|
Size Model of Critical Temperature for Grain Growth in Nano V and Au
LU Yun-Bin, LIAO Shu-Zhi**, PENG Hao-Jun, ZHANG Chun, ZHOU Hui-Ying, XIE Hao-Wen, OUYANG Yi-Fang, ZHANG Bang-Wei,
Chin. Phys. Lett. 2011, 28 (8):
080502
.
DOI: 10.1088/0256-307X/28/8/080502
The intrinsic thermodynamical factors that dominate the stability of nanocrystallines are investigated through the microcosmic process of grain growth. The results suggest that nanocrystallines grows at a certain temperature and the critical temperature is determined by the vacancy formation energy and diffusion activation energy of the nanocrystallines. Based on the hypothesis, a simple model is proposed to predict the size-dependent critical temperature of grain growth. Within this model, we investigate the thermal stability of nanocrystallines V and Au, compared with the results available. It is shown that the critical temperature decreases with decreasing size, showing an evident size effect. The research reveals that the thermal stability is dependent on the energetic state of the nanocrystallines and the mobility of the inner atoms.
|
|
Room-Temperature NH Gas Sensor Based on Hydrothermally Grown ZnO Nanorods
WEI Ang, WANG Zhao, PAN Liu-Hua, LI Wei-Wei, XIONG Li, DONG Xiao-Chen**, HUANG Wei**
Chin. Phys. Lett. 2011, 28 (8):
080702
.
DOI: 10.1088/0256-307X/28/8/080702
A NH3 gas sensor based on a ZnO nanorod array is fabricated by hydrothermal decomposition on a Au electrode. The as−grown ZnO nanorods have uniform diameter distribution and good crystal structure, shown by scanning electron microscopy, x-ray diffraction, high resolution transmission electron microscopy and photoluminescence emission characterizations. The gas sensing results show that the ZnO nanorod-based device responds well to ammonia gas at room temperature (sensitivity S is about 8).
|
|
Measurement of Cross Sections for the 10B(n,α)7Li Reaction at 4.0 and 5.0MeV Using an Asymmetrical Twin Gridded Ionization Chamber
ZHANG Guo-Hui**, LIU Xiang, LIU Jia-Ming, XUE Zhi-Hua, WU Hao, CHEN Jin-Xiang
Chin. Phys. Lett. 2011, 28 (8):
082801
.
DOI: 10.1088/0256-307X/28/8/082801
Cross sections of the 10B(n,α)7Li reaction (including the total, the “leaking” alpha, forward alpha and backward alpha parts) at En =4.0 and 5.0 MeV were measured using an asymmetrical twin gridded ionization chamber and two back−to-back 10B samples. Measurements were performed at the 4.5 MV Van de Graaff accelerator of Peking University. Monoenergetic neutrons were produced through the 2H(d,n)3He reaction with a deuterium gas target. Absolute neutron flux was determined by a 238U sample set inside the gridded ionization chamber and a BF3 long counter was employed as a neutron flux monitor and for normalization. The present results are compared with previous measurements and evaluations.
|
|
Intensity and Polarization Effects in Short-Pulse Multiphoton Ionization of Xenon
KANG Hui-Peng, **, WANG Chuan-Liang, LIN Zhi-Yang, CHEN Yong-Ju, WU Ming-Yan, QUAN Wei, LIU Hong-Ping, LIU Xiao-Jun***
Chin. Phys. Lett. 2011, 28 (8):
083201
.
DOI: 10.1088/0256-307X/28/8/083201
We present photoelectron spectra (PES) of xenon subject to ultrashort intense laser pulses at 400 nm. The intensity-dependent PES exhibit the dominance of ac-Stark-shifted multiphoton resonances in a multiphoton ionization process. A distinct difference in the spectra with different laser polarization states (i.e., linearly and circularly polarized states) is revealed and can be understood in terms of the quantum selection rule, which restricts the angular momentum of states that may shift into multiphoton resonances. Furthermore, the intensity dependence of the resonance-enhanced electron yield is analyzed in the context of multiphoton Landau–Zener theory. The model calculation results considering the focal volume effect are in good agreement with the experimental observation.
|
|
Investigation of Linear Tetra-Atomic Negative Ion by Photodetached-Electron Spectra
A. Rahman, Iftikhar Ahmad, **, A. Afaq, M. Haneef, H. J. Zhao
Chin. Phys. Lett. 2011, 28 (8):
083301
.
