Charge Transfer Plasmon Resonance Research Articles

Charge-Transfer Plasmon Resonance in a Dimer of Gold Nanoparticles Connected with a Carbon Nanotube

Charge-Transfer Plasmon Resonance in a Dimer of Gold Nanoparticles Connected with a Carbon Nanotube

Multifunctional charge transfer plasmon resonance sensors

Abstract Charge transfer plasmon (CTP) modes arise when metallic nanoparticle dimers are connected by a conductive junction. This offers a unique opportunity to explore electron transport at optical frequencies as well as to attain narrow plasmon resonances that can be broadly modulated from visible to IR regimes, implying their potentials for applications in single-molecule electronics and sensing. This article showcases recent developments in theory and applications of charge transfer plasmon resonances (CTPRs) in various configurations of conductively linked plasmonic nanodimers. In particular, we give a due attention to exploiting ultratunable spectral features of charge transfer plasmon resonances for developing multifunctional plasmonic sensors for bulk, surface, gas and molecular sensing applications. We also discuss the implications of the charge and energy transfer between two plasmonic nanoparticles linked by sub-nanometer thick self-assembled monolayers for single-molecule conductance sensing and molecular electronics. In addition to the well-established plasmonic sensing schemes based on propagating and localized surface plasmon resonances, charge transfer plasmon resonance sensors may open up a new route in efforts to develop multifunctional sensing technologies.

Uncovering the Evolution of Low-Energy Plasmons in Nanopatterned Aluminum Plasmonics on Graphene.

We report adjusting the charge-transfer-plasmon (CTP) resonances of aluminum (Al) bowties on suspended monolayer graphene via controlled nanofabrication and focused electron-beam irradiation. CTP resonances of bowties with a conductive junction blue-shift with an increase in junction width, whereas their 3λ/2 and λ resonances barely red-shift. These plasmon modes are derived and confirmed by an LC circuit model and electromagnetic simulations performed with boundary-element and frequency-domain methods. A monotonic decay of the CTP lifetime is observed, while the junction width is extended. Instead, the lifetimes of 3λ/2 and λ resonances are nearly independent of junction width. When the junction is shrunk by electron-beam irradiation, all antenna resonances red-shift. Having created an electron-beam-induced sub 5 nm gap in bowties, we monitor the unambiguous transition of a CTP into a bonding-type gap mode, which is highly sensitive to the separation distance. Meanwhile, the 3λ/2 and λ resonances evolve into dipolar bright and dipolar dark modes.

Numerical simulation study of surface enhancement coherent anti-Stokes Raman scattering reinforced substrate

Plasma nanostructures are of particular significance for serving as a substrate for spectroscopic detection and identification of individual molecules. By combining the excitation wavelength of the molecule with the resonance wavelength of the nanostructure, the sensitive single-molecule Raman detection can be achieved. A high and stable plasma substrate for coherent anti-Stokes Raman scattering(CARS) is very useful for developing the surface-enhanced coherent anti-Stokes Raman scattering (SECARS). In the plasma nanostructures, the strong coupling of plasmonic nanoparticles with an inter-particle gap smaller than the diameter of the individual nanoparticles results in the hybridization of the optical properties of these individual nanoparticles. There are also the charge transfer plasmons(CTP) appearing in conductive bridging nanoparticles. Their unique properties make linked nanosystems a suitable candidate for building artificial molecules, nanomotors, sensors, and other optoelectronic devices. In this work, we, starting from reality, theoretically design a new linked nanosystem SECARS substrate where Fano resonance can be generated by the plasmon hybridization (PH) model resonance and the charge transfer plasmon resonance. The introduction of charge transfer plasma improves the tunability of structural resonance. By adjusting the conductivity of the conductive junction, the wavelength of the charge transfer plasma resonance can be easily adjusted to change the wavelength position of the Fano resonance. The data obtained by numerical simulation of the Raman mode at 1557 cm<sup>–1</sup> of L-tryptophan when a 1064 nm light source is used as the pump light show that this spatially symmetrical structure can generate multiple high-enhancement hot spots that do not depend on the polarization direction of the incident light. Ordinary CARS signal can generally be enhanced by 10<sup>12</sup>, and its maximum can reach 10<sup>14</sup>. Due to the ultrastrong field enhancement and insensitive-to-polarization, this method of using charge transfer plasma to design a substrate can be used in the practical substrate of SECARS and provide new ideas for designing other nonlinear optical processes such as four wave mixing and stimulated Raman scattering.

