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Control of plasmon dephasing time using stacked nanogap gold structures for strong near-field enhancement
摘要： The construction of metallic nanostructures with strong near-field enhancement is becoming increasingly significant for the practical use of plasmonic devices, such as plasmonic sensors and light-energy conversion systems. Importantly, the near-field enhancement effect depends on the plasmon dephasing time. Here, we propose a method for controlling plasmon dephasing time by utilizing plasmonic coupling for stronger near-field enhancement. Ordered arrays of stacked nanogap gold (Au) structures composed of a metal/insulator/metal nanostructure were fabricated by electron beam lithography and dry etching processes on a niobium-doped titanium dioxide substrate. The dark plasmon mode was excited by the near-field coupling between the upper and lower Au nanostructures separated by an alumina layer with a thickness of 15 nm. A strong near-field enhancement effect was induced by the localization of the electromagnetic field between the upper and lower Au nanostructures and the longer plasmon dephasing time based on the excitation of the dark plasmon mode. It is noteworthy that the dephasing time of the dark plasmon mode measured by time-resolved photoemission electron microscopy was extended 3-fold compared with that of the plasmon mode of the Au nanoblock, which can be controlled by the structural design of the stacked nanogap Au structures.
关键词： Dark plasmon mode,Plasmon dephasing,Near-field enhancement,Photoemission electron microscopy (PEEM),Surface plasmon resonance
更新于2025-09-23 15:23:52
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Current-induced domain wall oscillations in a nanowire imaged by time-resolved photoemission electron microscopy
摘要： We study reversible domain wall motion in half-ring Ni80Fe20 nanowires on a nanosecond (ns) timescale in a truly current-induced pump-probe experiment using an energy filtered, aberration-corrected photoemission electron microscope. The x-ray magnetic circular dichroism signal is probed at different time delays before, during and after the current pulse in a stroboscopic mode with circularly polarized synchrotron radiation in the energy range of the Fe L3-edge (707 eV). We observe lateral domain wall oscillations with a frequency of ～ 0.4 GHz. Comparing the results to a proposed string model, we find that the domain wall oscillations can be described as string-like asymmetric oscillations.
关键词： Synchrotron radiation,Photoemission electron microscopy,X-ray magnetic circular dichroism,Pump-probe mode
更新于2025-09-23 15:23:52
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Ultrafast Electron Cooling and Decay in Monolayer WS <sub/>2</sub> Revealed by Time- and Energy-Resolved Photoemission Electron Microscopy
摘要： A comprehensive understanding of the ultrafast electron dynamics in two-dimensional transition metal dichalcogenides (TMDs) is necessary for their applications in optoelectronic devices. In this work, we contribute a study of ultrafast electron cooling and decay dynamics in the supported and suspended monolayer WS2 by time- and energy-resolved photoemission electron microscopy (PEEM). Electron cooling in the Q valley of the conduction band is clearly resolved in energy and time, on a timescale of 0.3 ps. Electron decay is mainly via defect trapping process on a timescale of several picoseconds. We observed that the trap states can be produced and increased by laser illumination under ultra-high vacuum, and the higher local optical-field intensity led to the faster increase of trap states. The enhanced defect trapping could significantly modify the carrier dynamics and should be paid attention to in photoemission experiments for two-dimensional materials.
关键词： transition metal dichalcogenides,defect trapping,ultrafast dynamics,energy-resolved,electron cooling,photoemission electron microscopy
更新于2025-09-23 15:21:01
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Manipulation of the dephasing time by strong coupling between localized and propagating surface plasmon modes
摘要： Strong coupling between two resonance modes leads to the formation of new hybrid modes exhibiting disparate characteristics owing to the reversible exchange of information between different uncoupled modes. Here, we realize the strong coupling between the localized surface plasmon resonance and surface plasmon polariton Bloch wave using multilayer nanostructures. An anticrossing behavior with a splitting energy of 144 meV can be observed from the far-field spectra. More importantly, we investigate the near-field properties in both the frequency and time domains using photoemission electron microscopy. In the frequency domain, the near-field spectra visually demonstrate normal-mode splitting and display the extent of coupling. Importantly, the variation of the dephasing time of the hybrid modes against the detuning is observed directly in the time domain. These findings signify the evolution of the dissipation and the exchange of information in plasmonic strong coupling systems and pave the way to manipulate the dephasing time of plasmon modes, which can benefit many applications of plasmonics.
关键词： Surface plasmon polariton Bloch wave,Strong coupling,Dephasing time,Photoemission electron microscopy,Localized surface plasmon resonance
更新于2025-09-23 15:21:01
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Plasmonics of regular shape particles, a simple group theory approach
摘要： A simple hand calculation method based on group theory is proposed to predict the near field maps of finite metallic nanoparticles (MNP) of canonical geometries: prism, cube, hexagon, disk, sphere, etc. corresponding to low order localized surface plasmon resonance excitations. In this article, we report the principles of the group theory approach and demonstrate, through several examples, the general character of the group theory method which can be applied to describe the plasmonic response of particles of finite or infinite symmetry point groups. Experimental validation is achieved by collection of high-resolution subwavelength near-field maps by photoemission electron microscopy (PEEM) on a representative set of Au colloidal particles exhibiting either finite (hexagon) or infinite (disk, sphere) symmetry point groups.
