Surface phonon-polaritons in slabs of polar ternary mixed crystals are investigated with the modified random-element-isodisplacement model and the Born-Huang approximation, based on Maxwell＇s equations with the usual...Surface phonon-polaritons in slabs of polar ternary mixed crystals are investigated with the modified random-element-isodisplacement model and the Born-Huang approximation, based on Maxwell＇s equations with the usual boundary conditions. The numerical results of the surface phonon-polariton frequencies as functions of the wave-vector and thickness for slabs of ternary mixed crystals AlxGa1-xAs, Znx Cd1-x S,and Gax In1-x N are obtained and discussed. It is shown that there are four branches of surface phonon-polaritons in slab systems. The “two-mode” and “one-mode” behaviors of surface phonon-polaritons are also shown in their dispersion curves.展开更多
A surface femtosecond two-photon photoemission （2PPE） spectrometer devoted to the study of ultrafast excited electron dynamics and photochemical kinetics on metal and metal oxide surfaces has been constructed. Low e...A surface femtosecond two-photon photoemission （2PPE） spectrometer devoted to the study of ultrafast excited electron dynamics and photochemical kinetics on metal and metal oxide surfaces has been constructed. Low energy photoelectrons are measured using a hemispherical electron energy analyzer with an imaging detector that allows us to detect the energy and the angular distributions of the photoelectrons simultaneously. A Mach-Zehnder interferom- eter was built for the time-resolved 2PPE （TR-2PPE） measurement to study ultrafast surface excited electron dynamics, which was demonstrated on the Cu（111） surface. A scheme for measuring time-dependent 2PPE （TD-2PPE） spectra has also been developed for studies of surface photochemistry. This technique has been applied to a preliminary study on the photochemical kinetics on ethanol/TiO2（110）. We have also shown that the ultrafast dynamics of photoinduced surface excited resonances can be investigated in a reliable way by combining the TR-2PPE and TD-2PPE techniques.展开更多
Electrochemical （EC） reactions play vital roles in many disciplines, and its molecular-level understanding is highly desired, in particular under reactions. The vibration spectroscopy is a powerful in situ technique...Electrochemical （EC） reactions play vital roles in many disciplines, and its molecular-level understanding is highly desired, in particular under reactions. The vibration spectroscopy is a powerful in situ technique for chemical analysis, yet its application to EC reactions is hindered by the strong attenuation of infrared （IR） light in both electrodes and electrolytes. Here we demonstrate that by incorporating appropriate sub-wavelength plasmonic structures at the metal electrode, the IR field at the EC interface can be greatly enhanced via the excitation of surface plasmon. This scheme facilitates in situ vibrational spectroscopic studies, especially using the surface-specific sum-frequency generation technique.展开更多
The surface exciton-polaritons in ternary mixed crystals are investigated. The numerical calculations for several Ⅲ-V and II-VI compound systems are performed and the polariton frequencies as functions of the wave-ve...The surface exciton-polaritons in ternary mixed crystals are investigated. The numerical calculations for several Ⅲ-V and II-VI compound systems are performed and the polariton frequencies as functions of the wave-vector and the compositions for ternary mixed crystals AlxGaI_xAS, CdZnl.xSe and AlxGal.xN as examples are given and discussed. The results show that the dependence of the energies of surface polaritons on the composition of ternary mixed crystals are slightly nonlinear different from the bulk modes.展开更多
We have investigated the self-assembly and light emission properties of organic α- sexithiophene （α-6T） molecules on Ag（100） under different coverage by scanning tunneling microscopy （STM）. At very low coverag...We have investigated the self-assembly and light emission properties of organic α- sexithiophene （α-6T） molecules on Ag（100） under different coverage by scanning tunneling microscopy （STM）. At very low coverage, the α-6T molecules form a unique enantiomer by grouping four molecules into a windmill supermolecular structure. As the coverage is increased,α-6T molecules tend to pack side by side into a denser stripe structure. Further increase of the coverage will lead to the layer-by-layer growth of molecules on Ag（100） with the lower-layer stripe pattern serving as a template. Molecular fluorescence for α-6T molecules on Ag（100） at a coverage of