| dc.description.abstract | In situ scanning tunneling microscopy (STM) and cyclic voltammetry (CV) have been used to investigate the effect of chloride ion, bis-3-sodiumsulfopropyl disulfide and polyethylene glycol on the electrodeposition of copper onto Au(111). Chloride ion can accelerate the reduction rate of copper ion, but this effect is insignificant when the copper concentration is lower than 0.1mM. Stepping the potential from 0.5 to -0.4 V to observe copper deposition in 0.1M Sulfuric acid and 0.1mM KCl with STM, which reveals 2D deposition mode of Cu on the ordered Au(111) electrode. This contrasts markedly with the 3D growth of Cu on Au(111) in a sulfate medium. The adsorption of chloride on Cu deposit is confirmed by STM imaging. The adsorbed Cl- adlayer increases the surface diffusion rate of Cu adatoms, helping them to transfer across the step barrier.
SPS molecules are adsorbed in highly ordered array at 0.8 V, characterized as Au(111) - (6 × 2√21). In situ STM imaging reveals that Cu deposition grows in 3D in 0.1mM SPS, which is proposed to result from slow surface diffusion rate of Cu adatoms likely capped by segregated SPS molecules. However, it is intriguing that it is bisulfate anions structure, not the SPS, imaged by STM. When Cu deposit is stripped off, STM images a defected adlayer of SPS.
The effect of PEG on Cu deposition on Au(111) is always suppressing, regardless of the presence of Cl-, which results from PEG’s high viscosity and slow-down of Cu2+ diffusion rate. STM imaging reveals rough Cu deposit when the potential is made negatively in steps in the presence of PEG6000 in the sulfate media. By contrast, abrupt adjusting from 0.5 to -0.4 V in the same medium, the copper film grows laterally, yielding a Cu smooth film on which a highly ordered bisulfate adlayer characterized as (√3 × √7) is imaged. Copper deposition in the presence of PEG and Cl yielded different processes and film morphology. The synergistic effect of PEG and Cl- indeed suppresses Cu deposition, as evidenced by the negative shift of the onset potential of copper deposition. STM imaging shows that Cu deposit grows in 3D when the potential is gradually made negative. By contrast, switching the potential abruptly from 0.5 to -0.4 V, Cu deposit nucleated at steps and on terraces, followed by
lateral growth and coalescence of Cu islands at the latter stage. | en_US |