Seeing inside a Plasmonic Nanogap: Few-molecule Orientation and Preferential Adsorption
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 introduce 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 discover that the non-resonant (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.
Versions
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BibTeX
@misc{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},
howpublished = {arXiv},
year = {2026},
month = jul,
doi = {10.48550/arxiv.2607.08922},
eprint = {2607.08922},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2607.08922},
note = {CC BY-NC-ND 4.0},
}
RIS
TY - UNPB
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 - 2026/07/09
PB - arXiv
DO - 10.48550/arxiv.2607.08922
UR - https://arxiv.org/abs/2607.08922
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 introduce 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 discover that the non-resonant (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.
ER -