Cu nanofilm formation by electrochemical atomic layer deposition (ALD) in the presence of chloride ions

The effect of Cl− on the structure of Cu nanofilms deposited with electrochemical ALD, using surface limited redox replacement (SLRR), is described. These investigations involved ultrahigh vacuum analytical methodologies coupled directly with electrochemical studies (UHV-EC), as well as in situ scanning tunneling microscopic (STM) studies. Pb was chosen as the sacrificial metal as it forms atomic layers on Cu via underpotential deposition (UPD). In addition, it is significantly more reactive than Cu, less noble, and thus undergoes redox replacement by Cu. Pb UPD was formed at −0.44 V versus Ag/AgCl, for 20 s. The substrates used in these studies were Ar+ ion bombarded and annealed Au(1 1 1) single crystal substrates. The resulting Pb UPD coated Au(1 1 1) was immersed in a Cu2+ ion solution at open circuit for 10 s, allowing redox replacement of the Pb UPD by Cu. Nanofilms were then formed by repeating this process of Pb UPD followed by exchange for Cu. The resulting Cu nanofilms were characterized using low energy electron diffraction (LEED), Auger electron spectroscopy (AES), and in situ STM. The total Cu in a deposit was estimated by anodic stripping. Up to five cycles of Pb replacement by Cu were performed in these studies. The structures formed displayed a (5 × 5) unit cell, consisting of a 4 by 4 arrangement of Cl atoms on the Cu surface. The degree of surface order appeared to decrease gradually as the number of replacement cycles was increased, though a relatively clear LEED pattern was still observed after five replacement cycles.