five monolayers has been detected by light excitations, which indicates a well decoupled electronic states for the top-layer α-6T molecules. However, the STM induced luminescent spectra for the same sample reveal only plasmonic-like emission. The absence of intramolecular fluorescence in this case suggests that the electronic decoupling is not a sufficient condition for generating photon emission from molecules. For intramolecular fluorescence to occur, the orientation of the dynamic dipole moment of molecules and the energy-level alignment at the molecule-metal interface are also important so that molecules can be effectively excited through efficient dipolar coupling with local plasmons and by injecting holes into the molecules.展开更多
An annealed Inconel 718 alloy was surface-treated by pulsed laser at three different powers（100, 50 and 25 W）. Microstructural changes induced by the laser treatments were characterized by use of electron backscatte...An annealed Inconel 718 alloy was surface-treated by pulsed laser at three different powers（100, 50 and 25 W）. Microstructural changes induced by the laser treatments were characterized by use of electron backscatter diffraction and electron channeling contrast imaging techniques. Results show that both annealing twins and strengthening precipitates profusely existing in the as-received specimen are dissolved at elevated temperatures during the laser irradiation. Meanwhile, in the melting zone（MZ）, densities of low angle boundaries（LABs） are greatly increased with a large number of Laves phases preferentially distributed along such LABs. For different specimens, widths and depths of their MZs are found to be gradually reduced with decreasing the laser powers. Orientation analyses reveal that the columnar grains in the MZ of the 100 W specimen could inherit orientations existing in the matrix while lower laser powers promote the formation of more nuclei with scattered orientations to grow to be granular grains in the MZ. Hardness tests reveal that the MZs of all laser-treated specimens are softer than the matrix probably due to both precipitate dissolution and grain coarsening.展开更多
In this paper, we theoretically discuss the soliton properties of light pulse transportation on the surface of an ionic crystal having strong nonlinear interactions between ions of unit cells. We analyze in detail the...In this paper, we theoretically discuss the soliton properties of light pulse transportation on the surface of an ionic crystal having strong nonlinear interactions between ions of unit cells. We analyze in detail the dark solitons when the nonlinear coefficient g is positive and negative, respectively. It is found that whether the nonlinear coefficient g is positive or negative, the dark solitons can be formed over the whole dispersion relation area of surface polaritons considering nonlinear effects. Attention should be paid to the fact that around , the light pulse can form advanced dark solitons, and there is a switching area from advanced dark soliton to retarded dark soliton near . We also discuss the effects of higher nonlinear dispersion on the solitons.展开更多
The transmission properties of terahertz （THz） wave passing through semiconductor aperture have been investigated. The dispersion relationship for surface plasmon polariton （SPP） at different temperatures has been...The transmission properties of terahertz （THz） wave passing through semiconductor aperture have been investigated. The dispersion relationship for surface plasmon polariton （SPP） at different temperatures has been numerically calculated. The results show that the dispersion relationship increases with the increasing of frequency and the decreasing of temperature, the thickness of slab has to be taken into consideration because of the large skin depth for semiconductor slab. In addition, the propagation constant increases with the increasing of frequency and the decreasing of temperature.展开更多
Suspended gold nanoparticles have been synthesized via electrochemical method.Fluorescence excitation and emission spectra were obtained using a spectrofluorophotometer.With varying the excitation wavelength,an emissi...Suspended gold nanoparticles have been synthesized via electrochemical method.Fluorescence excitation and emission spectra were obtained using a spectrofluorophotometer.With varying the excitation wavelength,an emission peak fixed at 485 nm has always been observed.We believe that this peak is attributed to the surface plasmon resonance.When the detection wavelength was fixed at 485 nm (0.619×10 15 Hz),a double frequency exciting peak at 242 nm(2×0.619×10 15 Hz), a 3/2 fraction frequency exciting peak at 330 nm (about 3/2×0.619×10 15 Hz)and a 3/4 fraction frequency exciting peak at 640 nm(3/4×0.619×10 15 Hz)display.The nonlinear exciting peak at 640 nm corresponds to the two-photon absorption.Therefore,as the excitation wavelength is at 320 and 640 nm respectively,single-photon and two-photon absorption induced surface plasmon resonance emission peaks were observed. These nonlinear surface plasmon resonance emission characters of Au colloidal nanoparticles make it possible to enhance the sensitivity of conventional surface plasmon resonance device.展开更多
