arXiv subjects

Tamitake Itoh

Publications and source records attributed to Tamitake Itoh.

17 recordsLinked to original sources

arXiv2026

Electromagnetic coupling between subradiant plasmons and dye molecular excitons analyzed by spectral changes in ultrafast surface-enhanced fluorescence

Electromagnetic (EM) coupling between molecular exciton and plasmon has been studied using in Rayleigh scattering or extinction spectroscopy. However, evaluating EM coupling involving subradiant plasmon is challenging because this resonance does not manifest clearly in far-field spectra. In this study, we developed a method to evaluate such coupling using EM enhancement factors (FR) derived from ultrafast surface-enhanced fluorescence (ultrafast SEF). This SEF, which appears as a broad background in surface-enhanced resonant Raman scattering (SERRS) spectra, were measured using silver nanoparticle dimers containing dye molecules within their nanogaps. Our results show that the spectral peaks of FR for subradiant resonances appear near the dips in Rayleigh scattering spectra. Furthermore, these FR peaks exhibit blue-shifts during the quenching processes of both ultrafast SEF and SERRS. We examined these static and temporal spectral properties using a coupled oscillator model composed of radiant plasmons, subradiant plasmons, and molecular excitons. The static properties were reproduced by increasing the linewidths of the radiant plasmon resonance, while the temporal properties were captured by decreasing the EM coupling energies between the exciton and both plasmon oscillators. These findings indicate that this methodology is a powerful tool for evaluating EM coupling between subradiant plasmons and molecular excitons.

physics.optics↗

arXiv2025

Ultrabroad resonance of localized plasmon on a nanoparticle coupled with surface plasmon on a nanowire enabling two-photon excited emission via continuous-wave laser

This study found that plasmonic hotspots (HSs) between silver nanoparticles (NPs) and silver nanowires (NWs) generated two-photon excited emissions, including hyper-Rayleigh, hyper-Raman, and two-photon fluorescence of dye molecules with continuous-wave (CW) near-infrared (NIR) laser excitation. A comparison between experimental results and electromagnetic (EM) calculations revealed that a large EM enhancement factor (FR) at the HS appears in the visible to NIR regions owing to EM coupling between localized plasmons of the NP and surface plasmons of the NW. This ultrabroad resonance of the coupled plasmons enables the observation of two-photon-excited emissions with CW laser excitation. A comparison of the dependence of the NP diameter, NW diameter, and gap distance on two-photon-excited emissions further demonstrated that the large HS-by-HS variations in the emission intensities were mainly induced by the sensitivity of FR to the gap distance at the HSs. We also experimentally and theoretically investigated the propagation of two-photon-excited emission light to a neighboring NP on the NW via surface plasmons.

physics.optics↗

arXiv2025

Surface-enhanced Raman scattering and density functional theory study of selected-lanthanide-citrate complexes (lanthanide: La, Ce, Pr, Nd, Sm, Eu, and Gd)

In this study, we combined the surface-enhanced Raman scattering (SERS) with density functional theory (DFT) calculations to investigate the SERS spectra of lanthanide (Ln)-citrate complexes (Ln = La, Ce, Pr, Nd, Sm, Eu, and Gd) under 488, 532, and 660 nm laser excitations. Detailed vibrational analysis and peak assignments were performed based on SERS spectra simulated using an optimized DFT setting, in which small-core effective core potentials (ECPs) in the def2-tzvpd basis set were replaced by large-core ECPs. Characteristic SERS peaks appeared at 1065, 1315, and 1485 cm-1 were assigned to the {\gamma}(CH2)+v(C-O{\ldots}Ln), vsym(COO-)+{\gamma}(CH2), and vasym(COO-)+{\gamma}(CH2) vibrational bands, respectively. SERS intensity ratios were obtained by normalizing the peak intensity I near 1065 or 1485 cm-1 to that near 1315 cm-1. I1065/I1315 depended solely on the type of Ln3+ ion and was independent of the excitation wavelength. In contrast, I1485/I1315 increased with decreasing excitation wavelength, indicating additional enhancement by charge-transfer. Additionally, as the number of unpaired 4f electrons increased, Ln3+ in the coordination region attracted oxygen negative charges more strongly, reducing the electric dipole moment of the C-O bond and altering its symmetry.

