Atomically Precise Indium Arsenide Magic-Sized Cluster

In the domain of atomically precise nanoscale science, clusters serve as intermediate assemblies of atoms or molecules, stabilized with organic ligands. These formations, distinctly larger than a single atom yet considerably smaller than bulk materials, exhibit physicochemical properties divergent from established material systems. The elucidation of their structure is paramount because these clusters provide an ideal platform to clarify the intricate relationship between structure and physicochemical properties. Recently, magic-size clusters (MSCs) were discovered; these are atomically precise semiconductor clusters, and their structures have been unveiled. To clarify the relationship between the structure and physicochemical properties, the synthetic method, isolation, and characterization techniques must be refined. The Indium arsenide (InAs) quantum dot has emerged as a promising material for various infrared applications. During the synthesis of the InAs quantum dot, the presence of InAs MSC, as indicated by distinctive absorption peaks, was investigated. However, the isolation and characterization of InAs MSC have not been reported until now.<br/>Herein, we synthesized and isolated atomically precise InAs MSCs to scrutinize their structure. With the optimal synthetic temperature, the InAs MSC revealed two distinct optical transitions. To gain a theoretical understanding, we modeled the InAs MSC using density functional theory (DFT) calculations, identifying a structure with notable stability. This model displayed two optical transitions, from HOMO to LUMO, consistent with the optical transitions we observed. The X-ray diffraction spectrum also aligned with the simulation results. For a deeper atomic-level understanding, we employed X-ray absorption spectroscopy and characterized the cluster using X-ray absorption fine structure (XAFS) techniques. By comparing with an InAs quantum dot, which is larger than the InAs MSC, we noted increases in the In-As peaks and decreases in the In-O peaks, attributable to size-dependent surface-to-volume ratios. Furthermore, spectral intensity offered insights into coordination numbers. Our fitting analysis of the XAFS spectrum enabled precise estimations of coordination numbers for various bonds. Notably, the coordination number for the In-As bond in MSC agreed with our computational predictions. Collectively, these results not only validate our theoretical model but also deepen our understanding of the structural and optical properties of InAs MSCs.