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 Chin. Phys. Lett.
 Chin. Phys. Lett.--2017, 34 (01)   Published: 29 December 2016
GENERAL
Jun-Chao Chen, Zheng-Yi Ma, Ya-Hong Hu
Chin. Phys. Lett. 2017, 34 (01): 010201 doi: 10.1088/0256-307X/34/1/010201
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The integrability of the coupled, modified KdV equation and the potential Boiti–Leon–Manna–Pempinelli (mKdV-BLMP) system is investigated using the Painlevé analysis approach. It is shown that this coupled system possesses the Painlevé property in both the principal and secondary branches. Then, the consistent Riccati expansion (CRE) method is applied to the coupled mKdV-BLMP system. As a result, it is CRE solvable for the principal branch while non-CRE solvable for the secondary branch. Finally, starting from the last consistent differential equation in the CRE solvable case, soliton, multiple resonant soliton solutions and soliton-cnoidal wave interaction solutions are constructed explicitly.
Yun-Kai Liu, Biao Li
Chin. Phys. Lett. 2017, 34 (01): 010202 doi: 10.1088/0256-307X/34/1/010202
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The (2+1)-dimension nonlocal nonlinear Schrödinger (NLS) equation with the self-induced parity-time symmetric potential is introduced, which provides spatially two-dimensional analogues of the nonlocal NLS equation introduced by Ablowitz et al. [Phys. Rev. Lett. 110 (2013) 064105]. General periodic solutions are derived by the bilinear method. These periodic solutions behave as growing and decaying periodic line waves arising from the constant background and decaying back to the constant background again. By taking long wave limits of the obtained periodic solutions, rogue waves are obtained. It is also shown that these line rogue waves arise from the constant background with a line profile and disappear into the constant background again in the $(x,y)$ plane.
Kang-Kang Ju, Cui-Xian Guo, Xiao-Yin Pan
Chin. Phys. Lett. 2017, 34 (01): 010301 doi: 10.1088/0256-307X/34/1/010301
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We investigate the effects of the initial-slip term by studying the dissipation-induced transition probabilities between any two eigenstates of a simple harmonic oscillator. The general analytical expressions for the transition probabilities are obtained, then the special cases of transition probabilities ignoring the Brownian motion from the ground state to the first few excited states are discussed. It is found that the initial-slip term not only makes the forbidden transitions between states of different parity possible but also lifts the initial value of the transition probabilities.
Xiao-Xiong Zeng, Xin-Yun Hu, Li-Fang Li
Chin. Phys. Lett. 2017, 34 (01): 010401 doi: 10.1088/0256-307X/34/1/010401
Show Abstract
Holographic thermalization for a black hole surrounded by phantom dark energy is probed. The result shows that the smaller the phantom dark energy parameter is, the easier the is plasma to thermalize as the chemical potential is fixed, the larger the chemical potential is, and the harder the plasma is to thermalize as the dark energy parameter is fixed. The thermalization velocity and thermalization acceleration are presented by fitting the thermalization curves.
NUCLEAR PHYSICS
Yi Han, Bing-Sheng Li, Zhi-Guang Wang, Jin-Xin Peng, Jian-Rong Sun, Kong-Fang Wei, Cun-Feng Yao, Ning Gao, Xing Gao, Li-Long Pang, Ya-Bin Zhu, Tie-Long Shen, Hai-Long Chang, Ming-Huan Cui, Peng Luo, Yan-Bin Sheng, Hong-Peng Zhang, Xue-Song Fang, Si-Xiang Zhao, Jin Jin, Yu-Xuan Huang, Chao Liu, Dong Wang, Wen-Hao He, Tian-Yu Deng, Peng-Fei Tai, Zhi-Wei Ma
Chin. Phys. Lett. 2017, 34 (01): 012801 doi: 10.1088/0256-307X/34/1/012801
Show Abstract
Radiation-induced defect annealing in He$^{+}$ ion-implanted 4H-SiC via H$^{+}$ ion irradiation is investigated by Raman spectroscopy. There are 4H-SiC wafers irradiated with 230 keV He$^{+}$ ions with fluences ranging from $5.0\times10^{15}$ cm$^{-2}$ to $2.0\times10^{16}$ cm$^{-2}$ at room temperature. The post-implantation samples are irradiated by 260 keV H$^{+}$ ions at a fluence of $5.0\times10^{15}$ cm$^{-2}$ at room temperature. The intensities of Raman lines decrease after He implantation, while they increase after H irradiation. The experimental results present that the magnitude of Raman line increment is related to the concentration of pre-existing defects formed by He implantation. A strong new peak located near 966 cm$^{-1}$, which is assigned to 3C-SiC LO (${\it \Gamma}$) phonon, is found in the He-implanted sample with a fluence of $5.0\times10^{15}$ cm$^{-2}$ followed by H irradiation. However, for the He-implanted sample with a fluence of $2.0\times10^{16}$ cm$^{-2}$ followed by H irradiation, no 3C-SiC phonon vibrations are found. The detailed reason for H irradiation-induced phase transformation in the He-implanted 4H-SiC is discussed.