DOI: 10.1088/0256-307X/28/8/083301
Photodetachment spectra from a linear tetra-atomic negative ion is investigated by treating the detached-electron wave function quantum mechanically. A plane polarized laser light, perpendicular to the axis of the ion, is used to detach the electron from the ion. Analytical expressions for the electron flux and total photodetachment cross section are derived. The electron flux on screen shows strong-energy-dependent oscillations with different frequencies. The total cross section of the tetra-atomic negative ion reduces the cross section of mono-atomic, diatomic and triatomic negative ions for high energy photons, while for low energy photons it becomes four times the cross section of mono-atomic negative ions.
|
|
Photoassociative Production and Detection of Ultracold Polar RbCs Molecules
JI Zhong-Hua, ZHANG Hong-Shan, WU Ji-Zhou, YUAN Jin-Peng, ZHAO Yan-Ting**, MA Jie, WANG Li-Rong, XIAO Lian-Tuan, JIA Suo-Tang
Chin. Phys. Lett. 2011, 28 (8):
083701
.
DOI: 10.1088/0256-307X/28/8/083701
We have produced ultracold polar RbCs molecules via photoassociation starting from laser-cooled 85Rb and 133Cs atoms in a dual−species, forced dark magneto-optical trap. The formed electronically excited RbCs∗ molecules correlated to the Rb(5S1/2)+Cs(6P1/2) dissociation limit are observed by trap loss spectroscopy. Following the decay of these excited RbCs* molecules, the formed ground state molecules are directly ionized by a two-photon single-color pulse dye laser, which is a new ionization mechanism for ground state RbCs molecules and thence detected by time-of-flight mass spectroscopy.
|
|
A High Power Single Frequency Diode Side-Pumped Nd:YAG Ring Laser
XIE Shi-Yong, **, BO Yong, XU Jia-Lin, WANG Zhi-Chao, PENG Qin-Jun, CUI Da-Fu, XU Zu-Yan
Chin. Phys. Lett. 2011, 28 (8):
084207
.
DOI: 10.1088/0256-307X/28/8/084207
We demonstrate a high-power single-frequency diode-side pumped Nd:YAG laser at 1064 nm. A bow-tie ring cavity configuration comprising two plane and two curved mirrors with two-rod birefringence compensation is employed. The influence of length Lx between two curved mirrors on output power and beam quality is investigated theoretically and experimentally while the separation of the flat mirrors is set to be 656 mm and the fold angle is 10°. When the pump powers are 358, 343 and 329 W at 808 nm, the maximal output powers of 31.9, 26 and 14.1 W are obtained with beam quality factors M2 = 1.41, 1.12 and 1.20 for Lx = 205, 215 and 230 mm, respectively.
|
|
Experimental Observation of Near-Field Deterioration Induced by Stimulated Rotational Raman Scattering in Long Air Paths
WANG Jing, ZHANG Xiao-Min, HAN Wei, LI Fu-Quan, ZHOU Li-Dan**, FENG Bin, XIANG Yong
Chin. Phys. Lett. 2011, 28 (8):
084211
.
DOI: 10.1088/0256-307X/28/8/084211
We report the experimental investigation of a stimulated rotational Raman scattering effect in long air paths on SG-III TIL, with a 1053 nm, 20-cm-diameter, linearly polarized, 3 ns flat-topped laser pulse. An intense speckle pattern of near field with thickly dotted hot spots is observed at the end of propagation with an intensity-length product above 17 TW/cm. The Stokes developing from the scattering of the laser beam by quantum fluctuations is characterized by a combination of high spatial frequency components. The observed speckle pattern with small-diameter hot spots results from the combination of the nonlinear Raman amplification and the linear diffraction propagation effect of the Stokes with a noise pattern arising from the spontaneous Raman scattering. A new promising suppression concept based on the special characteristic of the Stokes, called active and selective filtering of Stokes, is proposed.
|
|
Compact 2×2 Multi-Mode Interference Couplers with Uneven Splitting-Ratios Based on Silicon Nanowires
ZHOU Jing-Tao**, SHEN Hua-Jun, YANG Cheng-Yue, LIU Huan-Ming, TANG Yi-Dan, LIU Xin-Yu
Chin. Phys. Lett. 2011, 28 (8):
084212
.
DOI: 10.1088/0256-307X/28/8/084212
Two types of uneven splitting-ratio 2×2 multi−mode interference (MMI) couplers based on silicon nanowires are designed, fabricated and characterized. The splitting ratios are 85:15 and 72:28, respectively. The devices have compact sizes and low excess losses. The footprints of the rectangular MMI region are only about 3 µm×18 µm and 3 µm×14 µm, and the minimum excess losses (ELs) are 1.30 dB and 0.82 dB. The measured splitting−ratios are consistent with the designed values. Based on their performance, these 2×2 MMI couplers are suitable candidates for the coupling section of microring resonators where a large resonance bandwidth is required for high speed signal processing. The uneven splitting capability also provides a convenient way to further optimize the Q factor and the bandwidth of the resonator.
|
|
Measurement of Temperature Change in Nonlinear Optical Materials by Using the Z-Scan Technique
DONG Shu-Guang, YANG Jun-Yi, SHUI Min, YI Chuan-Xiang, LI Zhong-Guo, SONG Ying-Lin**
Chin. Phys. Lett. 2011, 28 (8):
084213
.
