A group of researchers led by Prof. YANG Liangbao from Hefei Institutes of Physical Science, Chinese Academy of Sciences successfully improved the accuracy of a technique called surface-enhanced Raman spectroscopy (SERS) in measuring the strength of plasmonic fields. This achievement can help expand the use of plasmonic enhancement in various applications.
The study was published in The Journal of Physical Chemistry Letters.
The team has been engaged in the research of surface-enhanced Raman spectroscopy (SERS). However, during the continuous innovation and development of the SERS detection technique, they have found that the longitudinal near-field intensity distribution at the nanoscale is uneven. Moreover, the team has discovered that there is an unclear quantitative relationship between the SERS intensity and the near-field intensity, which means that the SERS intensity does not accurately reflect the true near-field distribution.
Therefore, in this research, they used self-assembled monolayers of 4-mercaptobenzonitrile (MBN) as a gap spacer in a nanoparticle-on-mirror (NPoM) structure to effectively create ultrahigh field enhancement and observe Stark shifts of chemical bonds. By measuring transverse position-dependent Stark shifts of ν(C═C) and ν(C≡N) in individual nanocavities using surface-enhanced Raman scattering (SERS) experiments and density functional theory (DFT) simulations, they accurately revealed the inhomogeneous plasmonic field transverse distribution and quantified the transverse plasmonic field strength up to ～1.9 × 109 V/m. These results match those predicted by finite element method (FEM) simulation.
By quantifying the true near-field enhancement distribution, this work will assist other measurement methods in revealing the near-field distribution at higher resolution.
Scientists quantify the inhomogeneous distribution of the true transverse near-field within a single-particle nanocavity using the vibrational Stark effect. (Image by CHEN Siyu)