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Chin. Phys. B  
  Chin. Phys. B--2018, Vol.27, No.9
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SPECIAL TOPIC—Recent advances in thermoelectric materials and devices
ELECTROMAGNETISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS

Two-frequency amplification in a semiconductor tapered amplifier for cold atom experiments

Zhi-Xin Meng, Yu-Hang Li, Yan-Ying Feng
Chin. Phys. B 2018, 27 (9): 094201;  doi: 10.1088/1674-1056/27/9/094201
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Simultaneous two-frequency amplification is highly desirable in cold atom experiments. The nonlinear response would appear in the two-frequency amplification with a semiconductor tapered amplifier (TA) and has a direct influence on the experimental result. We investigated in detail the effects of frequency difference, total power, and power ratio of two seeding lasers on the output components based on a simplified theoretical model. The simulation results showed that the multiple sideband generation in the amplifier due to self-phase and amplitude modulation could be suppressed and the TA tended to linearly amplify the power ratio between two-frequency components, when the two seeding lasers had a large frequency difference. This was verified experimentally in the output power ratio measurement via a calibrated Fabry-Perot interferometer method with a good linearity and an uncertainty of 1%. We also discussed the consequences of power ratio responses in the amplification in light of cold atom experiments, especially in the ac Stark shift related phase error of Raman-type atom interferometers (AIs). It was shown that the fluctuation of intensity ratio of Raman beams may induce significant systematic errors for an AI gyroscope.

Lensless two-color ghost imaging from the perspective of coherent-mode representation

Bin Luo, Guohua Wu, Longfei Yin
Chin. Phys. B 2018, 27 (9): 094202;  doi: 10.1088/1674-1056/27/9/094202
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The coherent-mode representation theory is firstly used to analyze lensless two-color ghost imaging. A quite complicated expression about the point-spread function (PSF) needs to be given to analyze which wavelength has a stronger affect on imaging quality when the usual integral representation theory is used to ghost imaging. Unlike this theory, the coherent-mode representation theory shows that imaging quality depends crucially on the distribution of the decomposition coefficients of the object imaged in a two-color ghost imaging. The analytical expression of the decomposition coefficients of the object is unconcerned with the wavelength of the light used in the reference arm, but has relevance with the wavelength in the object arm. In other words, imaging quality of two-color ghost imaging depends primarily on the wavelength of the light illuminating the object. Our simulation results also demonstrate this conclusion.

Nonuniform sampled angular spectrum method by using trigonometric interpolation

Qiu-Hu Cheng, Shi-Yu Wang, Meng-Yao Wu, Zhen Guo, De-Fang Cai, Bing-Bin Li
Chin. Phys. B 2018, 27 (9): 094203;  doi: 10.1088/1674-1056/27/9/094203
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The angular spectrum method (ASM) is a popular numerical approach for scalar diffraction calculations. However, traditional ASM has an inherent problem in that nonuniform sampling is precluded. In an attempt to address this limitation, an improved trigonometric interpolation ASM (TIASM) is proposed, in which the fast Fourier transform (FFT) is replaced by a trigonometric interpolation. The results show that TIASM is more suitable to situations in which the source field has a simple and strong frequency contrast, irrespective of whether the original phase distribution is a plane wave or a Fresnel zone plate phase distribution.

Effect of residual Doppler averaging on the probe absorption in cascade type system: A comparative study

Suman Mondal, Arindam Ghosh, Khairul Islam, Dipankar Bhattacharyya, Amitava Bandyopadhyay
Chin. Phys. B 2018, 27 (9): 094204;  doi: 10.1088/1674-1056/27/9/094204
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Effect of residual Doppler averaging on the probe absorption in an alkali vapor medium in the presence of a coherent pump beam is studied analytically for the Ξ type system. A coherent probe field is assumed to connect the ground level with the intermediate level whereas a coherent control beam is supposed to act between the intermediate energy level and the uppermost level. Optical Bloch equations (OBE) for a three-level Ξ type system and a four-level Ξ type system are derived by using density matrix formalism. These equations are solved by an analytic method to determine the probe response, which not only depends on the wavelength difference between the control (pump) field and the probe field but shows substantially different features depending on whether the wavelength of the control field is greater than that of the probe field or the reverse. The effect of temperature on probe response is also shown. Enhancement in probe absorption and additional features are noticed under a strong probe limit at room temperature. The four-level Ξ type system has two ground levels and this leads to substantial modification in the simulated probe absorption as compared to the three-level system.

Laser frequency offset-locking using electromagnetically induced transparency spectroscopy of 85Rb in magnetic field

Han-Mu Wang, Hong Cheng, Shan-Shan Zhang, Pei-Pei Xin, Zi-Shan Xu, Hong-Ping Liu
Chin. Phys. B 2018, 27 (9): 094205;  doi: 10.1088/1674-1056/27/9/094205
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We have experimentally offset-locked the frequencies of two lasers using electromagnetically induced transparency (EIT) spectroscopy of 85Rb vapor with a buffer gas in a magnetic field at room temperature. The magnetic field is generated by a permanent magnet mounted on a translation stage and its field magnitude can be varied by adjusting the distance between the magnet and Rb cell, which maps the laser locking frequency to the space position of the magnet. This frequency-space mapping technique provides an unambiguous daily laser frequency detuning operation with high accuracy. A repeatability of less than 0.5 MHz is achieved with the locking frequency detuned up to 184 MHz when the magnetic field varies from 0 up to 80 G.

Fractional squeezing-Hankel transform based on the induced entangled state representations

Cui-Hong Lv, Su-Qing Zhang, Wen Xu
Chin. Phys. B 2018, 27 (9): 094206;  doi: 10.1088/1674-1056/27/9/094206
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Based on the fact that the quantum mechanical version of Hankel transform kernel (the Bessel function) is just the transform between |q,r> angle and (s,r'|, two induced entangled state representations are given, and working with them we derive fractional squeezing-Hankel transform (FrSHT) caused by the operator e-iα(a1a2+a1a2)e-iπa2a2, which is an entangled fractional squeezing transform operator. The additive rule of the FrSHT can be explicitly proved.

