Gradient nanostructured metallic materials with a gradual change of grain boundary and dislocation density display unprecedent mechanical properties. Herein

we uncover a gradient of point defects concentration and concomitant gradient bandgap (

E

g

) narrowing in metal oxide nanoparticles processed by a combination of severe shearing and frictional sliding deformation. Using the valence electron-energy loss spectroscopy technique

we find a gradual decrease of

E

g

from 2.93 eV in the interior to 2.43 eV at the edge of the high-pressure torsion processed ZnO flake-shaped particle. This work paves the way to strain engineering of gradient-structured metal oxide semiconductors for unique functional properties.

IMPACT STATEMENT

We uncover a gradient of oxygen vacancy concentration and concomitant bandgap narrowing in an individual metal oxide nanoparticle processed by a combination of severe shearing and frictional sliding deformation.