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Volume 32 Issue 07
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GENERAL
Groups Analysis and Localized Solutions of the (2+1)-Dimensional Ito Equation
HU Xiao-Rui, CHEN Jun-Chao, CHEN Yong
Chin. Phys. Lett. 2015, 32 (07): 070201 .   DOI: 10.1088/0256-307X/32/7/070201
Abstract   PDF(pc) (840KB) ( 698 )
By means of the modified Clarkson and Kruskal (CK) direct method and the variable separation approach, we investigate the (2+1)-dimensional Ito equation which was constructed by Ito in 1980. The full symmetry group with the Kac–Moody–Virasoro algebra structure and the variable separation solutions are obtained. By selecting appropriate arbitrary functions, some special soliton excitations are shown graphically. The results presented here would be beneficial for understanding the (2+1)-dimensional Ito equation better.
Transfer Matrix Approach for Two-State Scattering Problem with Arbitrary Coupling
Diwaker, Aniruddha Chakraborty
Chin. Phys. Lett. 2015, 32 (07): 070301 .   DOI: 10.1088/0256-307X/32/7/070301
Abstract   PDF(pc) (591KB) ( 396 )
The present work deals with the calculation of transition probability between two diabatic potentials coupled by any arbitrary coupling. The method presented in this work is applicable to any type of coupling while for numerical calculations we have assumed the arbitrary coupling as Gaussian coupling. This arbitrary coupling is expressed as a collection of Dirac delta functions and by the use of the transfer matrix technique the transition probability from one diabatic potential to another diabatic potential is calculated. We examine our approach by considering the case of two constant potentials coupled by Gaussian coupling as an arbitrary coupling.
Fidelity Tradeoff in Estimation of Partial Entanglement State with Local Operation and Classic Communication
ZHANG Sheng-Li, WANG-Kun, GUO Jian-Sheng, SHI Jian-Hong
Chin. Phys. Lett. 2015, 32 (07): 070302 .   DOI: 10.1088/0256-307X/32/7/070302
Abstract   PDF(pc) (1720KB) ( 348 )

In quantum mechanics, there is no measurement process that could gain some information of an unknown quantum state without causing any disturbance. A tradeoff bound between the amount of information gain �� and the concomitant disturbance ? in the measurement process of a bipartite entangled state is actually ingrained. Such a bound is fundamental and closely connected with the entangled degree b. In this work, the bound for estimation of a partial entangled state with a local strategy is investigated. It is shown that, with local operation with classical communication, a monotonic change in the ?–�� picture will be spotted. This is due to the fact that the partial entanglement gradually becomes two individual qubits and, consequently, the optimal operation boils down to local operations. A quantum circuit which achieves the optimal tradeoff is also obtained.

A High-Sensitivity Refractive-Index Sensor Based on Plasmonic Waveguides Asymmetrically Coupled with a Nanodisk Resonator
XIAO Li-Ping, WANG Fa-Qiang, LIANG Rui-Sheng, ZOU Shi-Wei, HU Miao
Chin. Phys. Lett. 2015, 32 (07): 070701 .   DOI: 10.1088/0256-307X/32/7/070701
Abstract   PDF(pc) (723KB) ( 380 )
A high-sensitivity plasmonic refractive-index sensor based on the asymmetrical coupling of two metal-insulator-metal waveguides with a nanodisk resonator is proposed and simulated in the finite-difference time domain. Both analytic and simulated results show that the resonance wavelengths of the sensor have an approximate linear relationship with the refractive index of the materials which are filled into the slit waveguides and the disk-shaped resonator. The working mechanism of this sensor is exactly due to the linear relationship, based on which the refractive index of the materials unknown can be obtained from the detection of the resonance wavelength. The measurement sensitivity can reach as high as 6.45×10?7, which is nearly five times higher than the results reported in the recent literature [Opt. Commun. 300 (2013) 265]. With an optimum design, the sensing value can be further improved, and it can be widely applied into the biological sensing. The sensor working for temperature sensing is also analyzed.
The Approach of Compensation of Air Refractive Index in Thermal Expansion Coefficients Measurement Based on Laser Feedback Interferometry
ZHENG Fa-Song, DING Ying-Chun, TAN Yi-Dong, LIN Jing, ZHANG Shu-Lian
Chin. Phys. Lett. 2015, 32 (07): 070702 .   DOI: 10.1088/0256-307X/32/7/070702
Abstract   PDF(pc) (619KB) ( 437 )
We present the thermal expansion coefficient (TEC) measurement technology of compensating for the effect of variations in the refractive index based on a Nd:YAG laser feedback system, the beam frequency is shifted by a pair of acousto-optic modulators and then the heterodyne phase measurement technique is used. The sample measured is placed in a muffle furnace with two coaxial holes opened on the opposite furnace walls. The measurement beams hit perpendicularly and coaxially on each surface of the sample. The reference beams hit on the reference mirror and the high-reflectivity mirror, respectively. By the heterodyne configuration and computing, the influences of the vibration, distortion of the sample supporter and the effect of variations in the refractive index are measured and largely minimized. For validation, the TECs of aluminum samples are determined in the temperature range of 298–748 K, confirming not only the precision within 5×10?7 K?1 and the accuracy within 0.4% from 298 K to 448 K but also the high sensitivity non-contact measurement of the lower reflectivity surface induced by the sample oxidization from 448 K to 748 K.
THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
Heun Functions Describing Fermions Evolving in Parallel Electric and Magnetic Fields
MARINA–AURA Dariescu, CIPRIAN Dariescu
Chin. Phys. Lett. 2015, 32 (07): 071101 .   DOI: 10.1088/0256-307X/32/7/071101
Abstract   PDF(pc) (384KB) ( 381 )
The present work deals with the behavior of fermions moving in a static magnetic induction and a time-harmonic electric field, both oriented along Oz. For the ultra-relativistic particles described by a Heun double confluent equation, we derive the corresponding wave functions and the conserved current density components.
NUCLEAR PHYSICS
Three-Body Calculation of 4He(αα,γ)12C Reaction at Stellar Energies
Firoozabadi M. M., Sadeghi H.
Chin. Phys. Lett. 2015, 32 (07): 072101 .   DOI: 10.1088/0256-307X/32/7/072101
Abstract   PDF(pc) (494KB) ( 294 )
The triple-alpha reaction is the key to our understanding about the nucleosynthesis and the observed abundance of 12C in stars. On the basis of our model, the triple-alpha radiative capture process is studied by using the three-body Faddeev approach as well as two- and three-body electromagnetic currents. The bound and resonance states of 12C are calculated via an inverse process: three-α photodisintegration of a 12C nucleus.
A Model Comparison Study of Fragment Production in 140 A MeV 58,64Ni+9Be Reactions
MA Chun-Wang, ZHANG Yan-Li, WANG Shan-Shan, QIAO Chun-Yuan
Chin. Phys. Lett. 2015, 32 (07): 072501 .   DOI: 10.1088/0256-307X/32/7/072501
Abstract   PDF(pc) (1024KB) ( 327 )

The cross sections of fragments produced in the 140 A MeV 58,64Ni+9Be projectile fragmentation reactions are calculated by using the antisymmetrized molecular dynamics (AMD) model, the modified statistical abrasion-ablation (SAA) model, and the empirical EPAX2/EPAX3 formulae. The Gogny-g0 interaction is taken as the effective nucleon-nucleon interaction in the AMD calculation, and the decays of fragments obtained from the AMD results are calculated by using the GEMINI code. The calculated cross sections of fragments are compared.

