|
Surface and Volume Symmetry Energy Coefficients of a Neutron-Rich Nucleus
MA Chun-Wang, YANG Ju-Bao, YU Mian, PU Jie, WANG Shan-Shan, WEI Hui-Ling
Chin. Phys. Lett. 2012, 29 (9):
092101
.
DOI: 10.1088/0256-307X/29/9/092101
Using an isobaric method, the symmetry-energy coefficient (asym) of a neutron-rich nucleus is obtained from experimental binding energies. The shell effects are shown in asym*/A≡4asym/A of nuclei. A (sub)magic neutron magic number N=40 is suggested in a very neutron-rich nucleus, and asym*/A of a nucleus is found to decrease when its mass increases. The asym*/A of a very neutron-rich nucleus with large mass saturates. The volume-symmetry coefficients (bv) and surface-symmetry coefficients (bs) of a neutron-rich nucleus are extracted from a sym*/A by a correlation asym*/A=bv/A?b s/A4/3. It is found that bv and bs decrease when the nucleus becomes more neutron-rich, and tend to saturate in the very neutron-rich nucleus. A linear correlation between b v and bs is obtained in nuclei with different neutron-excess I, and bv of I>7 nuclei is found to coincide with the results of infinite nuclear matter a sym=32 ±4 MeV, and bs/bv of the nucleus is found to coincide with the results of the finite-range liquid-drop model results.
|
|
The ab initio Calculation of Electric Field Gradient at the Site of P Impurity in α-Al3O2
ZHANG Qiao-Li, YUAN Da-Qing, ZHANG Huan-Qiao, FAN Ping, ZUO Yi, ZHENG Yong-Nan, K. Masuta, M. Fukuda, M. Mihara, T. Minamisono, A. Kitagawa, ZHU Sheng-Yun
Chin. Phys. Lett. 2012, 29 (9):
092102
.
DOI: 10.1088/0256-307X/29/9/092102
An ab initio calculation of the electric-field gradient (EFG) at the site of a phosphorous impurity substituting an Al atom in α-Al2O3 is carried out using the WIEN2k code with the full-potential linearized augmented plane wave plus local orbital method (LAPW+lo) in the frame of density functional theory. The atomic lattice relaxations caused by the implanted impurities were calculated for two different charged states to well describe the electronic structure of the doped system. The EFG at the site of the phosphorous impurity in the charged supercell calculated with the exchange-correlation potential of the Wu-Cohen generalized gradient approximation (WC-GGA) is 0.573×1021 V/m2. Then, the nuclear quadrupole moment of the I=3 state in 28P is deduced to be 137 mb from the quadrupole interaction frequency of 190 kHz measured recently by the β-NQR method.
|
|
Near-Yrast Structures in Odd-Odd 122I Nucleus
LIU Gong-Ye, LI Li, LI Xian-Feng, YU De-Yang, SUN Ji, LI Cong-Bo, MA Ying-Jun, WU Xiao-Guang, HE Chuang-Ye, ZHENG Yun, ZHU Li-Hua, ZHAO Yan-Xin
Chin. Phys. Lett. 2012, 29 (9):
092301
.
DOI: 10.1088/0256-307X/29/9/092301
Excited states of the odd-odd nucleus 122I are investigated via the fusion-evaporation reaction 116Cd(11B,5n) at a beam energy of 68 MeV. The two most strongly populated bands in 122I are observed up to excitation energies around 10.5 MeV. Their possible configurations at lower spins are assigned to πh11/2?νh11/2 and πh11/2?νd5/2 based on the observed population, B(M1)/B(E2) values, alignments and signature splitting. E1 transitions are observed connecting the πh11/2?νd5/2 band to the πh11/2?νh11/2 band, which may be evidence of octupole collectivity. Band terminations caused by the full alignment of the valence nucleons outside the 114Sn core are observed in both bands.
|
|
Influences of Both Δ? and Δ0 Particles on the Neutron Star Cooling
DING Wen-Bo, LI Ying, MI Geng
Chin. Phys. Lett. 2012, 29 (9):
092601
.
