Self-Organization of Plasmonic and Excitonic Nanoparticles into Resonant Chiral Supraparticle Assemblies

• Published in: Nano letters 2014-12, Vol.14 (12), p.6799-6810
• Main Authors: Hu, Tao, Isaacoff, Benjamin P, Bahng, Joong Hwan, Hao, Changlong, Zhou, Yunlong, Zhu, Jian, Li, Xinyu, Wang, Zhenlong, Liu, Shaoqin, Xu, Chuanlai, Biteen, Julie S, Kotov, Nicholas A
• Format: Article
• Language: English
• Subjects: Assemblies; Cadmium tellurides; Collective excitations (including excitons, polarons, plasmons and other charge-density excitations); Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Dimers; Electron states; Electronic structure and electrical properties of surfaces, interfaces, thin films and low-dimensional structures; Exact sciences and technology; Excitation; Excitons and related phenomena; Joining; Low-dimensional structures (superlattices, quantum well structures, multilayers): structure, and nonelectronic properties; Materials science; Nanocrystalline materials; Nanoscale materials and structures: fabrication and characterization; Nanostructure; Physics; Plasmons; Semiconductors; Surface and interface electron states; Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties)
• ISSN: 1530-6984; 1530-6992
• DOI: 10.1021/nl502237f

Chiral nanostructures exhibit strong coupling to the spin angular momentum of incident photons. The integration of metal nanostructures with semiconductor nanoparticles (NPs) to form hybrid plasmon–exciton nanoscale assemblies can potentially lead to plasmon-induced optical activity and unusual chiroptical properties of plasmon–exciton states. Here we investigate such effects in supraparticles (SPs) spontaneously formed from gold nanorods (NRs) and chiral CdTe NPs. The geometry of this new type of self-limited nanoscale superstructures depends on the molar ratio between NRs and NPs. NR dimers surrounded by CdTe NPs were obtained for the ratio NR/NP = 1:15, whereas increasing the NP content to a ratio of NR/NP = 1:180 leads to single NRs in a shell of NPs. The SPs based on NR dimers exhibit strong optical rotatory activity associated in large part with their twisted scissor-like geometry. The preference for a specific nanoscale enantiomer is attributed to the chiral interactions between CdTe NP in the shell. The SPs based on single NRs also yield surprising chiroptical activity at the frequency of the longitudinal mode of NRs. Numerical simulations reveal that the origin of this chiroptical band is the cross talk between the longitudinal and the transverse plasmon modes, which makes both of them coupled with the NP excitonic state. The chiral SP NR–NP assemblies combine the optical properties of excitons and plasmons that are essential for chiral sensing, chiroptical memory, and chiral catalysis.