Weak Plasmon Research Articles

Evidence of electron correlation and weak bulk plasmon in SrMoO3

We investigate the electronic structure of highly conducting perovskite SrMoO3 using valence band photoemission spectroscopy and electronic structure calculations. Large intensity corresponding to coherent feature close to Fermi level is captured by density functional theory (DFT) calculation. An additional satellite at ∼3 eV binding energy remains absent in DFT, hybrid functional (DFT-hybrid) and dynamical mean field theory (DFT + DMFT) calculations. Mo 4d spectra obtained with different surface sensitive photoemission spectroscopy suggest different surface and bulk electronic structures. DFT + DMFT spectral function is in excellent agreement with the coherent feature in the bulk Mo 4d spectra, revealing moderate electron correlation strength. A large plasmon satellite and signature of strong electron correlation are observed in the surface spectra, while the bulk spectra exhibits a weak plasmon satellite.

Electrical activating of the “nonradiative” terahertz plasmon modes in a periodic grating-gate graphene structure with asymmetrical gating

Electrical tuning the radiative damping of “nonradiative” (weak) terahertz plasmon mode in a periodic dual-grating-gate graphene structure is studied theoretically. Tuning the dc voltage value applied to one of the gate subgratings can change the radiative damping of the weak plasmon mode from zero to the dissipative damping of the plasmons in high-quality graphene allowing for maximum energy conversion from the incident wave to “nonradiative” plasmon mode. Radiative damping increases due to the increase of the dipole moment of this mode by virtue of its asymmetrical gating. Using the weak plasmon modes is important for effective excitation of the plasmon resonances in high-quality graphene as well as for realizing the concept of low-threshold terahertz lasers based on graphene plasmonic structures. Data availabilityData underlying the results presented in this paper are not publicly available at this time but may be obtained from the authors upon reasonable request.

Water-phase synthesis of Au and Au-Ag nanowires and their SERS activity.

Metal nanowires (NWs) with a diameter of a few nanometers have attracted considerable attention as a promising one-dimensional nanomaterial due to their inherent flexibility and conductive properties and their weak plasmon absorption in the visible region. In a previous paper, we reported the synthesis of ultrathin 1.8 nm-diameter Au NWs using toluene-solubilized aqueous solutions of a long-chain amidoamine derivative (C18AA). This study investigates the effect of different organic solvents solubilized in C18AA aqueous solutions on the morphology of the Au products and demonstrates that solubilizing methylcyclohexane yields thick 2.7 nm-diameter Au NWs and 3.3 nm-diameter Au-Ag alloy NWs. Further, the surface-enhanced Raman scattering sensitivity of ultrathin Au NWs, thick Au NWs, and thick Au-Ag alloy NWs were assessed using 4-mercaptopyridine and found that their enhancement factors are 104-105 and the order is Au-Ag NWs > thick Au NWs > ultrathin Au NWs.

Weak plasmon modes in periodic structures for terahertz detection and amplification

Weak plasmon modes in periodic structures with a two-dimensional electron gas without an inversion center are studied theoretically. The asymmetry of the electric field and Fourier harmonics of weak plasmon modes can lead to the excitation of a travelling plasmon by an electromagnetic wave normally incident on the structure and to the appearance of nonlinear effects leading to the rectification of the incident radiation. The low radiation damping of weak plasmon modes can be used to increase the efficiency of terahertz plasmon amplifiers.

Nanoparticles exploring the macroscopic world

Nanoparticles exploring the macroscopic world

Terahertz Lasing with Weak Plasmon Modes in Periodic Graphene Structures

The achievement of the laser regime upon the excitation of weak plasmon modes in structures based on active graphene has been theoretically investigated. The weak ``acoustic'' plasmon modes in two-layer structures and weak ``nonradiative'' gated modes in noncentrosymmetric grating-gated structures are investigated. The radiative damping and gain rate of strong and weak plasmon modes in graphene structures are calculated. The possibilities of changing the radiative damping of plasmon modes by changing the geometry of the structure are considered. It is proposed to use weak plasmon modes with low radiative damping for decreasing the threshold for the laser plasmon regime in periodic graphene structures.

