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Peer-reviewedCC BY 4.0ACS Nano

Seeing Inside a Plasmonic Nanogap: Few-Molecule Orientation and Preferential Adsorption

  • Francesco Ciccarello1
  • Nobuaki Oyamada1
  • Thwahira Shirin Alampara1
  • Konstantin Malchow1
  • Christophe Galland1,2
  1. 1Institute of Physics, Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
  2. 2Center for Quantum Science and Engineering, Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
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Abstract

Molecule–surface interactions are central to many research and technological areas, spanning from heterogeneous catalysis and polymer science to electrochemistry. Of particular relevance are metallic nanogaps used in molecular electronics and near-field spectroscopy. Due to the buried nature of these double interfaces, few methods exist to monitor side-specific interactions and relative molecular orientation inside the gap. In this work, we employ plasmon-enhanced nonlinear vibrational spectroscopy as an efficient tool to investigate surface molecular adsorption within metallic nanojunctions. By exploiting simultaneous vibrational sum- and difference-frequency generation in dual-resonant nanocavities, we resolve molecular orientation and preferential binding to one of the two gold surfaces, with few-molecule sensitivity. We also notice that the nonresonant (electronic) second-order nonlinear response is not an intrinsic property of the metal surface, but is instead governed by the molecule–surface interaction. Our findings provide a powerful analytical tool, easily implementable as an add-on to Raman spectroscopy, thanks to commercially available mid-infrared quantum cascade lasers.

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Cite

BibTeXRIS
BibTeX
@article{ciccarello2026seeing,
  title = {{Seeing Inside a Plasmonic Nanogap: Few-Molecule Orientation and Preferential Adsorption}},
  author = {Francesco Ciccarello and Nobuaki Oyamada and Thwahira Shirin Alampara and Konstantin Malchow and Christophe Galland},
  journal = {ACS Nano},
  year = {2026},
  month = oct,
  doi = {10.1021/acsnano.6c12575},
  url = {https://doi.org/10.1021/acsnano.6c12575},
  note = {CC BY 4.0},
}
RIS
TY  - JOUR
TI  - Seeing Inside a Plasmonic Nanogap: Few-Molecule Orientation and Preferential Adsorption
AU  - Francesco Ciccarello
AU  - Nobuaki Oyamada
AU  - Thwahira Shirin Alampara
AU  - Konstantin Malchow
AU  - Christophe Galland
PY  - 2026
DA  - 2026/10/15
JO  - ACS Nano
DO  - 10.1021/acsnano.6c12575
UR  - https://doi.org/10.1021/acsnano.6c12575
AB  - Molecule–surface interactions are central to many research and technological areas, spanning from heterogeneous catalysis and polymer science to electrochemistry. Of particular relevance are metallic nanogaps used in molecular electronics and near-field spectroscopy. Due to the buried nature of these double interfaces, few methods exist to monitor side-specific interactions and relative molecular orientation inside the gap. In this work, we employ plasmon-enhanced nonlinear vibrational spectroscopy as an efficient tool to investigate surface molecular adsorption within metallic nanojunctions. By exploiting simultaneous vibrational sum- and difference-frequency generation in dual-resonant nanocavities, we resolve molecular orientation and preferential binding to one of the two gold surfaces, with few-molecule sensitivity. We also notice that the nonresonant (electronic) second-order nonlinear response is not an intrinsic property of the metal surface, but is instead governed by the molecule–surface interaction. Our findings provide a powerful analytical tool, easily implementable as an add-on to Raman spectroscopy, thanks to commercially available mid-infrared quantum cascade lasers.
SN  - 1936-0851
SN  - 1936-086X
ER  -