A glass that won't break: Oxide glasses are important for applications ranging from smartphone screens to window panes. One familiar feature of glass is that it fractures and shatters when rapidly deformed, limiting the number of potential uses. However, Frankberg et al. found that they could deform thin films of glassy alumina (Al ₂ O ₃ ) with high strain rates at room temperature (see the Perspective by Wondraczek). This surprising observation is supported by simulations of the material that show that dense and flawless glassy alumina samples can deform this way. The discovery provides important insight into designing new glasses that might be more fracture resistant. Science , this issue p. 864 ; see also p. 804

For decades, nanoindentation has been used for measuring mechanical properties of films with the widely used assumption that if the indentation depth does not exceed 10% of the film thickness, the substrate influence is negligible. The 10% rule was originally deduced for much thicker metallic films on steel substrates and involved only the hardness measurement. Thus, the boundaries of usability for measuring thin film elastic modulus may differ. Two known material systems of Mo and MoTa thin films on Si substrates are examined with nanoindentation and numerical modeling to show the limitations in measuring elastic moduli. An assessment of the hardness and elastic modulus as a function of contact depth and accurate modeling of the film/substrate deformation confirms the 10% rule for hardness measurements. For elastic modulus, the indentation depths should be much smaller. Results provide a recommended testing protocol for accurate assessment of thin film elastic modulus using nanoindentation. Graphical abstract

More and more flexible, bendable, and stretchable sensors and displays are becoming a reality. While complex engineering and fabrication methods exist to manufacture flexible thin film systems, materials engineering through advanced metallic thin film deposition methods can also be utilized to create robust and long-lasting flexible devices. In this review, materials engineering concepts as well as electro-mechanical testing aspects will be discussed for metallic films. Through the use of residual stress, film thickness, or microstructure tailoring, all controlled by the film deposition parameters, long-lasting flexible film systems in terms of increased fracture or deformation strains, electrical or mechanical reliability, can be generated. These topics, as well as concrete examples, will be discussed. One objective of this work is to provide a toolbox with sustainable and scalable methods to create robust metal thin films for flexible, bendable, and stretchable applications.