Electron inelastic mean free path （IMFP） is an important parameter for surface chemical quantification by surface electron spectroscopy techniques. It can be obtained from analysis of elastic peak electron spectrosc...Electron inelastic mean free path （IMFP） is an important parameter for surface chemical quantification by surface electron spectroscopy techniques. It can be obtained from analysis of elastic peak electron spectroscopy （EPES） spectra measured on samples and a Monte Carlo simulation method. To obtain IMFP parameters with high accuracy, the surface excitation effect on the measured EPES spectra has to be quantified as a surface excitation parameter （SEP）, which can be calculated via a dielectric response theory. However, such calculated SEP does not include influence of elastic scattering of electrons inside samples during their incidence and emission processes, which should not be neglected simply in determining IMFP by an EPES method. In this work a Monte Carlo simulation method is employed to determine surface excitation parameter by taking account of the elastic scattering effect. The simulated SEPs for different primary energies are found to be in good agreement with the experiments particularly for larger incident or emission angles above 60° where the elastic scattering effect plays a more important role than those in smaller incident or emission angles. Based on these new SEPs, the IMFP measurement by EPES technique can provide more accurate data.展开更多
In this work,electron energy spectroscopic mapping of surface plasmon of Ag nanostructures on highly oriented pyrolytic graphite is reported.Benefitting from the angular dispersive feature of the present scanning prob...In this work,electron energy spectroscopic mapping of surface plasmon of Ag nanostructures on highly oriented pyrolytic graphite is reported.Benefitting from the angular dispersive feature of the present scanning probe electron energy spectrometer,a multi-channel detection mode is developed.By scanning along one direction,the two-dimensional intensity distribution of Ag surface plasmon excitation due to the collision of electron emitted from the tip can be obtained in parallel.The spectroscopic spatial resolution is determined to be around 80 nm.展开更多
The preparation of calcium phosphate （CP） coating on alumina ceramics using electric pulse stimulating methoe has been investigated. The cup-shaped alumina ceramics were soaked in a simulated body fluid （SBF）, and...The preparation of calcium phosphate （CP） coating on alumina ceramics using electric pulse stimulating methoe has been investigated. The cup-shaped alumina ceramics were soaked in a simulated body fluid （SBF）, and a square pulse potential with frequency of 1 Hz and voltage of 110 V was applied between the inner and outer surfaces of the alumina cup. Surface morphology of CP coatings during different deposition periods was observed by a Philips XL-30 scanning electron microscope （SEM）. Compositional analysis was examined by EDAX. The mechanism of nucleation and growth of CP coating was discussed. SEM result indicates that the coating comprises of a large number of tiny needle-like grains and has a porous microstructure. There is a strong bond between the deposited layer and Al2O3 substrate, which may be due to the gentle growth of the biomimetic method. The EDAX analysis indicates that main composition of the coating is calcium and phosphor. The formation of CP coating may be contributed to the stimulation of electric pulse and the high ions concentration which is 1.5 times of the concentration of SBF solution （1.5SBF solution）. Such surface functionalization method by electric pulse potential can be used to prepare CP coating on various electric-insulating bioinert materials for improving their bioactive character.展开更多
