Modulation Structure And Mechanical Behavior Of Fe/Cu Nanometer-scale Multilayers

Fe/Cu nanometer-scale multilayers with nominal modulation wavelengths ranging from 5to 40 nm and alternating Fe and Cu sublayers thickness ratio 1:1 are direct current sputteringdeposited onto single crystal Si (100) substrates with dimensions of 30 mm×3 mm×380μmat room temperature using the high-vacuum duplex chamber multi-functional magnetronsputtering apparatus with a base pressure better than 2×10^-5 Pa. The working pressure ofresearch-grade Ar and the target power are 0.3 Pa and 100 W, respectively. Modulationstructures including concentration profile, phase state and interfacial structure arecharacterized by using small angle / wide angle x-ray diffraction (SA/WAXRD) and highresolution transmission electron microscopy (HRTEM). Residual stress and nanoindentationhardness are examined by using profilometry and nanoindentation, respectively. The actualsublayer thickness ratio is close to 1:1, and the actual modulation wavelengths are 5.63-34.0nm, which agree with the designed values. Fe/Cu nanometer-scale multilayers have clearinterfaces between the alternating Fe and Cu sublayers which are planar near the substrate andwaved near the surface. There is an amorphous layer with a thickness of 2 nm betweenmultlayers and substrate. In all conditions, the multilayers have Fe (110) and Cu (111)textures. For the multilayers with nominal modulation wavelength of 5 nm, the crystalstructure of Fe sublayers is bcc, and the one of Cu sublayers is alternative stable bcc andmetastable fcc. The columnar grains of Fe and Cu grow through the sublayers, and theaverage grain size increases from 5 to 19 nm with increasing the modulation wavelength from5 to 40 nm. The tensile residual stress in the Fe/Cu multilayers which relaxes insignificantlyincreases from 183 to 627 MPa with increasing the modulation wavelength from 5 to 40 nm.The evolution of the residual stress is interpreted by the increasing grain size. Thermal misfitsignificantly contributes to the residual stress. The hardness of the Fe/Cu multilayersincreases firstly and then deceases with increasing the modulation wavelength, and reachespeak value of 7.29±0.29 GPa at the nominal modulation wavelength of 10 nm. The evolutionof the hardness of the multilayers depends on layer miscibility and modulus differencebetween sublayers.