Two groups of coated conductor samples with different thicknesses of CeO2 cap layers deposited by pulsed laser deposition （PLD） under the same conditions have been studied. Of them, one group is of CeO2 films, which...Two groups of coated conductor samples with different thicknesses of CeO2 cap layers deposited by pulsed laser deposition （PLD） under the same conditions have been studied. Of them, one group is of CeO2 films, which are deposited on stainless steel （SS） tapes coated by IBAD-YSZ （IBAD-YSZ/SS）, and the other group is of CeO2/YSZ/Y2O3 multilayers, which are deposited on NiW substrates by PLD for the fabrication of YBCO-coated conductor through the RABiTS approach. YBCO film is then deposited on the tops of both types of buffer layers by PLD. The effects of the thickness of the CeO2 film on the texture of the CeO2 film and the critical current density （Jc） of the YBCO film are analysed. For the case of CeO2 film on IBAD-YSZ/SS, there appears a self-epitaxy effect with increasing thickness of the CeO2 film. For CeO2/YSZ/Y2O3/NiW, in which the buffer layers are deposited by PLD, there occurs no self-epitaxy effect, and the optimal thickness of CeO2 is about 50 nm. The surface morphologies of the two groups of samples are examined by SEM.展开更多
It is significant for low-cost preparation of YBa2Cu3O7-δ（YBCO） coated conductors to make clear the mechanism of orientation, copper segregation, and nucleation density in BaF2-derived YBCO crystallization. In the ...It is significant for low-cost preparation of YBa2Cu3O7-δ（YBCO） coated conductors to make clear the mechanism of orientation, copper segregation, and nucleation density in BaF2-derived YBCO crystallization. In the present work,a distinct nucleation mechanism was proposed based on a transient liquid phase induced by the size effect as well as near-equilibrium assumption. With this scheme the nucleation of YBCO prepared by metal–organic deposition（MOD） or the physical vapor deposition BaF2 process was semi-quantitatively analyzed, revealing that the direct driving force for nucleation is YBCO supersaturation in the liquid phase. The theoretical analysis on the nucleation orientation portion is evidenced by the experimental result.展开更多
MgO thin films with different textures are fabricated by the ion beam assisted （IBAD） method on the Y2O3/Al2O3 buffered C276 tape. Then a CaO2 layer is directly grown on the IBAD-MgO film by the pulsed laser deposit...MgO thin films with different textures are fabricated by the ion beam assisted （IBAD） method on the Y2O3/Al2O3 buffered C276 tape. Then a CaO2 layer is directly grown on the IBAD-MgO film by the pulsed laser deposition （PLD） method. Effects of lBAD-MgO texture, substrata temperature and thickness on the grain alignment of the CeO2 layer are investigated. Film characterization is performed by x-ray diffraction and atomic force microscopy. It is found that the orientation and texture degree of the CaO2 layer are very sensitive to the IBAD-MgO texture. By optimizing the IBAD-MgO texture, CeO2 has pure （002） orientation and excellent biaxial texture deposited in a broad substrata temperature range. In addition, the PLD-CeO2 layer has a thickness effect. Under the optimized experimental condition, the PLD-CeO2 layer has a high in-plane texture of △φ = 2.9° and a smooth surface with an rms surface roughness of less than 2nm. The critical current density Jc of a 0.4μm-thick YBCO film deposited on the CeO2 layer is 6.25 × 106 A/cm2 at 77K and a self-field.展开更多
Several types of REBa2Cu3O7-x （REBCO, RE=Y, Ho etc.） films are prepared on single crystal substrate LaAIO3 by TFA-MOD method. The phase transformation and optimized growth conditions in the crystallization are studi...Several types of REBa2Cu3O7-x （REBCO, RE=Y, Ho etc.） films are prepared on single crystal substrate LaAIO3 by TFA-MOD method. The phase transformation and optimized growth conditions in the crystallization are studied. Compared with SmBCO and GdBCO, high quality YBCO and HoBCO films are relatively easy to produce. It is revealed that the YBCO grains can form at low temperatures such as 730 ℃ during the initial heating ramp. With a high heating rate of 20 K/min and a low oxygen pressure of 100 ppm, the optimum growth temperature is around 780℃, at which the films show a Jc value of 2.88 MMcm2. Further decrease of the heating rate may produce the highquality YBCO Film with a higher Jc of 3.65 MA/cm2. The temperature dependence of resistances in various magnetic fields up to 9 T shows that the present TFAMOD YBCO and HoBCO films have similar superonducting transition temperature and magnetotransport properties.展开更多
