Ductile van der Waals materials

Normally brittle, single crystals of InSe can be mechanically rolled like a metal into thin films Van der Waals (vdW) materials are made up of strongly bonded two-dimensional (2D) layers that are bound in the third dimension through weaker dispersion forces. Graphite is a vdW material broadly used in industry in electrodes, lubricants, fibers, heat exchangers, and batteries. Its single-layer form, graphene ( 1 ), ushered in the new era of 2D materials that have tunable thickness and bandgap, as well as electronic confinement effects ( 2 ). Although these thin materials are inherently flexible ( 3 ), most vdW materials other than silver sulfide (Ag 2 S) ( 4 ) are intrinsically brittle in their bulk form, which can limit how they are processed, as well as their applications. On page 542 of this issue, Wei et al. ( 5 ) report that indium selenide (InSe), in its single-crystalline form, exhibits exceptional plasticity under compressive stress.