We studied the near-field properties of localized surface plasmon resonances in finite linear gold nanochains using photoemission electron microscopy(PEEM).The localization of the electromagnetic field in the near-fie...We studied the near-field properties of localized surface plasmon resonances in finite linear gold nanochains using photoemission electron microscopy(PEEM).The localization of the electromagnetic field in the near-field region was mapped at high spatial resolution.By tuning the excitation laser wavelength,we can obtain the near-field spectra,from which the energy splitting between longitudinal(L)and transverse(T)plasmon modes can be revealed.In particular,the L-mode red shifts and the T-mode blue shifts with increasing chain length.The red shift of the L-mode is highly dependent on the gap distance.In contrast,the T-mode almost remains constant within the range of gap distance we investigated.This energy splitting between the L-mode and the T-mode of metallic chains is in agreement with previous far-field measurements,where it was explained by dipole-dipole near-field coupling.Here,we provide direct proof of this near-field plasmon coupling in nanochains via the above-described near-field measurements using PEEM.In addition,we explore the energy transport along the gold nanochains under excitation at oblique illumination via PEEM measurements together with numerical simulations.展开更多
Two-dimensional (2D) periodic TiO2 pillar arrays, applicable to photonic crystals and micro-channels, were fabricated by direct patterning of a TiO2-organic hybrid material by multi-beam laser interference lithography...Two-dimensional (2D) periodic TiO2 pillar arrays, applicable to photonic crystals and micro-channels, were fabricated by direct patterning of a TiO2-organic hybrid material by multi-beam laser interference lithography and calcination of hybrid patterns. 2D periodic pillars of a TiO2– organic hybrid material were prepared by irra-diation with the interference pattern of femto-second laser beams and removal of the non- irradiated portions. Two types of periodic pillar arrays, standing pillars and top-gathering pillars (four pillars gathered at the top), were obtained, depending on laser irradiation conditions. After calcination of TiO2–organic hybrid pillars, TiO2 pillar arrays were obtained without collapse.展开更多
The near infrared (NIR) fluorescence enhancement by local surface plasmon resonanoce from arrayed gold (Au) nanoblocks was investigated by NIR fluorescent dyes, IR780, immobilized in hydrophobic DNA thin film on glass...The near infrared (NIR) fluorescence enhancement by local surface plasmon resonanoce from arrayed gold (Au) nanoblocks was investigated by NIR fluorescent dyes, IR780, immobilized in hydrophobic DNA thin film on glass substrates, to clarify the gap mode effect on the fluorescence enhancement. In the substrate with Dimer type Au nanoblock arrangement, average total fluorescence intensity was larger by 10.0, 2.4, and 12.4 times for non-polarized, P- and S- polarization as compared with that on a glass substrate alone, respectively. These findings suggested that enhancement of excitation light intensity at nanogap in the Dimer type Au nanoblock arrangement affected the fluorescence intensity. Average total fluorescence intensity, on the other hand, was smaller by 0.63 times as compared with that on a glass substrate alone in the checkerboard type Au array. It is suggested that the fluorescence quenching was caused by the energy transfer from the excited state of IR780 to Au nanoblocks or by the increased deactivation of excited dye molecules induced by resonance with Au nanoblocks at the checkerboard arrangement. We have firstly achieved the NIR fluorescence enhancement by LSPR due to the gap mode.展开更多
Localized surface plasmon resonance(LSPR)can be supported by metallic nanoparticles and engineered nanostructures.An understanding of the spatially resolved near-field properties and dynamics of LSPR is important,but ...Localized surface plasmon resonance(LSPR)can be supported by metallic nanoparticles and engineered nanostructures.An understanding of the spatially resolved near-field properties and dynamics of LSPR is important,but remains experimentally challenging.We report experimental studies toward this aim using photoemission electron microscopy(PEEM)with high spatial resolution of sub-10 nm.Various engineered gold nanostructure arrays(such as rods,nanodisk-like particles and dimers)are investigated via PEEM using near-infrared(NIR)femtosecond laser pulses as the excitation source.When the LSPR wavelengths overlap the spectrum of the femtosecond pulses,the LSPR is efficiently excited and promotes multiphoton photoemission,which is correlated with the local intensity of the metallic nanoparticles in the near field.Thus,the local field distribution of the LSPR on different Au nanostructures can be directly explored and discussed using the PEEM images.In addition,the dynamics of the LSPR is studied by combining interferometric time-resolved pump-probe technique and PEEM.Detailed information on the oscillation and dephasing of the LSPR field can be obtained.The results identify PEEM as a powerful tool for accessing the near-field mapping and dynamic properties of plasmonic nanostructures.展开更多
