Determining drivers of chemical diffusion of hydrogen in the thin transition metallic glass <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msub> <mml:mi mathvariant="normal">V</mml:mi> <mml:mn>80</mml:mn> </mml:msub> <mml:m

We demonstrate the feasibility of using optical transmission to determine concentration-dependent hydrogen diffusion coefficients and activation energies of thin metallic glass films over a wide range of temperatures and concentrations. The hydrogen concentration's temporal and spatial profiles are simultaneously extracted without requiring a metal-insulator transition or hydride formation. Different contributions to chemical hydrogen diffusion are quantified and compared. The concentration dependence of the activation energy is in stark contrast to the activation energy found in epitaxial vanadium films of similar thickness. The chemical diffusion is found to increase with hydrogen concentration in the glass, whereas it decreases in the crystalline case driven by differences in the activation energy at concentrations below <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"> <a:mrow> <a:mn>0.3</a:mn> <a:mspace width="0.16em"/> <a:mi mathvariant="normal">H</a:mi> <a:mo>/</a:mo> <a:mi mathvariant="normal">M</a:mi> </a:mrow> </a:math> and the thermodynamic factor at concentrations above that. This technique provides detailed insight into the concentration dependence of hydrogen diffusion and constrains theories treating the correlated motion of hydrogen and short-range hydrogen-hydrogen interaction. The method can be applied to other materials that show an optical response to hydrogen uptake.