Poly(Ethylene Oxide) Mediated Synthesis of Sub-100-nm Aluminum Nanocrystals for Deep Ultraviolet Plasmonic Nanomaterials

Aluminum nanocrystals (Al NCs) are sustainable plasmonic nanomaterials with unique localized surface plasmonic resonance (LSPR) in the ultraviolet (UV) region. Chemical synthesis of sub-100-nm Al NCs remains a considerable challenge due to the lack of effective ligands to control their growth. Here, we describe a precise size-controlled synthesis of small colloidal Al NCs (25-100 nm) with strong and tunable LSPR peak from 250 to 372 nmin the UV spectral region by the use of poly(ethylene oxide) (PEO) as a polydentate surface ligand. The LSPR band matched well with the numerical simulation results. Additionally, the molecular weight of the PEO played an essential role in tuning the size of Al NCs. The PEO showed a strong affinity with Al {111} crystal facets, resulting in octahedral- and prism- shaped Al NCs. Owing to the passive oxide layer generated on the surface of Al NCs, their LSPR peak positions showed negligible changes after storage in tetrahydrofuran for 4 months. The passivation layer also impeded the metal Al core to react with deionized water. Further, the use of biocompatible PEO ligand and the subsequent generation of the sub-100-nm size of the Al NCs pave a path for bioapplications of such NCs.