Optothermally Tuned Charge Transfer Plasmons in Au-Ge2Sb2Te5 Core-Shell Assemblies

ABSTRACTTunable plasmonic resonances across the visible and near infrared spectra have provided novel ways to develop next-generation nanophotonic devices. Here, by utilizing optothermally controllable phase-changing material (PCM), we studied highly tunable charge transfer plasmon (CTP) resonance modes. To this end, we have designed a two-member dimer assembly including gold cores and Ge2Sb2Te5 (GST) shells in distant, touching, and overlapping conditions. We successfully demonstrated that toggling between amorphous (dielectric) and crystalline (conductive) phases of GST allows for achieving tunable dipolar and CTP resonances along the near-infrared spectrum. The proposed dimer structures can help forming optothermally controlled devices without further morphological variations in the geometry of the design, and having strong potential for advanced plasmon modulation and fast data routing.

Optothermally Controlled Charge Transfer Plasmons in Au-Ge2Sb2Te5 Core-Shell Dimers

Functional and reversible plasmonic resonances across the visible and near-infrared spectrum have opened new avenues for developing advanced next-generation nanophotonic devices. In this study, by using optothermally controlled phase-change material (PCM) for plasmonic nanostructures, we successfully induced highly tunable charge transfer plasmon (CTP) resonance modes. To this end, we have chosen a two-member dimer assembly consisting of gold cores and Ge2Sb2Te5 (GST) shells in distant, touching, and overlapping regimes. We show that switching between amorphous (dielectric) and crystalline (conductive) phases of GST allows for achieving tunable dipolar and CTP resonances and enables an effective interplay between these modes along the near-infrared spectrum. By analyzing electromagnetically calculated spectral responses for the dimer antenna in tunneling and direct charge transfer regimes, we confirmed that the induced CTPs in touching and overlapping regimes are highly controllable and pronounced in comparison to the quantum tunneling regime. We also use the precise, fast, and controllable switching between dipolar and CTP resonant modes to develop a telecommunication switch based on a simple metallodielectric dimer. The proposed structures can help designing optothermally controlled devices without morphological variations in the geometry of the design, and having strong potential for advanced plasmon modulation and fast data routing.

Charge transfer plasmons: Recent theoretical and experimental developments

The unique property of a charge transfer plasmon (CTP) that emerges in conductively bridged plasmonic nanoparticles makes linked nanosystems suitable candidates for building artificial molecules, nanomotors, sensors, and other optoelectronic devices. In this focused review, we present recent theoretical and experimental developments in fundamentals and applications of CTPs in conductively coupled metallic nanoparticles of various sizes and shapes. The underlying physics of charge transfer in linked nanoparticles with nanometer- and atomic-scale inter-particle gap is described from both classical and quantum mechanical perspectives. In addition, we present a detailed discussion of mechanisms of controlling charge transfer and tuning the corresponding CTP spectra in bridged nanoparticles as functions of junction conductance and nanoparticle parameters. Furthermore, the active control of reversible switching between capacitive and conductive coupling in plasmonic nanoshell particles and dynamic evolution of related plasmon modes are emphasized. Finally, after highlighting the implication of the CTP resonance shift for surface-based sensing applications, we end up with the current challenges and future outlooks of the topic that need to be addressed.

Controlled Plasmon Resonance Properties of Hollow Gold Nanosphere Aggregates

Hollow gold nanospheres (HGNs) ranging from 29.9 nm/8.5 nm (outer diameter/shell thickness) to 51.5 nm/4.5 nm and having aspect ratios spanning 3.5-11.7 were employed to investigate the ability to tailor charge oscillations of HGN aggregates by systematic variation of particle aspect ratio, interparticle gap, and nanosphere inner surface spatial separation. Altering these properties in aggregated HGNs led to control over the interparticle plasmon resonance. Thiol-mediated aggregation was accomplished using either ethanedithiol or cysteine, resulting in dimeric structures in which monomer subunits were spatially separated by <3 Å and 1.2 ± 0.7 nm, respectively. Particle dimensions and separation distances were confirmed by transmission electron microscopy. Experimental absorption spectra obtained for high-aspect ratio nanospheres dimerized using ethanedithiol exhibited an obvious blue shift of the surface plasmon resonance (SPR) relative to that observed for the native, monomeric HGN. This spectral difference likely results from a charge-transfer plasmon resonance at the dimer interface. The extent of the blue shift was dependent upon shell thickness. Dimers comprised of thin-shelled HGNs exhibited the largest shift; aggregates containing HGNs with thick shells (≥7 nm) did not display a significant SPR shift when the individual particles were in contact. By comparison, all cysteine-induced aggregates examined in this study displayed large interparticle gaps (>1 nm) and a red-shifted SPR, regardless of particle dimensions. This effect can be described fully by a surface mode coupling model. All experimental measurements were verified by finite difference time domain calculations. In addition, simulated electric field maps highlighted the importance of the inner HGN surface in the interparticle coupling mechanism. These findings, which describe structure-dependent SPR properties, may be significant for applications derived from the plasmonic nanostructure platform.