In Situ Scanning Tunneling Microscopy of Electrodeposition of Indium on a Copper Thin Film Electrode Predeposited on Pt(111) Electrode

Abstract

Indium deposition is involved in preparing semiconducting thin films of copper indium gallium selenide (CIGS)a material of great use in fabricating solar cells. In situ scanning tunneling microscopy (STM) was used to study electrodeposition of indium (In) on a copper (Cu) thin film electrode in 0.1 M K 2 SO 4 + 1 mM H 2 SO 4 + 1 mM In 2 (SO 4 ) 3 (pH 3) electrolyte solutions without and with 1 mM chloride. A Cu thin film predeposited on platinum (111) comprised Cu(111) oriented layers stacked on the Pt(111) substrate. This highly ordered Cu(111)-like substrate rendered detailed characterization of underpotential and overpotential deposition (UPD and OPD) at potentials positive and negative of −0.60 V (vs Ag/AgCl), respectively. Both bisulfate and chloride anions preoccupied the Cu substrate impeded In UPD. Atomic resolution STM imaging revealed that In nucleated preferentially at surface defects, followed by lateral growth to form an organized indium adlayer, identified as a (√37 × √37)R25.3°structure. Indium adatoms aggregated, rather than distributing evenly on the Cu substrate. Indium deposit did not mix with the Cu substrate until the second stage of In UPD. This In/Cu interfacial mixing occurred first at steps and vacancy defects.

Atomic-level characterization of liquid/solid interface

“…For example, the bisulfate and chloride can compete with metal adatom for surface sites or even impede the UPD process. [50,52,53] While in some cases, metal atoms tend to combine with anions to form a bilayer for their lattice match with substrate, such as the Cd layer sandwiched between a Cl overlayer and the first layer of the Cu (111) substrate, generated by exchanging between the preadsorbed Cl anions and adsorbing Cd cations. [54] Similar CuCl structure was also found on Pt (111) surface.…”