ATOMIC AND MOLECULAR PHYSICS
The Analytical Potential Energy Function of NH Radical Molecule in External Electric Field
WU Dong-Lan, TAN Bin, WAN Hui-Jun, XIE An-Dong, DING Da-Jun
Chin. Phys. Lett. 2015, 32 (07): 073101 .   DOI: 10.1088/0256-307X/32/7/073101
Abstract   PDF(pc) (481KB) ( 384 )
The geometric structures of an NH radical in different external electric fields are optimized by using the density functional B3P86/cc-PV5Z method, and the bond lengths, dipole moments, vibration frequencies and IR spectrum are obtained. The potential energy curves are gained by the CCSD (T) method with the same basis set. These results indicate that the physical property parameters and potential energy curves may change with the external electric field, especially in the reverse direction electric field. The potential energy function of zero field is fitted by the Morse potential, and the fitting parameters are in good accordance with the experimental data. The potential energy functions of different external electric fields are fitted adopting the constructed potential model. The fitted critical dissociation electric parameters are shown to be consistent with the numerical calculation, and the relative errors are only 0.27% and 6.61%, hence the constructed model is reliable and accurate. The present results provide an important reference for further study of the molecular spectrum, dynamics and molecular cooling with Stark effect.
Isotope Shift Calculations of Stable and Short-Lived Beryllium Isotopes
YU Geng-Hua, GENG Ying-Ge, ZHOU Chao, DUAN Cheng-Bo, LI Long, CHAI Rui-Peng, YANG Yong-Ming
Chin. Phys. Lett. 2015, 32 (07): 073102 .   DOI: 10.1088/0256-307X/32/7/073102
Abstract   PDF(pc) (467KB) ( 325 )
The isotope shifts of the 2s2 1S0 to 2s2p 1P1 and 3P1 transitions in the four-electron beryllium atom are calculated by using the multi-configuration Dirac–Hartree–Fock method and the relativistic configuration interaction approach for the stable and short-lived beryllium isotopes. The results provided herein can be employed for the consistency check with the nuclear rms charge radii from the experimental isotope shifts by using the corresponding transitions for the short-lived nuclei 7,10?12Be and 14Be. The analogous isotope shift results could also be obtained for the beryllium-like ions by the methods used here.
A Precise Description of the Electronic Structures and Spin-Allowed Transition Properties of PF and Its Cation: All-Electron Configuration-Interaction Investigations Including Relativistic Effect
LI Qi-Nan, ZHAO Shu-Tao, ZHANG Xiao-Mei, LUO Wang, LI Rui, YAN Bing
Chin. Phys. Lett. 2015, 32 (07): 073103 .   DOI: 10.1088/0256-307X/32/7/073103
Abstract   PDF(pc) (806KB) ( 390 )
The electronic structures of PF and PF+ are calculated with the high-level configuration interaction method. To improve the precision of calculations, the spin-orbit coupling effect, the scalar relativistic effect, and the Davidson correction(+Q) are also considered. The spectroscopic parameters of bound states are derived by the electronic structures of PF and PF+, which are in good accordance with the measurements. The transition dipole moments of spin-allowed transitions are evaluated, and the radiative lifetimes of several ΛS states of PF and PF+ are obtained.
Calculation of the Duration of the Atomic Tunneling Ionization in a Strong Electrostatic Field by Using Bohmian Trajectories Approach
GUO Fu-Ming, CHEN Ji-Gen, LI Su-Yu, YANG Yu-Jun
Chin. Phys. Lett. 2015, 32 (07): 073201 .   DOI: 10.1088/0256-307X/32/7/073201
Abstract   PDF(pc) (522KB) ( 308 )
The duration of a bound electron tunneling through the barrier formed by atomic potential and electrostatic field is calculated by the Bohmian trajectories scheme. The time of the tunneling ionization decreases with the increase of the amplitude of the electrostatic field. By using the information about the position, velocity and force of the Bohmian trajectories, the dynamical process of tunneling through the barrier is investigated.
Multiple Ionization of Argon Induced by Carbon Ions at 20–500 keV/u Energies
NIU Shu-Tong, LIU Wen-Biao, YANG Ai-Xiang, HAN Cheng-Zhi, HU Wei, WEN Zhi-Wen, GAO Zhi-Min, SHAO Jian-Xiong, CHEN Xi-Meng
Chin. Phys. Lett. 2015, 32 (07): 073401 .   DOI: 10.1088/0256-307X/32/7/073401
Abstract   PDF(pc) (577KB) ( 254 )
We measure the multiple ionization cross-section ratios Rk1 of Ar impacted by Cq+ (q=1–3) ions in the energy range of 20–500 keV/u. The measured ratios Rk1 increase with the projectile energy at lower energies, and reach the maximum at energies of 50–150 keV/u, then decrease for higher energies. We also use the classical over barrier ionization model to calculate the ratios Rk1, and the calculation results are in good agreement with the data, which suggest that the multiple ionization process is described by the sequential over-barrier ionization process.
FUNDAMENTAL AREAS OF PHENOMENOLOGY(INCLUDING APPLICATIONS)
Polarimetric Laser Range-Gated Underwater Imaging
GUAN Jin-Ge, ZHU Jing-Ping, TIAN Heng
Chin. Phys. Lett. 2015, 32 (07): 074201 .   DOI: 10.1088/0256-307X/32/7/074201
Abstract   PDF(pc) (677KB) ( 4482 )
For conventional laser range-gated underwater imaging (RGI) systems, the target image is obtained based on the reflective character of the target. One of the main performance limiting factors of conventional RGI is that, when the underwater target has the same reflectivity as the background, it is difficult to distinguish the target from the background. An improvement is to use the polarization components of the reflected light. On the basis of conventional RGI, we propose a polarimetric RGI system that employs a polarization generator and a polarization analyzer to detect and recognize underwater objects. Experimental results demonstrate that, by combining polarization with intensity information, we are better able to enhance identification of the underwater target from other objects of the same reflectivity.
Low-Threshold Broadband Spectrum Generation by Amplification of Cascaded Stimulated Raman Scattering in an Ytterbium-Doped Fiber Amplifier
LEI Cheng-Min, SONG Rui, JIN Ai-Jun, HOU Jing
Chin. Phys. Lett. 2015, 32 (07): 074202 .   DOI: 10.1088/0256-307X/32/7/074202
Abstract   PDF(pc) (1724KB) ( 337 )
We present an experimental study on low-threshold broadband spectrum generation mainly due to the amplification of the cascaded stimulated Raman scattering (SRS) effect in a four-stage fiber master oscillator power amplifier system. The cascaded SRS is achieved by using a long passive fiber pumped by a pulsed fiber laser centered at wavelength 1064 nm. The amplified spontaneous emission during the amplification process is efficiently suppressed by cutting the length of the passive fiber and by using a double-clad ytterbium-doped fiber amplifier. The generated broadband spectrum spans from 960 nm to 1700 nm with maximum average output 13.6 W and average spectral power density approximately 17.7 mW/nm.
Multipeaked Solitons in Parity-Time Complex Superlattice with Dual Periods
WANG Hong-Cheng, LING Dong-Xiong, HE Ying-Ji
Chin. Phys. Lett. 2015, 32 (07): 074203 .   DOI: 10.1088/0256-307X/32/7/074203
Abstract   PDF(pc) (794KB) ( 348 )
The existence and stability of multipeaked solitons are investigated in a parity-time symmetric superlattice with dual periods under both self-focusing and self-defocusing nonlinearity. For self-defocusing nonlinearity, dipole solitons with low power and all the odd-peak solitons can exist stably in the first gap, while dipole solitons with high power and even-peak (except two) solitons are unstable. For self-focusing nonlinearity, even-peak out-of-phase solitons can propagate stably in the infinite gap, while odd-peak in-phase solitons are unstable.