DOI: 10.1088/0256-307X/29/9/092601
The influences of Δ quartet, especially Δ? and Δ0 particles, on the neutrino scatting and cooling properties of neutron stars are discussed. The results show that Δ quartet can change the density range of direct Urca process of nucleons for muons, as well as the neutrino emissivity and luminosity. The role of Δ on the cooling rates is complicated. It is found that Δ quartet slows the neutron star cooling obviously in hyperonic neutron star matter. However in nuclear matter, Δ can not influence the cooling too much, unless the neutron star is quite massive. The Δ-meson coupling constants can also impact on the results, and the relatively smaller value, the stronger effects of Δ quartet.
|
|
High Power Q-Switched Dual-End-Pumped Ho:YAG Laser
DUAN Xiao-Ming, SHEN Ying-Jie, DAI Tong-Yu, YAO Bao-Quan, WANG Yue-Zhu
Chin. Phys. Lett. 2012, 29 (9):
094202
.
DOI: 10.1088/0256-307X/29/9/094202
We report the high power acousto-optically Q-switched operation of a dual-end-pumped Ho:YAG laser at room temperature. For the Q-swithched mode, a maximum pulse energy of 2.4 mJ and a minimum pulse width of 23 ns at the repetition rate of 10 kHz are achieved, resulting in a peak power of 104.3 kW. The beam quality factor of M 2~1.5, which is demonstrated by a knife-edge method. In addition, the Ho:YAG laser is employed as a pumping source of ZGP optical parametric oscillator, and its total average output power is 13.2 W at 3.9 μm and 4.4 μm with a slope efficiency of 68.4%.
|
|
High Conversion Efficiency and Power Stability of 532 nm Generation from an External Frequency Doubling Cavity
ZHAO Yang, LIN Bai-Ke, LI Ye, ZHANG Hong-Xi, CAO Jian-Ping, FANG Zhan-Jun, LI Tian-Chu, ZANG Er-Jun
Chin. Phys. Lett. 2012, 29 (9):
094210
.
DOI: 10.1088/0256-307X/29/9/094210
We present a high-efficiency 532 nm green light conversion from an external cavity-enhanced second harmonic generation (SHG) with a periodically poled KTP crystal (PPKTP). The cavity is a bow-tie ring configuration with a unitized structure. When the impedance matching is optimized, the coupling efficiency of the fundamental is as high as 95%. Taking into account both the high power output of the second harmonic and the stability of the system, we obtain over 500 mW green passing through the output cavity mirror, corresponding to a net conversion efficiency higher than 75.2%. Under these operating conditions, the power stability is better than ±0.25% during 5 h. It is the highest conversion efficiency and power stability ever produced in the bow-tie ring cavity with PPKTP for 532 nm generation.
|
|
Subgrid-Scale Fluid Statistics along the Inertial Particle Trajectory in Isotropic Turbulence
YI Chao, LI Jing, LIU Zhao-Hui, WANG Lin, ZHENG Chu-Guang
Chin. Phys. Lett. 2012, 29 (9):
094701
.
DOI: 10.1088/0256-307X/29/9/094701
Fluctuations of sub-grid scale (SGS) velocity and its influence on the motion of particles are important issues for large eddy simulation (LES) of gas-particle turbulence. We obtain the SGS statistics from the direct numerical simulation (DNS) data of homogeneous isotropic turbulent flow, which is filtered by the top filter in physical space. The result shows that the SGS kinetic energy seen by particles reach a minimum value when the Stokes number St closes to 1. Moreover, the turning point shifts towards a larger St as the filter width increases. Different from that observed in DNS, the Lagrangian integral time scale is larger than the Eulerian integral time scale in SGS. For small particles, the Lagrangian timescale of SGS fluid seen by particle is very close to that of the fluid itself. For particles which are large enough, it approaches the Eulerian timescale of SGS fluid. For the intermediate particles, the predicted curve of SGS fluid timescale seen by particle varies with St and its variation is non-monotonic.
|
|
Effective Opacity for Gold-Doped Foam Plasmas
HUANG Cheng-Wu, SONG Tian-Ming, ZHAO Yang, ZHU Tuo, SHANG Wan-Li, XIONG Gang, ZHANG Ji-Yan, YANG Jia-Min, JIANG Shao-En
Chin. Phys. Lett. 2012, 29 (9):
095201
.