CeO2/YSZ/CeO2 buffer layers were prepared on biaxial textured Ni-5at.%W substrate by direct-current magnetron reactive sputtering with the optimum process. YBCO thin films were deposited on CeO2/YSZ/CeO2 buffered Ni-5...CeO2/YSZ/CeO2 buffer layers were prepared on biaxial textured Ni-5at.%W substrate by direct-current magnetron reactive sputtering with the optimum process. YBCO thin films were deposited on CeO2/YSZ/CeO2 buffered Ni-5at.%W substrate at temperature ranging from 500℃ to 700℃ by diode de sputtering. By optimizing substrate temperature, pure c-axis oriented YBCO films were obtained. The mierostruetures of CeO2/YSZ/CeO2 buffer layers were characterized by X-ray diffraction. A smooth, dense and crack-free surface morphology was observed with scanning electron microscopy. The critical current density Jc about 0.75 MA/cm2 at 77 K was obtained.展开更多
Manipulating the directional movement of liquid droplets is of significance for design and fabrication of some microfluidic devices, An energy-based method is adopted to analyse the directional movement of a droplet d...Manipulating the directional movement of liquid droplets is of significance for design and fabrication of some microfluidic devices, An energy-based method is adopted to analyse the directional movement of a droplet deposited in a conical tube or on a conical fibre. We perform an experiment to investigate the directional motion of a droplet in an open conical tube. Our theoretical analysis and experimental observations both demonstrate that surface tension can drive the droplet to move in the conical tube. The critical condition of the liquid moving in the conical tube is presented. We also analyse a droplet on a conical hydrophilic fibre, which can move from the thinner to the thicker end.展开更多
A 2 1/2-dimensional electromagnetic particle-in-cell （PIC） simulation code is used to investigate electron behaviour in collisionless magnetic reconnectfon. The results show that the ion/electron mass ratio （mi/me...A 2 1/2-dimensional electromagnetic particle-in-cell （PIC） simulation code is used to investigate electron behaviour in collisionless magnetic reconnectfon. The results show that the ion/electron mass ratio （mi/me） almost has no impact on the reconnection rate, however it can significantly affect electron behaviour in the diffusion region. For the case with larger mass ratio, the width of electron current sheet becomes smaller and the outflow region along the separatrix is smaller, hence the peak of the electron outflow speed is essentially larger. Density cavities and the parallel electric field E// along the separatrix can be found in the case with larger mass ratio, which may have significant influences on the acceleration and heating of the electrons near the X point.展开更多
We design and prepare three-layer graded ZnO nanowhisker/polyester composites. The dispersion configuration of ZnO nanowhiskers in the polyester is investigated, and their microwave reflectivity curves are also measur...We design and prepare three-layer graded ZnO nanowhisker/polyester composites. The dispersion configuration of ZnO nanowhiskers in the polyester is investigated, and their microwave reflectivity curves are also measured. Experimental results have shown that the graded dispersion with ZnO nanowhiskers contributes to broadband microwave absorption. In other words, the absorption band depends on the graded dispersion configuration of ZnO nanowhiskers in polyester matrix.展开更多
We theoretically analyse the temperature effects on a surface plasmon resonance （SPR） sensor in Kretschmann configuration. The temperature effects include the thermo-optic effect and the dispersion of thermal-optic ...We theoretically analyse the temperature effects on a surface plasmon resonance （SPR） sensor in Kretschmann configuration. The temperature effects include the thermo-optic effect and the dispersion of thermal-optic coefficient in the dielectric along with the thermal expansion effect, phonon-electron scattering and electron-electron scattering in the metal layer. We simulate the temperature dependence of the resonance position and the sensitivity of the SPR sensor under wavelength-interrogation and angular-interrogation mode of operation and the differences are pointed out in the two modes.展开更多
We report a femtosecond optical parametric oscillator based on MgO-doped PPLN synchronously pumped by a mode-locked Ti：sapphire laser. The wavelengths of the signal and idler are continuously tuned from 1100 to 1300h...We report a femtosecond optical parametric oscillator based on MgO-doped PPLN synchronously pumped by a mode-locked Ti：sapphire laser. The wavelengths of the signal and idler are continuously tuned from 1100 to 1300hm and from 2080 to 2930nm, respectively, by changing the pump wavelength and the OPO cavity length. The maximum signal output power of 130mW at the wavelength of 1225nm is obtained, pumped by 900roW of 800hm laser radiation. This corresponds to a total conversion efficiency of 22.1%. The signal pulse duration is measured to be 167fs by intensity autocorrelation with chirped mirrors for intracavity dispersion compensation.展开更多