The wave guides and optical fibers have long been known to transmit light and electromagnetic fields in large dimensions. Recently, surface plasmons, which are collective plasma oscillations of valence electrons at me...The wave guides and optical fibers have long been known to transmit light and electromagnetic fields in large dimensions. Recently, surface plasmons, which are collective plasma oscillations of valence electrons at metal surfaces, have been introduced as an entity that is able to guide light on the surfaces of the metal and to concentrate light in subwavelength volumes. It has been found that periodic array of metallic nanospheres, could be able to enhance the light transmission, and guiding light at nanoscale. The coupling between two nanoparticles in these devices is very important. The Bloch-Jensen hydrodynamical method has been used for computing surface plasmons＇ frequencies of a single metallic nanosphere. It contains the entire pole spectrum automatically, so it is more exactly than the other computational methods. In this research, we have computed the surface plasmons＇ frequencies of two adjacent nanospheres by Bloch-Jensen hydrodynamical model for the first time. The results show that there are two modes for this system, which depend explicitly on interparticle spacing. In addition, we have shown that the excitation modes yield to a single mode of a nanoparticle as the interparticle spacing increases.展开更多
文摘Surface phonon-polaritons in slabs of polar ternary mixed crystals are investigated with the modified random-element-isodisplacement model and the Born-Huang approximation, based on Maxwell＇s equations with the usual boundary conditions. The numerical results of the surface phonon-polariton frequencies as functions of the wave-vector and thickness for slabs of ternary mixed crystals AlxGa1-xAs, Znx Cd1-x S,and Gax In1-x N are obtained and discussed. It is shown that there are four branches of surface phonon-polaritons in slab systems. The “two-mode” and “one-mode” behaviors of surface phonon-polaritons are also shown in their dispersion curves.
文摘A surface femtosecond two-photon photoemission （2PPE） spectrometer devoted to the study of ultrafast excited electron dynamics and photochemical kinetics on metal and metal oxide surfaces has been constructed. Low energy photoelectrons are measured using a hemispherical electron energy analyzer with an imaging detector that allows us to detect the energy and the angular distributions of the photoelectrons simultaneously. A Mach-Zehnder interferom- eter was built for the time-resolved 2PPE （TR-2PPE） measurement to study ultrafast surface excited electron dynamics, which was demonstrated on the Cu（111） surface. A scheme for measuring time-dependent 2PPE （TD-2PPE） spectra has also been developed for studies of surface photochemistry. This technique has been applied to a preliminary study on the photochemical kinetics on ethanol/TiO2（110）. We have also shown that the ultrafast dynamics of photoinduced surface excited resonances can be investigated in a reliable way by combining the TR-2PPE and TD-2PPE techniques.
文摘Electrochemical （EC） reactions play vital roles in many disciplines, and its molecular-level understanding is highly desired, in particular under reactions. The vibration spectroscopy is a powerful in situ technique for chemical analysis, yet its application to EC reactions is hindered by the strong attenuation of infrared （IR） light in both electrodes and electrolytes. Here we demonstrate that by incorporating appropriate sub-wavelength plasmonic structures at the metal electrode, the IR field at the EC interface can be greatly enhanced via the excitation of surface plasmon. This scheme facilitates in situ vibrational spectroscopic studies, especially using the surface-specific sum-frequency generation technique.
基金supported partly by PhD Progress Foundation ofhigher education institutions of China (N0. 20040126003)the Natural Science Foundation of Inner Mongol of China ( No200408020101)
文摘The surface exciton-polaritons in ternary mixed crystals are investigated. The numerical calculations for several Ⅲ-V and II-VI compound systems are performed and the polariton frequencies as functions of the wave-vector and the compositions for ternary mixed crystals AlxGaI_xAS, CdZnl.xSe and AlxGal.xN as examples are given and discussed. The results show that the dependence of the energies of surface polaritons on the composition of ternary mixed crystals are slightly nonlinear different from the bulk modes.
基金Author to whom correspondence should be addressed. E-mail： zcdong@ustc.edu.cn, FAX： ＋86-551-3600103 This work was supported by the National Basic Research Program of China （No.2006CB922003 and No.2011CB921402）, the Chinese Academy of Sciences （No.KJCX2.YW.H06）, and the National Natural Science Foundation of China （No.91021004, No.10574117, and No.10974186）.
