Controlling the Chemistry of Nanoclusters: From Atomic Precision to Controlled Assembly

Metal nanoclusters have gained prominence in nanomaterials sciences, owing to their atomic precision, structural regularity, and unique chemical composition. Additionally, the ligands stabilizing the clusters provide great opportunities for linking the clusters in higher order dimensions, eventually leading to the formation of a repertoire of nanoarchitectures. This makes the chemistry of atomic clusters worth exploring. In this mini review, we aim to focus on the chemistry of nanoclusters. Firstly, we summarize the important strategies developed so far for the synthesis of atomic clusters. For each synthetic strategy, we highlight the chemistry governing the formation of nanoclusters. Next, we discuss the key techniques in the purification and separation of nanoclusters, as the chemical purity of clusters is deemed important for their further chemical processing. Thereafter which we provide an account of the chemical reactions of nanoclusters. Then, we summarize the chemical routes to the spatial organization of atomic clusters, highlighting the importance of assembly formation from an application point of view. Finally, we raise some fundamentally important questions with regard to the chemistry of atomic clusters, which, if addressed, may broaden the scope of research pertaining to atomic clusters.

Orbital-Dependent Photodynamics of Strongly Correlated Clusters

Understanding the role of defect sites on the mechanism and lifetime of photoexcited state relaxation is critical for the ration-al design of advanced materials. Here, the ultrafast electronic relaxation dynamics of neutral nickel oxide clusters were inves-tigated with femtosecond pump-probe spectroscopy and supported with theoretical calculations to reveal that their excited state lifetimes are strongly dependent on the nature of the electronic transition. Absorption of a UV photon produces short lived (lifetime ~110 fs) dynamics in stoichiometric (NiO)n clusters (n < 6) that are attributed to a ligand to metal charge transfer (LMCT) and produces metallic-like electron-electron scattering. Oxygen vacancies introduce excitations with Ni-3d→Ni-4s and 3d→4p character, which increases the lifetimes of the sub-picosecond response by up to 80% and enables the formation of long-lived (lifetimes > 2.5 ps) states. The atomic precision and tunability of gas phase clusters are employed to highlight a unique reliance on the Ni orbital contributions to the photoexcited lifetimes, providing new insights to the anal-ogous band edge excitation dynamics of strongly correlated bulk-scale NiO materials.

Visualizing designer quantum states in stable macrocycle quantum corrals

Creating atomically precise quantum architectures with high digital fidelity and desired quantum states is an important goal in a new era of quantum technology. The strategy of creating these quantum nanostructures mainly relies on atom-by-atom, molecule-by-molecule manipulation or molecular assembly through non-covalent interactions, which thus lack sufficient chemical robustness required for on-chip quantum device operation at elevated temperature. Here, we report a bottom-up synthesis of covalently linked organic quantum corrals (OQCs) with atomic precision to induce the formation of topology-controlled quantum resonance states, arising from a collective interference of scattered electron waves inside the quantum nanocavities. Individual OQCs host a series of atomic orbital-like resonance states whose orbital hybridization into artificial homo-diatomic and hetero-diatomic molecular-like resonance states can be constructed in Cassini oval-shaped OQCs with desired topologies corroborated by joint ab initio and analytic calculations. Our studies open up a new avenue to fabricate covalently linked large-sized OQCs with atomic precision to engineer desired quantum states with high chemical robustness and digital fidelity for future practical applications.