We investigate the influence of precursor molar ratio of [S^2-]/[Zn^2＋] on particle size and photoluminescence （PL） of ZnS：Mn^2＋ nanocrystMs. By changing the [S^2-]/[Zn^2＋] ratio from 0.6 （Zn-rich） to 2.0 （S-...We investigate the influence of precursor molar ratio of [S^2-]/[Zn^2＋] on particle size and photoluminescence （PL） of ZnS：Mn^2＋ nanocrystMs. By changing the [S^2-]/[Zn^2＋] ratio from 0.6 （Zn-rich） to 2.0 （S-rich）, the particle size increases from nearly 2. 7nm to about 4.Ohm. The increase in the ratio of [S^2-]/[Zn^2＋] cadses a decrease of PL emission intensity of ZnS host while a distinct increase of Mn^2＋ emission. The maximum intensity for the luminescence of Mn^2＋ emission is observed at the ratio of [S^2-]/[Zn^2＋] ≈ 1.5. The possible mechanism for the results is discussed by filling of S^2- vacancies and the increase of Mn^2＋ ions incorporated into ZnS lattices.展开更多
We investigate the influence of vacuum organic contaminations on laser-induced damage threshold （LIDT） of optical coatings. Anti-reflective （AIR） coatings at 1064 nm made by Ta2 O5/SiO2 are deposited by the ion be...We investigate the influence of vacuum organic contaminations on laser-induced damage threshold （LIDT） of optical coatings. Anti-reflective （AIR） coatings at 1064 nm made by Ta2 O5/SiO2 are deposited by the ion beam sputtering method. The LIDTs of AR coatings are measured in vacuum and in atmosphere, respectively. It is exhibited that contaminations in vacuum are easily to be absorbed onto optical surface because of lower pressure, and they become origins of damage, resulting in the decrease of LIDT from 24.5J/cm^2 in air to 15.TJ/cm^2 in vacuum. The LIDT of coatings in vacuum has is slightly changed compared with the value in atmosphere after the organic contaminations are wiped off. These results indicate that organic contaminations are the main reason of the LIDT decrease in vacuum. Additionally, damage morphologies have distinct changes from vacuum to atmosphere because of the differences between the residual stress and thermal decomposability of filmy materials.展开更多
The ground-state energy and effective mass of an acoustic polaron in one dimension are calculated by using an electron-longitudinal-acoustic-phonon interaction Hamiltonian derived here. The self-trapping of the acoust...The ground-state energy and effective mass of an acoustic polaron in one dimension are calculated by using an electron-longitudinal-acoustic-phonon interaction Hamiltonian derived here. The self-trapping of the acoustic polaron is discussed. It is found that the critical coupling constant shifts toward weaker electron-phonon interaction with the increasing cutoff wave vector and the products of the critical coupling constant by the cutoff wave vector tend to a certain value. The self-trapping of acoustic polarons in one dimension is easier to be realized than that in three- and two-dimensional systems. The self-trapping transition of acoustic polarons is expected to be observed in the one dimensional systems of alkali halides and wide-band-gap semiconductors.展开更多
For a nonholonomic mechanics system with the action of small disturbance, the Lie symmetrical perturbation and adiabatic invariants of generalized Hojman type are studied under general infinitesimal transformations of...For a nonholonomic mechanics system with the action of small disturbance, the Lie symmetrical perturbation and adiabatic invariants of generalized Hojman type are studied under general infinitesimal transformations of groups in which the generalized coordinates and time are variable. On the basis of the invariance of disturbed nonholonomic dynamical equations under general infinitesimal transformations, the determining equations, the constrained restriction equations and the additional restriction equations of Lie symmetries of the system are constructed, which only depend on the variables t, qs and q^.s. Based on the definition of higher-order adiabatic invariants of a mechanical system, the perturbation of Lie symmetries for a nonholonomic system with the action of small disturbance is investigated, and the Lie symmetrical adiabatic invariants, the weakly Lie symmetrical adiabatic invariants and the strongly Lie symmetrical adiabatic invariants of generalized Hojman type of disturbed nonholonomic systems are obtained. An example is given to illustrate applications of the results.展开更多
