Characterization of electrodeposited metal coatings by secondary ion mass spectrometry

This paper reports the results of the elemental identification and depth profiling by secondary ion mass spectrometry (SIMS) of electroplated Ru, Pd and Au coatings on a brass substrate precoated with a nickel layer. The measurements were performed by a low-cost, custom-built instrument based on standard commercial components. The secondary ion species were identified using DECO computer code. X-ray photoelectron spectroscopy (XPS) was applied for complementary surface elemental analysis of the samples. The sputter-produced crater was measured by a stylus profiler, and the nondestructive estimation of the nickel underlayer thickness was carried out by energy dispersive X-ray fluorescence analysis (EDXRFA). It is shown that thickness of the Ru film is ca. 2.6 μm, and for the Pd and Au coatings its number lies within the range of 0.4–0.5 μm. The experimental data indicate that the Ru film contains only a few percents of nickel, and the Ru–Ni interface, in contrast with the Pd–Ni and Au–Ni interlayer boundaries, appears to be sharp due to low mutual solubility in the Ni–Ru system. On the contrary, the Pd coating can be considered as a Ni–Pd alloy with Ni concentration amounting up to 90 at.% by the SIMS and XPS estimation. The appreciable content of Ni (ca. 35–40 at.%) is revealed on the surface of the Au film by XPS. For the Ru coating, the thickness of the Ni underlayer estimated by EDXRFA is 12.2 μm; the evaluated thickness of the Ni substrate for the Pd and Au coatings is about 4.5 μm and less than 1 μm, respectively, and it can be taken only as “apparent” values because of formation of solid solutions in these systems.