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 asy...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.展开更多
The THz generation efficiency and the plasma density generated by a filament in air have been found anti-correlated when pumped by 800 nm+1600 nm two-color laser field.The plasma density near zero delay of two laser p...The THz generation efficiency and the plasma density generated by a filament in air have been found anti-correlated when pumped by 800 nm+1600 nm two-color laser field.The plasma density near zero delay of two laser pulses has a minimum value,which is opposite to the trend of THz generation eficiency and contradicts common sense.The lower plasma density cannot be explained by the static tunneling model according to the conventional photocurrent model,but it might be attributed to the electron trapping by the excited states of nitrogen molecule.The present work also clarifies the dominant role of the drifting velocity accelerated by the two-color laser field during the THz pulse generation process.The results promote our understanding on the optimization of the THz generation efficiency by the two-color laser filamentation.展开更多
We experimentally verify that surface plasmon （SP） enhances the photoluminescence （PL） of visible light from Tb3＋-doped 60SiO2-20Al2O3-20CaF2：0.3Tb3＋, 20Yb3＋ glass ceramics by using electron beam lithog- raphy...We experimentally verify that surface plasmon （SP） enhances the photoluminescence （PL） of visible light from Tb3＋-doped 60SiO2-20Al2O3-20CaF2：0.3Tb3＋, 20Yb3＋ glass ceramics by using electron beam lithog- raphy to fabricate silver nanoparticles on the surface of the glass ceramics. Numerical calculation for the SP enhancement spectroscopy is achieved by using the finite-difference time-domain algorithm. A PL enhancement of Tb3＋ by as much as 1.6 times is observed. The PL enhancement is mainly due to the coupling of excitation from 7F6 to 5D4 transition dipole of Tb3＋ ion with SP mode induced from the silver nanoparticles.展开更多
基金Grants-in-Aid for Scientific Research(Grant Nos.JP18H05205,JP17H01041,JP17H05245,and JP17H05459)We acknowledge the support from the Nanotechnology Platform(Hokkaido University)and Dynamic Alliance for Open Innovation Bridging Human,Environment and Materials(Five-Star Alliance)of MEXT.QSun also acknowledges the support from the National Natural Science Foundation of China(NSFC)(No.11527901).
文摘We studied the near-field properties of localized surface plasmon resonances in finite linear gold nanochains using photoemission electron microscopy(PEEM).The localization of the electromagnetic field in the near-field region was mapped at high spatial resolution.By tuning the excitation laser wavelength,we can obtain the near-field spectra,from which the energy splitting between longitudinal(L)and transverse(T)plasmon modes can be revealed.In particular,the L-mode red shifts and the T-mode blue shifts with increasing chain length.The red shift of the L-mode is highly dependent on the gap distance.In contrast,the T-mode almost remains constant within the range of gap distance we investigated.This energy splitting between the L-mode and the T-mode of metallic chains is in agreement with previous far-field measurements,where it was explained by dipole-dipole near-field coupling.Here,we provide direct proof of this near-field plasmon coupling in nanochains via the above-described near-field measurements using PEEM.In addition,we explore the energy transport along the gold nanochains under excitation at oblique illumination via PEEM measurements together with numerical simulations.
文摘Two-dimensional (2D) periodic TiO2 pillar arrays, applicable to photonic crystals and micro-channels, were fabricated by direct patterning of a TiO2-organic hybrid material by multi-beam laser interference lithography and calcination of hybrid patterns. 2D periodic pillars of a TiO2– organic hybrid material were prepared by irra-diation with the interference pattern of femto-second laser beams and removal of the non- irradiated portions. Two types of periodic pillar arrays, standing pillars and top-gathering pillars (four pillars gathered at the top), were obtained, depending on laser irradiation conditions. After calcination of TiO2–organic hybrid pillars, TiO2 pillar arrays were obtained without collapse.