We perform a theoretical study on a low dark current InGaAs/GaAs very-long-wavelength （〉 12 μm） quantum well infrared photodetector （VLW-QWIP）, based on a double barrier resonant tunnelling structure （DBRTS）. ...We perform a theoretical study on a low dark current InGaAs/GaAs very-long-wavelength （〉 12 μm） quantum well infrared photodetector （VLW-QWIP）, based on a double barrier resonant tunnelling structure （DBRTS）. The ground tunnelling state of the central quantum well （QW） of the DBRTS can resonate with the first excited bound state of the doped InGaAs QW by adjusting the structure parameters of the DBRTS. Investigation of the carrier transport performance of this device is carried out based on quantum wave transport theory. It has been shown that the dark current in this device can be significantly reduced by two orders compared to conventional InGaAs/GaAs VLW-QWIPs, while the photocurrent is almost the same as those in conventional VLW-QWIPs. This DBRTS integrated VLW-QWIP structure may stimulate the experimental investigation for VLW-QWIPs at high operation temperatures.展开更多
Tunable diode laser absorption spectroscopy detection of N2 0 around 2.1 μm is demonstrated by using a homemade InGaAsSb/AlGaAsSb MQW laser diode and an InGaAs wavelength extended photodiode. Details of the devices a...Tunable diode laser absorption spectroscopy detection of N2 0 around 2.1 μm is demonstrated by using a homemade InGaAsSb/AlGaAsSb MQW laser diode and an InGaAs wavelength extended photodiode. Details of the devices and the detection system are described. In the system, the laser is driven by low frequency pulses with long duration to form a wavelength scan around 4741 cm^-1; the absorption information is obtained from the detected signal of the photodiode. By using a gas cell with 15cm path length, a detection limit is estimated to be smaller than 0.2 Torr.展开更多
Lead-free piezoelectric ceramics 0.92（Bi0.5Na0.5）TiO3-0.08BaTiO3 ＋ xmol% Co3＋ （BNBT-Co, x = 0-8） are prepared by the solid state reaction method. Effects of the amount of Co^3＋ on the electrical properties and ...Lead-free piezoelectric ceramics 0.92（Bi0.5Na0.5）TiO3-0.08BaTiO3 ＋ xmol% Co3＋ （BNBT-Co, x = 0-8） are prepared by the solid state reaction method. Effects of the amount of Co^3＋ on the electrical properties and phase transition are studied. The results indicate that the addition of Co^3＋ enhances the mechanical quality factor Q^3＋ significantly, whereas the dissipation factor tanδ has a minimum value at x = 3.5. Meanwhile, addition of Co^3＋ leads to small decreases of piezoelectric constant d33, and planar electromechanical coupling kp. The present 0.92（Bio.aNao.5） TiO3-0.08BaTiO3＋3.5 moi% Co^3＋ ceramics exhibit good performance with mechanical quality factor Qm = 910, piezoelectric constant d33 = 106pC/N, planar electromechanical coupling kp =10% and dissipation factor tanδ = 1.1% at 1 kHz. Saturated polarization hysteresis loops have been obtained for BNBT-Co ceramics. Two dielectric peaks at depolarization temperature Td and Tm appear in the curves of ε33^T vs temperature for the pure BNBT ceramics. However, the first dielectric peak Td disappears after the addition of Co^3＋, which means that the transition from ferroelectric to antiferroelectric phase has been eliminated.展开更多
A scanning multi-axis differential optical absorption spectroscopy （DOAS） system is developed for monitoring tropospheric NO2 abundance. Measurements at different viewing angles near the horizon can be performed seq...A scanning multi-axis differential optical absorption spectroscopy （DOAS） system is developed for monitoring tropospheric NO2 abundance. Measurements at different viewing angles near the horizon can be performed sequentially with one telescope collecting scattered sunlight reflected by a moving mirror. Tropospheric NO2 diurnal variations can be derived from slant column densities （SCDs） of different elevation angles. The result from a field campaign in Beijing in summer of 2005 reveals potential possibility for the monitoring of tropospheric NO2 by multi-axis DOAS technique.展开更多
The subband energy and lasing wavelength of compressively strained triangular Ino.53Ga0.47As/InAs quantum well are calculated and compared with the conventional rectangular ones with the same strain contents. The stra...The subband energy and lasing wavelength of compressively strained triangular Ino.53Ga0.47As/InAs quantum well are calculated and compared with the conventional rectangular ones with the same strain contents. The strain compensation using Al0.33In0.36Ga0.31As barrier is introduced. The results show that lasing wavelength can be extended dramatically to beyond 2.8μm by changing the energy band from the conventional rectangular shape to a triangular one, the realization of such a structure using molecular beam epitaxy technology is also discussed.展开更多
