Ammonia decomposition will be performed ex situ at different temperatures on silicon surfaces with 50 nm of either iron or ruthenium. The main objective of the neutron reflectometry analysis is to determine the concentrations of the different nitride phases, such that we are able to find out which nitride phase is the most active in decomposing ammonia. This will also provide information about the reverse reaction of ammonia formation on iron and ruthenium surfaces, which is of great industrial importance (ammonia is synthesised on the hundred-megatonne scale each year), as well as the industrial process of nitriding.