Xiao-Wen Zhu, Yuan-Rong Lu, Kun Zhu, Xue-Qing Yan, Hu Wang, Shu-Li Gao, Yu-Bin Zou, Zhi-Yu Guo
Chin. Phys. Lett. 2017, 34 (01): 012901 doi: 10.1088/0256-307X/34/1/012901
Show Abstract
The Peking University neutron imaging facility (PKUNIFTY), an RFQ-based neutron source, aims at developing industrial applications. During the past 3 y operation, some problems have appeared, such as RF sparking for the RFQ high power operation, full power level instability of RF transmitter, and the misalignment of RFQ electrodes assembling and deformation. The PKUNIFTY upgrade endeavors to adopt a modest inter-voltage beam dynamics design. The new beam dynamics design of 201.5 MHz RFQ of PKUNIFTY, which accelerates 35 mA of D$^{+}$ from 50 keV to 2.0 MeV at 10% duty factor, is performed. The averaged D$^{+}$ beam will be about 3 mA. The source will deliver a fast neutron yield of 2.5$\times$10$^{12}$ n/s via the deuteron–beryllium reaction, which is about 10 times higher than the current status.
Un-Nisa Zaib, Shigeki Fukuda, Zu-Sheng Zhou, Dong Dong, Sheng-Chang Wang, Ou-Zheng Xiao, Zhi-Jun Lu, Guo-Xi Pei
Chin. Phys. Lett. 2017, 34 (01): 012902 doi: 10.1088/0256-307X/34/1/012902
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We present the first phase R&D for the 800 kW cw, 650 MHz klystron for the future circular electron–positron collider (CEPC) project in China. The CEPC requires 192 klystrons and it is desired to be designed in the Institute of High Energy Physics, CAS, and manufactured domestically. Therefore, we present the manufacturing schedule of this project; the three-stage development from the beam test tube to the klystron having a high efficiency structure. Design of the beam test tube that comprises electron gun and collector is presented. First, gun simulation having a modulating anode is performed using DGUN software. The uniform beam trajectories with a beam perveance of 0.64 $\mu$A/V$^{3/2}$ are simulated. We employ a Ba-dispenser cathode of radius 35 mm with $\phi$10 hole at the center and obtain a current density on cathode less than 0.45 A/cm$^{2}$. The beam trajectories are also simulated over beam test tube of length about 2 m with a magnetic field of 213 Gauss. Thermal analysis of the collector is performed using the ANSIS-CFX code and hence the cooling structure is determined. Mechanical design is almost carried out and it is in manufacturing stage.
ATOMIC AND MOLECULAR PHYSICS
Shao-Yang Dai, Kun-Qian Li, Yue-Yang Zhai, Wei Xia, Qing Wang, Wei Xiong, Xiang-Hui Qi, Xu-Zong Chen
Chin. Phys. Lett. 2017, 34 (01): 013201 doi: 10.1088/0256-307X/34/1/013201
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The optical frequency comb has been widely used in precision measurement. In this study, a multi-peak fitting approach is first proposed to fit the two-photon transition spectrum which overlaps with the neighboring transition in $^{87}$Rb. The multi-peak fitting approach is used to eliminate the frequency shift affected by the neighboring transition. With locking the carrier envelope offset frequency at 1/4 repetition frequency, the transition frequency is measured to be 770569132739.9$\pm$5.8 kHz, which agrees well with the previous result recommended by Comité International des Poids et Mesures.