DOI: 10.1088/0256-307X/28/8/084213
Spatial and temporal changes of temperature in a novel polymer are investigated by using the Z−scan technique under ns laser pulse excitation. According to the open aperture Z−scan experimental results, the nonlinear absorption coefficient of the polymer is determined. By solving the diffusion equation of heat conduction induced by optical absorption, the spatial and temporal changes in temperature are obtained. This change in temperature drives the photo-acoustic and electromagnetic wave propagating in the polymer and induces the change in refractive index, which serves as a negative lens, and the closed aperture Z−scan shows a peak and valley profile. Based on the numerical calculation, we achieve a good fit to the closed-aperture Z−scan curve with an optimized nonlinear refractive index. This consistency attests the existence of temperature change in the solution, and the Z-scan technique is suitable to investigate this change in temperature.
|
|
A Digital Phase Lock Loop for an External Cavity Diode Laser
WANG Xiao-Long, TAO Tian-Jiong, CHENG Bing, WU Bin, XU Yun-Fei, WANG Zhao-Ying, LIN Qiang**
Chin. Phys. Lett. 2011, 28 (8):
084214
.
DOI: 10.1088/0256-307X/28/8/084214
A digital optical phase lock loop (OPLL) is implemented to synchronize the frequency and phase between two external cavity diode lasers (ECDL), generating Raman pulses for atom interferometry. The setup involves all-digital phase detection and a programmable digital proportional-integral-derivative (PID) loop in locking. The lock generates a narrow beat-note linewidth below 1 Hz and low phase-noise of 0.03 rad2 between the master and slave ECDLs. The lock proves to be stable and robust, and all the locking parameters can be set and optimized on a computer interface with convenience, making the lock adaptable to various setups of laser systems.
|
|
A Low Voltage Driven Digital-Droplet-Transporting-Chip by Electrostatic Force
GAO An-Ran, LIU Xiang, GAO Xiu-Li, LI Tie**, GAO Hua-Min, ZHOU Ping, WANG Yue-Lin
Chin. Phys. Lett. 2011, 28 (8):
084706
.
DOI: 10.1088/0256-307X/28/8/084706
A low-voltage-driven digital-droplet-transporting chip with an open structure is designed, fabricated and characterized. The digital microfluidic chip is fabricated by the silicon planar process. Using only a single electrode panel, the droplet on the chip can be manipulated by electrostatic force under a dc driving voltage. The actuation principle is proposed and verified by the experiment. The experimental results show that the minimum driving voltage decreases as the thickness of the dielectric layer decreases. The driving voltage for a 3 µL deionized (DI) water droplet is reduced to 15 V in air and 13.5 V in oil by employing a thin dielectric layer of 600 nm with a high dielectric constant and a coating hydrophobic layer on the top. The DI water droplets are also demonstrated to be transported in two dimensions smoothly in a programmable manner, and the maximum transport speed reaches 96 mm/s. The droplets of normal saline, a solution of 0.9 wt% NaCl, are also successfully manipulated on the chip.
|
|
Preliminary Investigation of a Dielectric Barrier Discharge Lamp in Open Air at Atmospheric Pressure
LIU Feng, WANG Wei-Wei, CHANG Xi-Jiang, LIANG Rong-Qing**
Chin. Phys. Lett. 2011, 28 (8):
085201
.
DOI: 10.1088/0256-307X/28/8/085201
A dielectric barrier discharge (DBD) lamp is investigated by using sinusoidal power with a 10 kHz frequency in open air at atmospheric pressure. With increasing applied voltages, the different discharge phenomena appear. At relatively low voltages, the discharge states are general stochastic filamentary discharges with weak light. However, at relatively high voltages, the walls of quartz tubes are heated sharply by plasma, and then the dazzling light is emitted very quickly to form the DBD Lamp, corresponding to the low maintaining voltage that is lower than the ignited voltage. The discharge state or mode of the DBD lamp that corresponds to the glow discharge is deduced according to the wave form of the circuit current, which is evidently different from the filamentary discharges. Under these conditions, the spectrum of the DBD lamp is continuous in the range 400–932 nm, which is scanned in the range 300–932 nm. It is also shown that there is another discharge state or mode that is different from the traditional filamentary discharges. Therefore, it is concluded that the discharge state or mode of the DBD lamp is a glow discharge.
|
|
Shock-Timing Experiment Using a Two-Step Radiation Pulse with a Polystyrene Target
WANG Feng**, PENG Xiao-Shi, JIAO Chun-Ye, LIU Shen-Ye, JIANG Xiao-Hua, DING Yong-Kun
Chin. Phys. Lett. 2011, 28 (8):
085202
.
