Experiments were performed for the study of the influence of impurities on the microstructure and hardness of nanocrystalline Ni films. The samples were prepared by electrodeposition using two basic electrolyte solutions (a sulfate-type bath and a Watts-type bath). The effect of saccharin as organic additive on the microstructure, texture and hardness was studied. It was found that the Watts bath without saccharin yielded a larger grain size compared to its sulfatetype counterpart. For both electrolyte solutions, (220) out-of-plane texture was formed in the saccharin-free films. The additive saccharin eliminated the texture and yielded very fine microstructures with high dislocation densities and twin fault probabilities for both solution types. The influence of saccharin on the defect density was higher for the film prepared from the sulfate-type bath. It was revealed that there is a correlation between the defect density and the grain size. When saccharin was added to the Watts bath, the combined effect of nickelchloride and saccharin led to a bimodal grain size distribution. An additional sample was deposited from an electrolyte containing trisodium citrate to investigate the sodium incorporation in the Ni layers. The correlation between the microstructure and the hardness of the films was discussed in detail.
The microstructure of electrodeposited Ni films produced without and with organic additives (formic acid and saccharin) was investigated by X-ray diffraction (XRD) line profile analysis and cross-sectional transmission electron microscopy (TEM). Whereas the general effect of these additives on the microstructure (elimination of columnar growth as well as grain refinement) was reproduced, the pronounced intention of this study was to compare the results of various seldom-used high-performance structural characterization methods on identical electrodeposited specimens in order to reveal fine details of structural changes qualitatively not very common in this field. In the film deposited without additives, a columnar structure was observed showing similarities to the T-zone of structure zone models. Both formic acid and saccharin additives resulted in equiaxed grains with reduced size, as well as increased dislocation and twin fault densities in the nanocrystalline films. Moreover, the structure became homogeneous and free of texture within the total film thickness due to the additives. Saccharin yielded smaller grain size and larger defect density than formic acid. A detailed analysis of the grain size and twin boundary spacing distributions was carried out with the complementary application of TEM and XRD, by carefully distinguishing between the TEM and XRD grain sizes.
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