DOI: 10.1088/0256-307X/29/9/095201
Radiation flow through gold-doped hydrocarbon foam is investigated and a model is presented to calculate effective opacity for an inhomogeneous, pressure-equilibrated gold/foam mixture based on the Levermore–Pomraning method for binary stochastic media. The effective opacity dependance on the size of the gold particles and the foam temperature are studied. The results suggest that when the mixture temperature is lower than 250 eV, the opacity difference between the 5 μm particle mix case and the atomic mix case is large enough to induce a significant discrepancy in radiation transport, which is confirmed by the hydrodynamic simulation.
|
|
Optoelectronic Response of GeZn2O4 through the Modified Becke–Johnson Potential
Iftikhar Ahmad, B. Amin, M. Maqbool, S. Muhammad, G. Murtaza, S. Ali, N. A. Noor
Chin. Phys. Lett. 2012, 29 (9):
097102
.
DOI: 10.1088/0256-307X/29/9/097102
A first-principles technique capable of describing the nearly excited states of semiconductors and insulators, namely the modified Becke–Johnson (mBJ) potential approximation, is used to investigate the electronic band structure and optical properties of spinel oxides: GeZn2O4. The predicted band gaps using the mBJ approximation are significantly more accurate than the proposed previous theoretical work using the common LDA and GGA. Band gap dependent optical parameters, like the dielectric constant, index of refraction, reflectivity and optical conductivity are calculated and analyzed. The results from the dielectric constant shows that the numerical value of the static dielectric, after dropping constantly, becomes less than zero and the material exhibits metallic behavior. The refractive index also drops below unity for photons higher than 18 eV, which indicates that the velocities of incident photons are greater than the velocity of light. However, these phenomena can be explained by the fact that a signal must be transmitted as a wave packet rather than a monochromatic wave. This comprehensive theoretical study of the optoelectronic properties predicts that these materials can effectively be used in optical devices.
|
|
Spin Dynamics in (111) GaAs/AlGaAs Undoped Asymmetric Quantum Wells
WANG Gang, YE Hui-Qi, SHI Zhen-Wu, WANG Wen-Xin, MARIE Xavier, BALOCCHI Andrea, AMAND Thierry, LIU Bao-Li
Chin. Phys. Lett. 2012, 29 (9):
097204
.
DOI: 10.1088/0256-307X/29/9/097204
The electron spin dynamics is investigated by the time-resolved Kerr rotation technique in a pair of special GaAs/AlGaAs asymmetric quantum well samples grown on (111)-oriented substrates, whose structures are the same except for their opposite directions of potential asymmetry. A large difference of spin lifetimes between the two samples is observed at low temperature. This difference is interpreted in terms of a cancellation effect between the Dresselhaus spin-splitting term in the conduction band and another term induced by interface inversion asymmetry. The deviation decreases with the increasing temperature, and almost disappears when T>100 K because the cubic Dresselhaus term becomes more important.
|
|
High Quantum Efficiency Back-Illuminated AlGaN-Based Solar-Blind Ultraviolet p–i–n Photodetectors
WANG Guo-Sheng, LU Hai, XIE Feng, CHEN Dun-Jun, REN Fang-Fang, ZHANG Rong, ZHENG You-Dou
Chin. Phys. Lett. 2012, 29 (9):
097302
.
DOI: 10.1088/0256-307X/29/9/097302
AlGaN-based back-illuminated solar-blind ultraviolet (UV) p–i–n photodetectors (PDs) with high quantum efficiency are fabricated on sapphire substrates. To improve the overall performance of the PD, a series of structural design considerations and growth procedures are implemented in the epitaxy process. A distinct wavelength-selective photo-response peak of the PD is obtained in the solar-blind region. When operating in photovoltaic mode, the PD exhibits a solar-blind/UV rejection ratio of up to 4 orders of magnitude and a peak responsivity of ~113.5 mA/W at 270 nm, which corresponds to an external quantum efficiency of ~52%. Under a reverse bias of ?5 V, the PD shows a low dark current of ~1.8 pA and an enhanced peak quantum efficiency of ~64%. The thermal noise limited detectivity is estimated to be ~3.3×1013 cm?Hz1/2W?1.
|
|
Confined Mie Plasmons in Monolayer Hexagonal-Close-Packed Metallic Nanoshells
CHEN Jing, DONG Wen, WANG Qiu-Gu, TANG Chao-Jun, CHEN Zhuo, WANG Zhen-Lin
Chin. Phys. Lett. 2012, 29 (9):
097303
.