Nanocrystallites Au particles are deposited on a well-aligned silicon nanoporous pillar array （Si-NPA） surface through immersion plating to form an Au/Si-NPA composite system. It is found that a large number of Au n...Nanocrystallites Au particles are deposited on a well-aligned silicon nanoporous pillar array （Si-NPA） surface through immersion plating to form an Au/Si-NPA composite system. It is found that a large number of Au nanoparticles are accumulated on the bottom of Si pillars to form a regular network structure. By studying the field emission properties of such an Au/Si-NPA composite system, we find that the Au/Si-NPA exhibits good field emission properties, with staring field about 2 V/μm and emission current density 67μA/cm^2 at 7.59 V/μm. The enhanced field emission can be deduced from the unique morphology and structure of Au/Si-NPA.展开更多
文摘Two groups of coated conductor samples with different thicknesses of CeO2 cap layers deposited by pulsed laser deposition （PLD） under the same conditions have been studied. Of them, one group is of CeO2 films, which are deposited on stainless steel （SS） tapes coated by IBAD-YSZ （IBAD-YSZ/SS）, and the other group is of CeO2/YSZ/Y2O3 multilayers, which are deposited on NiW substrates by PLD for the fabrication of YBCO-coated conductor through the RABiTS approach. YBCO film is then deposited on the tops of both types of buffer layers by PLD. The effects of the thickness of the CeO2 film on the texture of the CeO2 film and the critical current density （Jc） of the YBCO film are analysed. For the case of CeO2 film on IBAD-YSZ/SS, there appears a self-epitaxy effect with increasing thickness of the CeO2 film. For CeO2/YSZ/Y2O3/NiW, in which the buffer layers are deposited by PLD, there occurs no self-epitaxy effect, and the optimal thickness of CeO2 is about 50 nm. The surface morphologies of the two groups of samples are examined by SEM.
基金Project supported by the Science and Technology Commission of Shanghai Municipality,China(Grant Nos.13111102300 and 11dz1100302)the National Natural Science Foundation of China(Grant Nos.11174193 and 51202141)+1 种基金the National Basic Research Program of China(Grant Nos.2011CBA00105)the Science and Technology Commission of Shanghai Municipality,China(Grant No.14DZ2260700)
文摘It is significant for low-cost preparation of YBa2Cu3O7-δ（YBCO） coated conductors to make clear the mechanism of orientation, copper segregation, and nucleation density in BaF2-derived YBCO crystallization. In the present work,a distinct nucleation mechanism was proposed based on a transient liquid phase induced by the size effect as well as near-equilibrium assumption. With this scheme the nucleation of YBCO prepared by metal–organic deposition（MOD） or the physical vapor deposition BaF2 process was semi-quantitatively analyzed, revealing that the direct driving force for nucleation is YBCO supersaturation in the liquid phase. The theoretical analysis on the nucleation orientation portion is evidenced by the experimental result.
基金Supported by the ITER Project of the Ministry of Science and Technology of China under Grant No 2011GB113004the Shanghai Commission of Science and Technology under Grant Nos 09DZ1206000 and 11DZ1100402the Youth Fund of Natural Science Foundation of China under Grant No 11204174
文摘MgO thin films with different textures are fabricated by the ion beam assisted （IBAD） method on the Y2O3/Al2O3 buffered C276 tape. Then a CaO2 layer is directly grown on the IBAD-MgO film by the pulsed laser deposition （PLD） method. Effects of lBAD-MgO texture, substrata temperature and thickness on the grain alignment of the CeO2 layer are investigated. Film characterization is performed by x-ray diffraction and atomic force microscopy. It is found that the orientation and texture degree of the CaO2 layer are very sensitive to the IBAD-MgO texture. By optimizing the IBAD-MgO texture, CeO2 has pure （002） orientation and excellent biaxial texture deposited in a broad substrata temperature range. In addition, the PLD-CeO2 layer has a thickness effect. Under the optimized experimental condition, the PLD-CeO2 layer has a high in-plane texture of △φ = 2.9° and a smooth surface with an rms surface roughness of less than 2nm. The critical current density Jc of a 0.4μm-thick YBCO film deposited on the CeO2 layer is 6.25 × 106 A/cm2 at 77K and a self-field.
基金This work was supported by the National Natural Science Foundation of China under Grant No. 50672057, 50702033 and 10774098the National Science Foundation of China (973 Projects) under Grant No. 2006CB601005+1 种基金the Science and Technology Commission of Shanghai Municipality under Grant No. 0752nm017the Project Based Personnel Exchange Program between China and Germany under Grant No. [2006] 3139.
