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Ag nanocrystals with nearly ideal optical quality: synthesis, growth mechanism, and characterizations
摘要： Though Ag nanocrystals are predicted as the best material for localized surface plasmon resonances (LSPR) in the visible light region, realization of their ideal LSPR properties is hindered by the stringent requirement, i.e., simultaneous control of their size, shape, crystallinity, and surface structure. To achieve this goal, a synthetic scheme in non-polar solvent coupled with mild oxidative-etching by H+ ions is established. With a trace amount of Cl- ions as catalysts, H+ ions (in the form of carboxylic acids) become active for selectively etching the nuclei (and small nanocrystals) with imperfect crystal structure, which results in a new growth mechanism for formation of monodisperse nanocrystals, namely “self-focusing of size/crystallinity distribution”. H+ ions, ligands, and other reagents in the scheme are confirmed to possess negligible effects on the surface dielectric properties of Ag nanocrystals. To eliminate radiative damping of LSPR, single-crystalline and monodisperse spherical Ag nanocrystals in the size range between 7 and 20 nm are synthesized using this one-pot scheme. With excellent control of all the structural parameters, the full-width-at-half-maximum of LSPR spectra of single-crystalline Ag nanocrystals match theoretical predictions in the entire size range, and the maximum quality factor (~20) of LSPR predicted by theory is realized. Raman enhancement factor of the single-crystalline Ag nanocrystals for crystal violet (excitation at 514 nm) is 5 times higher than that of the typical multi-twinned ones with the same size.
关键词： localized surface plasmon resonances,oxidative-etching,monodisperse,single-crystalline,Ag nanocrystals,Raman enhancement
更新于2025-09-23 15:21:21
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Strong Exciton-Plasmon Coupling and Hybridization of Organic-Inorganic Exciton-Polaritons in Plasmonic Nanocavity <sup>*</sup>
摘要： We investigate strong exciton-plasmon coupling and plasmon-mediated hybridization between the Frenkel (F) and Wannier–Mott (WM) excitons of an organic-inorganic hybrid system consisting of a silver ring separated from a monolayer WS2 by J-aggregates. The extinction spectra of the hybrid system calculated by employing the coupled oscillator model are consistent with the results simulated by the finite-difference time-domain method. The calculation results show that strong couplings among F excitons, WM excitons, and localized surface plasmon resonances (LSPRs) lead to the appearance of three plexciton branches in the extinction spectra. The weighting efficiencies of the F exciton, WM exciton and LSPR modes in three plexciton branches are used to analyze the exciton-polaritons in the system. Furthermore, the strong coupling between two different excitons and LSPRs is manipulated by tuning F or WM exciton resonances.
关键词： coupled oscillator model,finite-difference time-domain method,localized surface plasmon resonances,plasmonic nanocavity,exciton-plasmon coupling,Frenkel excitons,organic-inorganic hybrid system,Wannier–Mott excitons
更新于2025-09-23 15:21:01
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Effect of Ligand Treatment on the Tuning of Infrared Plasmonic Indium Tin Oxide Nanocrystal Electrochromic Devices
摘要： Electrochromic devices operating in the near infrared are being developed as a part of smart windows that can dynamically modulate visible light and heat transmittance of solar irradiation, dependent on weather conditions and personal preferences. Here, doped metal-oxide nanocrystals are used to obtain the desired effect in the infrared spectral region. Specifically, the infrared transmittance is electrochemically modulated by control of the carrier concentration in the nanocrystals. While indium-tin-oxide nanocrystals are already known to provide this effect, the consequence of ligand treatment during preparation of the nanocrystal electrode on the electrochromic properties are studied. The type of ligand treatment is shown to affect the surface morphology, as well as the localized plasmon resonance energy of the nanocrystal films. A short and convenient treatment by ethanedithiol cross linking ligands is shown to provide superior results as compared to the formic acid treatment used in the previous work. Future work combining windows based on optimized electrochromic effects in the near infrared combined with those in the visible spectral range will simultaneously improve building energy efficiency and indoor human comfort.
