Quantitative study by atomic force microscopy and spectrophotometry of the roughness and brightness of electrodeposited nickel in the presence of additives

Abstract

The effects of saccharin and 2-butyne-l,4-diol, and their mixture on the surface roughness and brightness of electrodeposited nickel from a Watts bath have been studied by atomic force microscopy and spectrophotometry, respectively. The inhibiting effect of these additives on the reduction of nickel ion increases in the order saccharin, saccharin plus 2-butyne-1,4-diol, and 2-butyne-1,4-diol. In the best electrodeposition conditions the roughness obtained with 2-butyne-1,4-diol and with a 2-butyne-1,4-diol-saccharin mixture are similar, reaching a root mean square (RMS) roughness value of about 8 nm, about twice less than that obtained with saccharin alone. The large granular electrodeposits obtained from the Watts bath in the absence of organic additives have a RMS roughness value about 20 times larger than that of the brightest platings. The RMS roughness and the specular reflectivity of the coatings have been correlated. Brightness increases in line with decreasing roughness, following an approximate gaussian law to reach its maximum when the RMS roughness is around 5 nm. Below this value, the atomic force microscope reveals itself to be a privileged technique in appreciating the effects of additives on the grain smallness of the deposits.