Design of an Electrically Written and Optically Read Non-volatile Memory Device Employing BiFeO3/Au Heterostructures with Strong Absorption Resonance
XIAO Peng-Bo, ZHANG Wei, QU Tian-Liang, HUANG Yun, HU Shao-Min
Chin. Phys. Lett. 2015, 32 (07): 074204 .   DOI: 10.1088/0256-307X/32/7/074204
Abstract   PDF(pc) (1137KB) ( 319 )
Exploiting new concepts for dense, fast, and nonvolatile random access memory with reduced energy consumption is a significant issue for information technology. Here we design an 'electrically written and optically read' information storage device employing BiFeO3/Au heterostructures with strong absorption resonance. The electro-optic effect is the basis for the device design, which arises from the strong absorption resonance in BiFeO3/Au heterostructures and the electrically tunable significant birefringence of the BiFeO3 film. We first construct a simulation calculation of the BiFeO3/Au structure spectrum and identify absorption resonance and electro-optical modulation characteristics. Following a micro scale partition, the surface reflected light intensity of different polarization units is calculated. The results depend on electric polarization states of the BiFeO3 film, thus BiFeO3/Au heterostructures can essentially be designed as a type of electrically written and optically read information storage device by utilizing the scanning near-field optical microscopy technology based on the conductive silicon cantilever tip with nanofabricated aperture. This work will shed light on information storage technology.
Focusing Properties of Partially Coherent Controllable Dark-Hollow Beams through a Thin Lens
ZENG Xiang-Mei
Chin. Phys. Lett. 2015, 32 (07): 074205 .   DOI: 10.1088/0256-307X/32/7/074205
Abstract   PDF(pc) (716KB) ( 283 )
Analytical propagation formulas are derived for partially coherent controllable dark-hollow beams (CDHBs) through a thin lens based on the generalized Huygens–Fresnel integral. The expressions of the position for maximum irradiance on-axis and the relative focal shift are evaluated by the analytical propagation formulas. Our numerical results show that both the relative focal shift and the effective beam width of focused partially coherent CDHBs are mainly determined by the initial transverse coherence width δg and the Fresnel number Nw, which are also affected by the changes of both the dark-size adjusting parameter p and the order N of CDHBs.
Single Mode 2 µm GaSb Based Laterally Coupled Distributed Feedback Quantum-Well Laser Diodes with Metal Grating
SONG Yu-Zhi, ZHANG Yu, SONG Jia-Kun, LI Kang-Wen, ZHANG Zu-Yin, XU Yun, SONG Guo-Feng, CHEN Liang-Hui
Chin. Phys. Lett. 2015, 32 (07): 074206 .   DOI: 10.1088/0256-307X/32/7/074206
Abstract   PDF(pc) (764KB) ( 355 )
Room-temperature operation of a GaSb based laterally coupled distributed feedback quantum-well laser diode emitting at 2 μm is demonstrated. The device exhibits single longitudinal mode characteristic as a result of the first order Cr-Bragg gratings alongside the narrow ridge waveguide. We design the laser structure to obtain a critical coupling condition corresponding to a coupling coefficient of 12 cm?1. For a 1-mm-long uncoated laser diode with a 3-μm-wide stripe, a single mode output spectrum with side mode suppression ratio as high as 28.5 dB is achieved, and the maximum single mode continuous-wave output power is about 11 mW at room temperature.
A Linearly Polarized Ho:YAG Laser at 2.09 µm with Corner Cube Cavity Pumped by Tm:YLF Laser
WU Jing, JU You-Lun, DAI Tong-Yu, LIU Wei, YAO Bao-Quan, WANG Yue-Zhu
Chin. Phys. Lett. 2015, 32 (07): 074207 .   DOI: 10.1088/0256-307X/32/7/074207
Abstract   PDF(pc) (618KB) ( 355 )
A linearly polarized operation Ho:YAG laser at 2090.5 nm with a corner cube cavity is demonstrated. A polarizer with high reflectivity for the s-polarized light at the laser wavelength is employed to achieve a linearly polarized laser. In the same case of resonator length, the corner cube can be used to cut the volume of the Ho:YAG laser and to enhance the stability of the system. The maximum linearly polarized output power of 5.8 W is achieved at the absorbed pump power of 23.3 W, corresponding to a slope efficiency of 29.7%, and the optical-optical conversion efficiency is around 24.9%. The M2 factors of the 2.09 μm laser are 2.4 and 1.2 along the horizontal and vertical directions, respectively.
Tunable Optical Filters Based on Different Configurations with Cholesteric Liquid Crystals
CHEN Dan, YIN Xiang-Bao, LIU Yong-Jun, ZHANG Ling-Li, MA Ji, SUN Wei-Min
Chin. Phys. Lett. 2015, 32 (07): 074208 .   DOI: 10.1088/0256-307X/32/7/074208
Abstract   PDF(pc) (641KB) ( 358 )
Optical filters with different configurations based on cholesteric liquid crystals (CLCs) are designed. The central wavelength from CLCs can be tuned by the electric field or temperature. For the electric field tuning, the ITO is designed with circular patterns, which can make the tunable range 18 nm. For the temperature tuning, two-layer-CLC configurations are used. The experimental results indicate that a deepened or broadened bandgap from the CLC can be achieved by different handedness or concentrations of chiral dopants. The spectrum study is carried out.
Wide-Field Vibrational Phase Contrast Imaging Based on Coherent Anti-Stokes Raman Scattering Holography
LV Yong-Gang, JI Zi-Heng, DONG Da-Shan, SHI Ke-Bin, GONG Qi-Huang
Chin. Phys. Lett. 2015, 32 (07): 074209 .   DOI: 10.1088/0256-307X/32/7/074209
Abstract   PDF(pc) (1717KB) ( 268 )
We propose and implement a wide-field vibrational phase contrast detection to obtain imaging of imaginary components of third-order nonlinear susceptibility in a coherent anti-Stokes Raman scattering (CARS) microscope with full suppression of the non-resonant background. This technique is based on the unique ability of recovering the phase of the generated CARS signal based on holographic recording. By capturing the phase distributions of the generated CARS field from the sample and from the environment under resonant illumination, we demonstrate the retrieval of imaginary components in the CARS microscope and achieve background free coherent Raman imaging.
Kuznetsov–Ma Soliton in Coupled Quantum Wells
DU Ying-Jie, XIE Xiao-Tao, YU Jin-Ying, BAI Jin-Tao
Chin. Phys. Lett. 2015, 32 (07): 074210 .   DOI: 10.1088/0256-307X/32/7/074210
Abstract   PDF(pc) (511KB) ( 363 )

We show the possibility to generate Kuznetsov–Ma solitons based on bound-to-bound intersubband transitions in an asymmetric two-coupled well structure. By presenting the modulation instability of the nonlinear system provided by the interaction between light fields and quantum wells, we show that the plane wave with small perturbation can evolve into periodic trains of pulses at high while controllable repetition rates. It is found that the formation of Kuznetsov–Ma solitons as well as their period is determined by the combination of group velocity dispersion, Kerr nonlinearity and the initial amplitude of the background wave. The present research may be useful for generating subpicosecond and femtosecond pulses.

PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
Direct Laser-Driven Quasi-Isentropic Compression on HEAVEN-I Laser
ZHANG Pin-Liang, TANG Xiu-Zhang, LI Ye-Jun, WANG Zhao, TIAN Bao-Xian, YIN Qian, LU Ze, XIANG Yi-Huai, GAO Zhi-Xing, LI Jing, HU Feng-Ming, GONG Zi-Zheng
Chin. Phys. Lett. 2015, 32 (07): 075201 .   DOI: 10.1088/0256-307X/32/7/075201
Abstract   PDF(pc) (713KB) ( 278 )
The HEAVEN-I laser is used for direct drive quasi-isentropic compression up to ~18 GPa in samples of aluminum without being temporal pulse shaped. The monotonically increasing loading is with a rise time over 17 ns. The compression history is well reproduced by the 1D radiation hydrodynamics simulation. We find that a small shock precursor where the backward integration method cannot process is formed at the beginning of illumination. We compare the loading process of HEAVEN-I with the typical profile (concave down, prefect pulse shape), the results show that a typical profile can obtain more slowly rising and higher pressure, and the shock precursor has significant effects on temperature and entropy production. However, it is demonstrated that the HEAVEN-I is an excellent optical source for direct laser-driven quasi-isentropic compression, even if it produces more temperature rise and entropy than the typical profile.
Modeling of the Distinctive Ground-State Atomic Oxygen Density Profile in Plasma Needle Discharge at Atmospheric Pressure
QIAN Mu-Yang, YANG Cong-Ying, CHEN Xiao-Chang, NI Geng-Song, LIU-Song, WANG De-Zhen
Chin. Phys. Lett. 2015, 32 (07): 075202 .   DOI: 10.1088/0256-307X/32/7/075202
Abstract   PDF(pc) (667KB) ( 301 )
A two-dimensional coupled model of neutral gas flow and plasma dynamics is presented to explain the two distinctive patterns of ground-state atomic oxygen density profiles that have been observed experimentally in the helium plasma needle discharge. When the gas flow rate is 0.25 standard liter per minute (SLM), the discharge is substantially sustained by the electron impact ionization of air near a dielectric surface, corresponding to the radial density peaks along the axis of the symmetry. However, as the flow rate is 1.1 SLM, Penning ionization between helium metastables and surrounding air dominates the ionization reactions and peaks at an off-center position (r=0.9 mm), which indicates the ring-shaped density distribution. The critical feeding gas flow rate is found to be around 0.4 SLM. The peak density is on the order of 1020 m?3 in our case. Previous reports of a flow-dependent bacterial killing pattern and ground-state atomic oxygen measurement support our simulation results.
CONDENSED MATTER: STRUCTURE, MECHANICAL AND THERMAL PROPERTIES
TEM Characterization of Helium Bubbles in T91 and MNHS Steels Implanted with 200 keV He Ions at Different Temperatures
WANG Ji, GAO Xing, WANG Zhi-Guang, WEI Kong-Fang, YAO Cun-Feng, CUI Ming-Huan, SUN Jian-Rong, LI Bing-Sheng, PANG Li-Long, ZHU Ya-Bin, LUO Peng, CHANG Hai-Long, ZHANG Hong-Peng, ZHU Hui-Ping, WANG Dong, DU Yang-Yang, XIE Er-Qing
Chin. Phys. Lett. 2015, 32 (07): 076101 .   DOI: 10.1088/0256-307X/32/7/076101
Abstract   PDF(pc) (1422KB) ( 463 )
Modified novel high silicon steel (MNHS, a newly developed reduced-activation martensitic alloy) and commercial alloy T91 are implanted with 200 keV He2+ ions to a dose of 5×1020 ions/m2 at 300, 450 and 550°C. Transmission electron microscopy (TEM) is used to characterize the size and morphology of He bubbles. With the increase of the implantation temperature, TEM observations indicate that bubbles increase in size and the proportion of 'brick shaped' cuboid bubbles increases while the proportion of polyhedral bubbles decreases in both the steel samples. For the samples implanted at the same temperature, the average size of He bubbles in MNHS is smaller than that in T91. This might be due to the abundance of boundaries and precipitates in MNHS, which provide additional sites for the trapping of He atoms, thus reduce the susceptibility of MNHS to He embrittlement.
Discontinuous Precipitation Reaction Front of Cellular Recrystallization for a Single-Crystal Superalloy Studied by Electron Microscopy
ZHUO Long-Chao, LIANG Shu-Hua, WANG Feng, LIU Yu-Feng, XIONG Ji-Chun
Chin. Phys. Lett. 2015, 32 (07): 076102 .   DOI: 10.1088/0256-307X/32/7/076102
Abstract   PDF(pc) (1507KB) ( 329 )
Combining analytical transmission electron microscopy systematic tilting, scanning transmission electron microscopy mapping and nano-beam electron diffraction operations, we obtain direct experimental proofs on the boundary type, elemental distribution and structure of the cellular recrystallization reaction front for a single-crystal superalloy. It is demonstrated that the cellular recrystallization reaction front usually corresponds to coincidence site lattice boundaries, and a thin layer of γ-forming elements such as Re, Cr, Mo and Co invariably exists in the direct reaction front. Furthermore, the thin layer with γ-forming elements is proved to be γ phase, with the same orientation as the neighboring original matrix.
Thermally Controllable Break Junctions with High Bandwidths and High Integrabilities
MENG Chao, HUANG Pu, ZHOU Jing-Wei, DUAN Chang-Kui, DU Jiang-Feng
Chin. Phys. Lett. 2015, 32 (07): 076201 .   DOI: 10.1088/0256-307X/32/7/076201
Abstract   PDF(pc) (702KB) ( 310 )
Break junctions are important in generating nanosensors and single molecular devices. The mechanically controllable break junction is the most widely used method for a break junction due to its simplicity and stability. However, the bandwidths of traditional devices are limited to about a few hertz. Moreover, when using traditional methods it is hard to allow independent control of more than one junction. Here we propose on-chip thermally controllable break junctions to overcome these challenges. This is verified by using finite element analysis. Adopting microelectromechanical systems produces features of high bandwidth and independent controllability to this new break junction system. The proposed method will have a wide range of applications on on-chip high speed independent controllable and highly integrated single molecule devices.
The 1.85 GPa AlSc Bulk Alloy with Abundant Nanoscale Growth Twins
ZHUO Long-Chao, LIANG Shu-Hua, ZHANG Tao
Chin. Phys. Lett. 2015, 32 (07): 076401 .   DOI: 10.1088/0256-307X/32/7/076401
Abstract   PDF(pc) (2542KB) ( 297 )
An in situ ultrahigh-strength ductile Al50Sc50 bulk alloy is produced by the copper mold casting method with a composite microstructure of micron-/submicron-sized grains and nanoscale twins. According to the microstructural investigations, hierarchical nanotwinned lamellar AlSc bundles with embedded micron-/submicron-sized Al2Sc and AlSc2 are observed. The as-cast alloy displays a unique act of ultrahigh strength of ~1.85 GPa together with pronounced work hardening and a large plasticity of ~14%. Further microstructural investigations on deformed specimens indicate that abundant hierarchical nanotwinned lamellar AlSc bundles are effective to dissipate localization of shear stress or block dislocations from spreading throughout the alloy and hinder the propagation of microcracks formed by local stress transition.
