Super Atomic Clusters: Design Rules and Potential for Building Blocks of Materials.

Atomic clusters, consisting of a few to a few thousand atoms, have emerged over the past 40 years as the ultimate nanoparticles, whose structure and properties can be controlled one atom at a time. One of the early motivations in studying clusters was to understand how the properties of matter evolve as a function of size, shape, and composition. Over the past few decades, more than 200 000 papers have been published in this field. These studies have not only led to a considerable understanding of this evolution from clusters to crystals, but also have revealed many unusual size-specific properties that make cluster science an interdisciplinary field on its own, bridging physics, chemistry, materials science, biology, and medicine. More importantly, the possibility of creating a new class of materials, composed of clusters instead of atoms as building blocks, has fueled the hope that one can synthesize materials from the bottom-up with unique and tailored properties. This Review focuses on the properties that set clusters apart from their corresponding bulk. Furthermore, this Review describes how different electron-counting rules can lead to the design of stable clusters, mimicking the chemistry of atoms. We highlight the potential of these "superatoms" as building blocks of cluster-assembled materials. Specifically, we emphasize cluster-inspired materials for energy applications. The concluding section includes a summary of the salient features of clusters, potential challenges that remain, and an outlook for the future of cluster science.