Probing the Mechanical Response of Luminescent Dithiol-Protected Ag<inf>29</inf>(BDT)<inf>12</inf>(TPP)<inf>4</inf> Cluster Crystals

Atomically precise clusters of noble metals are considered to be an important class of advanced materials. Crystals of these clusters composed of inorganic cores and organic ligands are fascinating owing to their tunable and unique properties. Understanding their mechanical properties can give more insight into the design of nanocluster-based devices. Here, we probe the mechanical response of single crystals of Ag29(BDT)12(TPP)4 cluster (BDT=1,3 benzenedithiol, TPP=triphenylphosphine) under both quasi-static and dynamic loading conditions. Surprisingly, the measured reduced Young's modulus (Er) and hardness (H) were 4.48 and 0.285 GPa, respectively, similar to those of polymers and much smaller than the values for bulk silver. These observations indicate a significant role of capping ligands on the physical properties of such materials. The observed storage modulus, loss modulus and loss factor were also found to be similar to those of polymers. The magnitude of loss factor suggested the ability of nanocrystals to absorb energy under dynamic loading. These studies of mechanical properties of cluster materials could be useful in developing their applications.