physics.chem-ph↗

arXiv2024

Plasmon-enhanced two photon excited emission from edges of one-dimensional plasmonic hotspots with continuous-wave laser excitation

One-dimensional junctions between parallel and closely arranged multiple silver nanowires (NWs) exhibit a large electromagnetic (EM) enhancement factor (FR) owing to both localized and surface plasmon resonances. Such junctions are referred to as one-dimensional (1D) hotspots (HSs). This study found that two-photon excited emissions, such as hyper-Rayleigh, hyper-Raman, and two-photon fluorescence of dye molecules, are generated at the edge of 1D HSs of NW dimers with continuous-wave near-infrared (NIR) laser excitation and propagated through the 1D HSs; however, they were not generated from the centers of 1D HSs. Numerical EM calculations showed that FR of the NIR region for the edges of 1D HSs was larger than that for the centers by approximately 104 times, resulting in the observation of two-photon excited emissions only from the edge of 1D HSs. The analysis of the NW dimer gap distance dependence of FR revealed that the lowest surface plasmon (SP) mode, compressed and localized at the edges of the 1D HSs, was the origin of the large FR in the NIR region. The propagation of two-photon-excited emissions was supported by higher-order coupled SP mode.

physics.optics↗

arXiv2023

Electromagnetic enhancement of one-dimensional plasmonic hotspots along silver nanowire dimer examined by ultrafast surface enhanced fluorescence

We investigated the spectral properties of electromagnetic (EM) enhancement of one-dimensional hotspots (1D HSs) generated between silver nanowire (NW) dimers. The EM enhancement spectra were directly derived by dividing the spectra of ultrafast surface-enhanced fluorescence (UFSEF) from single NW dimers with UFSEF obtained from large nanoparticle aggregates, which aggregate-by-aggregate variations in the UFSEF spectra were averaged out. Some NW dimers were found to exhibit EM enhancement spectra that deviated from the plasmon resonance Rayleigh scattering spectra, indicating that their EM enhancement was not generated by superradiant plasmons. These experimental results were examined by numerical calculation based on the EM mechanism by varying the morphology of the NW dimers. The calculations reproduced the spectral deviations as the NW diameter dependence of EM enhancement. Phase analysis of the enhanced EM near fields along the 1D HSs revealed that the dipole-quadrupole coupled plasmon, which is a subradiant mode, mainly generates EM enhancement for dimers with NW diameters larger than ~80 nm, which was consistent with scanning electron microscopic measurements.

physics.optics↗

arXiv2023

Classification of La3+ and Gd3+ rare earth ions using surface-enhanced Raman scattering

In this study, surface-enhanced Raman scattering (SERS) spectra of different rare earth (RE) ion-citrate complexes were investigated for the first time for the qualitative classification of RE3+ ions. With the addition of RE3+ ions to citrate-capped silver nanoparticles in aqueous solutions, the Raman signals of RE-citrate complexes were enhanced, and characteristic peaks appeared near 1065 cm-1 and 1315 cm-1. The I1065/I1315 ratios of La-citrate and Gd-citrate were approximately 1 and 0.5, respectively. Thus, different RE3+ ions were classified based on the ratio of characteristic SERS peaks near 1065 cm-1 and 1315 cm-1. In addition, the effects of RE3+ ions in the RE-citrate complexes were analyzed based on density functional theory (DFT) calculations. Calculation results show that these characteristic peaks are attributed to the coordination of carboxyl and hydroxyl groups of citrates with the RE3+ ions, suggesting that these are spin-related bands of the RE-citrate complexes.

