Relationship between Copper(II)-Lactate Complexes and Cu₂O Electrodeposited Using Highly Concentrated Alkaline Solutions

Abstract

The direct or indirect effects of two different copper(II)-lactate complex species, Cu(H‐₁L)L⁻ and Cu(H‐₁L)₂²⁻, on the orientation and electrical properties of Cu₂O electrodeposits were examined, where L⁻ = CH₃CH(OH)COO⁻ and H‐₁L²⁻ = CH₃CH(O⁻)COO⁻. To investigate the relationships between the copper(II)-lactate complex species and several properties of Cu₂O, a set of Cu₂O layers was electrodeposited from thermodynamically well-stabilized electrolytes of different pHs with unified overpotentials. The Cu₂O layers obtained at pH <9.5 had the 〈100〉 preferential orientation, whereas the orientation changed to the 〈111〉 preferential orientation at pH >9.5. In addition, marked differences were observed in the resistivity and carrier density of Cu₂O layers bordering pH 9.5, indicating the presence of a strong relationship between copper(II)-lactate complexes and these crystallographic or electrical properties. In terms of the cathodic reactivity of copper(II)-lactate complexes and changes in local pH in the vicinity of the cathode upon electrodeposition, we suggest that the two copper(II)-lactate complexes directly affected the electrical properties of Cu₂O and indirectly affected its crystallographic orientation.