Electrochemical deposition of silver and copper from a deep eutectic solvent studied using time-resolved neutron reflectivity

Here, we describe new developments in the study of electrodeposition processes with time-resolved dynamicneutron reflectivity (NR) methods to achieve insights into the differences between growth of metal films using arange of electrochemical control functions. We show that the temporal resolution has increased from 1 to 2 h perdata set (in our previous studies) to approximately 8 min. We have studied the electrochemical deposition ofcopper and silver as thin-film metals onto a gold electrode substrate from a deep eutectic solvent using po-tentiodynamic (PD), potentiostatic (PS) and galvanostatic (GS) electrochemical control functions. In particular,we have utilised novel developments in neutron reflectivity methods to acquire real-time data for the growingmetal films. Event mode capture of neutron scattering events, as a function of momentum transfer vector, Q,during electrochemical growth has enabled time-resolved measurement of the neutron reflectivity, R(Q), profilesof the growing metal films. Subsequent fitting and iterative optimisation of the R(Q, t ) data reveals the thickness,roughness and relative density (spatially resolved solvent content) of the metal film during growth. These datashow that the di fferent electrochemical growth methodologies exhibit different trends in thickness, roughnessand solvation. Silver films show an increasing roughness trend with time but these trends are largely in-dependent of growth method. In contrast, the roughness of copper films, grown under similar conditions, showsa strong dependency on growth method with PS methods producing smoothest films. These conclusions areconfirmed by ex-situ AFM measurements. The fitted NR data show that the Cu and Ag films contain between 5and 10% volume fraction solvent. Furthermore, we have explored different NR data fitting methodologies inorder to process the large numbers of data sets produced. Gratifyingly, the different methodologies and startingconditions yield a very consistent picture of metal film growth.