DOI: 10.1088/0256-307X/28/8/085202
A shock-timing experiment plays an important role in inertial confinement fusion studies, and the timing of multiple shock waves is crucial to the performance of inertial confinement fusion ignition targets. We present an experimental observation of a shock wave driven by a two-step radiation pulse in a polystyrene target. The experiment is carried out at Shen Guang III Yuan Xing (SGIIIYX) laser facility in China, and the generation and coalescence of the two shock waves, originating from each of the two radiation steps, is clearly seen with two velocity interferometers. This two-shock-wave coalescence is also simulated by the radioactive hydrodynamic code of a multi-1D program. The experimental measurements are compared with the simulations and quite good agreements are found, with relatively small discrepancies in shock timing.
|
|
Mechanical Property Evaluation of GaAs Crystal for Solar Cells
JIN Min**, FANG Yong-Zheng, SHEN Hui, JIANG Guo-Jian, WANG Zhan-Yong, XU Jia-Yue
Chin. Phys. Lett. 2011, 28 (8):
086101
.
DOI: 10.1088/0256-307X/28/8/086101
The mechanical properties of Si-doped (111) GaAs crystal for solar cells are investigated by means of a microindentation technique. Vickers' microhardness Hv exhibits a nonlinear relationship with the applied load. In the range of 0.1–1 kg, Hv is decreased from 5.59 GPa to 5.03 GPa. Such a phenomenon is explained on the basis of indenter penetration. The Hv value can effectively be presumed by Kick's law, and Meyer's index n is calculated to be 1.90. For the fracture toughness Kc of the GaAs crystal, it also displays nonlinear behavior related to the applied load, which is caused by energy dissipation during the development process of cracks on the wafer.
|
|
Effect of Iodine Additive on Thermostability of Bulk Amorphous Sulfur Prepared by Rapid Compression
LIN Sheng-Xiong, LIU Xiu-Ru**, SHAO Chun-Guang, SHEN Ru, HONG Shi-Ming
Chin. Phys. Lett. 2011, 28 (8):
086102
.
DOI: 10.1088/0256-307X/28/8/086102
Bulk amorphous sulfur (a-S) with 1 mol% of phosphorus, selenium and iodine additives and bulk amorphous pure sulfur samples were prepared by rapidly compressing the melts to 2 GPa within 20 ms. The results of x-ray diffraction, differential scanning calorimetry and in situ wide angle x-ray scattering of the recovered samples are presented and discussed. In the iodine doping case, obvious inhibiting effects on the crystallization and the melting process under high temperatures occurred, as well as on the structure relaxation of a-S at room temperature, suggesting that the thermal stability of amorphous sulfur is remarkably improved by the introduction of iodine additives.
|
|
Stability of TiO2 and Al2O3 Nanofluids
WANG Xian-Ju, LI Hai, LI Xin-Fang, WANG Zhou-Fei**, LIN Fang
Chin. Phys. Lett. 2011, 28 (8):
086601
.
DOI: 10.1088/0256-307X/28/8/086601
Aiming at the dispersion stability of nanofluids, we investigate the absorbency and the zeta potential of TiO2 and Al2O3 nanofluids under different pH values and different dispersant concentrations. The results show that in the mass fraction 0.05% alumina and 0.01% titanium dioxide nanosuspensions, the absolute value of the zeta potential and the absorbency of the two nanofluids with sodium dodecyl sulfate (SDS) dispersant are the highest at an optimal pH (pHAl2O3≈6.0, pHTiO2≈9.5) and that there is a good correlation between absorbency and zeta potential: the higher the absolute value of the zeta potential is, the greater the absorbency is, and the better the stability of the system is. The optimizing concentrations for SDS are 0.10% and 0.14%, respectively, at which the two nanofluids have the best dispersion results. The calculated DLVO interparticle interaction potentials verify the experimental results of the pH effect on the stability behavior.
|
|
Spectral Resolution Improvement of Mo/Si Multilayers
WU Wen-Juan**, WANG Zhan-Shan, ZHU Jing-Tao, ZHANG Zhong, WANG Feng-Li, CHEN Ling-Yan, ZHOU Hong-Jun, HUO Tong-Lin
Chin. Phys. Lett. 2011, 28 (8):
086801
.
