Evidence for the supermodulus effect and enhanced hardness in metallic superlattices

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Abstract
A study of the mechanical properties of Cu/Nb superlattices shows that for modulation wavelengths below ∼50 Å the biaxial modulus increases by ∼15%, the shear modulus decreases by ∼30%, and the flexural modulus does not change. These observations show that anomalies with different signs for elastic moduli can coexist in the same material. Measurements performed on both supported and unsupported films show that the anomalous effects are not induced by the presence of a substrate. The superlattices are also found to have a hardness larger than either Cu or Nb.