Shuang-Fei Lv, Feng-Dong Jia, Jin-Yun Liu, Xiang-Yuan Xu, Ping Xue, Zhi-Ping Zhong
Chin. Phys. Lett. 2017, 34 (01): 013401 doi: 10.1088/0256-307X/34/1/013401
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An ion–neutral hybrid trap is built to study low-energy ion–atom collisions. The ion–neutral hybrid trap is combined with two spatially concentric traps: a linear Paul trap for the ionic species and a magneto-optical trap (MOT) for the neutral species. The total ion–atom collision rate coefficient $k_{\rm ia}$ between$^{87}$Rb atoms and optically dark $^{87}$Rb$^+$ ions is measured by monitoring the reduction of the steady-state MOT atoms by sequentially introducing various mechanisms, namely photoionization and ion–atom collisions. In contrast to other experiments, a concise experimental procedure is devised to obtain the loss rates of the MOT atoms due to photoionization and ion–atom collisions in one experimental cycle, and then the collision rate $k_{\rm ia}$ of cold $^{87}$Rb atoms with $^{87}$Rb$^+$ ions is deduced to $0.94(\pm0.24)\times10^{-13}$ m$^3$/s with $T_{\rm i}=3770(\pm100)$ K measured by the time of flight of the ion signal. The measurements show good agreement with the collision rate derived from the Langevin model.
Kun Zhou, Jin-Ming Cui, Yun-Feng Huang, Zhao Wang, Zhong-Hua Qian, Qi-Ming Wu, Jian Wang, Ran He, Wei-Min Lv, Chang-Kang Hu, Yong-Jian Han, Chuan-Feng Li, Guang-Can Guo
Chin. Phys. Lett. 2017, 34 (01): 013701 doi: 10.1088/0256-307X/34/1/013701
Show Abstract
We demonstrate a fiber Fabry–Pérot cavity in the ultraviolet range, which covers the florescence wavelength for the $^{2}$P$_{1/2}$ to $^{2}$S$_{1/2}$ transition of Yb$^{+}$ and is designed in the bad cavity limit for florescence collection. Benefiting from both the small cavity mode volume and the large atom dipole, a cavity with moderate finesse and high transmission still supports a good cooperativity, which is made and tested in experiment. Based on the measured experimental parameters, simulation performed on the cavity and ion shows a Purcell factor better than 2.5 and a single-mode fiber collection efficiency over 10%. This technology can support ultra-bright single photon sources based on trapped ions and can provide the possibility to link remote atoms as a quantum network.
FUNDAMENTAL AREAS OF PHENOMENOLOGY(INCLUDING APPLICATIONS)
Ya Bai, Li-Wei Song, Peng Liu, Ru-Xin Li
Chin. Phys. Lett. 2017, 34 (01): 014201 doi: 10.1088/0256-307X/34/1/014201
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We study the energy scaling of terahertz (THz) emission through difference frequency generation of near-infrared pulses, and demonstrate that Gigawatt few-cycle THz transients at the central frequency of 30 THz are produced from GaSe crystal pumped by two pulses at 1.65 and 1.95 micrometers, with the high quantum yield of 28%. Our analysis indicates that the high yield of DFG originates from the largely reduced group velocity mismatch as the long-wavelength pumping pulses are employed.
