Nanostructured Zr-Cu metallic glass thin films with tailored electrical and optical properties

Nanostructured metallic glass thin films (NMGTF) have attracted increasing attention because they are amorphous materials of tunable microstructure, which allows tailoring their properties. Herein, we provide new insights into the formation of Zr-Cu NMGTF deposited by magnetron sputtering. By varying over a wide range the working-gas pressure during the sputtering process (from 0.3 to 2 Pa) and the alloy composition (from similar to 16-94 at % Cu), we show that the film microstructure can be tuned from homogeneous and compact to nanostructured, formed by nanocolumns. In particular, we demonstrate that the formation of nanocolumnar glassy films is promoted at high working pressures and low Cu contents. In addition, transmission electron microscopy and Xray diffraction analyses reveal that the microstructural transition from homogeneous to nanocolumnar films leads to an increase in the full-width at half-maximum of the first diffraction peak, suggesting a change in the local order of the glassy alloys. Furthermore, we prove that the microstructural change allows the electrical resistivity and the optical reflectance of the films to be tailored to a large extent. We show that the amorphous films exhibit a linear relationship between their reflectance and the square root of the resistivity, according to the free electron model. However, this linear relationship breaks down for high resistivity values, for which the reflectance no longer depends on the resistivity. We highlight that, by changing the working pressure, the electrical resistivity and optical reflectance can be tuned following the same scaling law, whatever the composition of the alloy. Our results shed light on the microstructure-properties relationship of NMGTF and could serve as a platform for future applications in the field of optoelectronics.