Fracture Analysis and Fatigue Strength Calculation of Anchor Bolt Used in Circulating Water Pump in Nuclear Power Plant.

A circulating water pump is a key equipment of cooling systems in nuclear power plants. Several anchor bolts were broken at the inlet rings of the same type of pumps. The bolts were turned by a special material for seawater corrosion protection. There were obvious turning tool marks at the root of the thread, which was considered as the source of the crack. The fatigue crack extended to the depth of the bolt, causing obvious radiation stripes on the fracture surface, which was a typical fatigue fracture. Obvious overtightening characteristics were found at the head of the broken bolt. Fracture and energy spectrum analysis showed that the bolt was not corroded. The axial vibration of the pump was measured. The static tensile stress along the bolt axis caused by the preload, the axial tensile stress caused by the axial vibration, and the torsional stress were calculated, respectively. According to the fatigue strength theory, the composite safety factor of the bolt fatigue strength was 1.37 when overtightening at 1.2 times the design torque, which was less than the allowable safety factor of 1.5-1.8, so the bolt was not safe, which further verified the conclusion of fracture analysis. The reason for the low safety factor was caused by the overtightening force. The improvement method was to control the bolt preload or increasing the bolt diameter.

Extrinsic Chirality by Interference between Two Plasmonic Modes on an Achiral Rectangular Nanostructure.

The optical near field (NF) induced by circularly polarized light (CPL) is a hot scientific topic. We observed a chiral NF intensity distribution on a series of achiral gold nanorectangular structures (Au-NRs) under CPL irradiation by using multiphoton photoemission electron microscopy (MP-PEEM). Additionally, the differential NF spectra under left and right CPL irradiation, which represent the asymmetry of the NF intensity distribution, were investigated. We propose an interpretation that the chiral NF intensity distribution on an achiral metallic nanostructure is extrinsically generated by the interference between two plasmonic modes by combining state-of-the-art MP-PEEM techniques and the classical oscillator model. Our interpretation well explains both the experimental and simulation results. Furthermore, the intensity of the NF and its phase angle of each mode under linearly polarized light irradiation were revealed to be critical factors for the generation of extrinsic chirality in the NF intensity distribution.

Revealing the Chiroptical Response of Plasmonic Nanostructures at the Nanofemto Scale.

The spatiotemporal origin of plasmonic chiroptical responses in nanostructures remains unexplored and unclear. Here, two orthogonally oriented Au nanorods as a prototype were investigated, with a giant chiroptical response caused by antisymmetric and symmetric mode excitations for obliquely incident left-handed circular polarization (LCP) and right-handed circular polarization (RCP) light. Time-resolved photoemission electron microscopy (PEEM) was employed to measure the near-field spatial distributions, spectra, and spatiotemporal dynamics of plasmonic modes associated with the chiroptical responses at the nanofemto scale, verifying the characteristic near-field distributions at the resonant wavelengths of the two modes and a very large spectral dichroism for LCP and RCP. More importantly, eigenmode excitations and their contributions to the ultrafast plasmonic chiroptical response in the space-time domain were directly revealed, promoting a full understanding of the ultrafast chiral origin in complex nanostructures. These findings open a way to design chiroptical nanophotonic devices for spatiotemporal control of chiral light-matter interactions.

Near-field engineering for boosting the photoelectrochemical activity to a modal strong coupling structure.

Near-field engineering is considered a significant strategy in constructing plasmonic nanostructures for efficient plasmonic chemistry. We demonstrate interfacial near-field engineering on a Au-NP/TiO2/Au-film (ATA) photoanode to improve the water oxidation efficiency. To tailor the near-field distribution, postdeposited Au on an ATA electrode (Au@ATA) is implemented using a facile constant potential electrolysis technique. As a result, the average photocurrent conversion efficiency of Au@ATA is approximately 1.3-fold higher than that of ATA.

Plasmon-induced electron injection into the large negative potential conduction band of Ga2O3 for coupling with water oxidation.

