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Description
Scanning tunnelling microscopy-induced luminescence (STML) enables optical spectroscopy with atomic-scale spatial resolution by probing plasmonic excitations within the tip–sample nanocavity [1]. Here, we investigate the optical response of atomically thin Bi layers grown on Ag(111), materials with intriguing electronic and optical properties for nanoscale optoelectronics, plasmonics and photo-catalysis [2].
Upon deposition on Ag(111), Bi forms two coexisting surface phases: the BiAg₂ surface alloy and α-bismuthene Bi(110), identified by scanning tunnelling microscopy (STM). The BiAg₂ surface alloy and α-bismuthene Bi(110), both exhibiting well-defined unoccupied states, as measured by scanning tunnelling spectroscopy (STS). STML spectra reveal that both Bi phases suppress plasmonic emission for tunnelling electrons whose energies coincide with the intense unoccupied Bi states. In contrast, electrons with enough energy to excite plasmonic modes that decay resonantly into the Bi states produces a pronounced enhancement of the optical emission. STML mapping further demonstrates that these modifications of the plasmonic response are spatially confined to the Bi regions with sub-nanometre resolution.
These results show how atomically thin Bi layers can be used to enhance and confine electron-to-light conversion processes with sub-nm precision. Achieving efficient electron-to-light conversion is a central requirement feature for modern optoelectronics and nanophotonic devices [3]. In addition, they highlight STML as a powerful probe the interplay between local electronic structure and optical excitations in low-dimensional materials [3].
The experiments were conducted in the UHV-Photon-STM of the SPM Platform, at ALBA Synchrotron [4].
[1] Martín-Jiménez, A. et al., Unveiling the radiative local density of optical states of a plasmonic nanocavity by STM. Nature Communications 11, 1021 (2020).
[2] García Diez, K. Structural and Electronic Properties of Bismuth Monolayers Grown on Metallic Substrates Studied by STM and ARPES. PhD thesis, Universitat Autònoma de Barcelona - ICN2, (2026).
[3] de Abajo, F. J. G. et al. Roadmap for Photonics with 2D Materials. ACS Photonics (2025).
[4] https://www.cells.es/en/instruments/microscopy-platform/incaem-facility/scanning-probe-microscopy-spm-platform/sm04-uhv-photon-spm