physics.chem-ph↗

arXiv2023

Electromagnetic enhancement generated by Ap term of cavity quantum electrodynamics demonstrated by single coupled systems between plasmon and molecular exciton

In non-relativistic quantum electrodynamics, an electromagnetic (EM) interaction between a photon and a molecular exciton can be expressed by a Ap term and A^2 term, where A and p are the operators of the vector potential of the EM field and the momentum of the exciton, respectively. We developed a method for investigating the contribution of the Ap and A^2 terms to EM enhancement, which occurs in coupled systems composed of a plasmon polariton and a molecular exciton. The spectral shapes of the Ap and A^2 terms terms, and the EM enhancement were experimentally obtained from absorption, Rayleigh scattering, and ultrafast surface enhanced fluorescence (ultrafast SEF) of the systems, respectively. The relationships between them reveal that the absorption spectra correctly reproduce EM enhancement, indicating that ultrafast SEF can be described as a two-step process using the Ap term. Furthermore, we demonstrate that the origin of spectral deviation between Rayleigh scattering and EM enhancement is subradiant plasmon resonance, which spectra are visualized in the absorption not in Rayleigh scattering, with numerical calculation based on electromagnetism.

physics.optics↗

arXiv2023

Correlated polarization dependences between surface-enhanced resonant Raman scattering and plasmon resonance elastic scattering showing spectral uncorrelation to each other

We investigated the origin of the identical polarization angle dependences between surface-enhanced resonant Raman scattering (SERRS) and plasmon resonance for two types of single silver nanoparticle aggregates. The first type (Type I), in which the SERRS spectral envelopes are similar to the plasmon resonance elastic scattering spectra, shows the identical polarization dependence between the SERRS and plasmon resonance. The second type (Type II), in which the SERRS envelopes largely deviate from the plasmon resonance, also exhibits identical polarization dependence. Scanning electron microscopy (SEM) observations indicated that these aggregates were dimers. Thus, this unintuitive result was examined by calculating the electromagnetic (EM) enhancement by changing the morphology of the dimers. The calculation revealed that Type I of dimer generates SERRS directly by superradiant plasmons. The Type II of dimer generates SERRS indirectly by subradiant plasmons, which receive light energy from the superradiant plasmons. This indirect SERRS process clarifies that the interaction between the superradiant and subradiant plasmons results in an identical polarization dependence between SERRS and plasmon resonance for Type II of dimers.

physics.optics↗

arXiv2023

Spectral correlation between surface-enhanced resonant Raman and far field scattering destructed by dipole quadrupole coupled plasmon resonance

The spectral relationships between surface enhanced resonant Raman scattering (SERRS) and plasmon resonance observed in far field scattering cross are investigated using single silver nanoparticle dimers with focusing on the lowest energy (superradiant) plasmon resonance. We find that these relationships can be classified into two types. The first is SERRS spectral envelopes with spectral shapes similar to those of plasmon resonance spectra. The second is SERRS envelopes exhibiting higher energy shifts from the plasmon resonance spectra. These results are examined as an effect of degree of morphological asymmetry in dimers based on an electromagnetic (EM) mechanism. The analysis of the first and second types reveals that dipole-dipole and dipole-quadrupole coupled plasmon resonance (subradiant Fano resonance) respectively determine the EM enhancement. This mechanism is commonly important for the development of plasmonic nanostructures for various surface enhanced spectroscopies.

