Adhesion strength of a metal plating film on Al substrate is known to be improved remarkably by introducing Fe alloy double zincate treatment as a pretreatment process for metal plating on Al. At each step of alkaline etching, desmutting, initial zincate treatment, HNO3 dipping, and the second Fe alloy zincate treatment in the double zincate process, depth profiles and the chemical state of the surface elements were measured extensively using XPS. Furthermore, a set of surface structure models in the process was proposed to explain the improvement of adhesion strength by Fe alloy double zincate treatment. By dipping the first zincate film in HNO3 solution, granular Zn-Fe alloy deposited on Al passivation film at the first zincate treatment was dissolved. Furthermore, approx. 10 nm particles of Fe-rich alloy were believed to be formed concurrently in the Al passivation film. In the second Fe alloy zincate treatment, the Fe-rich alloy particles are expected to be exposed to the second zincate solution to act as nuclei for the formation of a highly uniform and thin Zn-Fe alloy film. The adhesion improvement of Zn-Fe alloy film occurred because Fe-rich alloy particles were included with the Al passivation film. They were close to the metallic Al substrate where dipolar coupling of Alδ＋･･Oδ－･･Feδ＋ would act to improve the adhesion strength of Fe alloy double zincate film on the Al substrate.
To elucidate the catalytic reaction mechanism of BH4－ (a reducing agent) on metal surfaces during electroless deposition, its oxidation reaction was investigated theoretically using density functional theory (DFT) calculation. Particularly in this study, dehydrogenation reaction of BH4－ was modeled and analyzed because it is the most important elementary step of overall oxidation for the catalytic behavior of metal surfaces. To ascertain the tendencies of catalytic activity of metal surfaces, the reaction on Cu(111) and that on Pd(111) were compared. Actually, Cu shows little catalytic activity toward BH4－ oxidation, whereas Pd shows strong catalytic activity. Results of reaction energy calculations show that the BH4－ dehydrogenation occurs with difficulty on Cu(111), but it occurs easily on Pd(111), which corresponds to experimental results. Detailed analyses of reaction system electronic structures show that the d-band states of each surface are important to assess the background of the difference. Because the Pd surface has a high-energy d-band, it can interact with high-energy unoccupied orbitals of BH4－, leading to electron donation from the surface toward BH4－. This electron donation effect from Pd provides dissociation activity of the B-H bond, which promotes dehydrogenation of BH4－.