High-power and high optical conversion efficiency diode-end-pumped laser with multi-segmented Nd: YAG/Nd: YVO4

Meng-Yao Wu, Peng-Fei Qu, Shi-Yu Wang, Zhen Guo, De-Fang Cai, Bing-Bin Li
Chin. Phys. B 2018, 27 (9): 094207;  doi: 10.1088/1674-1056/27/9/094207
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A novel flat-flat resonator consisting of two crystals (Nd:YAG+Nd:YVO4) is established for power scaling in a diode-end-pumped solid-state laser. We systematically compare laser characteristics between multi-segmented (Nd:YAG+Nd:YVO4) and conventional composite (Nd:YAG+Nd:YAG) crystals to demonstrate the feasibility of spectral line matching for output power scale-up in end-pumped lasers. A maximum continuous-wave output power of 79.2 W is reported at 1064 nm, with Mx2=4.82, My2=5.48, and a pumping power of 136 W in the multi-segmented crystals (Nd:YAG+Nd:YVO4). Compared to conventional composite crystals (Nd:YAG+Nd:YAG), the optical-optical conversion efficiency of multi-segmented crystals (Nd:YAG+Nd:YVO4) from 808 nm to 1064 nm is enhanced from 30% to 58.8%, while the laser output sensitivity as affected by the diode-laser temperature is reduced from 55% to 9%.

Thermal analysis of GaN-based laser diode mini-array

Jun-Jie Hu, Shu-Ming Zhang, De-Yao Li, Feng Zhang, Mei-Xin Feng, Peng-Yan Wen, Jian-Pin Liu, Li-Qun Zhang, Hui Yang
Chin. Phys. B 2018, 27 (9): 094208;  doi: 10.1088/1674-1056/27/9/094208
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Thermal characteristics of multiple laser stripes integrated into one chip is investigated theoretically in this paper. The temperature pattern of the laser diode mini-array packaged in a TO-can is analyzed and optimized to achieve a uniform temperature distribution among the laser stripes and along the cavity direction. The temperature among the laser stripes varies by more than 5 K if the stripes are equally arranged, and can be reduced to less than 0.4 K if proper arrangement is designed. For conventional submount structure, the temperature variation along the cavity direction is as high as 7 K, while for an optimized trapezoid submount structure, the temperature varies only within 0.5 K.

High-power linearly-polarized tunable Raman fiber laser

Jiaxin Song, Hanshuo Wu, Jiangming Xu, Hanwei Zhang, Jun Ye, Jian Wu, Pu Zhou
Chin. Phys. B 2018, 27 (9): 094209;  doi: 10.1088/1674-1056/27/9/094209
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In this study, we demonstrate an all-fiber high-power linearly-polarized tunable Raman fiber laser system. An in-house high-power tunable fiber laser was employed as the pump source. A fiber loop mirror (FLM) serving as a high reflectivity mirror and a flat-cut endface serving as an output coupler were adopted to provide broadband feedback. A piece of 59-m commercial passive fiber was used as the Raman gain medium. The Raman laser had a 27.6 nm tuning range from 1112 nm to 1139.6 nm and a maximum output power of 125.3 W, which corresponds to a conversion efficiency of 79.4%. The polarization extinction ratio (PER) at all operational wavelengths was measured to be over 21 dB. To the best of our knowledge, this is the first report on a hundred-watt level linearly-polarized tunable Raman fiber laser.

Detection performance improvement of photon counting chirped amplitude modulation lidar with response probability correction

Yi-Fei Sun, Zi-Jing Zhang, Li-Yuan Zhao, Wei-Min Sun, Yuan Zhao
Chin. Phys. B 2018, 27 (9): 094213;  doi: 10.1088/1674-1056/27/9/094213
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Geiger mode avalanche photodiode detector (Gm-APD) possesses the ultra-high sensitivity. Photon counting chirped amplitude modulation (PCCAM) light detection and ranging (lidar) uses the counting results of the returned signal detected by Gm-APD to mix with the reference signal, which makes PCCAM lidar capable of realizing the ultra-high sensitivity, and this is very important for detecting the remote and weak signal. However, Gm-APD is a nonlinear device, different from traditional linear detectors. Due to the nonlinear response of Gm-APD, the counting results of the returned signal detected by Gm-APD are different from those of both the original modulation signal and the reference signal. This will affect the mixing effect and thus degrade the detection performance of PCCAM lidar. In this paper, we propose a response probability correction method. First, the response probability correction model is established on the basis of Gm-APD Poisson probability response model. Then, the response probability correction model is used to adjust the original modulation signal that is used to drive laser, in order to make the counting results of the returned signal detected by Gm-APD better mix with the local reference signal in the same form. Through this method, the detection performance of PCCAM lidar is enhanced efficiently.

Compact and high-efficient wavelength demultiplexing coupler based on high-index dielectric nanoantennas

Jingfeng Tan, Hua Pang, Fengkai Meng, Jin Jiang
Chin. Phys. B 2018, 27 (9): 094217;  doi: 10.1088/1674-1056/27/9/094217
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Wavelength demultiplexing waveguide couplers have important applications in integrated nanophotonic devices. Two of the most important indicators of the quality of a wavelength demultiplexing coupler are coupling efficiency and splitting ratio. In this study, we utilize two asymmetric high-index dielectric nanoantennas directly positioned on top of a silicon-on insulator waveguide to realize a compact wavelength demultiplexing coupler in a communication band, which is based on the interference of the waveguide modes coupled by the two nanoantennas. We add a Au substrate for further increasing the coupling efficiency. This has constructive and destructive influences on the antenna's in-coupling efficiency owing to the Fabry-Perot (FP) resonance in the SiO2 layer. Therefore, we can realize a wavelength demultiplexing coupler with compact size and high coupling efficiency. This coupler has widespread applications in the areas of wavelength filters, on-chip signal processing, and integrated nanophotonic circuits.

