Size-dependent properties of nanomaterials continue to intrigue scientist and engineers. In contrast to the optical and electronic properties, size-dependent mechanical properties remain less well understood. We discovered that defect-free colloidal semiconductor nanocrystals exhibit an unexpected compressibility with bimodal size-dependence. We analyzed this phenomenon using high-resolution synchrotron-based wide-angle X-ray scattering of colloidal NCs in a diamond-anvil pressure cell. To explain the observed trends, we introduce a core-shell model with distinct elasticity of the crystal near the surface and the core. Beyond new insights into the size-dependent mechanical properties of colloidal NCs reveal, for the first time, that the Debye temperature of PbS NCs exhibits a 
bimodal size dependence.
The work brings new insight into the structural and mechanical properties of colloidal PbS nanocrystals.
Check out the paper for more details: doi/abs/10.1021/jz501797y