The microRaman scattering of 4H-SiC films, fabricated by low pressure chemical vapor deposition under different growth conditions, is investigated at temperatures ranging from 80 K to 550K. The effects of growth condi...The microRaman scattering of 4H-SiC films, fabricated by low pressure chemical vapor deposition under different growth conditions, is investigated at temperatures ranging from 80 K to 550K. The effects of growth conditions on E2 （TO）, E1 （TO） and A1 （LO） phonon mode frequencies are negligible. The temperature dependences of phonon linewidth and lifetime of E2 （TO） modes are analyzed in terms of an anharmonic damping effect induced by thermal and growth conditions. The results show that the lifetime of E2 （TO） mode increases when the quality of the sample improves. Unlike other phone modes, Raman shift of A1 （longitudinal optical plasma coupling （LOPC）） mode does not decrease monotonously when the temperature increases, but tends to blueshift at low temperatures and to redshift at relatively high temperatures. Theoretical analyses are given for the abnormal phenomena of A1 （LOPC） mode in 4H-SiC.展开更多
The second-order optical nonlinearity of CdS nanoparticles with different diameters of 28.0, 30.0, 31.5, 50.0, and 91.0 A was studied by hyper-Rayleigh scattering technique. Results show that the first-order hyperpola...The second-order optical nonlinearity of CdS nanoparticles with different diameters of 28.0, 30.0, 31.5, 50.0, and 91.0 A was studied by hyper-Rayleigh scattering technique. Results show that the first-order hyperpolarizability P value per CdS partiele decreases as size is reduced to diameter of 31.5 A; however, as CdS size further decreases, this trend is reversed and (J value increases. Substantially, the normalized P value per CdS formula unit, β0, exhibits systematic enhancement with decreasing size. This phenomenon is interpreted in terms of a so-called surfaee contribution mechanism.展开更多
First-order Raman scatterings of hexagonal GaN layers deposited by the hydride vapour phase epitaxy and by metal-organic chemical vapour deposition on SiC and sapphire substrates are studied in a temperature range bet...First-order Raman scatterings of hexagonal GaN layers deposited by the hydride vapour phase epitaxy and by metal-organic chemical vapour deposition on SiC and sapphire substrates are studied in a temperature range between 303 K and 503 K. The temperature dependences of two GaN Raman modes （Al （LO） and E2 （high）） are obtained. We focus our attention on the temperature dependence of E2 （high） mode and find that for different types of GaN epilayers their temperature dependences are somewhat different. We compare their differences and give them an explanation. The simplified formulas we obtained are in good accordance with experiment data. The results can be used to determine the temperature of a GaN sample.展开更多
The evolution of solitons in Bose-Einstein condensates （BECs） with time-dependent atomic scattering length in an expulsive parabolic potential is studied. Based on the extended hyperbolic function method, we success...The evolution of solitons in Bose-Einstein condensates （BECs） with time-dependent atomic scattering length in an expulsive parabolic potential is studied. Based on the extended hyperbolic function method, we successfully obtain the bright and dark soliton solutions. In addition, some new soliton solutions in this model are found. The results in this paper include some in the literature （Phys. Rev. Lett. 94（2005）050402 and Chin. Phys. Lett. 22（2005） 1855）.展开更多
Sea-surface acoustic backscattering measurements at moderate to high frequencies were performed in the shallow water of the south Yellow Sea, using omnidirectional spherical sources and omnidirectional hydrophones. Se...Sea-surface acoustic backscattering measurements at moderate to high frequencies were performed in the shallow water of the south Yellow Sea, using omnidirectional spherical sources and omnidirectional hydrophones. Sea-surface backscattering data for frequencies in the 6–25 k Hz range and wind speeds of(3.0±0.5)and(4.5±1.0) m/s were obtained from two adjacent experimental sites, respectively. Computation of sea-surface backscattering strength using bistatic transducer is described. Finally, we calculated sea-surface backscattering strengths at grazing angles in the range of 16°–85°. We find that the measured backscattering strengths agree reasonably well with those predicted by using second order small-roughness perturbation approximation method with "PM" roughness spectrum for all frequencies at grazing angles ranged from 40° to 80°. The backscattering strengths varied slightly at grazing angles of 16°–40°, and were much stronger than roughness scattering. It is speculated that scattering from bubbles dominates the backscattering strengths at high wind speeds and small grazing angles. At the same frequencies and moderate to high grazing angles, the results show that the backscattering strengths at a wind speed of(4.5±1.0) m/s were approximately 5 d B higher than those at a wind speed of(3.0±0.5) m/s. However, the discrepancies of backscattering strength at low grazing angles were more than 10 d B. Furthermore the backscattering strengths exhibited no significant frequency dependence at 3 m/s wind speed. At a wind speed of 4.5 m/s, the scattering strengths increased at low grazing angles but decreased at high grazing angles with increasing grazing angle.展开更多
Polystyrene films were adsorbed onto a silver surface from dichloromethane solutions with concentrations of 0.1 to 12 wt%, and then studied by the surface enhanced Raman technique. A critical concentration for coil in...Polystyrene films were adsorbed onto a silver surface from dichloromethane solutions with concentrations of 0.1 to 12 wt%, and then studied by the surface enhanced Raman technique. A critical concentration for coil interpenetration was observed.展开更多
A nonpolar SiC（1120） substrate has been used to fabricate epitaxial graphene （EG）. Two EGs with layer numbers of 8-10 （referred to as MLG） and 2-3 （referred to as FLG） were used as representative to study the ...A nonpolar SiC（1120） substrate has been used to fabricate epitaxial graphene （EG）. Two EGs with layer numbers of 8-10 （referred to as MLG） and 2-3 （referred to as FLG） were used as representative to study the substrate effect on EG through temperature-dependent Raman scattering. It is found that Raman lineshifts of G and 2D peaks of the MLG with temperature are consistent with that of free graphene, as predicted by theory calculation, indicating that the substrate influence on the MLG is undetectable. While Raman G peak lineshifts of the FLG to that of the free graphene are obvious, however, its lineshift rate （-0.016 cm-1/K） is almost one third of that （-0.043 cm-1/K） of an EG on 6H-SiC （0001） in the temperature range from 300 K to 400 K, indicating a weak substrate effect from SiC （1120） on the FLG. This renders the FLG with a high mobility around 1812 cm2.V-1 .s -1 at room temperature even with a very high carrier concentration about 2.95 × 10 ^13 cm-2 （p-type）. These suggest SiC （1120） is more suitable for fabricating EG with high performance.展开更多
Surface-enhanced Raman scattering（SERS） spectra of different silver nanoplate selt-assembled tllmS at different excitation wavelengths were fairly compared. Shape conversion from silver nanoprisms to nanodisks on sl...Surface-enhanced Raman scattering（SERS） spectra of different silver nanoplate selt-assembled tllmS at different excitation wavelengths were fairly compared. Shape conversion from silver nanoprisms to nanodisks on slides was in situ carried out. The SERS spectra of 4-mercaptopyridine（4-MPY） on these anisotropic silver nanopar- ticle self-assembled films present that strong enhancement appeared when the excitation line and the surface plasmon resonance（SPR） band of silver substrate overlapped. In this model, the influence of the crystal planes of silver na- noplates on SERS enhancement could be ignored because the basal planes were nearly unchanged in two kinds of silver nanoplate self-assembled films.展开更多
Hadron production in lepton-nucleus deep inelastic scattering is studied in a quark energy loss model. The leading-order computations for hadron multiplicity ratios are presented and compared with the selected HERMES ...Hadron production in lepton-nucleus deep inelastic scattering is studied in a quark energy loss model. The leading-order computations for hadron multiplicity ratios are presented and compared with the selected HERMES pions production data with the quark hadronization occurring outside the nucleus by means of the hadron formation time. It is found that the obtained energy loss per unit length is 0.440±0.013 GeV/fm for an outgoing quark by the global fit. It is confirmed that the atomic mass number dependence of hadron attenuation is theoretically and experimentally in good agreement with the A2/3 power law for quark hadronization occurring outside the nucleus,展开更多