文摘Several types of REBa2Cu3O7-x （REBCO, RE=Y, Ho etc.） films are prepared on single crystal substrate LaAIO3 by TFA-MOD method. The phase transformation and optimized growth conditions in the crystallization are studied. Compared with SmBCO and GdBCO, high quality YBCO and HoBCO films are relatively easy to produce. It is revealed that the YBCO grains can form at low temperatures such as 730 ℃ during the initial heating ramp. With a high heating rate of 20 K/min and a low oxygen pressure of 100 ppm, the optimum growth temperature is around 780℃, at which the films show a Jc value of 2.88 MMcm2. Further decrease of the heating rate may produce the highquality YBCO Film with a higher Jc of 3.65 MA/cm2. The temperature dependence of resistances in various magnetic fields up to 9 T shows that the present TFAMOD YBCO and HoBCO films have similar superonducting transition temperature and magnetotransport properties.
文摘CeO2/YSZ/CeO2 buffer layers were prepared on biaxial textured Ni-5at.%W substrate by direct-current magnetron reactive sputtering with the optimum process. YBCO thin films were deposited on CeO2/YSZ/CeO2 buffered Ni-5at.%W substrate at temperature ranging from 500℃ to 700℃ by diode de sputtering. By optimizing substrate temperature, pure c-axis oriented YBCO films were obtained. The mierostruetures of CeO2/YSZ/CeO2 buffer layers were characterized by X-ray diffraction. A smooth, dense and crack-free surface morphology was observed with scanning electron microscopy. The critical current density Jc about 0.75 MA/cm2 at 77 K was obtained.
基金Supported by the National Natural Science Foundation of China under Grant Nos 10732050, 10525210 and 10121202
文摘Manipulating the directional movement of liquid droplets is of significance for design and fabrication of some microfluidic devices, An energy-based method is adopted to analyse the directional movement of a droplet deposited in a conical tube or on a conical fibre. We perform an experiment to investigate the directional motion of a droplet in an open conical tube. Our theoretical analysis and experimental observations both demonstrate that surface tension can drive the droplet to move in the conical tube. The critical condition of the liquid moving in the conical tube is presented. We also analyse a droplet on a conical hydrophilic fibre, which can move from the thinner to the thicker end.
基金Supported by the Knowledge Innovation Project of Chinese Academy of Sciences under Grant No KZCX3-SW-144, the National Science Foundation of China under Grant Nos 60608015, and the Doctoral Fund of Qingdao University of Science and Technology.
文摘A 2 1/2-dimensional electromagnetic particle-in-cell （PIC） simulation code is used to investigate electron behaviour in collisionless magnetic reconnectfon. The results show that the ion/electron mass ratio （mi/me） almost has no impact on the reconnection rate, however it can significantly affect electron behaviour in the diffusion region. For the case with larger mass ratio, the width of electron current sheet becomes smaller and the outflow region along the separatrix is smaller, hence the peak of the electron outflow speed is essentially larger. Density cavities and the parallel electric field E// along the separatrix can be found in the case with larger mass ratio, which may have significant influences on the acceleration and heating of the electrons near the X point.
基金Supported by the National Natural Science Foundation of China under Grant Nos 50572010, 50742007 and 10672020, the National Defense Founds of China under Grant Nos A2220061080, and the National Key Basic Research Programme of China under Grant No 5131803.
文摘We design and prepare three-layer graded ZnO nanowhisker/polyester composites. The dispersion configuration of ZnO nanowhiskers in the polyester is investigated, and their microwave reflectivity curves are also measured. Experimental results have shown that the graded dispersion with ZnO nanowhiskers contributes to broadband microwave absorption. In other words, the absorption band depends on the graded dispersion configuration of ZnO nanowhiskers in polyester matrix.
基金Supported by the National Basic Research Programme of China under Grant No 2006cb302905, the National Science Foundation of China under Grant No 10474093, the Knowledge Innovation Project of Chinese Academy of Sciences under Grant No KJCX3.Syw.H02, and the National High-Technology Research and Development Programme of China under Grant No 2007AA06Z420.
文摘We theoretically analyse the temperature effects on a surface plasmon resonance （SPR） sensor in Kretschmann configuration. The temperature effects include the thermo-optic effect and the dispersion of thermal-optic coefficient in the dielectric along with the thermal expansion effect, phonon-electron scattering and electron-electron scattering in the metal layer. We simulate the temperature dependence of the resonance position and the sensitivity of the SPR sensor under wavelength-interrogation and angular-interrogation mode of operation and the differences are pointed out in the two modes.
基金Supported by the National Natural Science Foundation of China under Grant Nos 60490280, 60621063 and 60308001. We gratefully acknowledge HC Photonics Co. for providing excellent PPLN crystal. We thank NIE Yu- Xin and HAN Hai-Nian for helpful discussions.