DOI: 10.1088/0256-307X/28/8/086801
Theoretically, the spectral resolution of a multilayer can be improved through a combination of utilizing high reflectance orders and by decreasing the thickness of the scattering layer. We fabricate Mo/Si multilayers in the first, second, third, fourth and fifth reflectance orders with Mo layer thicknesses of 3.0 nm and 2.0 nm, respectively, using direct current magnetron sputtering. The structure of the multilayers is characterized with a grazing angle x-ray diffractometer (XRD). Then the reflectivity of the multilayers is measured in a synchrotron radiation facility. The results show that the spectral resolution increases with the increasing reflectance order and with the decreasing Mo layer thickness. The highest spectral resolution is improved to 117.5 in the 5th order for dMo=2 nm, where the reflectivity is 18%.
|
|
Dynamics of Exciton Diffusion in PVK:Phosphorescent Materials/Al Hetero-Structures
YANG Shao-Peng**, HUANG Da, GE Da-Yong, LIU Bo-Ya, WANG Li-Shun, FU Guang-Sheng
Chin. Phys. Lett. 2011, 28 (8):
087101
.
DOI: 10.1088/0256-307X/28/8/087101
Exciton quenching dynamics in a polymer PVK doped with FirPic, Ir(piq)2(acac) and Ir(ppy)3 phosphorescent guest materials, respectively, due to the presence of metal films is analyzed using time−resolved photoluminescence. The quenching is directly governed by radiationless energy transfer to the metal and is further enhanced by diffusion of excitons into the depletion region of the exciton population at the polymer/metal interface. The influence of polymer layer thickness on the luminescence decay is described by a one-dimensional diffusion model. The energy transfer distance and exciton diffusion length are 10 nm, 9 nm, 15 nm and 29.3 nm, 30.1 nm, 30.9 nm for PVK doped with phosphorescent guest materials FirPic, Ir(piq)2(acac) and Ir(ppy)3, respectively. This can disentangle the contributions from direct energy transfer to the metal and exciton migration to the exciton quenching process. The lengths of the exciton quenching region of the three doping systems are 39.3 nm, 39.1 nm and 45.9 nm, respectively.
|
|
Growth and Properties of Blue and Amber Complex Light Emitting InGaN/GaN Multi-Quantum Wells
XIE Zi-Li**, ZHANG Rong, LIU Bin, XIU Xiang-Qian, SU Hui, LI Yi, HUA Xue-Mei, ZHAO Hong, CHEN Peng, HAN Ping, SHI Yi, ZHENG You-Dou
Chin. Phys. Lett. 2011, 28 (8):
087102
.
DOI: 10.1088/0256-307X/28/8/087102
Blue-red complex light emitting InGaN/GaN multi-quantum well (MQW) structures are fabricated by metal organic chemical vapor deposition (MOCVD). The structures are grown on a 2-inch diameter (0001) oriented (c−face) sapphire substrate, which consists of an approximately 2-µm−thick GaN template and a five-period layer consisting of a 4.9-nm-thick In0.18Ga0.82N well layer and a GaN barrier layer. The surface morphology of the MQW structures is observed by an atomic force microscope (AFM), which indicates the presence of islands of several tens of nanometers in height on the surface. The high resolution x−ray diffraction (XRD) θ/2θ scan is carried out on the symmetric (0002) of the InGaN/GaN MQW structures. At least four order satellite peaks presented in the XRD spectrum indicate that the thickness and alloy compositions of the individual quantum wells are repeatable throughout the active region. Besides the 364 nm GaN band edge emission, two main emissions of blue and amber light from these MQWs are found, which possibly originate from the carrier recombinations in the InGaN/GaN QWs and InGaN quasi-quantum dots embedded in the QWs.
|
|
Electronic Properties of Boron Nanotubes under Uniaxial Strain: a DFT study
PAN Li-Jun, JIA Yu, **, SUN Qiang, HU Xing
Chin. Phys. Lett. 2011, 28 (8):
087103
.
