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Epitaxial nanotwinned Cu films, with an average twin spacing ranging from 7 to 16 nm, exhibit a high ratio of strength-to-electrical resistivity, ∼400 MPa(μΩ cm)-1. The hardness of these Cu films approaches 2.8 GPa, and their electrical resistivities are comparable to that of oxygen-free high-conductivity Cu. Compared to high-angle grain boundaries, coherent twin interfaces possess inherently high resistance to the transmission of single dislocations, and yet an order of magnitude lower electron scattering coefficient, determined to be 1.5–5×10-7 μΩ cm2 at room temperature. Analytical studies as well as experimental results show that, in polycrystalline Cu, grain refinement leads to a maximum of the strength-to-resistivity ratio, ∼250 MPa(μΩ cm)-1, when grain size is comparable to the mean-free path of electrons. However, in twinned Cu, such a ratio increases continuously with decreasing twin spacing down to a few nanometers. Hence nanoscale growth twins are more effective to achieve a higher strength-to-resistivity ratio than high-angle grain boundaries. [ABSTRACT FROM AUTHOR]

We investigate the evolution of microstructure and mechanical properties of sputter-deposited Al/Nb multilayers with miscible fcc/bcc type interface and individual layer thickness, h, of 1–200 nm, subjected to helium ion irradiations: 100 keV He+ ions and a fluence of 6×1016/cm2. Helium bubbles, 1–2 nm in diameter, are observed. When h is greater than 25 nm, hardnesses of irradiated multilayers barely change, whereas radiation hardening is more significant at smaller h. Transmission electron microscopy and scanning transmission electron microscopy studies reveal the formation of a thin layer of Nb3Al intermetallic phase along the Al/Nb interface as a consequence of radiation induced intermixing. The dependence of radiation hardening on h is interpreted by using a composite model considering the formation of the hard Nb3Al intermetallic layer. [ABSTRACT FROM AUTHOR]

We have investigated the thermal stability of sputter-deposited Cu thin films with a high density of nanoscale growth twins by using high-vacuum annealing up to 800 °C for 1 h. Average twin lamella thickness gradually increased from approximately 4 nm for as-deposited films to slightly less than 20 nm after annealing at 800 °C. The average columnar grain size, on the other hand, rapidly increased from approximately 50 to 500 nm. In spite of an order of magnitude increase in grain size, the annealed films retained a high hardness of 2.2 GPa, reduced from 3.5 GPa in the as-deposited state. The high hardness of the annealed films is interpreted in terms of the thermally stable nanotwinned structures. This study shows that nanostructures with a layered arrangement of low-angle coherent twin boundaries may exhibit better thermal stability than monolithic nanocrystals with high-angle grain boundaries. [ABSTRACT FROM AUTHOR]

The evolution of microstructure and mechanical properties of sputter-deposited Al/Nb multilayers with miscible fcc/bcc type interface and individual layer thickness (h), subjected to helium ion irradiations, is examined. The dependence of radiation hardening on h is inferred by using a composite model considering the formation of the hard [Nb.sub.3]Al intermetallic layer.