Heat Transport in Double-Bond Linear Chains of Fullerenes
WEI Liang, XU Zhi-Cheng, ZHENG Dong-Qin, ZHANG Wei, ZHONG Wei-Rong
Chin. Phys. Lett. 2015, 32 (07): 076501 .   DOI: 10.1088/0256-307X/32/7/076501
Abstract   PDF(pc) (607KB) ( 316 )
Heat transport in one kind of double-bond linear chains of fullerenes (C60's) is investigated by the classical nonequilibrium molecular dynamics method. It is found that the negative differential thermal resistance (NDTR) is more likely to occur at larger temperature difference and shorter length. In addition, with the increase of the length, the thermal conductivity of the chains increases, and NDTR region shrinks and vanishes in the end. The temperature profiles reveal that a large temperature jump exists at a high-temperature boundary of the chains when NDTR occurs. These results may be helpful for designing thermal devices where low-dimensional C60 polymers can be used.
Time-Resolved Measurements of the Adsorption/Desorption of Rb Atoms on Octadecyltrichlorosilane Coated Surfaces
LIAO Kang-Jia, WANG Mei-Ling, ZHANG Gui-Ying, ZHAO Kai-Feng
Chin. Phys. Lett. 2015, 32 (07): 076801 .   DOI: 10.1088/0256-307X/32/7/076801
Abstract   PDF(pc) (541KB) ( 302 )
We carry out the first time-resolved measurement of Rb atoms desorbing from octadecyltrichlorosilane coated surfaces by polarizing the atoms near the surface using an evanescent wave pump pulse and watching the subsequent intensity change of another evanescent wave probe beam, and find the mean adsorption (dwell) time to be about 400 ns at a cell body temperature of 112°C. The adsorption energy is found to be 0.19 eV from the surface temperature dependence of the adsorption time. This method can be extended to study the adsorption/desorption process of other alkali atoms on other surfaces of transparent substrates with an ultimate time resolution limited by the flight time of atoms in the evanescent wave which is of the order of nanoseconds.
A Novel Method of Fabricating Flexible Transparent Conductive Large Area Graphene Film
FAN Tian-Ju, YUAN Chun-Qiu, TANG Wei, TONG Song-Zhao, LIU Yi-Dong, HUANG Wei, MIN Yong-Gang, Arthur J. Epstein
Chin. Phys. Lett. 2015, 32 (07): 076802 .   DOI: 10.1088/0256-307X/32/7/076802
Abstract   PDF(pc) (1679KB) ( 509 )
We fabricate flexible conductive and transparent graphene films on position-emission-tomography substrates and prepare large area graphene films by graphite oxide sheets with the new technical process. The multi-layer graphene oxide sheets can be chemically reduced by HNO3 and HI to form a highly conductive graphene film on a substrate at lower temperature. The reduced graphene oxide sheets show a high conductivity sheet with resistance of 476 Ω/sq and transmittance of 76% at 550 nm (6 layers). The technique used to produce the transparent conductive graphene thin film is facile, inexpensive, and can be tunable for a large area production applied for electronics or touch screens.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
Electronic Structure and Optical Properties in Uranium Dioxide: the First Principle Calculations
SUI Peng-Fei, DAI Zhen-Hong, ZHANG Xiao-Ling, ZHAO Yin-Chang
Chin. Phys. Lett. 2015, 32 (07): 077101 .   DOI: 10.1088/0256-307X/32/7/077101
Abstract   PDF(pc) (938KB) ( 654 )
We report a study of the electronic structure and optical properties of uranium dioxide (UO2) based on the ab-initio density-functional theory and using the generalized gradient approximation. To correctly describe the strong correlation between 5f electrons of a uranium atom, we employ the on-site Hubbard U correction term and optimize the correlation parameter of the bulk uranium dioxide. Then we give the structural and electronic properties of the ground state of uranium dioxide. Based on the accurate electronic structure, we calculate the complex dielectric function of UO2 and the related optical properties, such as reflectivity, refractive index, extinction index, energy loss spectra, and absorption coefficient.
N-Doped Zigzag Graphene Nanoribbons on Si(001): a First-Principles Calculation
LI Jing, YANG Shen-Yuan, LI Shu-Shen
Chin. Phys. Lett. 2015, 32 (07): 077102 .   DOI: 10.1088/0256-307X/32/7/077102
Abstract   PDF(pc) (1059KB) ( 356 )

The structural and electronic properties of N-doped zigzag graphene nanoribbons (N-ZGNRs) adsorbed on Si(001) substrates are investigated with first-principles density functional calculations. Compared with the free-standing N-ZGNRs, the energy difference between the substitutional doping at the edge and the inner sites is significantly decreased on the Si substrate. The distribution of the extra charge induced by the N substitutional dopant keeps the Friedel oscillation feature, and is a main effect that influences the C–Si bonding strength. When N is doped in regions with high C–Si bond densities, the strain induced by the dopant also plays an important role in determining the C–Si bonding interactions. Similar to the undoped case, the strong N-ZGNR/Si interaction destroys the antiferromagnetic coupling of the edge states in N-ZGNR, leading to a non-magnetic ground state for the N-ZGNR/Si heterostructures.

Memory Behaviors Based on ITO/Graphene Oxide/Al Structure
YI Ming-Dong, GUO Jia-Lin, HU Bo, XIA Xian-Hai, FAN Qu-Li, XIE Ling-Hai, HUANG Wei
Chin. Phys. Lett. 2015, 32 (07): 077201 .   DOI: 10.1088/0256-307X/32/7/077201
Abstract   PDF(pc) (1401KB) ( 374 )
We investigate the memory properties of the ITO/graphene oxide/Al diodes. It is found that the devices show different memory behaviors with the diverse geometry and thickness of Al. When the thickness of the Al electrode is relatively thick, the device of the cross-point Al electrode shows a three-level memory effect, and the counterpart device of the cross-bar Al electrode exhibits a volatile static random access memory effect. When the thickness of the Al electrode is thinner, the above devices demonstrate a flash memory effect. The different memory behaviors of ITO/GO/Al diodes are ascribed to the mode and degree of reduction and oxidation of GO.
Polymer Solar Cells Using a PEDOT:PSS/Cu Nanowires/PEDOT:PSS Multilayer as the Anode Interlayer
ZHANG Ruo-Chuan, WANG Meng-Ying, YANG Li-Ying, QIN Wen-Jing, YIN Shou-Gen
Chin. Phys. Lett. 2015, 32 (07): 077202 .   DOI: 10.1088/0256-307X/32/7/077202
Abstract   PDF(pc) (2283KB) ( 371 )
We compare the electrical, optical, and surface properties of the PEDOT:PSS/Cu nanowires (Cu NWs)/PEDOT: PSS (PCP) multilayer for organic solar cells. It is demonstrated that the electrical and optical properties of the PEDOT could be improved by the insertion of a Cu NW layer due to its very low resistivity and surface morphology. The organic bulk heterojunction solar cell fabricated on the multilayer exhibits a higher power conversion efficiency than devices based on the PEDOT:PSS or PEDOT:PSS/Cu NWs layer. Moreover, the PCP multilayer can improve cell-performances such as a fill factor and the internal resistance in the device due to horizontally well-aligned Cu NWs. The results suggest that the PCP multilayer is a promising low-cost and low-temperature processing buffer layer candidate for low-cost organic photovoltaics.
