Glancing angle extended x-ray absorption fine structure (EXAFS) has been applied to study structure, diffusion, and short-range order in ultrahigh vacuum evaporated C-Er bilayer and Er/C multilayer films, which provide a model for the influence of microstructure in x-ray multilayer reflectors. A lack of crystallinity in the C-Er bilayers and Er/C multilayers is indicated by x-ray diffraction. EXAFS spectra of C-Er bilayers and Er/C multilayers are substantially different from that of a 6000-Å erbium film, which shows local structure similar to pure erbium. For bilayers and multilayers a local ErC2-like environment has been found, even though only a small concentration of carbon is thought to have diffused into erbium layers. It is possible that carbon diffusion and Er - C bond formation prevent the crystallization of locally ordered hcp erbium metal clusters. That low Z atoms can diffuse into the high Z metal layers and change their structure appears to be a common feature for x-ray multilayer mirrors.