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Unidirectional light scattering by up–down Janus dimers composed of gold nanospheres and silicon nanorods
摘要： In this paper, a time-domain finite-difference (FDTD) method is used to simulate the scattering properties of a Janus dimer that a gold nanosphere is putted on the top of a silicon nanorod. We have demonstrated that the Janus dimer exhibits unidirectional scattering in the whole wavelength region of the sunlight. The unidirectionality of the dimer will improve with the height increase of the silicon nanorod and the gap decrease between two adjacent dimers. In our simulation, the forward-to-backward ratio (F/B) of the Janus dimer calculated dividing forward scattering spectra by backward scattering spectra can achieve the maximum of 20 when the height of silicon nanorod is 300 nm. What is more, we have applied the Janus dimers to amorphous silicon thin-film solar cells as antireflection structures. The reflectivity of the solar cells reduces by 39.40% and the short circuit current density improves by 5.04% than those of the reference. Therefore, the Janus dimers has a great application prospect in photovoltaic devices.
关键词： Amorphous silicon solar cells,Janus dimers,Unidirectional scattering,Electric and magnetic dipole resonance
更新于2025-09-23 15:23:52
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Spin density encodes intramolecular singlet exciton fission in pentacene dimers
摘要： The formation of two triplet excitons at the cost of one photon via singlet exciton fission in organic semiconductors can potentially enhance the photocurrent in photovoltaic devices. However, the role of spin density distribution in driving this photophysical process has been unclear until now. Here we present the significance of electronic spin density distribution in facilitating efficient intramolecular singlet exciton fission (iSEF) in π-bridged pentacene dimers. We synthetically modulate the spin density distribution in a series of pentacene dimers using phenyl-, thienyl- and selenyl- flanked diketopyrrolopyrrole (DPP) derivatives as π-bridges. Using femtosecond transient absorption spectroscopy, we find that efficient iSEF is only observed for the phenyl-derivative in ~2.4 ps while absent in the other two dimers. Electronic structure calculations reveal that phenyl-DPP bridge localizes α- and β-spin densities on distinct terminal pentacenes. Upon photoexcitation, a spin exchange mechanism enables iSEF from a singlet state which has an innate triplet pair character.
关键词： spin density,pentacene dimers,charge resonance,intramolecular,singlet exciton fission
更新于2025-09-23 15:23:52
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Dynamics of interatomic Coulombic decay in neon dimers by XUV-pump–XUV-probe spectroscopy
摘要： We apply the Monte Carlo wave-packet approach to study the interatomic Coulombic decay (ICD) dynamics of neon dimers after removing a 2s electron from one of the Ne atoms by one-photon absorption from an XUV pulse. This method reproduces well both the lifetime for the 2s inner-valence vacancy in Ne2+(2s?1) and the kinetic energy release (KER) spectra for the coincident Ne+ and Ne2+ fragments following triple ionization, i.e., two photoionizations and one ionization via ICD, of Ne2 measured in an XUV-pump–XUV-probe experiment [K. Schnorr et al., Phys. Rev. Lett. 111, 093402 (2013)]. Comparisons between the calculated and measured nuclear KER spectra give physical insights in the considered process. For example, an analysis of the ratios between the low- and high-energy peaks in the nuclear KER spectra for large delays provides an estimate of the photoionization cross sections for removing a 2p electron from the excited states in Ne2+(2s?1). Such comparisons also allow an estimate for the ICD rates for the 2s inner-valence vacancy in the single-site two-hole state in Ne2+(2s?12p?1). Finally, the influence of photon statistics of the free electron laser pulses on the nuclear KER spectra is considered.
关键词： neon dimers,interatomic Coulombic decay,kinetic energy release spectra,XUV-pump–XUV-probe spectroscopy,Monte Carlo wave-packet approach
更新于2025-09-23 15:23:52
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Photothermal-Assisted Optical Stretching of Gold Nanoparticles
摘要： The synergy of photothermal energy and optical forces generated by tightly focused laser beams can be used to transform the shape of gold nanoparticles. Here, the combination of these two effects is demonstrated to be an effective way of elongating gold nanoparticles (Au NPs), massively tuning their plasmonic properties. The photothermal effect of the laser increases the temperature of Au NPs above the melting point, and optical forces deform the molten Au NPs. As a result, the shape of Au NPs transforms from nanospheres into nanorods or dimers, depending on the power and time of irradiation as well as the surface energy of the substrate. This process is reversible by using high laser power to transform nanorods back to nanospheres due to capillary dewetting. Such light-induced transformations of nanostructures not only provide a facile way to tune plasmon resonances but also shed light on how the synergistic effect of photothermal energy and optical forces works on plasmonic nanoparticles.