Laser generation on weak modes in graphene structure with asymmetric unit cell

Problem formulating. Lasing on strong («radiative») plasmon resonance mode in graphene structure with dual grating gate with asymmetric unit cell requires strong gain. It is possible to achieve lasing in a weak ("non-radiative") mode at a lower gain rate. Goal. Theoretical study of laser generation on weak plasmonic resonance mode in single layer graphene structure screened by dual grating gate with asymmetric unit cell. Result. Laser generation on weak plasmonic resonance mode in single layer graphene structure screened by dual grating gate with asymmetric unit cell is reached. Excitation of a weak plasmon resonance mode requires less gain than excitation of a radiative one. Practical meaning. Results can be used to create sources of terahertz waves.

Alternating Coupling Regimes in a Plasmon–Molecule Hybrid Structure through a Phase-Change Material

Plasmon–molecule hybrid systems provide platforms for studying light–matter interactions. It is of great interest for systems where both strong and weak plasmon–molecule couplings exist and can transfer into each other freely. In this paper, we proposed a hybrid structure composed of a vanadium dioxide (VO2) layer sandwiched between a polymethyl methacrylate (PMMA) strip array and a gold substrate. The molecular vibration of PMMA interacts with the surface plasmon polaritons (SPPs) of the metal substrate, and the coupling regimes can be alternated through the phase transition of VO2. The electric fields at SPP resonances closely relate with the optical properties of VO2. When VO2 is an insulator, high electric fields in PMMA strips cause the strong plasmon–molecule coupling and new hybrid modes are formed. When VO2 is a metal, the electric fields in PMMA are moderate due to high loss of metallic VO2 and the plasmon–molecule coupling is in the weak coupling regime. The influence of the VO2 layer thickness on coupling properties was also discussed in detail for VO2 in different phases. Our study provides a new strategy to modulate the plasmon–molecule coupling and is inspiring for fundamental and practical research studies on light–matter interactions.

Weak plasmon–exciton coupling between monolayer molybdenum disulfide and aluminum disks

Manipulation of the photoluminescence (PL) of monolayer (ML) molybdenum disulfide (MoS2) with metallic plasmonic nanostructures has attracted much more attention for potential applications in optoelectronic devices. However, due to the limitation of resonance wavelength and oxidation properties, gold and silver are not the best selections for manipulating PL of MoS2. Here, we employ aluminum (Al) disks to tune the PL of ML MoS2. We have found that PL enhancement reaches the maximum when plasmonic resonances of Al disks overlap with the absorption peaks of ML MoS2. Near-field simulations show that PL enhancement is due to weak plasmon-exciton coupling.

Ultrasensitive Surface-Enhanced Raman Spectroscopy Detection Based on Amorphous Molybdenum Oxide Quantum Dots.

Surface-enhanced Raman spectroscopy (SERS) based on plasmonic semiconductive material has been proved to be an efficient tool to detect trace of substances, while the relatively weak plasmon resonance compared with noble metal materials restricts its practical application. Herein, for the first time a facile method to fabricate amorphous Hx MoO3 quantum dots with tunable plasmon resonance is developed by a controlled oxidization route. The as-prepared amorphous Hx MoO3 quantum dots show tunable plasmon resonance in the region of visible and near-infrared light. Moreover, the tunability induced by SC CO2 is analyzed by a molecule kinetic theory combined with a molecular thermodynamic model. More importantly, the ultrahigh enhancement factor of amorphous Hx MoO3 quantum dots detecting on methyl blue can be up to 9.5 × 105 with expending the limit of detection to 10-9 m. Such a remarkable porperty can also be found in this Hx MoO3 -based sensor with Rh6G and RhB as probe molecules, suggesting that the amorphous Hx MoO3 quantum dot is an efficient candidate for SERS on molecule detection in high precision.