关键词： hexagon,disk,photoemission electron microscopy (PEEM),group theory,sphere,surface plasmon resonance
更新于2025-09-23 15:19:57
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Correlation between Near-Field Enhancement and Dephasing Time in Plasmonic Dimers
摘要： Near-field enhancement and dephasing time play critical roles in several applications of localized surface plasmon resonance. Here, using an example gold dimer system, we reveal the correlation between the near-field enhancement and dephasing time via time-resolved photoemission electron microscopy. Compared with isolated particles, dimers with small gap sizes show stronger near-field enhancement and shorter dephasing times. These results are well reproduced by numerical simulations and further explained by a coupled dipole approximation model. The roles of near- and far-field coupling and plasmon localization in balancing near-field enhancement and dephasing time are also unveiled.
关键词： dephasing time,time-resolved photoemission electron microscopy,near-field enhancement,plasmonic dimers,coupled dipole approximation model
更新于2025-09-23 15:19:57
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Interferometric time- and energy-resolved photoemission electron microscopy for few-femtosecond nanoplasmonic dynamics
摘要： We report a time-resolved normal-incidence photoemission electron microscope with an imaging time-of-flight detector using ～7-fs near-infrared laser pulses and a phase-stabilized interferometer for studying ultrafast nanoplasmonic dynamics via nonlinear photoemission from metallic nanostructures. The interferometer’s stability (35 ± 6 as root-mean-square from 0.2 Hz to 40 kHz) as well as on-line characterization of the driving laser field, which is a requirement for nanoplasmonic near-field reconstruction, is discussed in detail. We observed strong field enhancement and few-femtosecond localized surface plasmon lifetimes at a monolayer of self-assembled gold nanospheres with ～40 nm diameter and ～2 nm interparticle distance. A wide range of plasmon resonance frequencies could be simultaneously detected in the time domain at different nanospheres, which are distinguishable already within the first optical cycle or as close as about ±1 fs around time-zero. Energy-resolved imaging (microspectroscopy) additionally revealed spectral broadening due to strong-field or space charge effects. These results provide a clear path toward visualizing optically excited nanoplasmonic near-fields at ultimate spatiotemporal resolution.
关键词： photoemission electron microscopy,nanoplasmonic dynamics,few-femtosecond,gold nanospheres,time-resolved
更新于2025-09-12 10:27:22
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Solvent influence on the surface morphology of P3HT thin films revealed by photoemission electron microscopy
摘要： Only rigorous understanding of the relationship between the nano-scale morphology of organic thin films and the performance of the devices built from them will ultimately lead to design rules that can guide a structured development on the field of organic electronics. Despite great effort, unraveling the nanoscale structure of the films is still a challenge in itself. Here we demonstrate that photoemission electron microscopy can provide valuable insights into the chain orientation, domains size and grain boundary characteristics of P3HT films spun cast from different solvents at room as well as at elevated temperatures.
关键词： surface morphology,photoemission electron microscopy,organic electronics,solvent influence,P3HT
更新于2025-09-11 14:15:04
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Airy Plasmon Pulses Investigated by Multiphoton Photoemission Electron Microscopy (PEEM)
摘要： Airy wave packets are a special class of non-diffractive solutions to the wave equation which accelerate along a bend trajectory. Their self-healing property makes them particularly interesting for integrated nanophotonic applications. Surface plasmon polaritons (SPPs), in contrast, have the beneficial property to be bound to the two-dimensional surface of a noble metal and enable sub-wavelength confinement. In two dimensions, Airy wave packets are the only non-diffracting solution of the wave equation. The high intrinsic bandwidth of a plasmonic excitation makes it ideal for ultrafast photonics. Photoemission Electron Microscopy (PEEM) represents an ideal tool to deliver images of these processes. The method has been successfully applied by us in the past to investigate the transient behavior of an optical nanoantenna emitting Hankel plasmon pulses. We have used PEEM in combination with a variable wavelength excitation from an optical parametric chirped pulse amplifier system (OPCPA) to experimentally investigate Airy plasmon pulses emitted by an excitation grating. The OPCPA system allows us to experimentally investigate the performance of the excitation in the wavelength range between 670 and 840 nm, where a 3-photon-process is necessary to emit an electron. In this way, we can sample the spectral response which is necessary to determine the ultrafast characteristics of the Airy plasmon pulse. We find that the excitation of stationary Airy plasmons is possible over a large bandwidth. However, the creation of an ultrafast hotspot requires also a matching of the spectral phase which is hard to fulfill in strong dispersing systems. We therefore accompany our measurements with rigorous finite-difference time domain simulations, a suitable nonlinear electron yield model, and analytic calculations to determine the modal purity of the Airy plasmon excitation based on reciprocity. Results support our experimental data and suggest that further improvements of the excitation scheme are necessary to obtain spatio-temporal hotspots.
关键词： PEEM,Surface plasmon polaritons,SPPs,ultrafast photonics,Multiphoton Photoemission Electron Microscopy,Airy plasmon pulses
更新于2025-09-11 14:15:04
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Characterization of ultrafast plasmon dynamics in individual gold bowtie by time-resolved photoemission electron microscopy
摘要： We report on the investigation of ultrafast dynamics of the plasmonic field in individual gold bowtie nanostructure by combining interferometric time-resolved photoemission electron microscopy with a damped harmonic oscillator model. We experimentally obtain different plasmon dephasing times in the tips of the bowtie nanostructure. In the meantime, we demonstrate that the experimental time-resolved photoemission signal can be used to directly compare resonance frequency and dephasing time of different hot spots. In addition, we find that the plasmon field, which is extracted from the photoemission signal, initially oscillates at the laser field frequency, and finally develops into its eigenfrequency after experiencing a few periods of frequency fluctuation due to the competition between forced and autonomous oscillation of the plasmons.
关键词： ultrafast plasmon dynamics,gold bowtie,resonance frequency,plasmon dephasing times,time-resolved photoemission electron microscopy
更新于2025-09-09 09:28:46