Effects of Additives on Kinetics, Morphologies and Lead-Sensing Property of Electrodeposited Bismuth Films

This study presents a systematic examination of the effects of bath additives and deposition conditions on the rates of electrodeposition of bismuth, obtained morphologies, and the ability of the bismuth films to detect trace concentrations of lead. Novel morphologies of bismuth are reported for the first time. The bath comprises bismuth nitrate, nitric acid, and a set of additives, viz., citric acid (complexant), poly­(vinyl alcohol) (surface inhibitor), and betaine (grain refiner). Rotating disk electrode voltammetry and cyclic voltammetry have been used to determine the mechanism and rates of bismuth electrodeposition. Scanning electron microscopy is used to study deposit morphologies, while X-ray diffraction and X-ray photoelectron spectroscopy have been used to examine crystallinity and composition of the deposited thin films. Even in the presence of additives, it is seen that bismuth deposition is diffusion-controlled process with progressive nucleation–growth of crystallites, and the reduction is a single-step, three-electron-transfer, quasi-reversible reaction. The films deposited from the bath without additives comprise micrometer-sized, hexagonal rods with controlled aspect ratios (1.83–2.05). Baths containing citric acid produce films with flower-like structures and cracked grains, but with poor adhesion to copper substrate. Introducing poly­(vinyl alcohol) significantly slows down bismuth deposition, increases the number of nuclei, produces cauliflower-like crystallites, and promotes adhesion to copper. Betaine smoothens these crystallites while retaining good adhesion. Pulsing the deposition current promotes growth of existing nuclei. In the absence of additives, fused flat disk-type spindles are seen. In the presence of additives, pulsed deposition results in sea-urchin-like morphologies. Adhesion of bismuth onto copper impacts the ability of the film to detect trace concentration of Pb²⁺ ions in aqueous solutions using anodic stripping voltammetry. The films obtained from baths with additives through direct current plating show the best sensor response for 50 ppb Pb²⁺

Tailored Formation of N‑Doped Nanoarchitectures by Diffusion-Controlled on-Surface (Cyclo)Dehydrogenation of Heteroaromatics

Surface-assisted cyclodehydrogenation and dehydrogenative polymerization of polycyclic (hetero)aromatic hydrocarbons (PAH) are among the most important strategies for bottom-up assembly of new nanostructures from their molecular building blocks. Although diverse compounds have been formed in recent years using this methodology, a limited knowledge on the molecular machinery operating at the nanoscale has prevented a rational control of the reaction outcome. We show that the strength of the PAH–substrate interaction rules the competitive reaction pathways (cyclodehydrogenation <i>versus</i> dehydrogenative polymerization). By controlling the diffusion of N-heteroaromatic precursors, the on-surface dehydrogenation can lead to monomolecular triazafullerenes and diazahexabenzocoronenes (N-doped nanographene), to N-doped oligomeric or polymeric networks, or to carbonaceous monolayers. Governing the on-surface dehydrogenation process is a step forward toward the tailored fabrication of molecular 2D nanoarchitectures distinct from graphene and exhibiting new properties of fundamental and technological interest