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Nanostructure, chemical composition, and mechanical properties of Cu-Cr thin film structures

The development of nanostructured metals and alloys with superior mechanical properties is of paramount importance for both, a fundamental scientific understanding of the structure property relationship of materials and future technological applications in modern micro- and nanotechnologies.

This study focused on the structural design of nanostructured Cu-Cr thin film alloys and multilayers. The thin films were synthesized under highly non-equilibrium conditions using vapor deposition techniques such as molecular beam epitaxy and sputter deposition. Therefore, the formation of supersaturated solid solutions within the immiscible binary system could be achieved by these techniques. In addition, varying the growth conditions allowed for tuning the film nanostructures in terms of grain size, modulation periodicity and interface structure in order to reach optimal mechanical properties.

Advanced transmission electron microscopy and X-ray diffraction techniques were used to characterize the nanostructure of the synthesized films, whereas atom probe tomography was utilized to analyze the local chemical composition of the films. In addition, nanoindentation experiments were performed to correlate the mechanical properties such as hardness and elastic modulus to the observed nanostructures.

Figure 1: Change of the lattice parameter of Cu (fcc phase regime) and Cr (bcc phase regime) as a function of film composition. The inset shows the relative change of the lattice parameter as a function of film composition. The change in lattice parameter is caused by the formation of supersaturated solid solutions.

Figure 2: Plan-view dark-field TEM micrograph of a single phase bcc Cu-Cr alloy film with an average grain size of roughly 30 nm.
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