A new technique for measuring the thickness and density of ultra-thin films has been developed. Films of the order of tens of angstroms have been studied by using a combination of X-ray standing waves generated in layered synthetic microstructures (LSM) and near-total external fluorescence study. The technique has been used to study C/Ni/C trilayers (deposited on Cr/C and W/C LSM) under heat load. It was found that variation on Ni and C layer parameters at elevated temperatures is affected primarily by the deposition conditions.