Anti-detection technology of cat eye target based on decentered field lens

Da-Lin Song, Jun Chang, Yi-Fei Zhao, Ze-Xia Zhang
Chin. Phys. B 2018, 27 (9): 094220;  doi: 10.1088/1674-1056/27/9/094220
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Optoelectronic imaging equipment is easy to expose to active laser detection devices because of “cat eye” effect. In this paper, we propose a new structure of optical system to reduce the retroreflector effect of a cat eye target. Decentered field lens structure is adopted in the design without sacrificing imaging quality and clear aperture. An imaging system with ±30° field of view is taken for example. The detailed design and simulation results are presented. The results indicate that this kind of optical system can reduce the retroreflection signal substantially and maintain acceptable imaging performance.

Pressure dependent modulation instability in photonic crystal fiber filled with argon gas

He-Lin Wang, Ai-Jun Yang, XiaoLong Wang, Bin Wu, Yi Ruan
Chin. Phys. B 2018, 27 (9): 094221;  doi: 10.1088/1674-1056/27/9/094221
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By using the designed photonic crystal fiber filled with argon gas, the effect of gas pressure on modulation instability (MI) gain is analyzed in detail. The MI gain bandwidth increases gradually as the argon gas pressure rises from 1P0 to 400P0 (P0 is one standard atmosphere), while its gain amplitude slightly decreases. Moreover, the increase of the incident light power also results in the increase of MI gain bandwidth in the Stokes or anti-Stokes region when the incident power increases from 1 W to 200 W. Making use of the optimal parameters including the higher argon gas pressure (400P0) and the incident light power (200 W), we finally obtain a 100 nm broadband MI gain. These results indicate that controlling the MI gain characteristic by changing the argon gas pressure in PCF is an effective way when the incident light source is not easy to satisfy the requirement of practical application. This method of controlling MI gain can be used in optical communication and laser shaping.

Influence of temperature on the properties of one-dimensional piezoelectric phononic crystals

Ahmed Nagaty, Ahmed Mehaney, Arafa H Aly
Chin. Phys. B 2018, 27 (9): 094301;  doi: 10.1088/1674-1056/27/9/094301
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The current study investigates the influence of temperature on a one-dimensional piezoelectric phononic crystal using tunable resonant frequencies. Analytical and numerical examples are introduced to emphasize the influence of temperature on the piezoelectric phononic crystals. It was observed that the transmission spectrum of a one-dimensional phononic crystal containing a piezoelectric material (0.7 PMN-0.3PT) can be changed drastically by an increase in temperature. The resonant peak can be shifted toward high or low frequencies by an increase or decrease in temperature, respectively. Therefore, we deduced that temperature can exhibit a large tuning in the phononic band gaps and in the local resonant frequencies depending on the presence of a piezoelectric material. Such result can enhance the harvesting energy from piezoelectric materials, especially those that are confined in a phononic crystal.

Performance improvement of magneto-acousto-electrical tomography for biological tissues with sinusoid-Barker coded excitation

Zheng-Feng Yu, Yan Zhou, Yu-Zhi Li, Qing-Yu Ma, Ge-Pu Guo, Juan Tu, Dong Zhang
Chin. Phys. B 2018, 27 (9): 094302;  doi: 10.1088/1674-1056/27/9/094302
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By combining magnetics, acoustics and electrics, the magneto-acoustic-electrical tomography (MAET) proves to possess the capability of differentiating electrical impedance variation and thus improving the spatial resolution. However, the signal-to-noise ratio (SNR) of the collected MAET signal is still unsatisfactory for biological tissues with low-level electrical conductivity. In this study, the formula of MAET measurement with sinusoid-Barker coded excitation is derived and simplified for a planar piston transducer. Numerical simulations are conducted for a four-layered gel phantom with the 13-bit sinusoid-Barker coded excitation, and the performances of wave packet recovery with side-lobe suppression are improved by using the mismatched compression filter, which is also demonstrated by experimentally measuring a three-layered gel phantom. It is demonstrated that comparing with the single-cycle sinusoidal excitation, the amplitude of the driving signal can be reduced greatly with an SNR enhancement of 10 dB using the 13-bit sinusoid-Barker coded excitation. The amplitude and polarity of the wave packet filtered from the collected MAET signal can be used to achieve the conductivity derivative at the tissue boundary. In this study, we apply the sinusoid-Barker coded modulation method and the mismatched suppression scheme to MAET measurement to ensure the safety for biological tissues with improved SNR and spatial resolution, and suggest the potential applications in biomedical imaging.

Contribution of terahertz waves to near-field radiative heat transfer between graphene-based hyperbolic metamaterials

Qi-Mei Zhao, Tong-Biao Wang, De-Jian Zhang, Wen-Xing Liu, Tian-Bao Yu, Qing-Hua Liao, Nian-Hua Liu
Chin. Phys. B 2018, 27 (9): 094401;  doi: 10.1088/1674-1056/27/9/094401
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Hyperbolic metamaterials alternately stacked by graphene and silicon (Si) are proposed and theoretically studied to investigate the contribution of terahertz (THz) waves to near-field radiative transfer. The results show that the heat transfer coefficient can be enhanced several times in a certain THz frequency range compared with that between graphene-covered Si bulks because of the presence of a continuum of hyperbolic modes. Moreover, the radiative heat transfer can also be enhanced remarkably for the proposed structure even in the whole THz range. The hyperbolic dispersion of the graphene-based hyperbolic metamaterial can be tuned by varying the chemical potential or the thickness of Si, with the tunability of optical conductivity and the chemical potential of graphene fixed. We also demonstrate that the radiative heat transfer can be actively controlled in the THz frequency range.