In this study, an interfacial modification layer was applied to improve the plasmon-induced light energy conversion of a gallium(iii) oxide (Ga2O3) photoelectrode, which possesses a much more negative conduction band potential compared with the reduction potential of photons to hydrogen. The plasmon-induced photocurrent generation under visible light irradiation was observed with Au nanoparticle-loaded Ga2O3 (Au-NPs/Ga2O3). An interfacial modification was carried out by depositing a titanium dioxide (TiO2) thin-film layer on Au-NPs/Ga2O3via atomic layer deposition. Since the surface states of TiO2 possess excellent hole-trapping ability, this interfacial modification remarkably improved the generation of plasmon-induced photocurrent in the visible region. The photoelectric conversion efficiency of interfacially modified Au-NPs/Ga2O3 showed a TiO2 thin-film thickness dependence because the migration of hot carriers was suppressed with increasing TiO2 thickness. The Au-NPs/Ga2O3 photoelectrode modified with 2 nm-thick TiO2 showed the best photoelectric conversion performance, and the thermodynamic energy conversion efficiency under irradiation with 600 nm light was approximately two times larger than that of the Au-NPs/TiO2-thin film due to the extremely negative onset potential of Au-NPs/Ga2O3 with TiO2. Therefore, the plasmonic Ga2O3 photoanode with the interfacial TiO2 modification could provide both a high reduction ability for H2 evolution and an oxidation ability for water oxidation, because of the negative conduction band of Ga2O3 and the hole-trapping property from TiO2, respectively.

Ultrafast photoemission electron microscopy: Capability and potential in probing plasmonic nanostructures from multiple domains.

The near-field properties and dynamics of plasmonic nanostructures play a crucial role in several fundamental concepts in physics and chemistry, and they are widely relevant in plasmonic applications. Ultrafast photoemission electron microscopy (PEEM) is a novel approach that has been widely applied to probe plasmonic nanostructures from multiple domains. Furthermore, PEEM is the only technique that provides nanometer spatial resolution, sub-femtosecond temporal resolution, and tens to hundreds of millielectron volt energy resolution. This allows for extremely sensitive observations of plasmonic field oscillations, field dephasing, and hot electrons. This Perspective provides a brief overview of the basic principles and main applications of ultrafast PEEM. The research progress of ultrafast PEEM in plasmonics is highlighted from three points of view: near-field imaging, near-field spectroscopy, and ultrafast dynamics. Future applications of PEEM in plasmonics for the probing of plasmonic hot electron dynamics in the energy and time domains are proposed and discussed.

Correlation between Near-Field Enhancement and Dephasing Time in Plasmonic Dimers.

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.

Chiral Second-Harmonic Generation from Monolayer WS2/Aluminum Plasmonic Vortex Metalens.

Two-dimensional spiral plasmonic structures have emerged as a versatile approach to generate near-field vortex fields with tunable topological charges. We demonstrate here a far-field approach to observe the chiral second-harmonic generation (SHG) at designated visible wavelengths from a single plasmonic vortex metalens. This metalens comprises an Archimedean spiral slit fabricated on atomically flat aluminum epitaxial film, which allows for precise tuning of plasmonic resonances and subsequent transfer of two-dimensional materials on top of the spiral slit. The nonlinear optical measurements show a giant SHG circular dichroism. Furthermore, we have achieved an enhanced chiral SHG conversion efficiency (about an order of magnitude greater than the bare aluminum lens) from monolayer tungsten disulfide (WS2)/aluminum metalens, which is designed at the C-exciton resonance of WS2. Since the C-exciton is not a valley exciton, the enhanced chiral SHG in this hybrid system originates from the plasmonic vortex field-enhanced SHG under the optical spin-orbit interaction.

Direct observation of ultrafast plasmonic hot electron transfer in the strong coupling regime.

Achieving strong coupling between plasmonic oscillators can significantly modulate their intrinsic optical properties. Here, we report the direct observation of ultrafast plasmonic hot electron transfer from an Au grating array to an MoS2 monolayer in the strong coupling regime between localized surface plasmons (LSPs) and surface plasmon polaritons (SPPs). By means of femtosecond pump-probe spectroscopy, the measured hot electron transfer time is approximately 40 fs with a maximum external quantum yield of 1.65%. Our results suggest that strong coupling between LSPs and SPPs has synergetic effects on the generation of plasmonic hot carriers, where SPPs with a unique nonradiative feature can act as an 'energy recycle bin' to reuse the radiative energy of LSPs and contribute to hot carrier generation. Coherent energy exchange between plasmonic modes in the strong coupling regime can further enhance the vertical electric field and promote the transfer of hot electrons between the Au grating and the MoS2 monolayer. Our proposed plasmonic strong coupling configuration overcomes the challenge associated with utilizing hot carriers and is instructive in terms of improving the performance of plasmonic opto-electronic devices.

