A real time in situ method for quantifying hydrogen accumulation in thin solid films using ion energy loss spectroscopy

Real-time quantification of hydrogen accumulation in materials is critical for hydrogen storage and energy technologies; however, conventional techniques provide only post-exposure information, and real-time quantitative measurements remain scarce. Here, we present an in situ method to measure hydrogen density evolution in thin films by analyzing the energy loss of protons transmitted through them. A simple model separates contributions from the pristine matrix and implanted hydrogen, enabling direct extraction of hydrogen density. The approach is demonstrated on nanometric Ta 2 O 5 films exposed to hydrogen beams, which act simultaneously as implantation source and probe. Measurements reveal non-linear hydrogen buildup and saturation at ≈0.05–0.10 g cm −3 for a fluence of 6.0 × 10 18 ions cm −2 , where saturation reflects the balance between implantation and diffusion. This methodology provides dynamic insight into hydrogen retention and transport in thin films, offering a broadly applicable tool for optimizing materials for hydrogen storage and related energy applications.