Reinforcing nanocolloidal crystals by tuning interparticle bonding via atomic layer deposition

Nanocolloidal crystals have emerging applications in photonics and optoelectronics, but their poor mechanical robustness is a major hindrance to their widespread application. In this study, we observed that atomic layer deposition could be used to tune the mechanical properties of nanocolloidal crystals and that atomic-layer-deposition-treated nanocolloidal crystals could be drastically stiffened by a factor of 30 and hardened by a factor of 150. Nanocolloidal crystals composed of monodisperse 254 nm and 289 nm SiO2 nanocolloids were characterized using nanoindentation, yielding low hardness and modulus values. The nanocolloidal crystals exhibit granular behavior with intrinsically weak interparticle bonding. The use of atomic layer deposition enabled us to precisely tune the interparticle bonding by depositing a reinforcing layer around all of the nanocolloids. By increasing the atomic-layer-deposition thickness, the deformation mechanism of nanocolloidal crystals transitions from granular to bonded granular and, finally, to particle-reinforced composite behavior. We believe this work presents the first-ever systematic study of such transitions based on both experimental and theoretical approaches. The mechanism-based models agree well with the experimental results, further validating the proposed transition mechanism. Our work comprehensively explains the effect of atomic layer deposition on the relationship between the structural and mechanical properties of nanocolloidal crystals, providing insights into the mechanical reinforcement mechanism of other types of porous materials and nanocolloidal assemblies. (C) 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.