文摘We report a femtosecond optical parametric oscillator based on MgO-doped PPLN synchronously pumped by a mode-locked Ti：sapphire laser. The wavelengths of the signal and idler are continuously tuned from 1100 to 1300hm and from 2080 to 2930nm, respectively, by changing the pump wavelength and the OPO cavity length. The maximum signal output power of 130mW at the wavelength of 1225nm is obtained, pumped by 900roW of 800hm laser radiation. This corresponds to a total conversion efficiency of 22.1%. The signal pulse duration is measured to be 167fs by intensity autocorrelation with chirped mirrors for intracavity dispersion compensation.
基金Supported by the National Natural Science Foundation of China under Grant No 10674074, and the Tianjin Natural Science Foundation under Grant Nos 06TXTJJC14601 and 07JCYBJC06400.
文摘We investigate the influence of precursor molar ratio of [S^2-]/[Zn^2＋] on particle size and photoluminescence （PL） of ZnS：Mn^2＋ nanocrystMs. By changing the [S^2-]/[Zn^2＋] ratio from 0.6 （Zn-rich） to 2.0 （S-rich）, the particle size increases from nearly 2. 7nm to about 4.Ohm. The increase in the ratio of [S^2-]/[Zn^2＋] cadses a decrease of PL emission intensity of ZnS host while a distinct increase of Mn^2＋ emission. The maximum intensity for the luminescence of Mn^2＋ emission is observed at the ratio of [S^2-]/[Zn^2＋] ≈ 1.5. The possible mechanism for the results is discussed by filling of S^2- vacancies and the increase of Mn^2＋ ions incorporated into ZnS lattices.
文摘We investigate the influence of vacuum organic contaminations on laser-induced damage threshold （LIDT） of optical coatings. Anti-reflective （AIR） coatings at 1064 nm made by Ta2 O5/SiO2 are deposited by the ion beam sputtering method. The LIDTs of AR coatings are measured in vacuum and in atmosphere, respectively. It is exhibited that contaminations in vacuum are easily to be absorbed onto optical surface because of lower pressure, and they become origins of damage, resulting in the decrease of LIDT from 24.5J/cm^2 in air to 15.TJ/cm^2 in vacuum. The LIDT of coatings in vacuum has is slightly changed compared with the value in atmosphere after the organic contaminations are wiped off. These results indicate that organic contaminations are the main reason of the LIDT decrease in vacuum. Additionally, damage morphologies have distinct changes from vacuum to atmosphere because of the differences between the residual stress and thermal decomposability of filmy materials.
基金Supported by the PhD Progress Foundation of Higher Education of China under Grant No 20040126003, and the Natural Science Foundation of Inner Mongol of China under Grant No 200408020101.
文摘The ground-state energy and effective mass of an acoustic polaron in one dimension are calculated by using an electron-longitudinal-acoustic-phonon interaction Hamiltonian derived here. The self-trapping of the acoustic polaron is discussed. It is found that the critical coupling constant shifts toward weaker electron-phonon interaction with the increasing cutoff wave vector and the products of the critical coupling constant by the cutoff wave vector tend to a certain value. The self-trapping of acoustic polarons in one dimension is easier to be realized than that in three- and two-dimensional systems. The self-trapping transition of acoustic polarons is expected to be observed in the one dimensional systems of alkali halides and wide-band-gap semiconductors.
基金Supported by the National Natural Science Foundation of China under Grant Nos 10372053 and 10472040.
文摘For a nonholonomic mechanics system with the action of small disturbance, the Lie symmetrical perturbation and adiabatic invariants of generalized Hojman type are studied under general infinitesimal transformations of groups in which the generalized coordinates and time are variable. On the basis of the invariance of disturbed nonholonomic dynamical equations under general infinitesimal transformations, the determining equations, the constrained restriction equations and the additional restriction equations of Lie symmetries of the system are constructed, which only depend on the variables t, qs and q^.s. Based on the definition of higher-order adiabatic invariants of a mechanical system, the perturbation of Lie symmetries for a nonholonomic system with the action of small disturbance is investigated, and the Lie symmetrical adiabatic invariants, the weakly Lie symmetrical adiabatic invariants and the strongly Lie symmetrical adiabatic invariants of generalized Hojman type of disturbed nonholonomic systems are obtained. An example is given to illustrate applications of the results.