We experimentally study the wavelength dependence of light propagation in a water suspension of lithium niobate microcrystalline particles.First,the ballistic transmission in the visible range of the suspension is mea...We experimentally study the wavelength dependence of light propagation in a water suspension of lithium niobate microcrystalline particles.First,the ballistic transmission in the visible range of the suspension is measured.The nonlinear relationship is observed between the transport mean free path and the wavelength of the incident light.Secondly,we measure the coherent backscattering (CBS) of the sample at different wavelengths.The full width at half maximum of the CBS cone at 532 nm is about 1.24 times as large as that at 671 nm.The results indicate that the light with a long wavelength propagates further than the short wavelength light and the localization state of the short one is stronger.Finally,we investigate the light-controllable CBS experiments in the disordered materials of anisotropic scatterers,which show that the configuration of pump light with the longer wavelength and the probe light with the shorter wavelength performs better.展开更多
This paper presents a highly parallelizable numerical method to solve time dependent acoustic obstacle scattering problems.The method proposed is a generalization of the“operator expansion method”developed by Recchi...This paper presents a highly parallelizable numerical method to solve time dependent acoustic obstacle scattering problems.The method proposed is a generalization of the“operator expansion method”developed by Recchioni and Zirilli[SIAM J.Sci.Comput.,25(2003),1158-1186].The numerical method proposed reduces,via a perturbative approach,the solution of the scattering problem to the solution of a sequence of systems of first kind integral equations.The numerical solution of these systems of integral equations is challenging when scattering problems involving realistic obstacles and small wavelengths are solved.A computational method has been developed to solve these challenging problems with affordable computing resources.To this aim a new way of using the wavelet transform and new bases of wavelets are introduced,and a version of the operator expansion method is developed that constructs directly element by element in a fully parallelizable way.Several numerical experiments involving realistic obstacles and“small”wavelengths are proposed and high dimensional vector spaces are used in the numerical experiments.To evaluate the performance of the proposed algorithm on parallel computing facilities,appropriate speed up factors are introduced and evaluated.展开更多
基金Supported by the National Natural Science Foundation of China under Grant Nos 61176085,11474365 and 61377055the Department of Education of Guangdong Province under Grant No gjhz1103the Open-Project Program of the State Key laboratory of Opto-Electronic Material and Technologies of Sun Yatsen University
文摘The microRaman scattering of 4H-SiC films, fabricated by low pressure chemical vapor deposition under different growth conditions, is investigated at temperatures ranging from 80 K to 550K. The effects of growth conditions on E2 （TO）, E1 （TO） and A1 （LO） phonon mode frequencies are negligible. The temperature dependences of phonon linewidth and lifetime of E2 （TO） modes are analyzed in terms of an anharmonic damping effect induced by thermal and growth conditions. The results show that the lifetime of E2 （TO） mode increases when the quality of the sample improves. Unlike other phone modes, Raman shift of A1 （longitudinal optical plasma coupling （LOPC）） mode does not decrease monotonously when the temperature increases, but tends to blueshift at low temperatures and to redshift at relatively high temperatures. Theoretical analyses are given for the abnormal phenomena of A1 （LOPC） mode in 4H-SiC.
基金supposed by the National Natural Science Foundation of China(Nos.50202009,10074023)the National Postdoctoral Foundation(No.2002031222).
文摘The second-order optical nonlinearity of CdS nanoparticles with different diameters of 28.0, 30.0, 31.5, 50.0, and 91.0 A was studied by hyper-Rayleigh scattering technique. Results show that the first-order hyperpolarizability P value per CdS partiele decreases as size is reduced to diameter of 31.5 A; however, as CdS size further decreases, this trend is reversed and (J value increases. Substantially, the normalized P value per CdS formula unit, β0, exhibits systematic enhancement with decreasing size. This phenomenon is interpreted in terms of a so-called surfaee contribution mechanism.
