Browsing by Author "Yang, Jinghuan"

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Control of plasmon dephasing time using stacked nanogap gold structures for strong near-field enhancement
(2019-03-01)
Ueno, Kosei
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Yang, Jinghuan
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Sun, Quan
;
Aoyo, Daisuke
;
Yu, Han
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. (C) 2018 Elsevier Ltd. All rights reserved.
Engineering Ultrafast Carrier Dynamics at the Graphene/GaAs Interface by Bulk Doping Level
(2019-10-01)
Yang, Jinghuan
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Sun, Quan
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Liu, Wei
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Zhang, Zhibin
;
Hu, Xiaoyong
Carrier dynamics, the most fundamental process in electronics and optoelectronics, has drawn great attentions owing to its crucial role in property engineering of materials. Exploration and regulation of carrier dynamics are essential for designing devices with specific functions and optimizing their performances. However, the lack of conventional tools with simultaneous ultrafast temporal and ultrasmall spatial resolution has impeded direct observation and manipulation of carrier dynamics at both the femtosecond and nanometer scale. In this study, the direct observation and modulation of ultrafast carrier dynamics at the graphene/gallium arsenide (GaAs) interface is achieved by tuning the doping level of bulk GaAs. This successful characterization is performed using advanced in situ photoemission electron microscopy combined with the ultrafast pump-probe technique. It is found that a change in the doping level in GaAs can change its band bending and switch the hot-carrier transfer direction at the graphene/GaAs interface with a lifetime reduction of nearly six times. This work paves the way of engineering ultrafast carrier dynamics at 2D interfaces by modifying the 3D bulk properties, and also provides a platform for fundamental studies of ultrafast physics with high spatial resolution.
Exotic Mode Suppression in Plasmonic Heterotrimer System
(2019-01-17)
Song, Hanfa
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Sun, Quan
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Li, Jie
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Yang, Fan
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Yang, Jinghuan
We investigate the far- and near-field properties of plasmonic heterotrimers with small detuning of the eigenfrequency numerically, theoretically, and experimentally. In our simulations, we find that the dipolar mode of the middle nanorod in the trimer system is greatly suppressed in both far and near fields. This phenomenon is confirmed by our subsequent experiments. The far-field suppression can be interpreted by the destructive interference due to the antiphase dipolar response of the respective nanorod. To deeply understand the underlying physics, an analytical model considering both the near-field-mediated direct coupling and radiative-field-mediated indirect coupling is adopted. We determine that the radiative field coupling, which is stronger in the trimer system with a smaller detuning, plays an essential role in mode suppression in the near field. Our work will provide new thoughts on the fundamental mechanisms of plasmon coupling and plasmon-based applications.
Exploring the Near-Field of Strongly Coupled Waveguide-Plasmon Modes by Plasmon-Induced Photocurrent Generation Using a Gold Nanograting-Loaded Titanium Dioxide Photoelectrode
(2017-10-05)
Guo, Jingchun
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Ueno, Kosei
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Yang, Jinghuan
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Shi, Xu
;
Li, Jie
Near-field spectrum measurement techniques, including near-field scanning optical microscopy, electron energy loss spectroscopy, and multiphoton photoemission electron microscopy, are powerful means to investigate near-field interactions directly on closely spaced metallic nanoparticles or a metallic nanostructure coupled with optical modes, such as whispering gallery mode and waveguide mode, which are called coupled plasmonic systems. In the present study, we have successfully measured the near-field spectra of coupled plasmonic systems using a simple photoelectrochemical measurement based on plasmon-induced water oxidation. Coupling was explored between the localized surface plasmon resonance (LSPR.) mode and waveguide mode of periodic gold nanogratings patterned on a thin titanium dioxide waveguide film. It is known that the far-field reflection spectrum of this waveguide-LSPR coupling system shows a complicated shape with multiple peaks, and the coupling has been explored by numerical electromagnetic simulations so far. However, in this study, it was clearly elucidated that an internal quantum efficiency (IQE) spectrum observed in the plasmon-induced photocurrent generation has successfully reproduced the near-field spectrum predicted by electromagnetic simulations under the coupling conditions. The photocurrent generation based on the plasmon-induced charge separation is due to the near-field effect, and it can be considered that the IQE spectrum corresponds to the near-field spectrum. This study paves a new way to indirectly measure the near-field spectrum of plasmonic systems.
Manipulation of the dephasing time by strong coupling between localized and propagating surface plasmon modes
(2018-11-19)
Yang, Jinghuan
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Sun, Quan
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Ueno, Kosei
;
Shi, Xu
;
Oshikiri, Tomoya
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.
Near-field spectral properties of coupled plasmonic nanoparticle arrays
(2017-03-20)
Yu, Han
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Sun, Quan
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Yang, Jinghuan
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Ueno, Kosei
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Oshikiri, Tomoya
We investigated the grating effect in complex gold dolmen structures, in which multiple plasmon modes are present due to plasmon hybridization, experimentally from both the far field and the near field. In particular, the near-field properties were investigated using photoemission electron microscopy, and it was demonstrated that two hybridized plasmon modes on the dolmen structures could be influenced by the grating effect. For comparison, we also investigated the grating effect in arrays of simple nanoblocks and heptamer structures, which were supposed to support a strong bright plasmon mode and a strong dark plasmon mode, respectively, in the near field. We found that the spectral responses of the two hybridized modes on the dolmen structures as the pitch size changed evolved in a manner similar to that of the bright dipole mode on the nanoblocks, whereas the dark mode on the heptamer structures is less sensitive to the pitch size. (C) 2017 Optical Society of America
Spatial evolution of the near-field distribution on planar gold nanoparticles with the excitation wavelength across dipole and quadrupole modes
(2017-06-01)
Yang, Jinghuan
;
Sun, Quan
;
Yu, Han
;
Ueno, Kosei
;
Misawa, Hiroaki
We investigate the superposition properties of the dipole and quadrupole plasmon modes in the near field both experimentally, by using photoemission electron microscopy (PEEM), and theoretically. In particular, the asymmetric near-field distributions on gold (Au) nanodisks and nanoblocks under oblique incidence with different polarizations are investigated in detail. The results of PEEM measurements show that the evolutions of the asymmetric near-field distributions are different between the excitation with s-polarized and p-polarized light. The experimental results can be reproduced very well by numerical simulations and interpreted as the superposition of the dipole and quadrupole modes with the help of analytic calculations. Moreover, we hypothesize that the electrons collected by PEEM are mainly from the plasmonic hot spots located at the plane in the interface between the Au particles and the substrate in the PEEM experiments. (C) 2017 Chinese Laser Press