31P Nuclear Magnetic Resonance of Charge-Density-Wave Transition in a Single Crystal of RuP
FAN Guo-Zhi, CHEN Rong-Yan, WANG Nan-Lin, LUO Jian-Lin
Chin. Phys. Lett. 2015, 32 (07): 077203 .   DOI: 10.1088/0256-307X/32/7/077203
Abstract   PDF(pc) (567KB) ( 365 )
We perform 31P nuclear magnetic resonance (NMR) measurements on a single crystal of RuP. The anomalies in resistivity at about TA=270 K and TB=330 K indicate that two phase transitions occur. The line shape of 31P NMR spectra in different temperature ranges is attributed to the charge density distribution. The Knight shift and spin-lattice relaxation rate 1/T1T are measured from 10 K to 300 K. At about TA=270 K, they both decrease abruptly with the temperature reduction, which reveals the gap-opening behavior. Well below TA, they act like the case of normal metal. Charge-density-wave phase transition is proposed to interpret the transition occurring at about TA.
Effects of Nonparabolicity on Electron Thermopower of Size-Quantized Semiconductor Films
BAHSHELI Guliyev, AKBAR Barati Chiyaneh, NOVRUZ Bashirov, GENBER Kerimli
Chin. Phys. Lett. 2015, 32 (07): 077204 .   DOI: 10.1088/0256-307X/32/7/077204
Abstract   PDF(pc) (452KB) ( 391 )
Effects of nonparabolicity of energy band on thermopower, in-plane effective mass and Fermi energy are investigated in size-quantized semiconductor films in a strong while non-quantized magnetic field. We obtain the expressions of these quantities as functions of thickness, concentration and nonparabolicity parameter. The influence of nonparabolicity is studied for degenerate and non-degenerate electron gases, and it is shown that nonparabolicity changes the character of thickness and the concentration dependence of thermopower, in-plane effective mass and Fermi energy. Moreover, the magnitudes of these quantities significantly increase with respect to the nonparabolicity parameter in the case of strong nonparabolicity in nano-films. The concentration dependence is also studied, and it is shown that thermopower increases when the concentration decreases. These results are in agreement with the experimental data.
AlGaN Channel High Electron Mobility Transistors with an AlxGa1−xN/GaN Composite Buffer Layer
LI Xiang-Dong, ZHANG Jin-Cheng, ZOU Yu, MA Xue-Zhi, LIU Chang, ZHANG Wei-Hang, WEN Hui-Juan, HAO Yue
Chin. Phys. Lett. 2015, 32 (07): 077205 .   DOI: 10.1088/0256-307X/32/7/077205
Abstract   PDF(pc) (1293KB) ( 385 )
We report an AlGaN channel high electron mobility transistor (HEMT) on a sapphire substrate with a 1000-nm AlxGa1?xN (x=0–0.18)/GaN composite buffer layer. With a significant improvement of crystal quality, the device features a high product of nsn. The AlGaN channel HEMTs presented show improved performance with respect to the conventional AlGaN channel HEMTs, including the on-resistance reduced from 31.2 to 8.1 Ω?mm, saturation drain current at 2 V gate bias promoted from 218 to 540 mA/mm, peak transconductance at 10 V drain bias promoted from 100 to a state-of-the-art value of 174 mS/mm, and reverse gate leakage current reduced from 1.85×10?3 to 2.15×10?5 mA/mm at VGD=?20 V.
Improvement of Performance of Organic Light-Emitting Diodes with Both a MoO3 Hole Injection Layer and a MoO3 Doped Hole Transport Layer
LIU Wei, LIU Guo-Hong, LIU Yong, LI Bao-Jun, ZHOU Xiang
Chin. Phys. Lett. 2015, 32 (07): 077206 .   DOI: 10.1088/0256-307X/32/7/077206
Abstract   PDF(pc) (687KB) ( 406 )
We improve the performance of organic light-emitting diodes (OLEDs) with both a MoO3 hole injection layer (HIL) and a MoO3 doped hole transport layer (HTL), and present a systematical and comparative investigation on these devices. Compared with OLEDs with only MoO3 HIL or MoO3 doped HTL, OLEDs with both MoO3 HIL and MoO3 doped HTL show superior performance in driving voltage, power efficiency, and stability. Based on the typical NPB/Alq3 heterojunction structure, OLEDs with both MoO3 HIL and MoO3 doped HTL show a driving voltage of 5.4 V and a power efficiency of 1.41 lm/W for 1000 cd/m2, and a lifetime of around 0.88 h with an initial luminance of 5268 cd/m2 under a constant current of 190 mA/cm2 operation in air without encapsulation. While OLEDs with only MoO3 HIL or MoO3 doped HTL show higher driving voltages of 6.4 V or 5.8 V and lower power efficiencies of 1.20 lm/W or 1.34 lm/W for 1000 cd/m2, and a shorter lifetime of 0.33 or 0.60 h with an initial luminance of around 5122 or 5300 cd/m2 under a constant current of 200 or 216 mA/cm2 operation. Our results demonstrate clearly that using both MoO3 HIL and MoO3 doped HTL is a simple and effective approach to simultaneously improve both the hole injection and transport efficiency, resulting from the lowered energy barrier at the anode interface and the increased hole carrier density in MoO3 doped HTL.
Shot Noise Suppression in a Quantum Point Contact with Short Channel Length
JEONG Heejun
Chin. Phys. Lett. 2015, 32 (07): 077301 .   DOI: 10.1088/0256-307X/32/7/077301
Abstract   PDF(pc) (897KB) ( 383 )

An experimental study on the current shot noise of a quantum point contact with short channel length is reported. The experimentally measured maximum energy level spacing between the ground and the first excited state of the device reached up to 7.5 meV, probably due to the hard wall confinement by using shallow electron gas and sharp point contact geometry. The two-dimensional non-equilibrium shot noise contour map shows noise suppression characteristics in a wide range of bias voltage. Fano factor analysis indicates spin-polarized transport through a short quantum point contact.

Characterization of Ge Doping on Sb2Te3 for High-Speed Phase Change Memory Application
ZHU Yue-Qin, ZHANG Zhong-Hua, SONG San-Nian, XIE Hua-Qing, SONG Zhi-Tang, SHEN Lan-Lan, LI Le, WU Liang-Cai, LIU Bo
Chin. Phys. Lett. 2015, 32 (07): 077302 .   DOI: 10.1088/0256-307X/32/7/077302
Abstract   PDF(pc) (817KB) ( 402 )
The phase change material of Ge-doped Sb2Te3 is shown to have higher crystallization temperature and better thermal stability compared with pure Sb2Te3. Ge0.11Sb2Te3 alloys are considered to be a potential candidate for phase change random access memories, as proved by a higher crystallization temperature, a better data retention ability, and a faster switching speed in comparison with those of Ge2Sb2Te5. In addition, Ge0.11Sb2Te3 presents extremely rapid reverse switching speed (10 ns), and up to 105 programming cycles are obtained with stable set and reset resistances.