关键词： metal oxide nanocrystals,localized surface plasmon resonances,Electrochromic windows,ligand exchange
更新于2025-09-23 15:21:01
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Large-area grain-boundary-free copper films for plasmonics
摘要： Ultrasmooth single-crystalline metallic thin films provide several key advantages for the fabrication of well-defined and high-resolution plasmonic nanostructures, particularly complex integrated nanocircuits. For this purpose, copper is generally regarded as a poor plasmonic material compared to gold and silver because of its notorious oxidation issues when subjected to air exposure. Here, we report on the use of large-area grain-boundary-free copper films grown epitaxially on sapphire substrates in combination with focused ion beam milling to pattern plasmonic nanostructures with superior quality. The copper surfaces prepared using a single-crystalline copper sputtering target exhibit a very low roughness without any grain boundaries for varying film thicknesses and a strong resistance to oxidation, overcoming the bottleneck in conventional copper film fabrication. Surface plasmon resonance measurements show that improved dielectric constants with higher conductivity and long-term stability can be achieved using the single-crystalline copper films. Plasmonic nanohole arrays patterned from these high-quality films are found to display a stronger field enhancement compared to those made from polycrystalline copper films, thus resulting in an enhanced extraordinary optical transmission performance. This study suggests that our fabrication method is ideally suited for applications in copper-based plasmonic and nanophotonic devices as well as integrated nanocircuits on a large scale.
关键词： Single-crystalline films,Polycrystalline films,Surface plasmon resonances,Copper,Extraordinary optical transmission
更新于2025-09-23 15:19:57
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Ultrathin Plasmonic Tungsten Oxide Quantum Wells with Controllable Free Carrier Densities
摘要： We report the colloidal synthesis of ~3 tungsten-oxygen (W-O) layer thick (~1 nm), two-dimensional (2D) WO3-x nanoplatelets (NPLs) (x ~ 0.55 — 1.03), which display tunable near-infrared localized surface plasmon resonances (LSPR) spectra and high free electron density (Ne) that arises predominantly from their large shape factor. Importantly, the W to O composition ratios inferred from their LSPR measurements show much higher percentage of oxygen vacancies than those determined by X-ray diffraction analysis, suggesting that the aspect ratio of ultrathin WO3-x NPLs is the key to producing an unprecedentedly large Ne, although synthesis temperature is also an independent factor. We find that NPL formation is kinetically controlled, whereas thermodynamic parameter manipulation leads to Ne as high as 4.13 X 1022 cm-3, which is close to that of plasmonic noble metals, and thus our oxide-based nanostructures can be considered as quasi-metallic. The unique structural properties of 2D nanomaterials along with the high Ne of WO3-x NPLs provide an attractive alternative to plasmonic noble metal nanostructures for energy conversions.
关键词： Ultrathin Plasmonic Tungsten Oxide,Quantum Wells,Colloidal Synthesis,Localized Surface Plasmon Resonances,Free Carrier Densities
更新于2025-09-23 15:19:57
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Arbitrary control of the diffusion potential between a plasmonic metal and a semiconductor by an angstrom-thick interface dipole layer
摘要： Localized surface plasmon resonances (LSPRs) are gaining considerable attention due to the unique far-field and near-field optical properties and applications. Additionally, the Fermi energy, which is the chemical potential, of plasmonic nanoparticles is one of the key properties to control hot-electron and -hole transfer at the interface between plasmonic nanoparticles and a semiconductor. In this article, we tried to control the diffusion potential of the plasmonic system by manipulating the interface dipole. We fabricated solid-state photoelectric conversion devices in which gold nanoparticles (Au-NPs) are located between strontium titanate (SrTiO3) as an electron transfer material and nickel oxide (NiO) as a hole transport material. Lanthanum aluminate as an interface dipole layer was deposited on the atomic layer scale at the three-phase interface of Au-NPs, SrTiO3, and NiO, and the effect was investigated by photoelectric measurements. Importantly, the diffusion potential between the plasmonic metal and a semiconductor can be arbitrarily controlled by the averaged thickness and direction of the interface dipole layer. The insertion of an only one unit cell (uc) interface dipole layer, whose thickness was less than 0.5 nm, dramatically controlled the diffusion potential formed between the plasmonic nanoparticles and surrounding media. This is a new methodology to control the plasmonic potential without applying external stimuli, such as an applied potential or photoirradiation, and without changing the base materials. In particular, it is very beneficial for plasmonic devices in that the interface dipole has the ability not only to decrease but also to increase the open-circuit voltage on the order of several hundreds of millivolts.
关键词： interface dipole,Fermi energy,strontium titanate,nickel oxide,hole transfer,hot-electron,lanthanum aluminate,gold nanoparticles,photoelectric conversion,Localized surface plasmon resonances
更新于2025-09-23 15:19:57
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2D Waveguided Bessel Beam Generated Using Integrated Metasurface-Based Plasmonic Axicon
摘要： Near-field imaging of the propagation of a diffraction-free Bessel-type beam in a guided wave configuration generated by means of a metasurface-based axicon lens integrated on a silicon waveguide is reported. The operation of the axicon lens with a footprint as small as 11μm2 is based on local engineering of the effective index of the silicon waveguide with plasmonic nanoresonators. This generic approach, which can be adapted to different types of planar lightwave circuit platforms, offers the possibility to design nano-engineered optical devices based on the use of plasmonic resonators to control light at the nanoscale.