文摘The near infrared (NIR) fluorescence enhancement by local surface plasmon resonanoce from arrayed gold (Au) nanoblocks was investigated by NIR fluorescent dyes, IR780, immobilized in hydrophobic DNA thin film on glass substrates, to clarify the gap mode effect on the fluorescence enhancement. In the substrate with Dimer type Au nanoblock arrangement, average total fluorescence intensity was larger by 10.0, 2.4, and 12.4 times for non-polarized, P- and S- polarization as compared with that on a glass substrate alone, respectively. These findings suggested that enhancement of excitation light intensity at nanogap in the Dimer type Au nanoblock arrangement affected the fluorescence intensity. Average total fluorescence intensity, on the other hand, was smaller by 0.63 times as compared with that on a glass substrate alone in the checkerboard type Au array. It is suggested that the fluorescence quenching was caused by the energy transfer from the excited state of IR780 to Au nanoblocks or by the increased deactivation of excited dye molecules induced by resonance with Au nanoblocks at the checkerboard arrangement. We have firstly achieved the NIR fluorescence enhancement by LSPR due to the gap mode.
基金This study was supported by funding from the Ministry of Education,Culture,Sports,Science,and Technology of Japan:KAKENHI Grant-in-Aid for Scientific Research No.23225006,Nanotechnology Platform(Hokkaido University)and the Low-Carbon Research Network of Japan.
文摘Localized surface plasmon resonance(LSPR)can be supported by metallic nanoparticles and engineered nanostructures.An understanding of the spatially resolved near-field properties and dynamics of LSPR is important,but remains experimentally challenging.We report experimental studies toward this aim using photoemission electron microscopy(PEEM)with high spatial resolution of sub-10 nm.Various engineered gold nanostructure arrays(such as rods,nanodisk-like particles and dimers)are investigated via PEEM using near-infrared(NIR)femtosecond laser pulses as the excitation source.When the LSPR wavelengths overlap the spectrum of the femtosecond pulses,the LSPR is efficiently excited and promotes multiphoton photoemission,which is correlated with the local intensity of the metallic nanoparticles in the near field.Thus,the local field distribution of the LSPR on different Au nanostructures can be directly explored and discussed using the PEEM images.In addition,the dynamics of the LSPR is studied by combining interferometric time-resolved pump-probe technique and PEEM.Detailed information on the oscillation and dephasing of the LSPR field can be obtained.The results identify PEEM as a powerful tool for accessing the near-field mapping and dynamic properties of plasmonic nanostructures.
基金Japan Society for the Promotion of Science(JSPS)(JP15H00856,JP15H01073,JP15K04589,JP23225006,JP26870014)National Natural Science Foundation of China(NSFC)(11527901)
文摘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.
基金supported by the National Key R&D Program of China(2018YFB0504400)the National Natural Science Foundation of China(12061131010 and 12074198)+1 种基金the Russian Science Foundation(21-49-00023)the Natural Science Foundation of Tianjin Municipality(20JCYBJCO1040).
文摘The THz generation efficiency and the plasma density generated by a filament in air have been found anti-correlated when pumped by 800 nm+1600 nm two-color laser field.The plasma density near zero delay of two laser pulses has a minimum value,which is opposite to the trend of THz generation eficiency and contradicts common sense.The lower plasma density cannot be explained by the static tunneling model according to the conventional photocurrent model,but it might be attributed to the electron trapping by the excited states of nitrogen molecule.The present work also clarifies the dominant role of the drifting velocity accelerated by the two-color laser field during the THz pulse generation process.The results promote our understanding on the optimization of the THz generation efficiency by the two-color laser filamentation.
基金supported by the National Natural Science Foundation of China (Nos. 50672087, 50872123,and 50802083)the Natural Science Foundation of Zhejiang province in China (No. Y1110499)+2 种基金H. Misawaalso acknowledges funding from the Ministry of Education, Culture, Sports, Science, and Technology of JapanKAKENHI Grants-in-Aid (No. 19049001)a Grant-in-Aid from Hokkaido Innovation through Nano Technology Support
文摘We experimentally verify that surface plasmon （SP） enhances the photoluminescence （PL） of visible light from Tb3＋-doped 60SiO2-20Al2O3-20CaF2：0.3Tb3＋, 20Yb3＋ glass ceramics by using electron beam lithog- raphy to fabricate silver nanoparticles on the surface of the glass ceramics. Numerical calculation for the SP enhancement spectroscopy is achieved by using the finite-difference time-domain algorithm. A PL enhancement of Tb3＋ by as much as 1.6 times is observed. The PL enhancement is mainly due to the coupling of excitation from 7F6 to 5D4 transition dipole of Tb3＋ ion with SP mode induced from the silver nanoparticles.