Physical and chemical effects of phosphorus-containing compounds on laminar premixed flame

Yongfeng Yin, Yong Jiang, Rong Qiu, Caiyi Xiong
Chin. Phys. B 2018, 27 (9): 094701;  doi: 10.1088/1674-1056/27/9/094701
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Phosphorus-containing compounds are the promising halon alternatives for flame inhibitions.However,some literatures suggested that the phosphorus-related inhibitors may behave as the unfavorable ones that will increase the burning velocity under lean-burn conditions,and this indeed posed potential threats to the fire prevention and fighting.To seek deeper insights into the reaction process,a numerical investigation was actualized to study the phosphorus-related effects on methane-air flames.By replacing a phosphorus-related inhibitor with the corresponding decomposed molecules,the detailed promoting and inhibiting effects of combustion were separated from the general chemical effect.A comparative study was carried out to identify the interaction between the two effects under different combustion conditions.It is observed that the promoting effect becomes the dominant factor during the reaction process when the equivalence ratio is smaller than 0.60.In this lean-burn condition,the exothermic reactions were faster than the others within the reaction chains due to the reduction of radical recombination in hydrocarbon oxidation.The results are believed to be useful for the further application and improvement of flame inhibitors.

Hopf bifurcation control of a Pan-like chaotic system

Liang Zhang, JiaShi Tang, Qin Han
Chin. Phys. B 2018, 27 (9): 094702;  doi: 10.1088/1674-1056/27/9/094702
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This paper is concerned with the Hopf bifurcation control of a modified Pan-like chaotic system. Based on the Routh-Hurwtiz theory and high-dimensional Hopf bifurcation theory, the existence and stability of the Hopf bifurcation depending on selected values of the system parameters are studied. The region of the stability for the Hopf bifurcation is investigated. By the hybrid control method, a nonlinear controller is designed for changing the Hopf bifurcation point and expanding the range of the stability. Discussions show that with the change of parameters of the controller, the Hopf bifurcation emerges at an expected location with predicted properties and the range of the Hopf bifurcation stability is expanded. Finally, numerical simulation is provided to confirm the analytic results.

Cavity formation during water entry of heated spheres

Jia-Chuan Li, Ying-Jie Wei, Cong Wang, Wei-Xue Xia
Chin. Phys. B 2018, 27 (9): 094703;  doi: 10.1088/1674-1056/27/9/094703
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We experimentally study the cavity formation when heated spheres impact onto water at low and high subcooling. The observations present that the formation and appearance of the cavity are affected by the boiling modes and the heat transfer intensity. In the nucleate-boiling regime, a rough cavity can be formed at a rather low impact velocity, while at the same velocity, the cavity formed in the film-boiling regime may have a very smooth interface with a stable vapor layer around the sphere. We discuss the effects of the impact speed, water and sphere temperatures on the stability of the vapor layer. For low subcooled water, the stable vapor layer will be disturbed when increasing the impact velocity, leading to a disturbed cavity. For high subcooled water, the film boiling has a particular boiling model in which the vapor layer around the sphere cannot keep its stability. In this particular film-boiling regime, no cavities can be formed at low impact velocities and only broken cavities can be formed at high impact velocities.

Phase field simulation of single bubble behavior under an electric field

Chang-Sheng Zhu, Dan Han, Sheng Xu
Chin. Phys. B 2018, 27 (9): 094704;  doi: 10.1088/1674-1056/27/9/094704
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Based on the Cahn-Hilliard phase field model, a three-dimensional multiple-field coupling model for simulating the motion characteristics of a rising bubble in a liquid is established in a gas-liquid two-phase flow. The gas-liquid interface motion is simulated by using a phase-field method, and the effect of the electric field intensity on bubble dynamics is studied without electric field, or with vertical electric field or horizontal electric field. Through the coupling effect of electric field and flow field, the deformation of a single rising bubble and the formation of wake vortices under the action of gravity and electric field force are studied in detail. The correctness of the results is verified by mass conservation, and the influences of different electric field directions and different voltages on the movement of bubbles in liquid are considered. The results show that the ratio of the length to axis is proportional to the strength of the electric field when the air bubble is stretched into an ellipsoid along the electric field line under the action of electrostatic gravity and surface tension. In addition, the bubble rising speed is affected by the electric field, the vertical electric field accelerates the bubble rise, and the horizontal direction slows it down.

Shock oscillation in highly underexpanded jets

Xiao-Peng Li, Rui Zhou, Xiao-Ping Chen, Xue-Jun Fan, Guo-Shan Xie
Chin. Phys. B 2018, 27 (9): 094705;  doi: 10.1088/1674-1056/27/9/094705
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The oscillatory motions of shocks in highly underexpanded jets with nozzle pressure ratios of 5.60, 7.47, 9.34, and 11.21 are quantitatively studied by using large eddy simulation. Two types of shock oscillations are observed:one is the Mach disk oscillation in the streamwise direction and the other is the shock oscillation in the radial direction. It is found that the Mach disk moves quickly in the middle of the oscillatory region but slowly at the top or bottom boundaries. The oscillation cycles of Mach disk are the same for different cases, and are all dominated by an axisymmetric mode of 5.298 kHz. For the oscillation in the radial direction, the shocks oscillate more toward the jet centerline but less in the jet shear layer, and the oscillation magnitude is an increasing function of screech amplitude. The cycles of the radial shock oscillation switch randomly between the two screech frequencies for the first two cases. However, the oscillation periodicity is more complex for the jets with high nozzle pressure ratios of 9.34 and 11.21 than for the jets with the low nozzle pressure ratios of 5.6 and 7.47. In addition, the shock oscillation characteristics are also captured by coarse mesh and Smagorinsky model, but the coarse mesh tends to predict a slower and weaker shock oscillation.

CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

Theoretical derivation of the crystallographic parameters of polytypes of long-period stacking ordered structures with the period of 13 and 14 in hexagonal close-packed system

Li Ye, Dong-Shan Zhao, Yuan-Lin Zhuang, Shuang-Feng Jia, Jia-Ping Zhou, Jia-Nian Gui, Jian-Bo Wang
Chin. Phys. B 2018, 27 (9): 096102;  doi: 10.1088/1674-1056/27/9/096102
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Based on crystallographic theory, there are 63 kinds of polytypes of 13H long-period stacking order (LPSO) structure, 126 kinds of polytypes of 14H LPSO structure, 120 kinds of polytypes of 39R LPSO structure, and 223 kinds of polytypes of 42R LPSO structure in a hexagonal close-packed (HCP) system, and their stacking sequences and space groups have been derived in detail. The result provides a theoretical explanation for the various polytypes of the LPSO structure.

Effect of microstructure on 3He migration in TiT1.9 films

Haifeng Wang, Shuming Peng, Wei Ding, Huahai Shen, Weidu Wang, Xiaosong Zhou, Xinggui Long
Chin. Phys. B 2018, 27 (9): 096103;  doi: 10.1088/1674-1056/27/9/096103
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Two kinds of films were prepared to study the effect of microstructure on helium migration in Ti tritides. Both films showed different release behaviors and helium bubble distributions. In the film consisting of columnar grains, a two-layered structure was observed. Inclusions with a strip feature were found at the grain boundary, and no helium bubbles were distributed in these inclusions. However, helium preferred to migrate to the boundaries of these inclusions. Bubble linkage as a ribbon-like feature developed parallel to the film surface in the film consisting of columnar grains. More cracks were developed at the grain boundaries of the film consisting of columnar grains, although the helium content in the film consisting of columnar grains was less than that in the film consisting of equiaxed grains. A surface region with a small number of bubbles, or “depleted zone”, was observed near the surface. The cracks extending to the film surface were the pathways of the critical helium released from the film. The helium migration was strongly influenced by the grain microstructure.

Structural and electrical properties of carbon-ion-implanted ultrananocrystalline diamond films

Hui Xu, Jian-Jun Liu, Hai-Tao Ye, D J Coathup, A V Khomich, Xiao-Jun Hu
Chin. Phys. B 2018, 27 (9): 096104;  doi: 10.1088/1674-1056/27/9/096104
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We investigate the structural and electrical properties of carbon-ion-implanted ultrananocrystalline diamond (UNCD) films. Impedance spectroscopy measurements show that the impedance of diamond grains is relatively stable, while that of grain boundaries (GBs) (Rb) significantly increases after the C+ implantation, and decreases with the increase in the annealing temperature (Ta) from 650 ℃ to 1000 ℃. This implies that the C+ implantation has a more significant impact on the conductivity of GBs. Conductive atomic force microscopy demonstrates that the number of conductive sites increases in GB regions at Ta above 900 ℃, owing to the formation of a nanographitic phase confirmed by high-resolution transmission electronic microscopy. Visible-light Raman spectra show that resistive trans-polyacetylene oligomers desorb from GBs at Ta above 900 ℃, which leads to lower Rb of samples annealed at 900 and 1000 ℃. With the increase in Ta to 1000 ℃, diamond grains become smaller with longer GBs modified by a more ordered nanographitic phase, supplying more conductive sites and leading to a lower Rb.

Exact transverse solitary and periodic wave solutions in a coupled nonlinear inductor-capacitor network

Serge Bruno Yamgoué, Guy Roger Deffo, Eric Tala-Tebue, François Beceau Pelap
Chin. Phys. B 2018, 27 (9): 096301;  doi: 10.1088/1674-1056/27/9/096301
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Through two methods, we investigate the solitary and periodic wave solutions of the differential equation describing a nonlinear coupled two-dimensional discrete electrical lattice. The fixed points of our model equation are examined and the bifurcations of phase portraits of this equation for various values of the front wave velocity are presented. Using the sine-Gordon expansion method and classic integration, we obtain exact transverse solutions including breathers, bright solitons, and periodic solutions.

Properties of negative thermal expansion β-eucryptite ceramics prepared by spark plasma sintering

Li-Min Zhao, Yong-Guang Cheng, Hao-Shan Hao, Jiao Wang, Shao-Hui Liu, Bao-Sen Zhang
Chin. Phys. B 2018, 27 (9): 096501;  doi: 10.1088/1674-1056/27/9/096501
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β-eucryptite powders are prepared by the sol-gel method through using tetraethoxysilane lithium nitrate and aluminum isopropoxide as starting materials. β-eucryptite ceramics are prepared by spark plasma sintering. The effects of sintering temperature on the negative thermal expansion properties of the β-eucryptite are investigated by x-ray diffraction (XRD), scanning electron microscopy, and thermal expansion test. The XRD results exhibit no change in the crystal structure of the sample prepared by different sintering processes. The negative thermal expansion properties increase with the increase of the sintering temperature. The coefficient of thermal expansion of β-eucryptite ceramics sintered at 1100 ℃ is calculated to be -4.93×10-6-1. Crystallization behaviors of the ceramics may play an important role in the increase of negative thermal expansion of β-eucryptite. High sintering temperature could improve the crystallization behaviors of the ceramics and reduce the residue glass phase, which can improve the negative thermal expansion properties of β-eucryptite ceramics.