基金Supported by the National Natural Science Foundation of China under Grant Nos 60476031 and 10474020
文摘We perform a theoretical study on a low dark current InGaAs/GaAs very-long-wavelength （〉 12 μm） quantum well infrared photodetector （VLW-QWIP）, based on a double barrier resonant tunnelling structure （DBRTS）. The ground tunnelling state of the central quantum well （QW） of the DBRTS can resonate with the first excited bound state of the doped InGaAs QW by adjusting the structure parameters of the DBRTS. Investigation of the carrier transport performance of this device is carried out based on quantum wave transport theory. It has been shown that the dark current in this device can be significantly reduced by two orders compared to conventional InGaAs/GaAs VLW-QWIPs, while the photocurrent is almost the same as those in conventional VLW-QWIPs. This DBRTS integrated VLW-QWIP structure may stimulate the experimental investigation for VLW-QWIPs at high operation temperatures.
文摘Tunable diode laser absorption spectroscopy detection of N2 0 around 2.1 μm is demonstrated by using a homemade InGaAsSb/AlGaAsSb MQW laser diode and an InGaAs wavelength extended photodiode. Details of the devices and the detection system are described. In the system, the laser is driven by low frequency pulses with long duration to form a wavelength scan around 4741 cm^-1; the absorption information is obtained from the detected signal of the photodiode. By using a gas cell with 15cm path length, a detection limit is estimated to be smaller than 0.2 Torr.
基金Supported by the National Natural Science Foundation of China under No 50562002, the New Century Excellent Talents in University （NCET-06-0576）, the Key Industrial Project of Jiangxi Provincial Department of Science and Technology [2005]52, Jiangxi Provincial Department of Education [2005]217, the Natural Science Foundation of Jiangxi Province （No 0650074）, and the Center for Smart Materials of The Hong Kong Polytechnic University.
文摘Lead-free piezoelectric ceramics 0.92（Bi0.5Na0.5）TiO3-0.08BaTiO3 ＋ xmol% Co3＋ （BNBT-Co, x = 0-8） are prepared by the solid state reaction method. Effects of the amount of Co^3＋ on the electrical properties and phase transition are studied. The results indicate that the addition of Co^3＋ enhances the mechanical quality factor Q^3＋ significantly, whereas the dissipation factor tanδ has a minimum value at x = 3.5. Meanwhile, addition of Co^3＋ leads to small decreases of piezoelectric constant d33, and planar electromechanical coupling kp. The present 0.92（Bio.aNao.5） TiO3-0.08BaTiO3＋3.5 moi% Co^3＋ ceramics exhibit good performance with mechanical quality factor Qm = 910, piezoelectric constant d33 = 106pC/N, planar electromechanical coupling kp =10% and dissipation factor tanδ = 1.1% at 1 kHz. Saturated polarization hysteresis loops have been obtained for BNBT-Co ceramics. Two dielectric peaks at depolarization temperature Td and Tm appear in the curves of ε33^T vs temperature for the pure BNBT ceramics. However, the first dielectric peak Td disappears after the addition of Co^3＋, which means that the transition from ferroelectric to antiferroelectric phase has been eliminated.
文摘A scanning multi-axis differential optical absorption spectroscopy （DOAS） system is developed for monitoring tropospheric NO2 abundance. Measurements at different viewing angles near the horizon can be performed sequentially with one telescope collecting scattered sunlight reflected by a moving mirror. Tropospheric NO2 diurnal variations can be derived from slant column densities （SCDs） of different elevation angles. The result from a field campaign in Beijing in summer of 2005 reveals potential possibility for the monitoring of tropospheric NO2 by multi-axis DOAS technique.
文摘The subband energy and lasing wavelength of compressively strained triangular Ino.53Ga0.47As/InAs quantum well are calculated and compared with the conventional rectangular ones with the same strain contents. The strain compensation using Al0.33In0.36Ga0.31As barrier is introduced. The results show that lasing wavelength can be extended dramatically to beyond 2.8μm by changing the energy band from the conventional rectangular shape to a triangular one, the realization of such a structure using molecular beam epitaxy technology is also discussed.
基金Supported by the National Natural Science Foundation of China under Grant No 10574112, and the Natural Science Foundation of Henan Province under Grant No 411011800.
文摘Nanocrystallites Au particles are deposited on a well-aligned silicon nanoporous pillar array （Si-NPA） surface through immersion plating to form an Au/Si-NPA composite system. It is found that a large number of Au nanoparticles are accumulated on the bottom of Si pillars to form a regular network structure. By studying the field emission properties of such an Au/Si-NPA composite system, we find that the Au/Si-NPA exhibits good field emission properties, with staring field about 2 V/μm and emission current density 67μA/cm^2 at 7.59 V/μm. The enhanced field emission can be deduced from the unique morphology and structure of Au/Si-NPA.