DOI: 10.1088/0256-307X/28/8/087103
Electronic structures of a uniaxially stretched boron nanotube (BNT) are studied by the density functional theory (DFT) and compared with a zigzag single-walled carbon nanotube (CNT). It is verified that modifications of the electronic band structures of CNTs may be classified into three patterns depending on their helicity under the applied strain up to 20%. However, for the BNT, the partial boron bonds will be broken as the applied strain is more than 10%, indicating its poor deformation ability as compated with CNTs. Moreover, the band gap of the BNT keeps or converts to zero regardless of its chirality as the applied strain increases, which is drastically distinct from the CNT. The special behavior of the BNT implies a potential application as an excellent stress sensor.
|
|
Oscillations of Low-Field Magnetoresistivity of Two-Dimensional Electron Gases in Al0.22Ga0.78N/GaN Heterostructures in a Weak Localization Region
HAN Kui, TANG Ning**, DUAN Jun-Xi, LU Fang-Chao, LIU Yu-Chi, SHEN Bo**, ZHOU Wen-Zheng, LIN Tie, SUN Lei, YU Guo-Lin, CHU Jun-Hao
Chin. Phys. Lett. 2011, 28 (8):
087302
.
DOI: 10.1088/0256-307X/28/8/087302
Low-field magnetotransport properties of two-dimensional electron gases (2DEGs) are investigated in Al0.22Ga0.78N/GaN heterostructures. By means of a tilting magnetic field, unexpected oscillations of magnetoresistivity are observed in a weak localization region. Qualitative understanding based on Altshuler–Aronov–Spivak oscillations is proposed for the case of interface disorder in Al0.22Ga0.78N/GaN heterostructures.
|
|
Rectifying Characteristics and Transport Behavior in a Schottky Junction of CaCu 3Ti4O12 and Pt
CHEN Cong, NING Ting-Yin, WANG Can**, ZHOU Yue-Liang, ZHANG Dong-Xiang, WANG Pei, MING Hai, YANG Guo-Zhen
Chin. Phys. Lett. 2011, 28 (8):
087304
.
DOI: 10.1088/0256-307X/28/8/087304
CaCu3Ti4O12 (CCTO) thin films were fabricated on ITO−covered MgO (100) substrates. The rectification characteristics were observed in the CCTO capacitance structure with Pt top electrodes at temperatures ranging from 150 K to 330 K, which are attributed to the formation of a Schottky junction between n-type semiconducting CCTO and Pt due to the difference of their work functions. At low forward-bias voltage, the current-voltage characteristics of the Schottky junction follow J=JsD exp[qV/(k0T)]. A strong decrease in ideality factor with the increasing temperature is obtained by linear fitting at the low bias voltage.
|
|
Dipolar and Quadrupolar Modes of SiO2/Au Nanoshell Enhanced Light Trapping in Thin Film Solar Cells
BAI Yi-Ming**, WANG Jun, CHEN Nuo-Fu, YAO Jian-Xi, ZHANG Xing-Wang, YIN Zhi-Gang, ZHANG Han, HUANG Tian-Mao
Chin. Phys. Lett. 2011, 28 (8):
087306
.
DOI: 10.1088/0256-307X/28/8/087306
Dipolar and quadrupolar resonance wavelengths of SiO2/Au nanoshell surface plasmons are designed at 560 nm to enhance the light trapping in thin film solar cells. In order to quantitatively describe the light trapping effect, the forward−scattering efficiency (FSE) and the light trapping efficiency (LTE) are proposed by considering the light scattering direction of SiO2/Au nanoshells. Based on the Mie theory, the FSE and the LTE are calculated for SiO2/Au nanoshells of different dimensions, and the contributions of the dipolar and quadrupolar modes to the light trapping effect are analyzed in detail. When the surface coverage of nanoshells is 5%, the LTEs are 21.7% and 46.9% for SiO2/Au nanoshells with sizes of (31 nm, 69 nm) and (53 nm, 141 nm), respectively. The results indicate that the SiO2/Au nanoshell whose quadrupolar mode peak is designed to the strongest solar energy flux density of the solar spectrum facilitates the further enhancement of light harvesting in thin film solar cells.
|
|
Structural, Electronic and Optical Properties of BiAl xGa1−xO3 (x=0, 0.25, 0.5 and 0.75)
GONG Sai, WANG Yue-Hua**, ZHAO Xin-Yin, ZHANG Min, ZHAO Na, DUAN Yi-Feng
Chin. Phys. Lett. 2011, 28 (8):
087402
.
DOI: 10.1088/0256-307X/28/8/087402
A first principles study using the full potential linearized augmented plane wave (FP-LAPW) method is applied to study the structural, electronic and optical properties of BiAlxGa1−xO3. The results show that the alloys become markedly hard as the Al concentration increases. The calculated structural parameters are in good agreement with the experimental data. The band structure and density of states are obtained, which indicate that BiAlxGa1−xO3 has an indirect band gap. Moreover, the optical properties are calculated and analyzed in detail. It is proposed that BiAlxGa1−xO3 is a promising dielectric material.
|
|
Fabrication of High-Quality Niobium Superconducting Tunnel Junctions
XU Qin-Yin, CAO Chun-Hai, LI Meng-Yue, JIANG Yi, ZHA Shi-Tong, KANG Lin, XU Wei-Wei, CHEN Jian**, WU Pei-Heng
Chin. Phys. Lett. 2011, 28 (8):
087403
.