Terahertz-infrared electrodynamics of single-wall carbon nanotube films

Broad-band (4–20 000 cm−1) spectra of real and imaginary conductance of a set of high-quality pristine and AuCl3-doped single-walled carbon nanotube (SWCNT) films with different transparency are systematically measured. It is shown that while the high-energy (≥1 eV) response is determined by well-known interband transitions, the lower-energy electrodynamic properties of the films are fully dominated by unbound charge carriers. Their main spectral effect is seen as the free-carrier Drude-type contribution. Partial localization of these carriers leads to a weak plasmon resonance around 100 cm−1. At the lowest frequencies, below 10 cm−1, a gap-like feature is detected whose origin is associated with the energy barrier experienced by the carriers at the intersections between SWCNTs. It is assumed that these three mechanisms are universal and determine the low-frequency terahertz-infrared electrodynamics of SWCNT wafer-scale films.

Plasmon‐Assisted Indirect Light Absorption Engineering in Small Transition Metal Catalyst Nanoparticles

Light absorption in plasmonic nanoantennas constitutes an interesting way of enhancing catalytic reactions occurring at surfaces of metals nanoparticles by forming hot electron–hole pairs. These can either directly transfer to empty orbitals of adsorbed species on the nanoparticle surface or thermalize via electron–phonon coupling and enhance reaction rates via a photothermal reaction channel. While this scheme, in principle, can be efficient for the well‐known plasmonic materials Ag and Au due to their large optical cross‐sections, other transition metals, which exhibit excellent catalytic properties, have spectrally broad and weak plasmon resonances. Thus, lower plasmon‐induced electron–hole pair excitation is expected, especially for sub‐10 nm nanoparticles, typical in heterogeneous catalysis. Here, a solution is presented to circumvent these limitations by challenging the established picture that plasmonic nanoparticles also constitute catalytically active entities in a plasmon mediated hot electron catalysis concept. Light absorption in catalyst nanoparticles can be engineered via an adjacent noble metal plasmonic nanoantenna that efficiently collects incident radiation with low losses, and couples it into the catalytic particles where the energy is dissipated due to the intrinsically high optical losses in transition metals at near‐visible frequencies. Absorption enhancement of 1–2 orders of magnitude is predicted in 3–4 nm sized Pd catalyst nanoparticles.

Absorption enhancement of molecules in the weak plasmon-exciton coupling regime.

We report on the experimental and theoretical investigations of enhancing the optical absorption of organic molecules in the weak plasmon-exciton coupling regime. A metal-organic hybrid structure consisting of dye molecules embedded in the polymer matrix is placed in close vicinity to thin metal films. We have observed a transition from a weak coupling regime to a strong coupling one as the thickness of the metal layer increases. The results indicate that absorption of the self-assembled J-aggregate nanostructures can be increased in the weak plasmon-exciton coupling regime and strongly quenched in the strong coupling regime. A theoretical model based on the transfer-matrix method qualitatively confirms the experimental results obtained from polarization-dependent spectroscopic reflection measurements.

Deep-ultraviolet surface plasmon resonance of Al and Alcore/Al2O3shell nanosphere dimers for surface-enhanced spectroscopy

The localized surface plasmon resonance properties of Al and Alcore/Al2O3shell nanosphere dimers with Al and Al core nanosphere radii of 20 nm and Al2O3 shell of 2 nm in the deep-ultraviolet region have been studied using the finite difference time domain method. The extinction spectra and the electric field distribution profiles of the two dimers for various gap distances between two individual nanospheres are compared with those of the corresponding monomers to reveal the extent of plasmon coupling. It is found that with the interparticle distance decreasing, a strong plasmon coupling between two Al or Alcore/Al2O3shell nanospheres is observed accompanied by a significant red shift in the extinction spectra at the parallel polarization direction of the incident light related to the dimer axis, while for the case of the perpendicular polarization direction, a weak plasmon coupling arises characterized by a slight blue shift in the extinction spectra. The electric field distribution profiles show that benefiting from the dielectric Al2O3 shell, the gap distance of Alcore/Al2O3shell nanosphere dimers can be tailored to < 1 nm scale and results in a very high electric field enhancement. The estimated surface-enhanced Raman scattering enhancement factors suggests that the Alcore/Al2O3shell nanosphere dimers with the gap of < 1 nm gave rise to an enhancement as high as 8.1 × 107 for interparticle gap = 0.5 nm. Our studies reveal that the Alcore/Al2O3shell nanosphere dimers may be promising substrates for surface-enhanced spectroscopy in the deep-ultraviolet region.