Microdroplet targeting induced by substrate curvature

Hongguang Zhang, Zhenjiang Guo, Shan Chen, Bo Zhang, Xianren Zhang
Chin. Phys. B 2018, 27 (9): 096801;  doi: 10.1088/1674-1056/27/9/096801
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Fundamental understanding of the wettability of curved substrates is crucial for the applications of microdroplets in colloidal science, microfluidics, and heat exchanger technologies. Here we report via lattice Boltzmann simulations and energetic analysis that microdroplets show an ability of transporting selectively to appropriate substrates solely according to substrate shape (curvature), which is called the substrate-curvature-dependent droplet targeting because of its similarity to protein targeting by which proteins are transported to the appropriate destinations in the cell. Two dynamic pathways of droplet targeting are identified:one is the Ostwald ripening-like liquid transport between separated droplets via evaporating droplets on more curved convex (or less curved concave) surfaces and growing droplets on less curved convex (or more curved concave) surfaces, and the other is the directional motion of a droplet through contacting simultaneously substrates of different curvatures. Then we demonstrate analytically that droplet targeting is a thermodynamically driven process. The driving force for directional motion of droplets is the surface-curvature-induced modulation of the work of adhesion, while the Ostwald ripening-like transport is ascribed to the substrate-curvature-induced change of droplet curvature radius. Our findings of droplet targeting are potentially useful for a tremendous range of applications, such as microfluidics, thermal control, and microfabrication.

Nondestructive determination of film thickness with laser-induced surface acoustic waves

Xiao Xia, Kong Tao, Qi Hai Yang, Qing Hui Quan
Chin. Phys. B 2018, 27 (9): 096802;  doi: 10.1088/1674-1056/27/9/096802
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The application of surface acoustic waves (SAWs) for thickness measurement is presented. By studying the impact of film thickness h on the dispersion phenomenon of surface acoustic waves, a method for thickness determination based on theoretical dispersion curve v (fh) and experimental dispersion curve v (f) is developed. The method provides a series of thickness values at different frequencies f, and the mean value is considered as the final result of the measurement. The thicknesses of six interconnect films are determined by SAWs, and the results are compared with the manufacturer's data. The relative differences are in the range from 0.4% to 2.18%, which indicates that the surface acoustic wave technique is reliable and accurate in the nondestructive thickness determination for films. This method can be generally used for fast and direct determination of film thickness.

CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

Electronic properties of defects in Weyl semimetal tantalum arsenide

Yan-Long Fu, Chang-Kai Li, Zhao-Jun Zhang, Hai-Bo Sang, Wei Cheng, Feng-Shou Zhang
Chin. Phys. B 2018, 27 (9): 097101;  doi: 10.1088/1674-1056/27/9/097101
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The tantalum arsenide (TaAs) is a topological Weyl semimetal which is a class of materials of gapless with three-dimensional topological structure. In order to develop a comprehensive description of the topological properties of the Weyl semimetal, we use the density functional theory to study several defects of TaAs after H irradiation and report the electronic dispersion curves and the density of states of these defects. We find that various defects have different influences on the topological properties. Interstitial H atom can shift the Fermi level. Both Ta vacancy with a concentration of 1/64 and As vacancy with a concentration of 1/64 destruct a part of the Weyl points. The substitutional H atom on a Ta site could repair only a part of the Weyl points, while H atom on an As site could repair all the Weyl points.

Site preferences of alloying transition metal elements in Ni-based superalloy: A first-principles study

Baokun Lu, Chong-Yu Wang, Zhihui Du
Chin. Phys. B 2018, 27 (9): 097102;  doi: 10.1088/1674-1056/27/9/097102
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Atomistic characterization of chemical element distribution is crucial to understanding the role of alloying elements for strengthening mechanism of superalloy. In the present work, the site preferences of two alloying elements X-Y in γ-Ni of Ni-based superalloy are systematically studied using first-principles calculations with and without spin-polarization. The doping elements X and Y are chosen from the 27 kinds of 3d, 4d, 5d group transition metals (Sc, Ti, V, Cr, Mn, Fe, Co, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, Hf, Ta, W, Re, Os, Ir, Pt, Au) and Al. We find that the spin-polarized calculations for Re-Re, Re-Ru, Re-Cr, Ru-Cr show a strong chemical binding affinity between the solute elements and are more consistent with the experimental results. The binding energies of pairs between the 28 elements have an obvious periodicity and are closely related the electronic configuration of the elements. When the d-electrons of the element are close to the half full-shell state, two alloying elements possess attractive binding energies, reflecting the effect of the Hund's rule. The combinations of early transition metals (Sc, Ti, V, Y, Zr, Nb, Hf, Ta) have a repulsive interaction in γ-Ni. These results offer insights into the role of alloying elements for strengthening mechanism of superalloy.

Pressure effect in the Kondo semimetal CeRu4Sn6 with nontrivial topology Hot!

Jiahao Zhang, Shuai Zhang, Ziheng Chen, Meng Lv, Hengcan Zhao, Yi-feng Yang, Genfu Chen, Peijie Sun
Chin. Phys. B 2018, 27 (9): 097103;  doi: 10.1088/1674-1056/27/9/097103
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Kondo semimetal CeRu4Sn6 is attracting renewed attention due to the theoretically predicted nontrivial topology in its electronic band structure. We report hydrostatic and chemical pressure effects on the transport properties of single-and poly-crystalline samples. The electrical resistivity ρ(T) is gradually enhanced by applying pressure over a wide temperature range from room temperature down to 25 mK. Two thermal activation gaps estimated from high-and low-temperature windows are found to increase with pressure. A flat ρ(T) observed at the lowest temperatures below 300 mK appears to be robust against both pressure and field. This feature as well as the increase of the energy gaps calls for more intensive investigations with respect to electron correlations and band topology.

Multiscale energy density algorithm and application to surface structure of Ni matrix of superalloy

Min Sun, Chong-Yu Wang, Ji-Ping Liu
Chin. Phys. B 2018, 27 (9): 097105;  doi: 10.1088/1674-1056/27/9/097105
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Multiscale materials modeling as a new technique could offer more accurate predictive capabilities. The most active area of research for multiscale modeling focuses on the concurrent coupling by considering models on disparate scales simultaneously. In this paper, we present a new concurrent multiscale approach, the energy density method (EDM), which couples the quantum mechanical (QM) and the molecular dynamics (MD) simulations simultaneously. The coupling crossing different scales is achieved by introducing a transition region between the QM and MD domains. In order to construct the energy formalism of the entire system, concept of site energy and weight parameters of disparate scales are introduced. The EDM is applied to the study of the multilayer relaxation of the Ni (001) surface structure and is validated against the periodic density functional theory (DFT) calculations. The results show that the concurrent EDM could combine the accuracy of the DFT description with the low computational cost of the MD simulation and is suitable to the study of the local defects subjected to the influence of the long-range environment.

