Al/AlN multilayered thin films with periodic thickness &lgr; less than 24 nm were developed by ion beam assisted deposition. A considerably small surface roughness comparable to that of the silicon substrate and much smaller than those of both monolithic Al and AlN films was obtained. Over the investigated range of &lgr;, all the multilayers are harder than the homogeneous AlN film, and a significant hardness enhancement by a factor of ∼2 over that of the AlN film was observed in the multilayer with &lgr; of 6 nm. Moreover, the hardness enhancement is not at the expense of the multilayer toughness, with the multilayer Al/AlN films showing improved plasticity as compared with the AlN film. ©1997 American Institute of Physics.