文摘We have investigated the self-assembly and light emission properties of organic α- sexithiophene （α-6T） molecules on Ag（100） under different coverage by scanning tunneling microscopy （STM）. At very low coverage, the α-6T molecules form a unique enantiomer by grouping four molecules into a windmill supermolecular structure. As the coverage is increased,α-6T molecules tend to pack side by side into a denser stripe structure. Further increase of the coverage will lead to the layer-by-layer growth of molecules on Ag（100） with the lower-layer stripe pattern serving as a template. Molecular fluorescence for α-6T molecules on Ag（100） at a coverage of five monolayers has been detected by light excitations, which indicates a well decoupled electronic states for the top-layer α-6T molecules. However, the STM induced luminescent spectra for the same sample reveal only plasmonic-like emission. The absence of intramolecular fluorescence in this case suggests that the electronic decoupling is not a sufficient condition for generating photon emission from molecules. For intramolecular fluorescence to occur, the orientation of the dynamic dipole moment of molecules and the energy-level alignment at the molecule-metal interface are also important so that molecules can be effectively excited through efficient dipolar coupling with local plasmons and by injecting holes into the molecules.
基金Project(CSTC2015ZDCY-ZTZX50002) supported by the Innovation Program of Common and Key Technologies in Major Industries of Chongqing,China
文摘An annealed Inconel 718 alloy was surface-treated by pulsed laser at three different powers（100, 50 and 25 W）. Microstructural changes induced by the laser treatments were characterized by use of electron backscatter diffraction and electron channeling contrast imaging techniques. Results show that both annealing twins and strengthening precipitates profusely existing in the as-received specimen are dissolved at elevated temperatures during the laser irradiation. Meanwhile, in the melting zone（MZ）, densities of low angle boundaries（LABs） are greatly increased with a large number of Laves phases preferentially distributed along such LABs. For different specimens, widths and depths of their MZs are found to be gradually reduced with decreasing the laser powers. Orientation analyses reveal that the columnar grains in the MZ of the 100 W specimen could inherit orientations existing in the matrix while lower laser powers promote the formation of more nuclei with scattered orientations to grow to be granular grains in the MZ. Hardness tests reveal that the MZs of all laser-treated specimens are softer than the matrix probably due to both precipitate dissolution and grain coarsening.
文摘In this paper, we theoretically discuss the soliton properties of light pulse transportation on the surface of an ionic crystal having strong nonlinear interactions between ions of unit cells. We analyze in detail the dark solitons when the nonlinear coefficient g is positive and negative, respectively. It is found that whether the nonlinear coefficient g is positive or negative, the dark solitons can be formed over the whole dispersion relation area of surface polaritons considering nonlinear effects. Attention should be paid to the fact that around , the light pulse can form advanced dark solitons, and there is a switching area from advanced dark soliton to retarded dark soliton near . We also discuss the effects of higher nonlinear dispersion on the solitons.
基金the National Fund for Distinguished Young Scholars of China under Grant No.60425415the Major Project of National Natural Science Foundation of China under Grant No 10390162the Shanghai Municipal Commission of Science and Technology
文摘The transmission properties of terahertz （THz） wave passing through semiconductor aperture have been investigated. The dispersion relationship for surface plasmon polariton （SPP） at different temperatures has been numerically calculated. The results show that the dispersion relationship increases with the increasing of frequency and the decreasing of temperature, the thickness of slab has to be taken into consideration because of the large skin depth for semiconductor slab. In addition, the propagation constant increases with the increasing of frequency and the decreasing of temperature.
文摘Suspended gold nanoparticles have been synthesized via electrochemical method.Fluorescence excitation and emission spectra were obtained using a spectrofluorophotometer.With varying the excitation wavelength,an emission peak fixed at 485 nm has always been observed.We believe that this peak is attributed to the surface plasmon resonance.When the detection wavelength was fixed at 485 nm (0.619×10 15 Hz),a double frequency exciting peak at 242 nm(2×0.619×10 15 Hz), a 3/2 fraction frequency exciting peak at 330 nm (about 3/2×0.619×10 15 Hz)and a 3/4 fraction frequency exciting peak at 640 nm(3/4×0.619×10 15 Hz)display.The nonlinear exciting peak at 640 nm corresponds to the two-photon absorption.Therefore,as the excitation wavelength is at 320 and 640 nm respectively,single-photon and two-photon absorption induced surface plasmon resonance emission peaks were observed. These nonlinear surface plasmon resonance emission characters of Au colloidal nanoparticles make it possible to enhance the sensitivity of conventional surface plasmon resonance device.