N. A. A. Kadir, E. I. Ismail, A. A. Latiff, H. Ahmad, H. Arof, S. W. Harun
Chin. Phys. Lett. 2017, 34 (01): 014202 doi: 10.1088/0256-307X/34/1/014202
Show Abstract
We demonstrate an ultrafast fiber laser based on transition metal dichalcogenide materials which are tungsten disulfide (WS$_{2}$) and molybdenum disulfide (MoS$_{2}$) as saturable absorber (SA). These materials are fabricated via a simple drop-casting method. By employing WS$_{2}$, we obtain a stable harmonic mode-locking at the threshold pump power of 184 mW, and the generated soliton pulse has 3.48 MHz of repetition rate. At the maximum pump power of 250 mW, we also obtain a small value of pulse duration, 2.43 ps with signal-to-noise ratio (SNR) of 57 dB. For MoS$_{2}$ SA, the pulse is generated at 105 mW pump power with repetition rate of 1.16 MHz. However, the pulse duration cannot be detected by the autocorrelator device as the pulse duration recorded is 468 ns, with the SNR value of 35 dB.
En-Ming Xu, Zu-Xing Zhang, Pei-Li Li
Chin. Phys. Lett. 2017, 34 (01): 014203 doi: 10.1088/0256-307X/34/1/014203
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A tunable single-passband microwave photonic filter is proposed and demonstrated, based on a laser diode (LD) array with multiple optical carriers and a Fabry–Perot (F-P) laser diode. Multiple optical carriers in conjunction with the F-P LD will realize a filter with multiple passbands. By adjusting the wavelengths of the multiple optical carriers, multiple passbands are merged into a single passband with a broadened bandwidth. By varying the number of the optical carrier, the bandwidth can be adjusted. The central frequency can be tuned by adjusting the wavelength of the multiple optical carriers simultaneously. A single-passband filter implemented by two optical carriers is experimentally demonstrated.
Zhe Sun, Guang-Hua Cheng, Huan Liu, Xi Wang, Yong-Gang Wang
Chin. Phys. Lett. 2017, 34 (01): 014204 doi: 10.1088/0256-307X/34/1/014204
Show Abstract
A black phosphorus (BP) saturable absorber (SA) solution with different concentrations (1.0 and 0.5 mg/ml) is fabricated with the liquid-phase exfoliation method. By using the BP-SA, a compact diode-pumped passively Q-switched Nd:YVO$_{4}$ laser is demonstrated. One reflecting Bragg gratings is used as the output coupler for mode selection. By inserting those BP-SA solutions in the laser cavity, the maximum single longitude mode, Q-switched output powers of 126 mW at 692.5 kHz and 149 mW at 630.3 kHz are achieved at the pump power of 8.0 W, corresponding to the pulse durations of 144 ns and 196 ns, respectively. Moreover, longitudinal-mode characteristics of Q-switched output laser in different optical cavity lengths based on two-kind BP-SA solution concentrations are investigated. Our results show that BP-SA could also be developed as an effective SA for the Q-switched, single longitudinal mode pulse laser.
Lan-Qing Zhou, Yan-Bang Zhang, Teng-Fei Yan, Ying Li, Guo-Zhi Jia, Huai-Zhe Xu, Xin-Hui Zhang
Chin. Phys. Lett. 2017, 34 (01): 014205 doi: 10.1088/0256-307X/34/1/014205
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The third-order nonlinear optical properties of water-soluble Cu$_{2-x}$Se nanocrystals are studied in the near infrared range of 700–980 nm using a femtosecond pulsed laser by the $Z$-scan technique. It is observed that the nonlinear optical response of Cu$_{2-x}$Se nanocrystals is sensitively dependent on the excitation wavelength and exhibits the enhanced nonlinearity compared with other selenides such as ZnSe and CdSe. The W-shaped $Z$-scan trace, a mixture of the reversed saturated absorption and saturated absorption, is observed near the plasmon resonance band of Cu$_{2-x}$Se nanocrystals, which is attributed to the state-filling of free carriers generated by copper vacancies (self-doping effect) of Cu$_{2-x}$Se nanocrystals as well as the hot carrier thermal effect upon intense femtosecond laser excitation. The large nonlinear optical response and tunable plasmonic band make Cu$_{2-x}$Se nanocrystals promising materials for applications in ultra-fast all-optical switching devices as well as nonlinear nanosensors.
