Effects of 2-buthyne-1,4-diol additive on electrodeposited Ni films from a Watts-type bath

Structures of Ni films electrodeposited from a Watts-type bath containing 2-buthyne-1,4-diol (BD) were investigated using SEM, cross-sectional SIM, XRD measurement with a pole profiling technique and electrochemical methods for controlling properties of Ni electrodeposits. Preferred orientation of Ni electrodeposits was assigned to potential domains for electrodeposition. Preferred orientation in the higher potential region was (1 1 0) or (1 0 0), that in the middle potential region were (1 1 1) and (3 1 1), and that in the lower potential region was (1 0 0). The growing axis of Ni electrodeposits seems to agree with the speculation from Pangarov's model based on the two-dimensional nuclei theory in the lower overpotential region in which the dominant growing plane is fundamentally determined by crystallization overpotential related to supersaturation of adatom, although the growth axes of Ni deposits do not always agree with the preferred orientation. For example, preferred orientation of (1 1 0) was assigned to growing (1 1 1) plane which tilts at 55° to the substrate. Adsorption of BD affects the structure and morphology of electrodeposits via an inhibitory effect related to its surface coverage depending on surface orientation, growth rate and BD concentration in the plating bath.