physics.optics↗

arXiv2022

Highly scalable, wearable surface-enhanced Raman spectroscopy

The last two decades have witnessed a dramatic growth of wearable sensor technology, mainly represented by flexible, stretchable, on-skin electronic sensors that provide rich information of the wearer's health conditions and surroundings. A recent breakthrough in the field is the development of wearable chemical sensors based on surface-enhanced Raman spectroscopy (SERS) that can detect molecular fingerprints universally, sensitively, and noninvasively. However, while their sensing properties are excellent, these sensors are not scalable for widespread use beyond small-scale human health monitoring due to their cumbersome fabrication process and limited multifunctional sensing capabilities. Here we demonstrate a highly scalable, wearable SERS sensor based on an easy-to-fabricate, low-cost, ultrathin, flexible, stretchable, adhesive, and bio-integratable gold nanomesh. It can be fabricated in any shape and worn on virtually any surface for label-free, large-scale, in-situ sensing of diverse analytes from low to high concentrations (10 nM - 1 mM). To show the practical utility of the wearable SERS sensor, we test the sensor for the detection of sweat biomarkers, drugs of abuse, and microplastics. This wearable SERS sensor represents a significant step toward the generalizability and practicality of wearable sensing technology.

physics.optics↗

arXiv2021

Propagation mechanism of surface-enhanced resonant Raman scattering light through one-dimensional plasmonic hotspot along silver nanowire dimer junction

We investigate the propagation of surface-enhanced resonant Raman scattering (SERRS) light by several micrometers through a one-dimensional hotspot (1D HS) located between a plasmonic nanowire dimer (NWD). The propagation exhibits the properties, e.g. an effective propagation induced by excitation and detection polarization orthogonal to the 1D HS long axis, the propagation profiles composed of bright short and dark long propagations, SERRS spectral shapes independent of localized plasmon (LP) resonance of NWDs, redshifts in the SERRS spectra at the edges of 1D HSs, and considerable NWD-by-NWD variations in the propagation lengths. These properties are well reproduced by numerical calculations based on electromagnetism. These calculations reveals the following propagation mechanism: excitation light resonantly coupled with LP at the edges of 1D HSs, and the light energy is transferred to two types of junction SP modes supporting the short and long propagations; these modes are attributed to the upper and lower branches of coupled two SP modes. This mechanism comprehensively clarifies the abovementioned properties.

physics.optics↗

arXiv2020

Porous carbon nanowire array for highly sensitive, biocompatible, reproducible surface-enhanced Raman spectroscopy

Surface-enhanced Raman spectroscopy (SERS) is a powerful tool for vibrational spectroscopy as it provides several orders of magnitude higher sensitivity than inherently weak spontaneous Raman scattering by exciting localized surface plasmon resonance (LSPR) on metal substrates. However, SERS is not very reliable, especially for use in life sciences, since it sacrifices reproducibility and biocompatibility due to its strong dependence on "hot spots" and large photothermal heat generation. Here we report a metal-free (i.e., LSPR-free), topologically tailored nanostructure composed of porous carbon nanowires in an array as a SERS substrate that addresses the decades-old problem. Specifically, it offers not only high signal enhancement due to its strong broadband charge-transfer resonance, but also extraordinarily high reproducibility or substrate-to-substrate, spot-to-spot, sample-to-sample, and time-to-time consistency in SERS spectrum due to the absence of hot spots and high compatibility to biomolecules due to its fluorescence quenching and negligible denaturation capabilities. These excellent properties make SERS suitable for practical use in diverse biomedical applications.

physics.chem-ph↗

arXiv2019

Anti-crossing properties of strong coupling system of silver nanoparticle dimers coated with thin dye molecular films analyzed by classical electromagnetism

The evidence of strong coupling between plasmons and molecular excitons for plasmonic nanoparticle (NP) dimers exhibiting ultra-sensitive surface enhanced resonant Raman scattering is the observation of anti-crossing in the coupled resonance. However, it is not easy to experimentally tune plasmon resonance of such dimers for the observation. In this work, we theoretically investigate the anti-crossing properties of the dimers coated by the thin dye films with thicknesses greater than 0.1 nm and gap distances larger than 1.2 nm according to the principles of classical electromagnetism. The plasmon resonance spectra of these dimers are strongly affected by their coupling with the exciton resonance of dye molecules. A comparison of the film thickness dependences of dimer spectral changes with those of silver ellipsoidal NPs indicates that the dipole plasmons localized in the dimer gap are coupled with molecular excitons of the film much stronger than the dipole plasmons of ellipsoidal NPs. Furthermore, the anti-crossing of coupled resonances is investigated while tuning plasmon resonance by changing the morphology and refractive index of the surrounding medium. The spectral changes observed for ellipsoidal NPs clearly exhibit anti-crossing properties; however, the anti-crossing behavior of dimers is more complex due to the strong coupling of dipoles and higher order plasmons with multiple molecular excitons. We find that the anti-crossing for dimers is clearly confirmed by the refractive index dependence of coupled resonance.

