An in situ method of measuring electrolyte solution at the solid–liquid interface with MeV He+ beam in a vacuum

The ion distribution and its dynamic at the interface between solid and liquid play the main role in many applications. Measuring the solution at the solid–liquid interface in situ and noninvasively has been challenging because the electrolyte solution is volatile. Traditional ion beam analysis suffers from the energy straggling caused by the thick window and high-resolution analysis requires in-vacuum measurement. In this work, a cell with a 25 nm thick entrance window was fabricated. Solution of 0.1 mol/l BaCl2 was measured with 2 MeV He+ at the solid-electrolyte interface. It was revealed that a double layer structure was observed from the RBS spectrum. After measuring the cell for 4 h, there was no visible damage to the window. Therefore, this method can be used to measure the electrolyte solution in a vacuum in situ. It can also be expanded to measure gas or other volatile samples.