Ultraviolet-Visible Chiroptical Activity of Aluminum Nanostructures

Ultraviolet (UV)-resonant metals (e.g., aluminum) typically have low melting point to cause a fabrication difficulty in helical sculpture to generate plasmons with chiroptical activity in the UV region. In this work, using glancing angle deposition (GLAD), two new methods are devised to generate crystalline chiral Al nanostructures that have stable chiroptical response in the UV-visible region originating from intrinsic helical structures. One approach involves fast substrate rotation during GLAD to fabricate Al nanoparticles (AlNPs) with hidden helicity; another is to deposit an achiral Al thin film on a host of plasmonic chiral NPs, such that the helical structures are duplicated from the chiral host to the achiral guest of Al nanocappings. The host@guest helicity duplication is a new GLAD methodology to generate chiroptically active plasmons, which can be generally adapted to diverse plasmonic metals for tailoring plasmonic chiroptical activity flexibly in the UV-visible region. More importantly, this work offers those two new methods to generate UV-active plasmonic chiral substrates, which can markedly enhance chiroptical activity of biomolecules. It would open a door to develop surface-enhanced chiroptical spectroscopies for sensitively monitoring stereobiochemical information, which is of prominent interest in understanding a wide range of homochirality-determined biological phenomena.