolysis for the analyzed amounts of electricity. Based on the similarity of the obtained morphologies at the macro level, it was concluded that the overpotential plays a crucial role in the formation of the electrolytically synthesized dendrites and that the controlled conditions of electrolysis could represent a suitable way for a synthesis of spherical Cu particles by electrolysis.

Morphology and microstructure of annealed Ni-Co alloy powders electrodeposited on copper substrates

Nickel and cobalt alloy powders from two different electrolyte compositions were obtained by electrodeposition from an ammonium sulfate solution. The structure of Ni-Co deposits formed by electrodeposition at a galvanostatic regime and the influence of current density and the bath composition were studied by SEM, DSC and X-ray diffraction methods. It was shown that the microstructure and morphology of the powders depended on the deposition current density as well as bath composition. Both, bath composition and current density affect strongly the deposit growth mechanism and the deposit composition, microstructure, grain size and surface morphology. It was found that the overpotential significantly affects the structure of the formed deposits. When electrodeposition was performed far from equilibrium conditions face-centered cubic (FCC) cobalt was deposited while at low overpotential hexagonal close packed (HCP) Co was formed with a lower rate of hydrogen evolution. The increase of HCP phase in the nanocrystalline deposits was caused by increase of the Co content in the powder as well by decrease of the deposition current density. It was shown that the powders change their structure in the temperature interval from 300?C to 600?C. In Co rich samples, structural changes during heating were attributed to the phase transformation of HCP to FCC.

STUDY OF PASSIVATED FILMS OF GaSb

Thin anodie oxides (5-10 μm) were formed on n-GaSb (100) substrates by electrochemical method under galvanostatic regime employing an aqueous solution (citric acid/hydrogen peroxide), at volume ratio of 5:1, changing the time of growth. The thickness and index of refraction, thermal diffusivity and quality of passivated films were obtained by IR reflectance spectroscopy, photoacoustic spectroscopy and finally photoluminescence spectroscopy.