Characteristics of Plasmonic at a Metal/Chiral Sculptured Thin Film Interface

The propagation of surface plasmon polariton at an interface of metallic thin film and chiral sculptured thin film theoretically has been investigated using the transfer matrix method in the Kretschman configuration. The optical absorption of structure as a function of polar incident angle for linear polarization P and S has been calculated at different structural parameters. The results show that exist multiple plasmon peaks for P polarization, while there are the weak plasmon peaks when incident of light is S-polarized plane wave.

Geometric effect on surface enhanced Raman scattering of nanoporous gold: Improving Raman scattering by tailoring ligament and nanopore ratios

We have synthesized nanoporous gold (NPG) films with a nanostructure consisting of small nanopores and large gold ligaments by the combination of chemical dealloying and electroless plating. The NPG films exhibit dramatic improvement in surface enhanced Raman scattering (SERS) in comparison with the conventional NPG. The superior SERS effect of the NPG films results from the confluence effect of enhanced local surface plasmon fields and electromagnetic coupling between ligaments, as well as the weak plasmon damping with increasing gold ligament sizes.

Template synthesis of nanoparticle arrays of gold, platinum and palladium in mesoporous silica films and powders

Mesoporous silica films were prepared on glass plates by a dip coating method, and the film/plate samples were used as a support for Au, Pt and Pd nanoparticles. By H2- or photo-reduction of metal precursors impregnated on the films, metal nanoparticles are formed with an ordered array structure in the mesopores. The nanoparticles are isolated by dissolving the silica film with a dilute HF solution, and the particles are stabilized with ligands such as 1-dodecanethiol and triphenylphosphine. The diameter of the separated nanoparticles is 2.5 nm with narrow distributions, showing that uniform particles are formed in the mesopores. Selective formation of metal nanoparticles rather than nanowires suggests that a 3D-hexagonal structure is involved in the 2D-hexagonal mesoporous silica films. To study the formation of nanoparticles in a 3D-hexagonal structure, HMM-2 powder was used as a support, and in fact Au and Pt nanoparticles are formed in the HMM-2 powders. The XRD study suggests that the Au nanoparticles in the film/plate have an anisotropic orientation in the mesoporous channels. The Au/film/plate sample gives a weak plasmon peak at 570–580 nm using diffuse-reflectance UV-visible spectroscopy, which is shifted to high wavelength by 50–60 nm compared with larger Au particles.

The plasmons of ErAs(100)

Momentum resolved inelastic electron energy loss has been exploited to measure the surface and bulk plasmons of ErAs(100). The effects of the electronic band structure are seen in the weak plasmon dispersion, and a contribution to the surface and bulk plasmons, from the Er 5d bands, is indicated in the decrease in the surface plasmon frequency by about 10% from the free electron value and to a ratio of the bulk and surface plasmon energies of about 3 .

A new hydrosol of gold clusters. 1. Formation and particle size variation

Aqueous reduction of hydrogen tetrachloroaurate(III) with alkaline tetrakis(hydroxymethyl)phosphonium chloride yields gold in an ultrafinely divided form as a stable colloidal hydrosol, with mean metal-cluster diameter between 1 and 2 nm, without the need for large organic stabilizing molecules. The ultraviolet-visible extinction spectrum is very similar to those of other gold colloids of similar dimensions and includes a weak plasmon feature. Dispersions with characteristics of yet finer clusters are prepared using lower initial concentrations of Au3+ ions. Boiling the sols in the presence of appropriate colloidal stabilizers (ionic and/or polymeric) is a route to coarser (3-10 nm particle diameter) gold hydrosols. © 1993 American Chemical Society.