Hong-Dan Zhang, Jing Guo, Yan Shi, Hui Du, Hai-Feng Liu, Xu-Ri Huang, Xue-Shen Liu, Jun Jing
Chin. Phys. Lett. 2017, 34 (01): 014206 doi: 10.1088/0256-307X/34/1/014206
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The high harmonic generation (HHG) from the CS$_2$ molecule in intense laser fields is investigated using the extended Lewenstein method. The initial state is the highest-occupied molecular orbital of the CS$_2$ molecule, which can be well described by Gaussian wave packet using GAMESS-UK package. Compared with the case of the elliptical laser, the HHG can be extended in two-color circularly polarized laser field. The time-frequency analysis and classical electron trajectory as well as the ionization yield curve are also presented to further explain the underlying mechanism. After adding a static electric field on the $z$-direction, the single quantum path control is realized and the supercontinuum spectra are obtained. Moreover, an isolated 110 as pulse can be obtained by superposing the harmonics from 130th to 180th order.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
Zhen-Wei Xia, Chun-Hua Li, Dan-Dan Zou, Wei-Hong Yang
Chin. Phys. Lett. 2017, 34 (01): 015201 doi: 10.1088/0256-307X/34/1/015201
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Using the Fourier helical decomposition, we obtain the absolute statistical equilibrium spectra of left- and right-handed helical modes in the incompressible ideal Hall magnetohydrodynamics (MHD). It is shown that the left-handed helical modes play a major role on the spectral transfer properties of turbulence when the generalized helicity and magnetic helicity are both positive. In contrast, the right-handed helical modes will play a major role when both are negative. Furthermore, we also find that if the generalized helicity and magnetic helicity have opposite signs, the tendency of equilibrium spectra to condense at the large or small wave numbers will be presented in different helical sectors. This indicates that the generalized helicity dominates the forward cascade and the magnetic helicity dominates the inverse cascade properties of the Hall MHD turbulence.
Hong-Jie Liu, Yu-Qiu Gu, Gang Li, Feng Lu, Bo Cui, Zeng-Hai Dai, Yan-Yun Ma, Wei-Min Zhou, Lei-Feng Cao, Bao-Han Zhang
Chin. Phys. Lett. 2017, 34 (01): 015202 doi: 10.1088/0256-307X/34/1/015202
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Thomson scattering imaging (TSI) is proposed and experimentally demonstrated to observe the fine structure of the laser wake field. By Thomson scattering a co-propagating laser pulse, we obtain clear images indicating that the wake field is like an acaleph swimming behind the pump laser. The wavelength of the wake field observed at different electron densities agrees well with the theory. Since no mathematics transformation is involved, TSI could be potentially used as an online monitor for future 'tabletop' plasma accelerators.
Bin-Bin Lin, Nong Xiang, Jing Ou, Xiao-Yun Zhao
Chin. Phys. Lett. 2017, 34 (01): 015203 doi: 10.1088/0256-307X/34/1/015203
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The ion saturation current is very important in probe theory, which can be used to measure the electron temperature and the floating potential. In this work, the effects of energetic ions on the ion saturation current are studied via particle-in-cell simulations. It is found that the energetic ions and background ions can be treated separately as different species, and they satisfy their individual Bohm criterion at the sheath edge. It is shown that the energetic ions can significantly affect the ion saturation current if their concentration is greater than $\sqrt {T_{\rm e}/(\gamma_{\rm i2}T_{\rm i2})}$, where $T_{\rm e}$ is the electron temperature, and $\gamma _{\rm i2}$ and $T_{\rm i2}$ represent the polytropic coefficient and temperature of energetic ions, respectively. As a result, the floating potential and the $I$–$V$ characteristic profile are strongly influenced by the energetic ions. When the energetic ion current dominates the ion saturation current, an analysis of the ion saturation current will yield the energetic ion temperature rather than the electron temperature.