The Effect of Oxygen Partial Pressure during Active Layer Deposition on Bias Stability of a-InGaZnO TFTs
HUANG Xiao-Ming, WU Chen-Fei, LU Hai, REN Fang-Fang, ZHU Hong-Bo, WANG Yong-Jin
Chin. Phys. Lett. 2015, 32 (07): 077303 .   DOI: 10.1088/0256-307X/32/7/077303
Abstract   PDF(pc) (652KB) ( 413 )
The effect of oxygen partial pressure (PO2) during the channel layer deposition on bias stability of amorphous indium-gallium-zinc oxide (a-IGZO) thin film transistors (TFTs) is investigated. As PO2 increases from 10% to 30%, it is found that the device shows enhanced bias stress stability with significantly reduced threshold voltage drift under positive gate bias stress. Based on the x-ray photoelectron spectroscopy measurement, the concentration of oxygen vacancies (OV) within the a-IGZO layer is suppressed by increasing PO2. Meanwhile, the low-frequency noise analysis indicates that the average trap density near the channel/dielectric interface continuously drops with increasing PO2. Therefore, the improved interface quality with increasing PO2 during the channel layer deposition can be attributed to the reduction of interface OV-related defects, which agrees with the enhanced bias stress stability of the a-IGZO TFTs.
Common Base Four-Finger InGaAs/InP Double Heterojunction Bipolar Transistor with Maximum Oscillation Frequency 535 GHz
NIU Bin, WANG Yuan, CHENG Wei, XIE Zi-Li, LU Hai-Yan, CHANG Long, XIE Jun-Ling
Chin. Phys. Lett. 2015, 32 (07): 077304 .   DOI: 10.1088/0256-307X/32/7/077304
Abstract   PDF(pc) (615KB) ( 399 )
A common base four-finger InGaAs/InP double heterojunction bipolar transistor with 535 GHz fmax by using the 0.5 μm emitter technology is fabricated. Multi-finger design is used to increase the input current. Common base configuration is compared with common emitter configuration, and shows a smaller K factor at high frequency span, indicating a larger breakpoint frequency of maximum stable gain/maximum available gain (MSG/MAG) and thus a higher gain near the cut-off frequency, which is useful in THz amplifier design.
Doping Induced Gap Anisotropy in Iron-Based Superconductors: a Point-Contact Andreev Reflection Study of BaFe2−xNixAs2 Single Crystals
ZHU Jun, WANG Zhao-Sheng, WANG Zhen-Yu, HOU Xing-Yuan, LUO Hui-Qian, LU Xing-Ye, LI Chun-Hong, SHAN Lei, WEN Hai-Hu, REN Cong
Chin. Phys. Lett. 2015, 32 (07): 077401 .   DOI: 10.1088/0256-307X/32/7/077401
Abstract   PDF(pc) (1234KB) ( 318 )

We report a systematic investigation on c-axis point-contact Andreev reflection (PCAR) in BaFe2−xNixAs2 superconducting single crystals from underdoped to overdoped regions (0.075≤x≤0.15). At low temperatures, an in-gap sharp peak at low-bias voltage is observed in PCAR for overdoped samples, in contrast to the case of underdoped junctions, in which an in-gap plateau is observed. The variety of the conductance spectra with doping can be well described by using a generalized Blonder–Tinkham–Klapwijk formalism with an angle-dependent gap. This gap shows a clear crossover from a nodeless in the underdoped side to a nodal feature in the overdoped region. This result provides evidence of the doping-induced evolution of the superconducting order parameter when the inter-pocket and intra-pocket scattering are tuned through doping, as expected in the s± scenario.

Surface State Bands in Superconducting (PtxIr1−x)Te2
KONG Wan-Dong, MIAO Hu, QIAN Tian, WANG Zhi-Jun, XU Gang, FANG Ai-Fang, HUANG Yao-Bo, ZHANG Peng, SHI Xun, FANG Zhong, DAI Xi, RICHARD Pierre, WANG Nan-Lin, DING Hong
Chin. Phys. Lett. 2015, 32 (07): 077402 .   DOI: 10.1088/0256-307X/32/7/077402
Abstract   PDF(pc) (1538KB) ( 372 )
Angle-resolved photoemission spectroscopy is performed to study the bulk and surface electronic structures of non-superconducting IrTe2 and superconducting Pt0.05Ir0.95Te2. In addition to the bulk electronic bands predicted by the local density approximation calculations, we observe two Dirac cone-like bands at the Brillouin zone center, which are non-dispersive along kz, suggesting that the extra bands are surface state bands. As the experimental results are well consistent with the ab initio calculations of surface states, the parity analysis proves that these surface state bands are topologically trivial and thus exclude (PtxIr1?x)Te2 as a possible topological superconductor candidate.
The Third-Order Nonlinear Optical Properties in Cobalt-Doped ZnO Films
YAN Teng-Fei, LI Ying, KANG Jun-Jie, ZHOU Peng-Yu, SUN Bao-Quan, ZHANG Kun, YAN Shi-Shen, ZHANG Xin-Hui
Chin. Phys. Lett. 2015, 32 (07): 077801 .   DOI: 10.1088/0256-307X/32/7/077801
Abstract   PDF(pc) (790KB) ( 354 )
We quantitatively investigate the third-order optical nonlinear response of Co-doped ZnO thin films prepared by magnetron sputtering using the Z-scan method. The two-photon absorption and optical Kerr effect are revealed to contribute to the third-order nonlinear response of the Co-doped ZnO films. The nonlinear absorption coefficient β is determined to be approximately 8.8×10?5 cm/W and the third-order nonlinear susceptibility χ(3) is 2.93×10?6 esu. The defect-associated energy levels within the band gap are suggested to be responsible for the enhanced nonlinear response observed in Co-doped ZnO films.
Optical Properties and Surface Morphology of Thin Silver Films Deposited by Thermal Evaporation
ZHOU Ming, LI Yao-Peng, ZHOU Sheng, LIU Ding-Quan
Chin. Phys. Lett. 2015, 32 (07): 077802 .   DOI: 10.1088/0256-307X/32/7/077802
Abstract   PDF(pc) (739KB) ( 854 )
Thin silver films with different thicknesses are deposited by thermal evaporation, and the Drude–Lorentz mode is used to describe the optical properties of samples measured by an ellipsometer, and the thickness uniqueness analysis and reflection spectrum testing are used to verify the simulated results. We obtain the surface morphologies of the samples using the scanning electron microscopy, and calculate the relationship of reflectance with film thickness at wavelength 800 nm using the Mathcad software. Moreover, the effective medium approximation mode is used to explain the differences of wavelength-dependent n and k as the thickness changes. As the silver film thickness decreases, the optical constant changes regularly, and the films show flat surface, small cracks, discontinuous and island distribution, respectively, while n and k of the island distributed silver film have an intersection point in the visible spectrum. Our experiments provide an in-depth research for the ultra-thin silver film under thermal evaporation deposition, and will be helpful for its application in multilayers and plasmonic devices.
Bandgap Engineering in Wurtzite GaAs Nanowires by Hydrostatic Pressure
YANG Shuang, DING Kun, DOU Xiu-Ming, YU Ying, NI Hai-Qiao, NIU Zhi-Chuan, JIANG De-Sheng, SUN Bao-Quan
Chin. Phys. Lett. 2015, 32 (07): 077803 .   DOI: 10.1088/0256-307X/32/7/077803
Abstract   PDF(pc) (874KB) ( 376 )
Band structure of wurtzite (WZ) GaAs nanowires (NWs) is investigated by using photoluminescence measurements under hydrostatic pressure at 6 K. We demonstrate that WZ GaAs NWs have a direct bandgap transition with an emission energy of 1.53 eV, corresponding to the optical transition between conduction band Γ7C and valence band Γ9V in WZ GaAs. The direct-to-pseudodirect bandgap transition can be observed by applying a pressure approximately above 2.5 GPa.