DOI: 10.1088/0256-307X/28/8/087403
For high-quality superconducting tunnel junctions (STJs), it is necessary to reduce leakage current as much as possible. We describe the fabrication of niobium STJs using the selective niobium (Nb) etching process and various ways to minimize the leakage current. The experiment shows that the leakage current mainly comes from shorts in the tunnel barrier layer rather than those around the junction edges. Through systematic analysis of the thin film stress, surface morphology and modified junction structures, we fabricate high-quality Nb STJs with a gap voltage of 2.8 mV and a leakage current at 1 mV as low as 8.1% and 0.023% at 4.2 K and 0.3 K, respectively.
|
|
Magnetic Performance of a Nanocomposite Permanent Material
LIU Min**, HAN Guang-Bing, GAO Ru-Wei
Chin. Phys. Lett. 2011, 28 (8):
087501
.
DOI: 10.1088/0256-307X/28/8/087501
We build a sandwiched structure model in which the intergranular phase (IP) is homogeneously distributed between soft and hard magnetic grains, and gives a continuously anisotropic expression of the coupling part under the assumption that the IP weakens the intergrain exchange-coupling interaction. Based on the idea that the hardening mechanism is of the pinning type, we calculate the effect of the IP's thickness d and its anisotropy constant K1(0) on the intrinsic coercivity of a nanocomposite permanent material. The calculated results indicate that the domain wall goes twice through irreversible domain wall displacement during the process of moving from soft to hard magnetic grains, and the intrinsic coercivity increases with increasing d, but decreases with increasing K1(0). When d and K1(0) take 2 nm and 0.7Kh, respectively, with Kh being the anisotropy constant in the inner part of the hard magnetic grain, the calculated intrinsic coercivity is in good agreement with the experimental data.
|
|
Femtosecond Pulse Propagation in a Symmetric Gap Surface Plasmon Polariton Waveguide
LU Zhi-Xin, YU Li, **, LIU Bing-Can, , ZHANG Kai, SONG Gang,
Chin. Phys. Lett. 2011, 28 (8):
087801
.
DOI: 10.1088/0256-307X/28/8/087801
We investigate the effect of a symmetric gap surface plasmon polariton (SPP) waveguide on ultrashort pulses with a central wavelength of 850 nm and a width of 20 fs using the finite-difference time-domain method. The length of the waveguide is 560 nm. Linear and nonlinear dielectrics are chosen to be the core layers whose thicknesses are set to be 20, 50, 100 and 200 nm, respectively. The results show that for the linear case, strong coupling of the SPP mode can lead to the pulse tailing phenomenon and spectrum compression due to waveguide resonance. For the nonlinear case, the output pulse is broadened and the fluctuation is more complex than the input pulse and can induce the spectrum splitting as well. The smaller the thickness of the core layer is, the more distinct the pulse distortion is, which may be due to the combined effects of dispersion, waveguide resonance and self-phase modulation.
|
|
Optical Temperature Sensor Using Infrared-to-Visible-Frequency Upconversion in Er 3+/Yb 3+−Codoped Bi3TiNbO9 Ceramics
CHEN Heng-Zhi, YANG Bin**, SUN Yan, ZHANG Ming-Fu, WANG Zhu, ZHANG Rui, ZHANG Zhi-Guo, CAO Wen-Wu,
Chin. Phys. Lett. 2011, 28 (8):
087804
.
DOI: 10.1088/0256-307X/28/8/087804
An optical temperature sensor based on infrared-to-visible upconversion emission in Er3+/Yb3+ co−doped Bi3TiNbØ9 (BTN) ceramics is reported. The fluorescence intensity ratio of the green upconversion photoluminescence (UC−PL) around 524 nm and 545 nm depends on temperature. The operating temperature range and the maximum sensitivity of Er3+/Yb3+ co−doped Bi3TiNbO9 ceramics are 123–693 K and 0.0032 K−1, respectively. BTN:Er3+/Yb3+ ceramic has good thermal, physical and chemical stability, great UC−PL intensity and low cost fabrication. The results imply that Er3+/Yb3+ co−doped Bi3TiNbO9 ceramic is promising for applications in wide-temperature-range sensors.
|
|
Raman and Mid-IR Spectral Analysis of the Atacamite-Structure Hydroxyl/Deuteroxyl Nickel Chlorides Ni2(OH/D)3Cl
LIU Xiao-Dong, **, Hagihala Masato, ZHENG Xu-Guang, **, MENG Dong-Dong, GUO Qi-Xin
Chin. Phys. Lett. 2011, 28 (8):
087805
.