CONDENSED MATTER: STRUCTURE, MECHANICAL AND THERMAL PROPERTIES
B. Merabet, H. Alamri, M. Djermouni, A. Zaoui, S. Kacimi, A. Boukortt, M. Bejar
Chin. Phys. Lett. 2017, 34 (01): 016101 doi: 10.1088/0256-307X/34/1/016101
Show Abstract
The ab initio generalized gradient approximation (GGA)+$U$ study of multiferroic (La$_{0.5}$Bi$_{0.5}$)$_{2}$FeCrO$_{6}$ in pnma structure and ferri-magnetic order, including Hubbard corrections ($U=4.1$ eV) for transition metal/rare earth $d$-electrons with 20 atoms cell, shows optimum local magnetic moments of (Cr$^{3+}$, Fe$^{3+})$ equal to ($-$2.56, 4.14) $\mu$B and an ideal spin-down band gap of 1.54 eV. Tuned-band gap La-substituted double oxide perovskites BFCO should exhibit enhanced visible-light absorption and carrier mobility, thus could be convenient light absorbers and then efficient alternatives to wide-gap chalcopyrite absorber-based solar cells failing to achieve highest power conversion efficiencies, and even compete with their metal-organic halide perovskites counterparts.
Shu-Xi Ren, Jun-Wei Li, Su-Hua Zhang, D. E. Logothetis, Hai-Long An, Yong Zhan
Chin. Phys. Lett. 2017, 34 (01): 016102 doi: 10.1088/0256-307X/34/1/016102
Show Abstract
As a member of the inwardly rectifying K$^{+}$ channel (Kir) family, Kir2.1 allows K$^{+}$ to influx the cell more easily than to efflux, a biophysical phenomenon named inward rectification. The function of Kir2.1 is to set the resting membrane potential and modulate membrane excitability. It has been reported that residue E224 plays a key role in regulating inward rectification. The mutant Kir2.1 (E224G) displays weaker inward rectification than the WT channel. Gating of Kir2.1 depends on the membrane lipid, PIP$_{2}$, such that the channel gates are closed in the absence of PIP$_{2}$. Here we perform electrophysiological and computational approaches, and demonstrate that E224 also plays an important role in the PIP$_{2}$-dependent activation of Kir2.1 in addition to its influence on inward rectification. The E224G mutant takes 4.5 times longer to be activated by PIP$_{2}$. To probe the mechanism by which E224G slows the channel opening kinetics, we perform targeted molecular dynamics simulations and find that the mutant weakens the interactions between CD-loop and C-linker (H221-R189) and the adjacent G-loops (R312-E303) which are thought to stabilize the open state of the channel in our previous work. These data provide new insights into the regulation of Kir2.1 channel activity and suggest that a common mechanism may be involved in the distinct biophysical processes, such as inward rectification and PIP$_{2}$-induced gating.
Xiao-Nian Liu, Li-Hua Dai, Bing-Xu Ning, Shi-Chang Zou
Chin. Phys. Lett. 2017, 34 (01): 016103 doi: 10.1088/0256-307X/34/1/016103
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The body current lowering effect of 130 nm partially depleted silicon-on-insulator (PDSOI) input/output (I/O) n-type metal-oxide-semiconductor field-effect transistors (NMOSFETs) induced by total-ionizing dose is observed and analyzed. The decay tendency of current ratio of body current and drain current $I_{\rm b}/I_{\rm d}$ is also investigated. Theoretical analysis and TCAD simulation results indicate that the physical mechanism of body current lowering effect is the reduction of maximum lateral electric field of the pinch-off region induced by the trapped charges in the buried oxide layer (BOX). The positive charges in the BOX layer can counteract the maximum lateral electric field to some extent.