DOI: 10.1088/0256-307X/29/9/097303
Using a double templating method by electroless deposition within a templating organic porous mold, we fabricate a monolayer of hexagonal-close-packed metallic nanoshells, each with a small opening. Light transmission spectra of the metallic nanoshell arrays are measured, which show transmission resonances at specific wavelengths whose positions are observed to be independent of the incident angle as well as light polarizations. More interestingly, the resonance wavelengths of Mie plasmon modes are also independent of the surrounding medium. Further numerical simulations confirm these transmission resonances and reveal that they are attributed to the excitations of highly localized dipolar, quadrupolar and hexapolar Mie plasmon modes, which are highly confined within metallic nanoshells.
|
|
Improved Efficiency Droop in a GaN-Based Light-Emitting Diode with an AlInN Electron-Blocking Layer
WEN Xiao-Xia, YANG Xiao-Dong, HE Miao, LI Yang, WANG Geng, LU Ping-Yuan, QIAN Wei-Ning, LI Yun, ZHANG Wei-Wei, WU Wen-Bo, CHEN Fang-Sheng, DING Li-Zhen
Chin. Phys. Lett. 2012, 29 (9):
097304
.
DOI: 10.1088/0256-307X/29/9/097304
GaN-based light-emitting devices (LEDs) with different electron blocking layers are theoretically studied and compared by using the advanced physical models of a semiconductor device simulation program. It is found that the structure with an AlInN electron blocking layer shows improved light output power, lower current leakage and efficiency droop. Based on numerical simulation and analysis, these improvements of the electrical and optical characteristics are mainly accounted for by efficient electron blocking. It can be concluded that Auger recombination is responsible for the dominant origin of the efficiency droop of a GaN-based LED as current increases.
|
|
Preparation and Characterization of Bimodal Magnetofluorescent Nanoprobes for Biomedical Application
LEI Jie-Mei, XU Xiao-Liang, LIU Ling, YIN Nai-Qiang, ZHU Li-Xin
Chin. Phys. Lett. 2012, 29 (9):
097803
.
DOI: 10.1088/0256-307X/29/9/097803
Magnetic-fluorescent bifunctional Fe3O4/SiO2-CdTeS nanocomposites are synthesized. Fe3O4 superparamagnetic nanoparticles are firstly prepared through the thermal decomposition of Fe oleate precursors and coated with a mesoporous silica shell using the St?ber method, and the silica surface is then modified with positively charged amino groups by adding 3-aminopropyltrimethoxysilane. Finally, negatively charged CdTeS quantum dots are linked and assembled onto the positively charged surface of Fe3O4/SiO2 through electrostatic interactions. X-ray diffraction, transmission electron microscopy, photoluminescence spectroscopy, and magnetometry are applied to characterize the nanocomposites. The results show that the bifunctional nanocomposites combine the optical properties of near-infrared CdTeS quantum dots with the superparamagnetic properties of Fe3O4 perfectly, expressing the potential application as a biocompatible magnetofuorescent nanoprobe for in vivo labelling.
|
|
White Hybrid Light-Emitting Devices Based on the Emission of Thermal Annealed Ternary CdSe/ZnS Quantum Dots
QU Da-Long, ZHANG Zhen-Song, YUE Shou-Zhen, WU Qing-Yang, YAN Ping-Rui, ZHAO Yi, LIU Shi-Yong
Chin. Phys. Lett. 2012, 29 (9):
097805
.
DOI: 10.1088/0256-307X/29/9/097805
We report on a white hybrid light-emitting device employing a mixture of ternary CdSe/ZnS quantum dots (QDs) as an emitting layer (EML) and a small molecular material tris(8-hydroxyquinoline) aluminum (Alq3) as an electron-transporting layer. The film morphology of the spin-coated mixture of QDs is strongly improved via thermal annealing, and therefore a close-packed QD-EML is realized between organic charge-transporting layers. As a result, compared to the device with an unannealed QD-EML, the emission of Alq3 is deeply suppressed. In addition, a maximum luminance of more than 1000 cd/m2 and a maximum luminous efficiency of 2.2 cd/A are achieved.
|
|
A Self-Aligned Process to Fabricate a Metal Electrode-Quantum Dot/Nanowire-Metal Electrode Structure with 100% Yield
FU Ying-Chun, WANG Xiao-Feng, FAN Zhong-Chao, YANG Xiang, BAI Yun-Xia, ZHANG Jia-Yong, MA Hui-Li, JI An, YANG Fu-Hua
Chin. Phys. Lett. 2012, 29 (9):
098102
.