关键词： rods,films,dimers,optical forces,plasmons
更新于2025-09-23 15:21:21
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Riboflavin-induced Type 1 photo-oxidation of tryptophan using a high intensity 365 nm light emitting diode
摘要： The mechanism of photo-oxidation of tryptophan (Trp) sensitized by riboflavin (RF) was examined employing high concentrations of Trp and RF, with a high intensity 365 nm light emitting diode (LED) source under N2, 20% and 100% O2 atmospheres. Dimerization of Trp was a major pathway under the N2 atmosphere, though this occurred with a low yield (DφTrp = 5.9 x 10-3), probably as a result of extensive back electron transfer reactions between RF●- and Trp(H)●+. The presence of O2 decreased the extent of this back electron transfer reaction, and the extent of Trp dimerization. This difference is attributed to the formation of O2●- (generated via electron transfer from RF●- to O2) which reacts rapidly with Trp● leading to extensive consumption of the parent amino acid and formation of peroxides and multiple other oxygenated products (N-formylkynurenine, alcohols, diols) of Trp, as detected by LC-MS. Thus, it appears that the first step of the Type 1 mechanism of Trp photo-oxidation, induced by this high intensity 365 nm light source, is an electron transfer reaction between the amino acid and 3RF, with the presence of O2 modulating the subsequent reactions and the products formed, as a result of O2●- formation. These data have potential biological significance as LED systems and RF-based treatments have been proposed for the treatment of pathological myopia and keratitis.
关键词： type 1/type 2 mechanisms,dimers,LED,N-formylkynurenine,trimers,riboflavin,photo-oxidation,electron transfer,photobleaching,tryptophan,triplet excited state
更新于2025-09-23 15:21:21
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Dark Plasmon Modes in Symmetric Gold Nanoparticle Dimers Illuminated by Focused Cylindrical Vector Beams
摘要： The plasmon hybridization model of electromagnetic coupling between plasmonic nanoparticles predicts the formation of lower energy “bonding” and higher energy “antibonding” modes in analogy with the quantum mechanical description of chemical bonding. For a symmetric metallic nanoparticle dimer excited by linearly polarized light, the hybridization picture predicts that in-phase coupling of the dipole moments is optically allowed, creating bright “modes”, whereas the out-of-phase coupling is dark due to the cancellation of the oppositely oriented dipole moments (in the quasistatic approximation). These bright modes are electric dipolar in nature and readily couple to scalar (i.e., linearly or circularly polarized) beams of light. We show that focused cylindrical vector beams, specifically azimuthally and radially polarized beams, directly excite dark plasmon modes in symmetric gold nanoparticle (AuNP) dimers at normal incidence. We use single-particle spectroscopy and electrodynamics simulations to study the resonance scattering of AuNP dimers illuminated by azimuthally and radially polarized light. The electric field distributions of the focused azimuthal or radial beams are locally polarized perpendicular or parallel to the AuNP dimer axis, but with opposite directions at each particle. Therefore, the associated combinations of single-particle dipole moments are out-of-phase, and the excitation (resonance) is of so-called “dark modes”. In addition, multipole expansion of the fields associated with each scattering spectrum shows that the vector beam excitation involves driving multipolar, e.g., magnetic dipolar and electric quadrupolar, modes, and that they even dominate the scattering spectra (vs electric dipole). This work opens new opportunities for investigating dark plasmon modes in nanostructures, which are difficult to selectively excite by conventional polarized light.
关键词： electrodynamics simulations,dark plasmon modes,plasmon hybridization,single-particle spectroscopy,gold nanoparticle dimers,cylindrical vector beams
更新于2025-09-23 15:21:21
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Plasmonics || Plasmonic Modes in Au and AuAg Nanowires and Nanowire Dimers Studied by Electron Energy Loss Spectroscopy
摘要： In this chapter, we review our recent work on the investigation of surface plasmon modes in metallic nanowires and nanowire dimers by means of electron energy loss spectroscopy combined with scanning transmission electron microscopy (STEM-EELS). Due to the very high spatial resolution, STEM-EELS is a powerful technique to visualize multipole order surface plasmon modes in nanowires and study the dependency of their resonance energies on different parameters such as nanowire dimensions or nanowire porosity. In addition, we investigate surface plasmon hybridization in nanowires separated by gaps of less than 10 nm or connected by small metallic bridges. In such structures new modes arise, which depend strongly on gap or bridge sizes. Experimental results are supported by finite element simulations. The investigated nanowires and dimers are fabricated by electrodeposition in etched ion-track templates, combined with a selective dissolution processes. The synthesis techniques and their advantages for the fabrication of plasmonic nanostructures are also discussed.