Imaging of Plasmonic Chiral Radiative Local Density of States with Cathodoluminescence Nanoscopy.

Chiral light-matter interactions as an emerging aspect of quantum optics enable exceptional physical phenomena and advanced applications in nanophotonics through the nanoscale exploitation of photon-emitter interactions. The chiral radiative properties of quantum emitters strongly depend on the photonic environment, which can be drastically altered by plasmonic nanostructures with a high local density of states (LDOS). Hence, precise knowledge of the chiral photonic environment is essential for manipulating the chirality of light-matter interactions, which requires high resolution chiral characterization techniques. In this work, chiral radiative LDOS distributions of single plasmonic nanostructures that directly govern the chiral radiative spontaneous decay of quantum emitters are imaged at the nanoscale by using cathodoluminescence nanoscopy, enabling precise and highly efficient control of chiral photon emission for chiroptical technologies. Radiative LDOS hot-spots with the chirality larger than 93% are obtained by properly designing chiral plasmonic modes of Au nanoantennas. After fabricating monolayered WSe2 nanodisks (NDs) at chiral radiative LDOS hot-spots and forming ND/Au hybrid nanostructures, the chiral radiative properties of WSe2 NDs are significantly modified, leading to chiral photoluminescence. Our experimental concept and method provide an effective way to characterize and manipulate chiral light-matter interactions at the nanoscale, facilitating future applications in chiral quantum nanophotonics such as single-photon sources and light emission devices.

Deep-Subwavelength Resolving and Manipulating of Hidden Chirality in Achiral Nanostructures.

The chiral state of light plays a vital role in light-matter interactions and the consequent revolution of nanophotonic devices and advanced modern chiroptics. As the light-matter interaction goes into the nano- and quantum world, numerous chiroptical technologies and quantum devices require precise knowledge of chiral electromagnetic modes and chiral radiative local density of states (LDOS) distributions in detail, which directly determine the chiral light-matter interaction for applications such as chiral light detection and emission. With classical optical techniques failing to directly measure the chiral radiative LDOS, deep-subwavelength imaging and control of circular polarization (CP) light associated phenomena are introduced into the agenda. Here, we simultaneously reveal the hidden chiral electromagnetic mode and acquire its chiral radiative LDOS distribution of a single symmetric nanostructure at the deep-subwavelength scale by using CP-resolved cathodoluminescence (CL) microscopy. The chirality of the symmetric nanostructure under normally incident light excitation, resulting from the interference between the symmetric and antisymmetric modes of the V-shaped nanoantenna, is hidden in the near field with a giant chiral distribution (∼99%) at the arm-ends, which enables the circularly polarized CL emission from the radiative LDOS hot-spot and the following active helicity control at the deep-subwavelength scale. The proposed V-shaped nanostructure as a functional unit is further applied to the helicity-dependent binary encoding and the two-dimensional display applications. The proposed physical principle and experimental configuration can promote the future chiral characterization and manipulation at the deep-subwavelength scale and provide direct guidelines for the optimization of chiral light-matter interactions for future quantum studies.

Reveal and Control of Chiral Cathodoluminescence at Subnanoscale.

Circularly polarized light is crucial for the modern physics research. Highly integrated nanophotonic device further requires the control of circularly polarized light at subnanoscale. Here, we report the tuning of chiral cathodoluminescence (CL) on single Au nanostructure under electron stimulation. The detected CL helicity is found ultrasensitive with the electron impinging position on the structure, and a helicity switch is achieved within a 1.86 nm electron-beam movement, which is applied to construct ternary notation sequence. The proposed configuration provides a delicate platform for the CL helicity control, which opens a way for the future chiral applications at subnanoscale like information coding and quantum communication.

Single-Nanoparticle Plasmonic Electro-optic Modulator Based on MoS2 Monolayers.

