"Metal nanoclusters," which contain anywhere from a few to several hundred metal atoms, exhibit unique physical and chemical properties with atomic arrangements different from those of bulk metals. While research is being widely conducted to create new functional materials using metal nanoclusters, methods for the precise control and integration of factors such as the number of atoms, distances, and symmetry of atomic placement within clusters have not yet been established.
A research team led by Professor Tatsuya Tsukuda of the Graduate School of Science at the University of Tokyo synthesized gold nanoclusters of various sizes by slowly reducing gold ions rather than using the conventional method of rapid reduction and investigated their geometric structures through single-crystal X-ray structural analysis. As a result, they discovered that gold nanoclusters synthesized by this method have electrons accommodated in orbitals with discrete energy values and possess anisotropic integration structures based on tetrahedral Au4 and triangular Au3 as fundamental units. Among these, they found two types of needle-shaped structures of just three gold atoms wide, which they named "gold quantum needles." Furthermore, experiments revealed that these gold quantum needles exhibit unique optical properties, with strong absorption peaks near 755 and 770 nanometers, and emission in the near-infrared region of 800 to 1100 nanometers.
Gold quantum needles are expected to find applications in hyperthermia therapy, bioimaging, and light energy conversion by leveraging their strong absorption and emission properties in the near-infrared region. Additionally, this new synthesis method is expected to contribute to the advancement of nanomaterial science.
(Article: Masanori Nakajo)
