Stability of Structure, Phase and Elemental Composition of ChemicallyDeposited and Electrodeposited Gold Layers in Multilayer SystemsAuchemically reduced; electrodeposited /Co-W/Cusputtered / Glass-Ceramics
The changes in the structure and elemental composition of Au and Co-W thin layers after thermal treatment of 200 h at 200-300 oC and 50 h at 450 oC were systematically studied using the X-ray microanalysis of scanning electron microscope XL-30 ESEN Philips. The phase stability was evaluated by X-ray diffraction (XRD). The electrodeposited Co-W layer (W 46.0-53.0 wt. % depending on the electrodeposition regime) is amorphous and maintains its amorphous state after heating at 200 oC for 200 h and subsequent heating (+) at 300 oC for 150 h. Co-W amorphous layers prevent interdiffusion of Au and Cu atoms and formation of intermetallics AuCu in the systems of layers Au chemically reduced; Au electrodeposited /Co-W/Cu sputtered / glass-ceramics. The chemically reduced 0.4 � m Au layers maintain their structure and phase in the systems of layers upon heating at 200 oC for 200 h and subsequent heating (+) at 300 oC for 50 h. The Au layer maintains its Au content 85-86 wt. % upon heating at 450 oC for 50 h, the cobalt content of the layer up to 8.6 wt. % and content of oxygen bonded to Au of 8.6 wt. %. The electrodeposited Au layers (0.8 - 1.0 � m) maintain their structure at heating at 200 oC and 300 oC for 200 h. After additional heating at 450 oC for 30-50 h gold content in the layer decreases from 98.4 wt. % to 85.0 wt. %, cobalt content increases to 7.6 wt. % and oxygen to 7.2 wt. %. Functional properties of the above multilayer systems deteriorate by mutual diffusion of metal atoms and formation of brittle intermetallics. The latter may give rise to the formation of monolithic films, cause the deterioration of mutual adhesion of the layers and complete reactions of the upper conducting Sn, Au layers with the base metal Ni, Cu, Ti, Sn (15, 16). This diffusion can worsen the properties of very thin (0.5-1.0 � m) metal layers electrodeposited on a Cu layer (1-2 � m) sputtered on glass-ceramics (15).
Characterization and microhardness of Co−W coatings electrodeposited at different pH using gluconate bath: A comparative study
Electrodeposition of Co–W alloy coatings has been carried out with DC and PC using gluconate bath at different pH. These coatings are characterized for their structure, morphology and chemical composition by X‐ray diffraction, field emission scanning electron microscopy, differential scanning calorimetry and X‐ray photoelectron spectroscopy (XPS). Alloy coatings plated at pH8 are crystalline, whereas coatings electrodeposited at pH5 are nanocrystalline in nature. XPS studies have demonstrated that as‐deposited alloy plated at pH8 with DC contain only Co2+ and W6+ species, whereas that alloy plated at pH5 has significant amount of Co0 and W0 along with Co2+ and W6+ species. Again, Co2+ and W6+ are main species in all as‐deposited PC plated alloys in both pH. Co0 concentration increases upon successive sputtering of all alloy coatings. In contrast, mainly W6+ species is detected in the following layers of all alloys plated with PC. Alloys plated at pH5 show higher microhardness compared to their pH8 counterparts. Copyright © 2013 John Wiley & Sons, Ltd.
Interdiffusion and reaction of metals: The influence and relaxation of mismatch-induced stress
The early interdiffusion stages in epitaxially grown Ag/Au and Cu/Au reaction couples are investigated by high-resolution and Z-contrast electron microscopy. While the interdiffusion in the lattice-matched system Ag/Au follows Fick's diffusion laws from the very beginning, a complex two-stage reaction is observed in the lattice-mismatched Cu/Au samples. A fast diffusion at the beginning of the heat treatment produces a planar zone of lattice defects along the interface, which release most of the induced stress. This first reaction stage stops after reaching a diffusion length of about 15 nm. Subsequent interdiffusion takes place by a recrystallization mechanism comprising heterogeneous nucleation of new grains and diffusion-induced grain boundary migration. During this second reaction stage, discontinuous composition profiles are determined, evidencing stress release at high-angle grain boundaries. The recrystallization mechanism also dominates the formation of ordered intermetallics at lower reaction temperatures.