The manipulation of light in an integrated circuit is crucial for the development of high-speed electro-optic devices. Recently, molybdenum disulfide (MoS2) monolayers generated broad interest for the optoelectronics because of their huge exciton binding energy, tunable optical emission, direct electronic band-gap structure, etc. Miniaturization and multifunctionality of electro-optic devices further require the manipulation of light-matter interaction at the single-nanoparticle level. The strong exciton-plasmon interaction that is generated between the MoS2 monolayers and metallic nanostructures may be a possible solution for compact electro-optic devices at the nanoscale. Here, we demonstrate a nanoplasmonic modulator in the visible spectral region by combining the MoS2 monolayers with a single Au nanodisk. The narrow MoS2 excitons coupled with broad Au plasmons result in a deep Fano resonance, which can be switched on and off by applying different gate voltages on the MoS2 monolayers. A reversible display device that is based on this single-nanoparticle modulator is demonstrated with a heptamer pattern that is actively controlled by the external gates. Our work provides a potential application for electro-optic modulation on the nanoscale and promotes the development of gate-tunable nanoplasmonic devices in the future.

Planar plasmonic chiral nanostructures.

A strong chiral optical response induced at a plasmonic Fano resonance in a planar Au heptamer nanostructure was experimentally and theoretically demonstrated. The scattering spectra show the characteristic narrow-band feature of Fano resonances for both left and right circular polarized lights, with a chiral response reaching 30% at the Fano resonance. Specifically, we systematically investigate the chiral response of planar heptamers with gradually changing the inter-particle rotation angles and separation distance. The chiral spectral characteristics clearly depend on the strength of Fano resonances and the associated near-field optical distributions. Finite element method simulations together with a multipole expansion method demonstrate that the enhanced chirality is caused by the excitation of magnetic quadrupolar and electric toroidal dipolar modes. Our work provides an effective method for the design of 2D nanostructures with a strong chiral response.

Active Light Control of the MoS2 Monolayer Exciton Binding Energy.

Plasmonic excitation of Au nanoparticles deposited on a MoS2 monolayer changes the absorption and photoluminescence characteristics of the material. Hot electrons generated from the Au nanoparticles are transferred into the MoS2 monolayers, resulting in n-doping. The doping effect of plasmonic hot electrons modulates the dielectric permittivity of materials, resulting in a red shift of both the absorption and the photoluminescence spectrum. This spectroscopic tuning was further investigated experimentally by using different Au nanoparticle concentrations, excitation laser wavelengths, and intensities. An analytical model for the photoinduced modulation of the MoS2 dielectric function and its exciton binding energy change is developed and used to estimate the doping density of plasmonic hot electrons. Our approach is important for the development of photonic devices for active control of light by light.

Pretreatment of corn stover for sugar production using dilute hydrochloric acid followed by lime.

In this study, a two stage process was evaluated to increase the sugar recovery. Firstly, corn stover was treated with diluted hydrochloric acid to maximize the xylose yield, and then the residue was treated with lime to alter the lignin structure and swell the cellulose surface. The optimal condition was 120 °C and 40 min for diluted hydrochloric acid pretreatment followed by lime pretreatment at 60 °C for 12h with lime loading at 0.1 g/g of substrate. The glucose and xylose yield was 78.0% and 97.0%, respectively, with cellulase dosage at 5 FPU/g of substrate. The total glucose yield increased to 85.9% when the cellulase loading was increased to 10 FPU/g of substrate. This two stage process was effective due to the swelling of the internal surface, an increase in the porosity and a decrease in the degree of polymerization.

[Determination of main flavone glycosides in Flos Chrysanthemi and observation of factors influenced contents].

OBJECTIVE: To determine and compare the content of luteolin-7-O-beta-D-glucoside and apigenin-7-O-beta-D-glucoside in Flos Chrysanthemi from different collection time, sources, grades and processes. METHOD: The contents were determined by RP-HPLC. Zorbax SB C18 column (4.6 mm x 250 mm, 5 microm) was used as analysis column, the mobile phase was acetonitrile-pH 2.0 phosphate buffer solution with gradient elution, the detector was set at 338 nm. RESULT: The contents of two components changed at some degree in Flos Chrysanthemi from different collection time, different plant sites or with different grades, while the contents varied obviously among Flos Chrysanthemi from different source and different sorts. No obvious difference was found in Flos Chrysanthemi from different year. CONCLUSION: The contents of two components were influenced by process, plane site, source and sorts, especially by source and sorts.