基金This work was supported by the National Natural Science Foundation of China （No.11274288 and No.11574289）. We thank the Supercomputing Center of USTC for support in performing parallel computations.
文摘Electron inelastic mean free path （IMFP） is an important parameter for surface chemical quantification by surface electron spectroscopy techniques. It can be obtained from analysis of elastic peak electron spectroscopy （EPES） spectra measured on samples and a Monte Carlo simulation method. To obtain IMFP parameters with high accuracy, the surface excitation effect on the measured EPES spectra has to be quantified as a surface excitation parameter （SEP）, which can be calculated via a dielectric response theory. However, such calculated SEP does not include influence of elastic scattering of electrons inside samples during their incidence and emission processes, which should not be neglected simply in determining IMFP by an EPES method. In this work a Monte Carlo simulation method is employed to determine surface excitation parameter by taking account of the elastic scattering effect. The simulated SEPs for different primary energies are found to be in good agreement with the experiments particularly for larger incident or emission angles above 60° where the elastic scattering effect plays a more important role than those in smaller incident or emission angles. Based on these new SEPs, the IMFP measurement by EPES technique can provide more accurate data.
基金supported by the National Key Research and Development Program of China(No.2017YFA0303500)the National Natural Science Foundation of China(No.11674302)。
文摘In this work,electron energy spectroscopic mapping of surface plasmon of Ag nanostructures on highly oriented pyrolytic graphite is reported.Benefitting from the angular dispersive feature of the present scanning probe electron energy spectrometer,a multi-channel detection mode is developed.By scanning along one direction,the two-dimensional intensity distribution of Ag surface plasmon excitation due to the collision of electron emitted from the tip can be obtained in parallel.The spectroscopic spatial resolution is determined to be around 80 nm.
文摘The preparation of calcium phosphate （CP） coating on alumina ceramics using electric pulse stimulating methoe has been investigated. The cup-shaped alumina ceramics were soaked in a simulated body fluid （SBF）, and a square pulse potential with frequency of 1 Hz and voltage of 110 V was applied between the inner and outer surfaces of the alumina cup. Surface morphology of CP coatings during different deposition periods was observed by a Philips XL-30 scanning electron microscope （SEM）. Compositional analysis was examined by EDAX. The mechanism of nucleation and growth of CP coating was discussed. SEM result indicates that the coating comprises of a large number of tiny needle-like grains and has a porous microstructure. There is a strong bond between the deposited layer and Al2O3 substrate, which may be due to the gentle growth of the biomimetic method. The EDAX analysis indicates that main composition of the coating is calcium and phosphor. The formation of CP coating may be contributed to the stimulation of electric pulse and the high ions concentration which is 1.5 times of the concentration of SBF solution （1.5SBF solution）. Such surface functionalization method by electric pulse potential can be used to prepare CP coating on various electric-insulating bioinert materials for improving their bioactive character.
文摘The wave guides and optical fibers have long been known to transmit light and electromagnetic fields in large dimensions. Recently, surface plasmons, which are collective plasma oscillations of valence electrons at metal surfaces, have been introduced as an entity that is able to guide light on the surfaces of the metal and to concentrate light in subwavelength volumes. It has been found that periodic array of metallic nanospheres, could be able to enhance the light transmission, and guiding light at nanoscale. The coupling between two nanoparticles in these devices is very important. The Bloch-Jensen hydrodynamical method has been used for computing surface plasmons＇ frequencies of a single metallic nanosphere. It contains the entire pole spectrum automatically, so it is more exactly than the other computational methods. In this research, we have computed the surface plasmons＇ frequencies of two adjacent nanospheres by Bloch-Jensen hydrodynamical model for the first time. The results show that there are two modes for this system, which depend explicitly on interparticle spacing. In addition, we have shown that the excitation modes yield to a single mode of a nanoparticle as the interparticle spacing increases.
