Elastic-constant softening in nonperiodic Mo/Ni multilayers

Surface-acoustic-wave velocity measurements on nonperiodic Mo/Ni multilayers show that an electronic mechanism based on minizone boundaries is not responsible for the softening of the c sub 44 elastic constant that occurs at small modulation wavelengths in periodic samples. The spacings between the X-ray satellite peaks of the nonperiodic multilayers are not equal. Model calculations predict these spacings and show that the satellite positions depend on the individual atomic interplanar spacings and not just the average modulation wavelength.