Nanoclusters

Nanoclusters are discrete aggregates of atoms with a size between molecular species and bulk materials, typically containing a few to several hundred atoms. They have dimensions on the nanometer scale but often exhibit properties that are not simply reductions of bulk matter because of quantum confinement and finite size effects.

They can be metallic (such as gold or silver), semiconducting, or bimetallic and may be stabilized by ligands or protective shells. The structure of nanoclusters is size- and composition-dependent, with common motifs including icosahedral and cuboctahedral arrangements; some clusters have pronounced ligand shells that influence reactivity and optical properties.

Synthesis methods include gas-phase approaches like laser ablation and chemical reduction in solution, sometimes with templates or stabilizers, as well as electrochemical routes. Characterization relies on mass spectrometry for precise composition, electron microscopy for size, and optical spectroscopy to probe electronic structure.

Properties often show sharp, molecule-like electronic transitions and size-dependent photoluminescence, particularly for small metal and semiconductor clusters, in contrast to the plasmonic behavior of larger nanoparticles. Applications span catalysis, sensing, bioimaging, and photovoltaics, with ligand design and protection guiding stability and selectivity.

Challenges include achieving narrow size distributions, preventing aggregation, and understanding how properties evolve with size and environment. Ongoing research combines synthetic control, advanced characterization, and theory to tailor nanoclusters for specific functions.