Revealing the Formation Dynamics of the Electric Double Layer by means of in-situ Rutherford Backscattering Spectrometry

We report on a new versatile experimental setup for in-situ Rutherford backscattering spectrometry at solid- liquid interfaces that enables investigations of electric double layers directly, in-situ and in a quantitative manner. A liquid cell equipped with a three electrode arrangement is mounted in front of the beam line and a thin Si3N4 window down to a thickness of 150 nm separates the vacuum of the detector chamber from the electrolyte in the cell. Since the contribution of the window to the measured spectra is minimized, a large variety of elements at the solid-liquid interface with sensitivities far below one mono layer can be monitored. The attachment of Ba onto the Si3N4 surface as a function of contact time and pH value of the electrolyte solution was chosen as example system. From our measurement we can not only read the evolution of the double layer but also derive limits for the point of zero charge for the Si3N4 surface. Our findings of 5.7 ≤ pH_PZC ≤ 6.2 are in good accordance with values found in the literature obtained by other techniques. Despite the measurements shown in this work, the presented setup allows for a large variety of in-situ investigations at solid-liquid interfaces such as tracing electro-chemical reactions, monitoring segregation, adsorption and dissolution and corrosion processes.