Researchers from the University of Illinois at Urbana-Champaign have demonstrated a new approach to modifying the light absorption and stretchability of 2D materials by surface topographic engineering using only mechanical strain. The highly flexible system has future potential for wearable technology and integrated biomedical optical sensing technology when combined with flexible light-emitting diodes.

The researchers state that this is the very first stretchable photodetector based exclusively on graphene with strain-tunable photoresponsivity and wavelength selectivity; Increasing graphene's low light absorption in visible range is an important prerequisite for its broad potential applications in photonics and sensing. The key element enabling increased absorption and stretchability requires engineering the 2D material into 3D "crumpled structures," increasing the graphene's areal density. The continuously undulating 3D surface induces an areal density increase to yield higher optical absorption per unit area, thereby improving photoresponsivity. Crumple density, height, and pitch are modulated by applied strain and the crumpling is fully reversible during cyclical stretching and release, introducing a new capability of strain-tunable photoabsorption enhancement and allowing for a highly responsive photodetector based on a single graphene layer.