Probing the Local Near-Field Intensity of Plasmonic Nanoparticles in the Mid-infrared Spectral Region

Quanbing Pei; Xiaoxuan Zheng; Junjun Tan; Yi Luo; Shuji Ye

doi:10.1021/acs.jpclett.4c00964

Probing the Local Near-Field Intensity of Plasmonic Nanoparticles in the Mid-infrared Spectral Region

J Phys Chem Lett. 2024 May 23;15(20):5390-5396. doi: 10.1021/acs.jpclett.4c00964. Epub 2024 May 13.

Authors

Quanbing Pei¹, Xiaoxuan Zheng¹, Junjun Tan², Yi Luo^{1

2}, Shuji Ye^{1

2}

Affiliations

¹ Hefei National Research Center for Physical Sciences at the Microscale, Department of Chemical Physics, University of Science and Technology of China, Hefei, Anhui 230026, China.
² Hefei National Laboratory, University of Science and Technology of China, Hefei, Anhui 230088, China.

PMID: 38739421
DOI: 10.1021/acs.jpclett.4c00964

Abstract

The enhanced local field of gold nanoparticles (AuNPs) in mid-infrared spectral regions is essential for improving the detection sensitivity of vibrational spectroscopy and mediating photochemical reactions. However, it is still challenging to measure its intensity at subnanometer scales. Here, using the NO₂ symmetric stretching mode (ν_NO₂) of self-assembled 4-nitrothiophenol (4-NTP) monolayers on AuNPs as a model, we demonstrated that the percentage of excited ν_NO₂ mode, determined by femtosecond time-resolved sum-frequency generation vibrational spectroscopy, allows us to directly detect the local field intensity of the AuNP surface in subnanometer ranges. The local-field intensity is tuned by AuNP diameters. An approximate 17-fold enhancement was observed for the local field on 80 nm AuNPs compared to the Au film. Additionally, the local field can regulate the anharmonicity of the ν_NO₂ mode by synergistic effect with molecular orientation. This work offers a promising approach to probe the local field intensity distribution around plasmonic NP surfaces at subnanometer scales.