Sample and electrolyte preparation The substrate consists of a Au film (˜50 nm thick) with a ˜5 nm Cr adhesion layer deposited by thermal evaporation on top of an n-type Silicon sample (Siegert Wafer) as a flat support. The solutions were prepared using CuSO 4 * 5H 2 O powder (99.995%, from Sigma-Aldrich) in MilliQ (TM) (18.2 MΩcm) water. The low concentration electrolyte was prepared before every experiment from a 1 mM CuSO 4 (aq) stockpile and diluted (100-1000x) using fresh MilliQ water. Before preparing the dilute electrolyte, all containers were rinsed (5-10 x), ultrasonicated, and rinsed again (5-10 x) using fresh MilliQ water. Both the container and electrochemical cell only contained the dilute copper electrolytes, after initially cleaning them by an overnight soak in 1 M HCl. All experiments were carried out in ambient conditions inside a fume hood. Samples and the electrochemical cell were stored in a 1% humidity nitrogen environment.