Oxide glass exhibits plasticity without fracture at room temperature

  • PDF / 1,273,189 Bytes
  • 2 Pages / 585 x 783 pts Page_size
  • 59 Downloads / 257 Views

DOWNLOAD

REPORT


b After Test

Oxide glass exhibits plasticity without fracture at room temperature

O

xide glasses are well known for their brittle nature, but new experimental research out of an international research consortium has revealed surprisingly high ductility in thin films of amorphous aluminum oxide (a-Al2O3), or alumina, at room temperature. As reported in Science (doi:10.1126/science.aav1254), the plasticity is activated when an a-Al2O3 sample free of flaws is subjected to a high stress at varying strain rates. Inorganic oxide glasses are appealing materials for electronic applications because they can be tailored for many different functional properties. They are chemically and thermally stable and transparent to visible light. However, at room temperature the glasses are prone to sudden, catastrophic failure. This has limited their usefulness. According to conventional theory, inorganic oxide glasses become ductile only when a high temperature activates a relaxation mechanism such as viscous flow or creep. Viscous flow occurs only above a critical temperature; viscous creep typically requires an external load and a critical temperature. Both viscous flow and viscous creep require a critical temperature well above room temperature so the material is effectively a solid at 300 K. As a graduate student at Tampere University in Finland, project leader Erkka Frankberg was studying the boundaries of plastic deformation in ceramics and glasses when preliminary results hinted that it might be possible to create ductile alumina at room temperature. Working with Erkki Levänen at Tampere University, Karine Masenelli-Varlot at the Université de Lyon in France, and Fabio Di Fonzo at the Istituto Italiano de Tecnologia, Frankberg initiated a collaborative effort to experimentally measure the viscosity of flawless a-Al2O3 thin films at room temperature. “We didn’t have exact knowledge that this would be possible, but there was a chance, so we took it,” he explains. The researchers prepared thin films of defect-free a-Al2O3 by pulsed laser

78

2075 nm

2220 nm

Transmission electron microscope (TEM) images of a freestanding sample under zero strain (a) and after increasing strain until the point of fracture (b). The change in length is due to tensile stress. The sample is highlighted with a white border; a film can be seen partially overlapping the sample on the bottom right but does not impact the test. Scale bars are 500 nm. Reprinted with permission from Frankberg et al., Science 366 (6467), 864 (2019).

deposition, with thicknesses of 40 nm and 60 nm. The samples were probed by a custom micromechanical testing device located inside a transmission electron microscope (TEM) at room temperature. The testing device could apply up to 1 mN of force and had two modes, applying either shear-compressive stress or tensile stress to samples. For each mechanical test, the applied force and sample displacement were measured in situ over time and verified by TEM images. While observing a test through the TEM, Frankberg realized the team cou

Data Loading...