DOI: 10.1088/0256-307X/28/8/087805
Vibrational spectra (Raman 4000–95 cm−1 and mid-IR 4000–400 cm−1) of the atacamite-structure Ni2(OH)3Cl, including a rarely reported kind of asymmetric trimetric hydrogen bond, as a member of the geometrically frustrated material series and its deuteride Ni2(OD)3Cl are, to the best of our knowledge, reported for the first time and analyzed at room temperature. Through a comparative study of four spectra according to their crystal structural parameters, we assign OH stretching modes v(OH) in a functional group region (3700–3400 cm−1) and their deformation modes δ(NiOH/D) in the correlation peak region (900–600 cm−1) with the corresponding mode frequency ratios ωv(OD)/ωv(OH)≈73% and ωδ(NiOD)/ωδ(NiOH)≈75%, and further self−consistently suggest Ni-O and Ni-Cl related modes in the fingerprint region (500–200 cm−1 and 200–0 cm−1, respectively) by use of the unified six-ligand NiO5Cl and NiO4Cl2 frames. This report may contribute to the spectral analysis of other hydroxyl transition-metal halides and to the understanding of the fundamental physics of their exotic magnetic geometrical frustration property from the spectral changes around the corresponding low transition temperatures.
|
|
Floating Zone Growth and Thermionic Emission Property of Single Crystal CeB6
BAO Li-Hong, ZHANG Jiu-Xing**, ZHOU Shen-Lin, ZHANG Ning, XU Hong
Chin. Phys. Lett. 2011, 28 (8):
088101
.
DOI: 10.1088/0256-307X/28/8/088101
Large-sized and high-quality cerium hexaboride (CeB6) single crystals are successfully grown by the optical floating zone method. The structure, chemical composition and thermionic emission properties of the crystal are characterized by x−ray diffraction, x-ray fluorescence and emission measurements, respectively. Based on the observation of single crystal diffraction, the relative density of feed rods has a great effect on the quality of the grown crystal. The thermionic emission measurement results show that the emission current density of the single crystal is 47.1 A/cm2 at 1873 K with an applied voltage of 1 kV, which is about two times larger than the value for polycrystalline samples. The single crystal possesses excellent emission current stability. Therefore, it is expected that CeB6 single crystal is a very promising material for thermionic cathode applications.
|
|
Department of Physics and Institute of Modern Physics, Ningbo University, Ningbo 315211
ZHANG Shao-Hua, **, FENG Xue-Shang, WANG Yi, YANG Li-Ping,
Chin. Phys. Lett. 2011, 28 (8):
089601
.
DOI: 10.1088/0256-307X/28/8/089601
The evolutionary process of magnetic reconnection under solar coronal conditions is investigated with our recently developed 2.5D adaptive mesh refinement (AMR) resistive magneto hydrodynamics (MHD) model. We reveal the successive fragmentation and merging of plasmoids in a long-thin current sheet with Lundquist number Rm=5.0×104. It is found that several big magnetic islands are formed eventually, with many slow-mode shocks bounding around the outflow regions. The multi-scale hierarchical-like structures of the magnetic reconnection are well resolved by the model and the AMR technique of the model can capture many fine pictures (e.g., the near-singular diffusion regions) of the development and simultaneously it can save a great deal of computing resources.
|
|
Bianchi Type-I Massive String Magnetized Barotropic Perfect Fluid Cosmological Model in the Bimetric Theory of Gravitation
N. P. Gaikwad**, M. S. Borkar, S. S. Charjan
Chin. Phys. Lett. 2011, 28 (8):
089803
.
DOI: 10.1088/0256-307X/28/8/089803
We investigate the Bianchi type-I massive string magnetized barotropic perfect fluid cosmological model in Rosen's bimetric theory of gravitation with and without a magnetic field by applying the techniques used by Latelier (1979, 1980) and Stachel (1983). To obtain a deterministic model of the universe, it is assumed that the universe is filled with barotropic perfect fluid distribution. The physical and geometrical significance of the model are discussed. By comparing our model with the model of Bali et al. (2007), it is realized that there are no big-bang and big-crunch singularities in our model and T=0 is not the time of the big bang, whereas the model of Bali et al. starts with a big bang at T=0. Further, our model is in agreement with Bali et al.(2007) as time increases in the presence, as well as in the absence, of a magnetic field.
|
99 articles
|