基金supported by the National Key Science & Technology Special Project (Grant No.2008ZX01002-002)the Fundamental Research Funds for the Central Universities (Grant No.JY10000904009)the Major Program and State Key Program of National Natural Science Foundation of China (Grant Nos.60890191 and 60736033)
文摘First-order Raman scatterings of hexagonal GaN layers deposited by the hydride vapour phase epitaxy and by metal-organic chemical vapour deposition on SiC and sapphire substrates are studied in a temperature range between 303 K and 503 K. The temperature dependences of two GaN Raman modes （Al （LO） and E2 （high）） are obtained. We focus our attention on the temperature dependence of E2 （high） mode and find that for different types of GaN epilayers their temperature dependences are somewhat different. We compare their differences and give them an explanation. The simplified formulas we obtained are in good accordance with experiment data. The results can be used to determine the temperature of a GaN sample.
基金Project supported by the National Natural Science Foundation of China （Grant Nos 1057508 and 10302018）, the Natural Science Foundation of Zhejiang Province, China （Grant No Y605056）.
文摘The evolution of solitons in Bose-Einstein condensates （BECs） with time-dependent atomic scattering length in an expulsive parabolic potential is studied. Based on the extended hyperbolic function method, we successfully obtain the bright and dark soliton solutions. In addition, some new soliton solutions in this model are found. The results in this paper include some in the literature （Phys. Rev. Lett. 94（2005）050402 and Chin. Phys. Lett. 22（2005） 1855）.
基金The National Natural Science Foundation of China under contract Nos 41330965 and 41527809the Opening Fund of Qingdao National Laboratory for Marine Science and Technology under contract No. QNLM2016ORP0209the Taishan Scholar Project Funding under contract No. tspd20161007.
文摘Sea-surface acoustic backscattering measurements at moderate to high frequencies were performed in the shallow water of the south Yellow Sea, using omnidirectional spherical sources and omnidirectional hydrophones. Sea-surface backscattering data for frequencies in the 6–25 k Hz range and wind speeds of(3.0±0.5)and(4.5±1.0) m/s were obtained from two adjacent experimental sites, respectively. Computation of sea-surface backscattering strength using bistatic transducer is described. Finally, we calculated sea-surface backscattering strengths at grazing angles in the range of 16°–85°. We find that the measured backscattering strengths agree reasonably well with those predicted by using second order small-roughness perturbation approximation method with "PM" roughness spectrum for all frequencies at grazing angles ranged from 40° to 80°. The backscattering strengths varied slightly at grazing angles of 16°–40°, and were much stronger than roughness scattering. It is speculated that scattering from bubbles dominates the backscattering strengths at high wind speeds and small grazing angles. At the same frequencies and moderate to high grazing angles, the results show that the backscattering strengths at a wind speed of(4.5±1.0) m/s were approximately 5 d B higher than those at a wind speed of(3.0±0.5) m/s. However, the discrepancies of backscattering strength at low grazing angles were more than 10 d B. Furthermore the backscattering strengths exhibited no significant frequency dependence at 3 m/s wind speed. At a wind speed of 4.5 m/s, the scattering strengths increased at low grazing angles but decreased at high grazing angles with increasing grazing angle.
基金This work was supported by the National Key Project for Fundamental Research "Macromolecular Condensed State", the State Science and Technology Commission of China and the Science Foundation of Polymer Physics Laboratory, Chinese Academy of Sciences.
文摘Polystyrene films were adsorbed onto a silver surface from dichloromethane solutions with concentrations of 0.1 to 12 wt%, and then studied by the surface enhanced Raman technique. A critical concentration for coil interpenetration was observed.
基金Project supported by the National Basic Research Program of China (Grant No. 2011CB932700)the Knowledge Innovation Project of the Chinese Academy of Sciences (Grant No. KJCX2-YW-W22)the National Natural Science Foundation of China (Grant Nos. 51072223 and 50972162)
文摘A nonpolar SiC（1120） substrate has been used to fabricate epitaxial graphene （EG）. Two EGs with layer numbers of 8-10 （referred to as MLG） and 2-3 （referred to as FLG） were used as representative to study the substrate effect on EG through temperature-dependent Raman scattering. It is found that Raman lineshifts of G and 2D peaks of the MLG with temperature are consistent with that of free graphene, as predicted by theory calculation, indicating that the substrate influence on the MLG is undetectable. While Raman G peak lineshifts of the FLG to that of the free graphene are obvious, however, its lineshift rate （-0.016 cm-1/K） is almost one third of that （-0.043 cm-1/K） of an EG on 6H-SiC （0001） in the temperature range from 300 K to 400 K, indicating a weak substrate effect from SiC （1120） on the FLG. This renders the FLG with a high mobility around 1812 cm2.V-1 .s -1 at room temperature even with a very high carrier concentration about 2.95 × 10 ^13 cm-2 （p-type）. These suggest SiC （1120） is more suitable for fabricating EG with high performance.