Single-Photon Emission from GaAs Quantum Dots Embedded in Nanowires
YANG Shuang, DOU Xiu-Ming, YU Ying, NI Hai-Qiao, NIU Zhi-Chuan, JIANG De-Sheng, SUN Bao-Quan
Chin. Phys. Lett. 2015, 32 (07): 077804 .   DOI: 10.1088/0256-307X/32/7/077804
Abstract   PDF(pc) (629KB) ( 332 )
A highly efficient single-photon source based on a semiconductor quantum dot (QD) is a promising candidate in quantum information processing. We report a single-photon source based on self-assembled GaAs QDs in nanowires with an extraction efficiency of 14%. The second-order correlation function g(2)(0) at saturate excitation power is estimated to be 0.28. The measured polarization of QD emission depends on the geometric relations between the directions of PL collection and the long axis of nanowires.
CROSS-DISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
Rice Husk Templated Mesoporous ZnO Nanostructures for Ethanol Sensing at Room Temperature
M. Chitra, K. Uthayarani, N. Rajasekaran, N. Neelakandeswari, E. K. Girija, D. Pathinettam Padiyan
Chin. Phys. Lett. 2015, 32 (07): 078101 .   DOI: 10.1088/0256-307X/32/7/078101
Abstract   PDF(pc) (945KB) ( 358 )
Mesoporous zinc oxide nanostructures are successfully synthesized via the sol-gel route by using a rice husk as the template for ethanol sensing at room temperature. The structure and morphology of the nanostructures are characterized by x-ray diffraction, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and nitrogen adsorption–desorption analyses. The mechanism for the growth of zinc oxide nanostructures over the biotemplate is proposed. SEM and TEM observations also reveal the formation of spherical zinc oxide nanoparticles over the interwoven fibrous network. Multiple sized pores having pore diameter ranging from 10–40 nm is also evidenced from the pore size distribution plot. The larger surface area and porous nature of the material lead to high sensitivity (40.93% for 300 ppm of ethanol), quick response (42 s) and recovery (40 s) towards ethanol at 300 K. The porous nature of the interwoven fibre-like network affords mass transportation of ethanol vapor, which results in faster surface accessibility, and hence it acts as a potential candidate for ethanol sensing at room temperature.
Fabrication of IBAD-MgO and PLD-CeO2 Layers for YBCO Coated Conductors
MU Qing-Qing, LIU Lin-Fei, LI Yi-Jie
Chin. Phys. Lett. 2015, 32 (07): 078102 .   DOI: 10.1088/0256-307X/32/7/078102
Abstract   PDF(pc) (626KB) ( 464 )
MgO thin films with different textures are fabricated by the ion beam assisted (IBAD) method on the Y2O3/Al2O3 buffered C276 tape. Then a CeO2 layer is directly grown on the IBAD-MgO film by the pulsed laser deposition (PLD) method. Effects of IBAD-MgO texture, substrate 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 CeO2 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 substrate 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 Δφ=2.9° and a smooth surface with an rms surface roughness of less than 2 nm. The critical current density Jc of a 0.4-μm-thick YBCO film deposited on the CeO2 layer is 6.25×106 A/cm2 at 77 K and a self-field.
Suppressing Charge Recombination in ZnO-Nanorod-Based Perovskite Solar Cells with Atomic-Layer-Deposition TiO2
DONG Juan, XU Xin, SHI Jiang-Jian, LI Dong-Mei, LUO Yan-Hong, MENG Qing-Bo, CHEN Qiang
Chin. Phys. Lett. 2015, 32 (07): 078401 .   DOI: 10.1088/0256-307X/32/7/078401
Abstract   PDF(pc) (845KB) ( 624 )
ZnO nanorods are passivated with a TiO2 interfacial layer prepared by the atomic layer deposition method and applied in the CH3NH3PbI3 perovskite solar cell, which show a positive effect on the fill factor and power conversion efficiency. With TiO2 interfacial passivation, the charge recombination in the ZnO/CH3NH3PbI3 interface is effectively suppressed and the maximum power conversion efficiency is enhanced from 11.9% to 13.4%.
The Storage Cell Circuit with Memristor Characteristics of Poly(N-Vinylcarbazole) Films
LI Lei, SUN Yan-Mei, WEN Dian-Zhong
Chin. Phys. Lett. 2015, 32 (07): 078501 .   DOI: 10.1088/0256-307X/32/7/078501
Abstract   PDF(pc) (1079KB) ( 354 )
A kind of non?conjugated polymer memory material, poly(N-vinylcarbazole), is used to investigate silicon-based storage performance with the fact that the one-bit storage cell circuit consists of a sandwiched indium-tin-oxide/poly(N-vinylcarbazole)/Al and an n-type metal-oxide-semiconductor field effect transistor. The memristor on the basis of a nano poly(N-vinylcarbazole) film exhibits electrical bistability and flash memory features, for which the switching-on voltage is -1 V and the on/off current ratio approaches 104. At ambient temperature, the memory circuit possesses higher reliability within the programming time 104 s. The output voltage is close to 0.5 V during logic 1, while it is approximately 14 mV in the logic 0. This paves the way for the study on the technology concerning the binary encoding and data storage of nonvolatile memories.
Smart Rewiring: Improving Network Robustness Faster
BAI Liang, XIAO Yan-Dong, HOU Lv-Lin, LAO Song-Yang
Chin. Phys. Lett. 2015, 32 (07): 078901 .   DOI: 10.1088/0256-307X/32/7/078901
Abstract   PDF(pc) (1861KB) ( 419 )
Previous work puts forward a random edge rewiring method which is capable of improving the network robustness noticeably, while it lacks further discussions about how to improve the robustness faster. In this study, the detailed analysis of the structures of improved networks show that regenerating the edges between high-degree nodes can enhance the robustness against a targeted attack. Therefore, we propose a novel rewiring strategy based on regenerating more edges between high-degree nodes, called smart rewiring, which could speed up the increase of the robustness index effectively. The smart rewiring method also explains why positive degree-degree correlation could enhance network robustness.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
Glitch Crisis or Not: a Microscopic Study
LI Ang
Chin. Phys. Lett. 2015, 32 (07): 079701 .   DOI: 10.1088/0256-307X/32/7/079701
Abstract   PDF(pc) (402KB) ( 373 )
The problem of glitch crisis has been a great deal of debate recently. It might challenge the standard two-component model, where glitches are thought to be triggered by the sudden unpinning of superfluid vortices in the neutron-star crust. It says that due to crustal entrainment the amount of superfluid in the crust cannot explain the changes in angular momentum required to account for the glitches. However, the argument of this crisis is based on the assumption that the core superfluid is completely coupled to the crust when a glitch happens. The fraction of the coupled core part is actually a quite uncertain problem so far. In this work, we take three possible values for the fraction of the coupled core part and study in detail the crisis problem for a 1.4 M? canonical star, based on a microscopic equation of state for the neutron star's core using the Brueckner–Hartree–Fock approach. For this purpose, two requisite parameters are chosen as follows: the core-crust transition pressure is in the range of Pt=0.2–0.65 MeV/fm3, and the fractional crust radius ΔR/R=0.082 based on experiments. To account for the possibility of a heavier star, a larger value of ΔR/R=0.15 is also chosen for comparison. Then we take the crustal entrainment into account, and evaluate the predictions for the fractional moment of inertia at various conditions. The results show that there is commonly no such glitch crisis, as long as one considers only a small fraction of the core neutron superfluid will contribute to the charged component of the star. Only if the core-crust transition pressure is determined to be a low value, the crisis problem may appear for complete core-crust coupling. This is consistent with a recent study in a phenomenological model.
56 articles