Temperature dependence on the electrical and physical performance of InAs/AlSb heterojunction and high electron mobility transistors

Jing Zhang, Hongliang Lv, Haiqiao Ni, Zhichuan Niu, Yuming Zhang
Chin. Phys. B 2018, 27 (9): 097201;  doi: 10.1088/1674-1056/27/9/097201
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In this report, the effect of temperature on the InAs/AlSb heterojunction and high-electron-mobility transistors (HEMTs) with a gate length of 2 μ are discussed comprehensively. The results indicate that device performance is greatly improved at cryogenic temperatures. It is also observed that the device performance at 90 K is significantly improved with 27% lower gate leakage current, 12% higher maximum drain current, and 22.5% higher peak transconductance compared to 300 K. The temperature dependence of mobility and the two-dimensional electron gas concentration in the InAs/AlSb heterojunction for the temperature range 90 K-300 K is also investigated. The electron mobility at 90 K (42560 cm2/V·s) is 2.5 times higher than its value at 300 K (16911 cm2/V·s) because of the weaker lattice vibration and the impurity ionization at cryogenic temperatures, which corresponds to a reduced scattering rate and higher mobility. We also noted that the two-dimensional electron gas concentration decreases slightly from 1.99×1012 cm-2 at 300 K to 1.7×1012 cm-2 at 90 K with a decrease in temperature due to the lower ionization at cryogenic temperature and the nearly constant ΔEc.

Thermal stability of the spin injection in Co/Ag/Co lateral spin valves

Le Wang, Lu-Chen Chen, Wen-Yu Liu, Shuo Han, Weiwei Wang, Zhanjie Lu, Shan-Shan Chen
Chin. Phys. B 2018, 27 (9): 097202;  doi: 10.1088/1674-1056/27/9/097202
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Spin injection, spin diffusion, and spin detection are investigated in Co/Ag/Co lateral spin valves at room temperature. Clear spin accumulation signals are detected by the non-local measurement. By fitting the results to the one-dimensional diffusion equation,~8.6% spin polarization of the Co/Ag interface and ~180 nm spin diffusion length in Ag are obtained. Thermal treatment results show that the spin accumulation signal drastically decreases after 100 ℃ annealing, and disappears under 200 ℃ annealing. Our results demonstrate that, compared to the spin diffusion length, the decrease and the disappearance of the spin accumulation signal are mainly dominated by the variation of the interfacial spin polarization of the Co/Ag interface.

Modeling capacitance–voltage characteristic of TiW/p-InP Schottky barrier diode

Yi-Dong Wang, Jun Chen
Chin. Phys. B 2018, 27 (9): 097203;  doi: 10.1088/1674-1056/27/9/097203
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The capacitance-voltage (C-V) characteristic of the TiW/p-InP Schottky barrier diodes (SBDs) is analyzed considering the effects of the interface state (Nss), series resistance (Rs), and deep level defects. The C-V of the Schottky contact is modeled based on the physical mechanism of the interfacial state and series resistance effect. The fitting coefficients α and β are used to reflect the Nss and Rs on the C-V characteristics, respectively. The α decreases with the increase of frequency, while β increases with the increase of frequency. The capacitance increases with the increase of α and the decrease of β. From our model, the peak capacitance and its position can be estimated. The experimental value is found to be larger than the calculated one at the lower voltage. This phenomenon can be explained by the effect of deep level defects.

The magneto-thermoelectric effect of graphene with intra-valley scattering

Wenye Duan, Junfeng Liu, Chao Zhang, Zhongshui Ma
Chin. Phys. B 2018, 27 (9): 097204;  doi: 10.1088/1674-1056/27/9/097204
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We present a qualitative and quantitative study of the magneto-thermoelectric effect of graphene. In the limit of impurity scattering length being much longer than the lattice constant, the intra-valley scattering dominates the charge and thermal transport. The self-energy and the Green's functions are calculated in the self-consistent Born approximation. It is found that the longitudinal thermal conductivity splits into double peaks at high Landau levels and exhibits oscillations which are out of phase with the electric conductivity. The chemical potential-dependent electrical resistivity, the thermal conductivities, the Seebeck coefficient, and the Nernst coefficient are obtained. The results are in good agreement with the experimental observations.

Ab initio study of H/O trapping and clustering on U/Al interface

Wenhong Ouyang, Wensheng Lai, Zhengjun Zhang
Chin. Phys. B 2018, 27 (9): 097303;  doi: 10.1088/1674-1056/27/9/097303
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Al coating on U surfaces is one of the methods to protect U against environmental corrosion. The behaviors of hydrogen and oxygen impurities near the Al/α-U interface have been studied in the density functional theory framework. It turns out that U vacancies tend to segregate to the interface with segregation energies of around 0.5-0.8 eV. The segregated U vacancy can act as a sink for H and O impurities, which is saturated when filled with 8 H or 6 O atoms, respectively. Moreover, the O impurities tend to stay in the Al layer while the H impurities prefer to diffuse into the U lattice, suggesting that the Al coating can play a significant role against oxidation but not against hydrogenation of U.