基金Supported by the National Natural Science Foundation of China(Nos.91027010,21073073,20903043,20973075,20773045)the Research Fund for the Doctoral Program of Higher Education of China(No.20090061120089)the Open Project of State Key Laboratory for Supramolecular Structure and Materials of China(No.201125)
文摘Surface-enhanced Raman scattering（SERS） spectra of different silver nanoplate selt-assembled tllmS at different excitation wavelengths were fairly compared. Shape conversion from silver nanoprisms to nanodisks on slides was in situ carried out. The SERS spectra of 4-mercaptopyridine（4-MPY） on these anisotropic silver nanopar- ticle self-assembled films present that strong enhancement appeared when the excitation line and the surface plasmon resonance（SPR） band of silver substrate overlapped. In this model, the influence of the crystal planes of silver na- noplates on SERS enhancement could be ignored because the basal planes were nearly unchanged in two kinds of silver nanoplate self-assembled films.
基金Supported by National Natural Science Foundation of China (11075044)Natural Science Foundation of Hebei Province (A2013209299)
文摘Hadron production in lepton-nucleus deep inelastic scattering is studied in a quark energy loss model. The leading-order computations for hadron multiplicity ratios are presented and compared with the selected HERMES pions production data with the quark hadronization occurring outside the nucleus by means of the hadron formation time. It is found that the obtained energy loss per unit length is 0.440±0.013 GeV/fm for an outgoing quark by the global fit. It is confirmed that the atomic mass number dependence of hadron attenuation is theoretically and experimentally in good agreement with the A2/3 power law for quark hadronization occurring outside the nucleus,
基金supported by the National Natural Science Foundation of China (Grant Nos. 10874093 and 10804055)the National Basic Research Program of China (Grant Nos. 2007CB307002 and 2010CB934101)+1 种基金the 111 Project (Grant No. B07013)the Program for NCET
文摘We experimentally study the wavelength dependence of light propagation in a water suspension of lithium niobate microcrystalline particles.First,the ballistic transmission in the visible range of the suspension is measured.The nonlinear relationship is observed between the transport mean free path and the wavelength of the incident light.Secondly,we measure the coherent backscattering (CBS) of the sample at different wavelengths.The full width at half maximum of the CBS cone at 532 nm is about 1.24 times as large as that at 671 nm.The results indicate that the light with a long wavelength propagates further than the short wavelength light and the localization state of the short one is stronger.Finally,we investigate the light-controllable CBS experiments in the disordered materials of anisotropic scatterers,which show that the configuration of pump light with the longer wavelength and the probe light with the shorter wavelength performs better.
文摘This paper presents a highly parallelizable numerical method to solve time dependent acoustic obstacle scattering problems.The method proposed is a generalization of the“operator expansion method”developed by Recchioni and Zirilli[SIAM J.Sci.Comput.,25(2003),1158-1186].The numerical method proposed reduces,via a perturbative approach,the solution of the scattering problem to the solution of a sequence of systems of first kind integral equations.The numerical solution of these systems of integral equations is challenging when scattering problems involving realistic obstacles and small wavelengths are solved.A computational method has been developed to solve these challenging problems with affordable computing resources.To this aim a new way of using the wavelet transform and new bases of wavelets are introduced,and a version of the operator expansion method is developed that constructs directly element by element in a fully parallelizable way.Several numerical experiments involving realistic obstacles and“small”wavelengths are proposed and high dimensional vector spaces are used in the numerical experiments.To evaluate the performance of the proposed algorithm on parallel computing facilities,appropriate speed up factors are introduced and evaluated.
