The optimization of the localized surface plasmon resonance (LSPR)-decaying channels of hotelectrons is essential for efficient optical and photochemical processes. Understanding and having the ability to control chemical interface damping (CID) channel contributions will bring about new possibilities for tuning the efficiency of plasmonic hot-electron energy transfer in artificial devices. In this scanning electron microscopy-correlated dark-field scattering study, the CID was controlled by focusing on the electronic nature of disubstituted benzene rings acting as adsorbates, as well as the effects of sharp tips on gold bipyramids (AuBPs) with similar aspect ratios to those of gold nanorods. The results showed that the sharp tips on single AuBPs, as well as the electronic effects of the adsorbate molecules, increase the interfacial contact between the nanoparticles and adsorbate molecules. Electron withdrawing groups (EWGs) on the adsorbates induce larger homogeneous LSPR line widths compared to those of electron donating groups (EDGs). Depending on the location (ortho, meta, and para) of the EDG, the effect of benzene rings with an EDG, which was considered to be induced by sulfur atoms bound to the nanoparticle surface, is weakened by the back transfer of electrons facilitated by the difference in the availability of the electrons of the EDG. Therefore, this study reports that the CID in the LSPR total decay channels can be tuned by controlling the electron withdrawing and electron donating features of adsorbate molecules with the surface topology of metal.

Plasmonic gold nanoparticles with sharp tips and vertices, such as gold bipyramids (AuBPs) and gold nanocubes (AuNCs), have been widely used for high-sensitivity localized surface plasmon resonance (LSPR) sensing. However, conventional LSPR sensors based on frequency shifts have a major disadvantage: the asymmetry and broadening of LSPR peaks because of instrumental, environmental, and chemical noises that limit the precise determination of shift positions. Herein, we demonstrated an alternative method to improve the efficiency of the sensors by focusing on homogeneous LSPR scattering inflection points (IFs) of single gold nanoparticles with a single resonant mode. In addition, we investigated the effect of the shape and vertices of AuNCs on the refractive index (RI) sensitivity of homogeneous LSPR IFs by comparing with gold nanospheres (AuNSs) of similar size. The results show that for both AuNCs and AuNSs, tracking homogeneous LSPR IFs allows for higher RI sensitivity than tracking the frequency shifts of the LSPR peaks. Furthermore, single AuNCs with vertices exhibited higher RI sensitivity than single AuNSs of similar size in the homogeneous LSPR IFs. Therefore, we provided a deeper insight into the RI sensitivity of homogeneous LSPR IFs of AuNCs with vertices for their use in LSPR-based biosensors.

Plasmon damping in gold nanorods (AuNRs) results in the broadening of the localized surface plasmon resonance (LSPR) linewidth. LSPR broadening of plasmonic nanoparticles is useful to maximize the fraction of light energy in light harvesting and energy conversion transferred to molecules attached on the surface. However, our understanding of plasmon decay channels in AuNRs is still limited, and chemical interface damping (CID) is the most poorly understood damping mechanism. Herein, to better understand plasmon damping including CID, we performed a single particle study of plasmonic anisotropic AuNRs using dark-field (DF) microscopy and spectroscopy. First, we examined the size-dependent broadening of the homogeneous LSPR linewidth of single AuNRs in water with three different aspect ratios (ARs) at a fixed diameter of 25 nm. The LSPR linewidth increased with a decrease in the AR of single AuNRs because of the reduced average distance of hot electrons to the surface. Second, we investigated the effect of refractive index variation of the surrounding medium on the LSPR linewidth in single AuNRs of three different sizes. The LSPR linewidth in single AuNRs remained almost constant regardless of their sizes while increasing the dielectric constant of the medium. Finally, we examined the effect of adsorbate thiol molecules on the homogeneous LSPR linewidth of single AuNRs in ethanol. The LSPR linewidth was broadened upon increasing the carbon chain length of 1-alkanethiol, and 4-nitrothiophenol with a strong electron withdrawing group induced a large broadening of the LSPR linewidth. Furthermore, single AuNRs with smaller ARs showed a larger broadening of the LSPR linewidth in the presence of adsorbate thiol molecules through CID. Therefore, this investigation provides a deeper insight into the size effect on plasmon damping including CID induced by the chemical interface effect in single AuNRs.

Chemical interface damping in plasmonic gold nanoparticles is closely connected with chemical enhancement in resonance SERS.