Abstract
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.
Highlights
The structural features of nanocrystalline materials have a deterministic effect on the macroscopic properties of the material
A crystallographic texture was detected by X-ray diffraction (XRD) where the (220) planes are parallel to the film surface
The film growth gradually transforms to a columnar grain morphology with more than 3 μm long and ~120 nm wide columns. The latter dimension is determined from the transmission electron microscopy (TEM) study; hereafter, this value will be regarded as grain size
Summary
The structural features of nanocrystalline materials have a deterministic effect on the macroscopic properties of the material. Grain boundaries and crystal defects increase electron scattering and hinder dislocation propagation, thereby increasing the electrical resistivity and the mechanical hardness of the material, respectively. It is essential to determine the fundamental structural parameters to understand the effect of the processing conditions on the materials properties. Both the grain size and defect density can be influenced by the purity of the material, the parameters of the synthesis process and the preparation method itself. Several papers have reported enhanced mechanical properties like increased hardness [2,11,12,13] or tensile strength [13,14,15,16,17,18]. Superhydrophobic nanostructured surfaces which produce the so-called lotus-effect can be achieved by electrodeposition of Ni [28]
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