physics.optics↗

arXiv2019

Absorption cross-section spectroscopy of single strong coupling system between plasmon and molecular exciton resonance using single silver nanoparticle dimer generating surface enhanced resonant Raman scattering

This study investigated spectral changes in the absorption cross-sections of single strong coupling systems composed of single silver nanoparticle dimers and a few dye molecules during the quenching of surface-enhanced resonant Raman scattering (SERRS). The absorption cross-section was obtained by subtracting the scattering cross-section from an extinction cross-section. The spectral changes in these cross-sections were evaluated using a classical hybridization model composed of a plasmon and a molecular exciton including a molecular multi-level property. The changes in the scattering and extinction cross-sections exhibit blue-shifts in their peak energy and increased peak intensities, respectively, during SERRS quenching. These properties are effectively reproduced in the model by decreasing the coupling energy. In particular, the peaks in the scattering and extinction cross-sections appear as peaks or dips in the absorption cross-sections depending on the degree of scattering loss, which reflects the dimer sizes. These results are useful for optimizing photophysical and photochemical effects mediated by the electronic excited states of strong coupling systems.

physics.optics↗

arXiv2018

Unified evaluation of surface-enhanced resonance Raman scattering and fluorescence under strong coupling regime

We demonstrate importance of molecular multiple excitons and higher-order plasmons for both enhancement and quenching of resonance Raman and fluorescence of single dye molecule located at plasmonic hotspot under strong coupling regime. The multiple excitons induce complicated spectral changes in plasmon resonance and higher-order plasmons yield drastic quenching for both resonant Raman and fluorescence. A coupled oscillator model composed of plasmon and multiple excitons reproduces the complicated spectral changes. Purcell factors derived from higher-order plasmons reproduce the drastic quenching with considering ultra-fast surface enhanced fluorescence.

physics.optics↗

arXiv2017

One-dimensional plasmonic hotspots located between silver nanowire dimers evaluated by surface-enhanced resonance Raman scattering

Hotspots of surface-enhanced resonance Raman scattering (SERRS) are localized within 1 nm at gaps or crevices of plasmonic nanoparticle (NP) dimers. We demonstrate SERRS hotspots with volumes that are extended in one dimension tens of thousand times compared to standard zero-dimensional hotspots using gaps or crevices of plasmonic nanowire (NW) dimers.

physics.optics↗

arXiv2016

Single-Molecule Surface-Enhanced Raman Scattering Spectrum of Non-Resonant Aromatic Amine Showing Raman Forbidden Bands

We present the experimentally obtained single-molecule (SM) surface-enhanced Raman scattering (SERS) spectrum of 4-aminibenzenethiol (4-ABT), also known as para-aminothiophenol (PATP). Measured at a 4-ABT concentration of 8 * 10^-10 M, the spectra show Raman forbidden modes. The SM-SERS spectrum of 4-ABT obtained using a non-resonant visible laser is different from the previously reported SERS spectra of 4-ABT, and could not be reconstructed using quantum mechanical calculations. Careful classical assignments (not based on quantum-mechanical calculations) are reported, and indicate that differences in the reported spectra of 4-ABT are mainly due to the appearance of Raman forbidden bands. The presence of Raman forbidden bands can be explained by the charge-transfer (CT) effect of 4-ABT adsorbed on the silver nanostructures, indicating a breakdown of Raman selection rules at the SERS hotspot.

physics.chem-ph↗