The structural and optical properties of Mo/Si and Ru/Si x-ray multilayers prepared by sputter deposition in argon have been examined using high-resolution transmission electron microscopy, optical profilometry, and x-ray and soft x-ray reflectance. We find that for Ru/Si, similar to previous results for Mo/Si, lower argon pressure during deposition results in smoother layers and higher reflectance. For low-pressure deposited multilayers, interfacial roughness is negligible compared to interfacial diffuseness; the presence of amorphous interlayer regions in both of these systems is the major cause of reduced reflectance.