Meng-Lin Qiu, Ying-Jie Chu, Guang-Fu Wang, Mi Xu, Li Zheng
Chin. Phys. Lett. 2017, 34 (01): 016104 doi: 10.1088/0256-307X/34/1/016104
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Negative ion-beam-induced luminescence (IBIL) measurements of a pure LiF crystal using 20 keV H$^{-}$ are performed to monitor the formation and annihilation of luminescence centers during ion irradiation. Several emission bands are observed in the IBIL spectra and the evolvement mechanisms of the corresponding centers are identified. The difference between the IBIL measurements using positive ions and negative ions is that the intensities of luminescence centers can reach the maxima at lower fluences under negative-ion irradiation due to free charge accumulation.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
De-Gang Zhao, De-Sheng Jiang, Ling-Cong Le, Jing Yang, Ping Chen, Zong-Shun Liu, Jian-Jun Zhu, Li-Qun Zhang
Chin. Phys. Lett. 2017, 34 (01): 017101 doi: 10.1088/0256-307X/34/1/017101
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The influences of InGaN/GaN multiple quantum wells (MQWs) and AlGaN electron-blocking layers (EBL) on the performance of GaN-based violet laser diodes are investigated. Compared with the InGaN/GaN MQWs grown at two different temperatures, the same-temperature growth of InGaN well and GaN barrier layers has a positive effect on the threshold current and slope efficiency of laser diodes, indicating that the quality of MQWs is improved. In addition, the performance of GaN laser diodes could be further improved by increasing Al content in the AlGaN EBL due to the fact that the electron leakage current could be reduced by properly increasing the barrier height of AlGaN EBL. The violet laser diode with a peak output power of 20 W is obtained.
Yan Lu, Wen-Gang Lu, Li Wang
Chin. Phys. Lett. 2017, 34 (01): 017102 doi: 10.1088/0256-307X/34/1/017102
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We explore the excitonic effects in chiral graphene nanoribbons (cGNRs), whose edges are composed alternatively of armchair-edged and zigzag-edged segments. For cGNRs dominated by armchair edges, their energy gaps and exciton energies decrease with increasing chirality angles, and they, as functions of widths, oscillate with the period of three, while the exciton binding energies do not have such distinct oscillation. On the other hand, for cGNRs dominated by zigzag edges, all the energy gaps, exciton energies, and exciton binding energies show oscillation properties with their widths, due to the interactions between the edge states localized at the opposite zigzag edges. In addition, the triplet excitons are energy degenerate when the electrons are spin-unpolarized, while the degeneracy split when the electrons are spin-polarized. All the studied cGNRs show strong excitonic effects with the exciton binding energies of hundreds of meV.
Lai Wang, Xiao Meng, Jung-Hoon Song, Tae-Soo Kim, Seung-Young Lim, Zhi-Biao Hao, Yi Luo, Chang-Zheng Sun, Yan-Jun Han, Bing Xiong, Jian Wang, Hong-Tao Li
Chin. Phys. Lett. 2017, 34 (01): 017301 doi: 10.1088/0256-307X/34/1/017301
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We propose and demonstrate to derive the Auger recombination coefficient by fitting efficiency–current and carrier lifetime–current curves simultaneously, which can minimize the uncertainty of fitting results. The obtained Auger recombination coefficient is $1.0\times10^{-31}$ cm$^{6}$s$^{-1}$ in the present sample, which contributes slightly to efficiency droop effect.
Yu-Feng An, Zhen-Hong Dai, Yin-Chang Zhao, Chao Lian, Zhao-Qing Liu
Chin. Phys. Lett. 2017, 34 (01): 017302 doi: 10.1088/0256-307X/34/1/017302
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Previous calculations show that the two-dimensional (2D) silicon carbide (SiC) honeycomb structure is a structurally stable monolayer. Following this, we investigate the electronic properties of the hydrogen and fluorine functionalized SiC monolayer by first-principles calculations. Our results show that the functionalized monolayer becomes metallic after semi-hydrogenation or semi-fluorination, while the semiconducting properties are obtained by the full functionalization. Compared with the bare SiC monolayer, the band gap of the fully hydrogenated system is increased, in comparison with the decrease of the gap in the fully fluorinated case. As a result, the band gap can be tuned from 0.73 to 4.14 eV by the functionalization. In addition to the metal–semiconductor transition, hydrogenation and functionalization also realize a direct-indirect semiconducting transition in the 2D SiC monolayer. These results provide theoretical guidance for design of photoelectric devices based on the SiC monolayer.
