Anomalously large spectral shifts near the quantum tunnelling limit in plasmonic rulers with subatomic resolution

Research output: Contribution to journalArticlepeer-review


  • Charlie Readman
  • Bart De Nijs
  • Istvan Szabo
  • Ryan Greenhalgh
  • Colm Durkan
  • Edina Rosta
  • Oren A. Scherman
  • Jeremy J. Baumberg

Colleges, School and Institutes

External organisations

  • University of Cambridge
  • King's College London
  • Cavendish Laboratory, Department of Physics
  • Nanophotonics Centre
  • Cavendish Laboratory


The resonance wavelength of a coupled plasmonic system is extremely sensitive to the distance between its metallic surfaces, resulting in “plasmon rulers”. We explore this behavior in the subnanometer regime using self-assembled monolayers of bisphthalocyanine molecules in a nanoparticle-on-mirror (NPoM) construct. These allow unprecedented subangstrom control over spacer thickness via choice of metal center, in a gap-size regime at the quantum-mechanical limit of plasmonic enhancement. A dramatic shift in the coupled plasmon resonance is observed as the gap size is varied from 0.39 to 0.41 nm. Existing theoretical models are unable to account for the observed spectral tuning, which requires inclusion of the quantum-classical interface, emphasizing the need for new treatments of light at the subnanoscale


Original languageEnglish
Pages (from-to)2051-2058
Number of pages8
JournalNano Letters
Issue number3
Early online date6 Feb 2019
Publication statusPublished - 13 Mar 2019


  • DFT, Nanocavities, SERS, nanoassembly, phthalocyanines, quantum plasmonics