关键词： Bessel beams,optical metasurfaces,Silicon photonics,surface plasmon resonances,Axicon
更新于2025-09-23 15:19:57
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Properties, fabrication and applications of plasmonic semiconductor nanocrystals
摘要： In semiconductor nanocrystals (NCs), a new regime has been opened in the plasmonic field since the discovery of localized surface plasmon resonances (LSPRs). LSPRs that lead to near-field enhancement, scattering, and resonant absorption around the NC can be tuned in the range from the visible to the near-infrared (NIR) region across a wide optical spectrum by synthetically varying the doping level, and post synthetically via electrochemical control, photochemical control, and chemical oxidation and reduction. In this review, we will focus on the three widely explored and interrelated examples and their manipulation methods of LSPR of (1) hydrogen molybdenum bronze (HxMoO3?y) NCs, (2) hydrogen tungsten bronze (HxWO3?y) NCs, and (3) oxygen vacancy doped molybdenum tungsten oxide (MoxW1?xO3?y) NCs. Finally, a brief outlook on the applications of these plasmonic NCs is presented.
关键词： hydrogen molybdenum bronze,localized surface plasmon resonances,hydrogen tungsten bronze,plasmonic semiconductor nanocrystals,molybdenum tungsten oxide
更新于2025-09-23 15:19:57
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Size- and Surface-Dependent Photoresponses of Solution-Processed Aluminum Nanoparticles
摘要： Plasmonic aluminum nanoparticles have emerged as an exciting new materials platform due to the high natural abundance of aluminum, their ability to be synthesized in the solution phase, and the potential of these materials to be used for photocatalysis and sensing. However, the photothermal properties of solution-processed aluminum nanoparticles, in particular, how phonon energy transfer depends on the particle size and surface properties, are critical for practical applications and are currently unexplored. Here we use transient absorption spectroscopy, in combination with simulations of phonon and thermal energy dissipation, to investigate the photoresponses of aluminum nanoparticles of various diameters (54, 85, 121, and 144 nm) suspended in 2-propanol. Fast thermal-transfer rates to the solvent (170?280 ps) are observed for particles of all sizes and are facilitated by native oxide coverage, as veri?ed by a two-interface thermal energy-transfer model. Size-dependent phonon “breathing”/vibrational modes are also observed as oscillations in the total cross-section. We ?nd that both the oscillation frequency and the damping rate increase as the diameter of the particles decreases. On the basis of the results of ?nite element calculations, we attribute the damping strength and oscillation period observed to a combination of the noncrystalline nature of the native oxide shell and the presence of surface-bound ligands, both of which increase the vibrational mode damping rates relative to bare Al and Al particles with a bare crystalline oxide shell. These insights should guide future work on controlling energy transfer through the use of size and surface tuning in sustainable aluminum nanomaterial systems for applications in catalysis and sensing.
关键词： aluminum,phonons,surface effects,transient absorption,heat transfer,localized surface plasmon resonances
更新于2025-09-23 15:19:57
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Plasmonic coupling in closed-packed ordered gallium nanoparticles
摘要： plasmonic gallium (Ga) nanoparticles (nps) are well known to exhibit good performance in numerous applications such as surface enhanced fluorescence and Raman spectroscopy or biosensing. However, to reach the optimal optical performance, the strength of the localized surface plasmon resonances (LSPRs) must be enhanced particularly by suitable narrowing the NP size distribution among other factors. With this purpose, our last work demonstrated the production of hexagonal ordered arrays of Ga NPs by using templates of aluminium (Al) shallow pit arrays, whose LSPRs were observed in the VIS region. The quantitative analysis of the optical properties by spectroscopic ellipsometry confirmed an outstanding improvement of the LSPR intensity and full width at half maximum (FWHM) due to the imposed ordering. Here, by engineering the template dimensions, and therefore by tuning Ga NPs size, we expand the LSPRs of the Ga NPs to cover a wider range of the electromagnetic spectrum from the UV to the IR regions. More interestingly, the factors that cause this optical performance improvement are studied with the universal plasmon ruler equation, supported with discrete dipole approximation simulations. the results allow us to conclude that the plasmonic coupling between nps originated in the ordered systems is the main cause for the optimized optical response.
关键词： plasmonic coupling,gallium nanoparticles,spectroscopic ellipsometry,discrete dipole approximation,localized surface plasmon resonances
更新于2025-09-19 17:13:59