关键词： nanowire dimers,scanning transmission electron microscopy,ion-track technology,electron energy loss spectroscopy,nanogaps,nanowires,electrodeposition,plasmon hybridization,etched ion-track membranes,surface plasmons,gold
更新于2025-09-23 15:21:01
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Color Routing via Cross-Polarized Detuned Plasmonic Nanoantennas in Large Area Metasurfaces
摘要： Bidirectional nanoantennas are of key relevance for advanced functionalities to be implemented at the nanoscale, and in particular for color routing in an ultracompact flat-optics configuration. Here we demonstrate a novel approach avoiding complex collective geometries and/or restrictive morphological parameters, based on cross-polarized detuned plasmonic nanoantennas in a uniaxial (quasi-1D) bimetallic configuration. The nanofabrication of such a flat-optics system is controlled over a large-area (cm2) by a novel self-organized technique exploiting ion-induced nanoscale wrinkling instability on glass templates to engineer tilted bimetallic nanostrip dimers. These nanoantennas feature broadband color routing with superior light scattering directivity figures, which are well described by numerical simulations and turn out to be competitive with the response of lithographic nanoantennas. These results demonstrate that our large-area self-organized metasurfaces can be implemented in real world applications of flat optics color routing from telecom photonics to optical nanosensing.
关键词： Tilted Nanostrips,Flat-Optics,Plasmonic Dimers,Plasmonic metasurfaces,Color Routing,Self-organized Nanoantennas
更新于2025-09-23 15:21:01
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Chlorinated Fullerene Dimers for Interfacial Engineering Toward Stable Planar Perovskite Solar Cells with 22.3% Efficiency
摘要： A major limit for planar perovskite solar cells is the trap-mediated hysteresis and instability, due to the defective metal oxide interface with the perovskite layer. Passivation engineering with fullerenes has been identified as an effective approach to modify this interface. The rational design of fullerene molecules with exceptional electrical properties and versatile chemical moieties for targeted defect passivation is therefore highly demanded. In this work, novel fulleropyrrolidine (NMBF-X, X=H or Cl) monomers and dimers are synthesized and incorporated between metal oxides (i.e. TiO2, SnO2) and perovskites (i.e. MAPbI3 and (FAPbI3)x(MAPbBr3)1-x). The fullerene dimers provide superior stability and efficiency improvements compared to the corresponding monomers, with chlorinated fullerene dimers being most effective at coordinating with both metal oxides and perovskite via the chlorine terminals. The non-encapsulated planar device delivers a maximum power conversion efficiency of 22.3% without any hysteresis, while maintaining over 98% of initial efficiency after ambient storage for 1000 h, and exhibiting an order of magnitude improvement of the T80 lifetime.
关键词： stability,perovskite solar cells,fullerene dimers,interfacial engineering
更新于2025-09-23 15:19:57
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Self-Organized Conductive Gratings of Au Nanostripe Dimers Enable Tunable Plasmonic Activity
摘要： Plasmonic metasurfaces based on quasi-one-dimensional (1D) nanostripe arrays are homogeneously prepared over large-area substrates (cm2), exploiting a novel self-organized nanofabrication method. Glass templates are nanopatterned by ion beam-induced anisotropic nanoscale wrinkling, enabling the maskless con?nement of quasi-1D arrays of out-of-plane tilted gold nanostripes, behaving as transparent wire-grid polarizer nanoelectrodes. These templates enable the dichroic excitation of localized surface plasmon resonances, easily tunable over a broadband spectrum from the visible to the near- and mid-infrared, by tailoring the nanostripes’ shape and/or changing the illumination conditions. The controlled self-organized method allows the engineering of the nanoantennas’ morphology in the form of Au-SiO2-Au nanostripe dimers, which show hybridized plasmonic resonances with enhanced tunability. Under this condition, superior near-?eld ampli?cation is achievable for the excitation of the hybridized magnetic dipole mode, as pointed out by numerical simulations. The high e?ciency of these plasmonic nanoantennas, combined with the controlled tuning of the resonant response, opens a variety of applications for these cost-e?ective templates, ranging from biosensing and optical spectroscopies to high-resolution molecular imaging and nonlinear optics.
关键词： biosensing,plasmon hybridization,nanostripe dimers,self-organized nanoantennas,transparent nanoelectrodes,large-area metasurfaces,wire-grid polarizers
更新于2025-09-23 15:19:57