Li-Guo Qin, Qin Wang
Chin. Phys. Lett. 2017, 34 (01): 017303 doi: 10.1088/0256-307X/34/1/017303
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We propose a new scheme on modulating the lasing performance of a quantum dot-cavity system. Compared to the conventional above-band pump, in our new scheme an additional resonant driving field is applied on the quantum dot-cavity system. By employing the master equation theory and the Jaynes–Cummings model, we are able to study the interesting phenomenon of the coupling system. To compare the different behaviors between using our new scheme and the conventional method, we carry out investigation for both the "good system" and "more realistic system", characterizing several important parameters, such as the cavity population, exciton population and the second-order correlation function at zero time delay. Through numerical simulations, we demonstrate that for both the good system and more realistic system, their lasing regimes can be displaced into other regimes in the presence of a resonant driving field.
S. İflazoğlu, V. E. Kafadar, B. Yazici, A. N. Yazici
Chin. Phys. Lett. 2017, 34 (01): 017801 doi: 10.1088/0256-307X/34/1/017801
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The thermoluminescent (TL) properties such as glow curve structure, relative thermoluminescence sensitivity, dose response linearity of lithium fluoride thermoluminescent dosimeters $^{6}$LiF:Ti,Mg (TLD-600) and $^{7}$LiF:Ti,Mg (TLD-700) are investigated after irradiation $^{252}$Cf neutron+gamma and $^{90}$Sr-$^{90}$Y beta sources at room temperature and then the obtained results are compared. The kinetic parameters, namely the order of kinetics $b$, activation energy $E_{\rm a}$ and the frequency factor $s$, are calculated using the computerized glow curve deconvolution (CGCD) program. The effect of heating rate on the glow curves of dosimeters is also investigated. The maximum TL peak intensities and the total area under the glow curves decrease with the increasing heating rate. There is no agreement with the kinetic parameters calculated by the CGCD program for both radiation sources.
CROSS-DISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
Hai-Long Yu, Hao-Yue Wu, Hai-Jun Zhu, Guo-Feng Song, Yun Xu
Chin. Phys. Lett. 2017, 34 (01): 018101 doi: 10.1088/0256-307X/34/1/018101
Show Abstract
We investigate the molecular beam epitaxy growth of GaSb films on GaAs substrates using compositionally graded GaAs$_{x}$Sb$_{1-x}$ buffer layers. Optimization of GaAs$_{x}$Sb$_{1-x}$ growth parameter is aimed at obtaining high GaSb crystal quality and smooth GaSb surface. The optimized growth temperature and thickness of GaAs$_{x}$Sb$_{1-x}$ layers are found to be 420$^\circ\!$C and 0.5 µm, respectively. The smallest full width at half maximum value and the root mean square surface roughness of 0.67 nm over $2\times2$ µm$^{2}$ area are achieved as a 250 nm GaSb film is grown under optimized conditions.
Hao Li, Jian-She Liu, Han Cai, Ying-Shan Zhang, Qi-Chun Liu, Gang Li, Wei Chen
Chin. Phys. Lett. 2017, 34 (01): 018401 doi: 10.1088/0256-307X/34/1/018401
It is well known that III-nitride semiconductors can generate the magnitude of MV/cm polarization electric field which is comparable with their ionization electric fields. To take full advantage of the polarization electric field, we design an N-face AlGaN solar-blind avalanche photodiode (APD) with an Al$_{0.45}$Ga$_{0.55}$N/Al$_{0.3}$Ga$_{0.7}$N heterostructure as separate absorption and multiplication (SAM) regions. The simulation results show that the N-face APDs are more beneficial to improving the avalanche gain and reducing the avalanche breakdown voltage compared with the Ga-face APDs due to the effect of the polarization electric field. Furthermore, the Al$_{0.45}$Ga$_{0.55}$N/Al$_{0.3}$Ga$_{0.7}$N heterostructure SAM regions used in APDs instead of homogeneous Al$_{0.45}$Ga$_{0.55}$N SAM structure can increase significantly avalanche gain because of the increased hole ionization coefficient by using the relatively low Al-content AlGaN in the multiplication region. Meanwhile, a quarter-wave AlGaN/AlN distributed Bragg reflector structure at the bottom of the device is designed to remain a solar-blind characteristic of the heterostructure SAM-APDs.