BSTRACT‘Smaller is stronger’ has been a well-established tenet for the mechanical strength of small-volume single crystals. However

emerging evidence suggests that this trend does not always hold in the deep sub-micrometre regime (∼10

2

 nm) when surface-mediated displacive and diffusive processes dominate. Here we present a perspective to highlight typical scenarios in which the single-crystal strength is influenced by surface stresses

diffusion-mediated surface creep

or dislocation-starvation-engendered high-stresses in the crystal interior

leading to ‘smaller is weaker’ or ‘plateau limited by ideal strength’. Such an unusual size dependence/independence of strength has implications for the reliability and stability of nano-structured devices.