DOI: 10.1088/0256-307X/29/9/098102
Using lateral phase change random access memory (PCRAM) for demonstration, we report a self-aligned process to fabricate a metal electrode-quantum dot(QD)/nanowire(NW)-metal electrode structure. Due to the good confinement and coupling between the Ge2Sb2Te5 (GST) QD and the tungsten electrodes, the device shows a threshold current and voltage as small as 2.50 μA and 1.08 V, respectively. Our process is highlighted with good controllability and repeatability with 100% yield, making it a promising fabrication process for nanoelectronics.
|
|
Effect of Aluminium Nanoparticles on the Performance of Bulk Heterojunction Organic Solar Cells
YANG Shao-Peng, YAO Ming, JIANG Tao, LI Na, ZHANG Ye, LI Guang, LI Xiao-Wei, FU Guang-Sheng
Chin. Phys. Lett. 2012, 29 (9):
098402
.
DOI: 10.1088/0256-307X/29/9/098402
Al nanoparticles (NPs) are incorporated in the active layers to enhance the performance of organic solar cells (OSCs). The improved short circuit current Jsc and power conversion efficiency (PCE) for OSCs with Al NPs are observed. A final PCE of 3.66wt% is achieved, which is an improvement of more than 30wt% compared to a standard cell with a PCE of 2.84wt%. When the mass of Al NPs is 10wt% of OSCs, the device performance is best. The optical performance of OSCs reveals that the absorption from sunlight increases. The external quantum efficiency spectra suggests that the Al NPs in the active layers influence the efficiency of converting photons into electrons, which leads to the improvements in the photocurrent. The enhanced photovoltaic performance induced by incorporating Al NPs in the active layer is discussed in the terms of increasing charge separation at the donor-acceptor interface and the effectively decreasing transmission distance of charge in polymer.
|
|
Enhanced Light Output of InGaN-Based Light Emitting Diodes with Roughed p-Type GaN Surface by Using Ni Nanoporous Template
YU Zhi-Guo, CHEN Peng YANG Guo-Feng, LIU Bin, XIE Zi-Li, XIU Xiang-Qian, WU Zhen-Long, XU Feng, XU Zhou, HUA Xue-Mei, HAN Ping, SHI Yi ZHANG Rong, ZHENG You-Dou
Chin. Phys. Lett. 2012, 29 (9):
098502
.
DOI: 10.1088/0256-307X/29/9/098502
Roughened surfaces of light-emitting diodes (LEDs) provide substantial improvement in light extraction efficiency. By preparing the self-assemble nanoporous Ni template through rapid annealing of a thin Ni film, followed by a low damage dry etching process, a p-side-up LED with a roughened surface has been fabricated. Compared to a conventional LED with plane surface, the light output of LEDs with nanoporous p-GaN surface increases up to 71% and 36% at applied currents of 1 mA and 20 mA, respectively. Meanwhile, the electrical characteristics are not degraded obviously after surface roughening.
|
|
Performance Improvement of Ambipolar Organic Field Effect Transistors by Inserting a MoO3 Ultrathin Layer
TIAN Hai-Jun, CHENG Xiao-Man, ZHAO Geng, LIANG Xiao-Yu, DU Bo-Qun, WU Feng
Chin. Phys. Lett. 2012, 29 (9):
098503
.
DOI: 10.1088/0256-307X/29/9/098503
We fabricate N,N'-ditridecylperylene-3,4,9,10-tetracarboxylic diimide and pentacene heterostructure organic field effect transistors with a MoO3 ultrathin layer between Al source-drain electrode and active layer. By inserting the MoO3 layer, the injection barrier of hole carriers is lowered and the contact resistance is reduced. Thus, the performance of the device is improved. The device shows typical ambipolar transport characteristics with effective hole mobility of 4.838×10?3 cm2/V?s and effective electron mobility of 1.909×10?3 cm2/V?s, respectively. This result indicates that using a MoO3 ultrathin 1ayer is an effective way to improve the performance of ambipolar organic field effect transistors.
|
64 articles
|