Electric field manipulation of multiple nonequivalent Dirac cones in the electronic structures of hexagonal CrB4 sheet

Jinkun Wang, Yajiao Ke, Qingxing Xie, Yanli Li, Jiafu Wang
Chin. Phys. B 2018, 27 (9): 097304;  doi: 10.1088/1674-1056/27/9/097304
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Two-dimensional materials with Dirac cones have significant applications in photoelectric technology. The origin and manipulation of multiple Dirac cones need to be better understood. By first-principle calculations, we study the influence of external fields on the electronic structure of the hexagonal CrB4 sheet with double nonequivalent Dirac cones. Our results show that the two cones are not sensitive to tensile strain and out-of-plane electric field, but present obviously different behaviors under the in-plane external electric field (along the B-B direction), i.e., one cone holds while the other vanishes with a gap opening. More interestingly, a new nonequivalent cone emerges under a proper in-plane electric field. We also discuss the origin of the cones in CrB4 sheet. Our study provides a new method on how to obtain Dirac cones by the external field manipulation, which may motivate potential applications in nanoelectronics.

Analysis of the inhomogeneous barrier and phase composition of W/4H-SiC Schottky contacts formed at different annealing temperatures

Sheng-Xu Dong, Yun Bai, Yi-Dan Tang, Hong Chen, Xiao-Li Tian, Cheng-Yue Yang, Xin-Yu Liu
Chin. Phys. B 2018, 27 (9): 097305;  doi: 10.1088/1674-1056/27/9/097305
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The electrical characteristics of W/4H-SiC Schottky contacts formed at different annealing temperatures have been measured by using current-voltage-temperatures (I-V-T) and capacitance-voltage-temperatures (C-V-T) techniques in the temperature range of 25 ℃-175 ℃. The testing temperature dependence of the barrier height (BH) and ideality factor (n) indicates the presence of inhomogeneous barrier. Tung's model has been applied to evaluate the degree of inhomogeneity, and it is found that the 400 ℃ annealed sample has the lowest T0 of 44.6 K among all the Schottky contacts. The barrier height obtained from C-V-T measurement is independent of the testing temperature, which suggests a uniform BH. The x-ray diffraction (XRD) analysis shows that there are two kinds of space groups of W when it is deposited or annealed at lower temperature (≤ 500 ℃). The phase of W2C appears in the sample annealed at 600 ℃, which results in the low BH and the high T0. The 500 ℃ annealed sample has the highest BH at all testing temperatures, indicating an optimal annealing temperature for the W/4H-SiC Schottky rectifier for high-temperature application.

Key technologies for dual high-k and dual metal gate integration

Yong-Liang Li, Qiu-Xia Xu, Wen-Wu Wang
Chin. Phys. B 2018, 27 (9): 097306;  doi: 10.1088/1674-1056/27/9/097306
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The key technologies for the dual high-k and dual metal gate, such as the electrical optimization of metal insert poly-Si stack structure, the separating of high-k and metal gate of n/pMOS in different regions of the wafer, and the synchronous etching of n/pMOS gate stack, are successfully developed. First, reasonable flat-band voltage and equivalent oxide thickness of pMOS MIPS structure are obtained by further optimizing the HfSiAlON dielectric through incorporating more Al-O dipole at interface between HfSiAlON and bottom SiOx. Then, the separating of high-k and metal gate for n/pMOS is achieved by SC1 (NH4OH:H2O2:H2O=1:1:5) and DHF-based solution for the selective removing of nMOS TaN and HfSiON and by BCl3-based plasma and DHF-based solution for the selective removing of pMOS TaN/Mo and HfSiAlON. After that, the synchronous etching of n/pMOS gate stack is developed by utilizing optimized BCl3/SF6/O2/Ar plasma to obtain a vertical profile for TaN and TaN/Mo and by utilizing BCl3/Ar plasma combined with DHF-based solution to achieve high selectivity to Si substrate. Finally, good electrical characteristics of CMOS devices, obtained by utilizing these new developed technologies, further confirm that they are practicable technologies for DHDMG integration.

Characteristics and threshold voltage model of GaN-based FinFET with recessed gate

Chong Wang, Xin Wang, Xue-Feng Zheng, Yun Wang, Yun-Long He, Ye Tian, Qing He, Ji Wu, Wei Mao, Xiao-Hua Ma, Jin-Cheng Zhang, Yue Hao
Chin. Phys. B 2018, 27 (9): 097308;  doi: 10.1088/1674-1056/27/9/097308
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In this work, AlGaN/GaN FinFETs with different fin widths have been successfully fabricated, and the recessed-gate FinFETs are fabricated for comparison. The recessed-gate FinFETs exhibit higher transconductance value and positive shift of threshold voltage. Moreover, with the fin width of the recessed-gate FinFETs increasing, the variations of both threshold voltage and the transconductance increase. Next, transfer characteristics of the recessed-gate FinFETs with different fin widths and recessed-gate depths are simulated by Silvaco software. The relationship between the threshold voltage and the AlGaN layer thickness has been investigated. The simulation results indicate that the slope of threshold voltage variation reduces with the fin width decreasing. Finally, a simplified threshold voltage model for recessed-gate FinFET is established, which agrees with both the experimental results and simulation results.

Effect of SiN: Hx passivation layer on the reverse gate leakage current in GaN HEMTs

Sheng Zhang, Ke Wei, Yang Xiao, Xiao-Hua Ma, Yi-Chuan Zhang, Guo-Guo Liu, Tian-Min Lei, Ying-Kui Zheng, Sen Huang, Ning Wang, Muhammad Asif, Xin-Yu Liu
Chin. Phys. B 2018, 27 (9): 097309;  doi: 10.1088/1674-1056/27/9/097309
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This paper concentrates on the impact of SiN passivation layer deposited by plasma-enhanced chemical vapor deposition (PECVD) on the Schottky characteristics in GaN high electron mobility transistors (HEMTs). Three types of SiN layers with different deposition conditions were deposited on GaN HEMTs. Atomic force microscope (AFM), capacitance-voltage (C-V), and Fourier transform infrared (FTIR) measurement were used to analyze the surface morphology, the electrical characterization, and the chemical bonding of SiN thin films, respectively. The better surface morphology was achieved from the device with lower gate leakage current. The fixed positive charge Qf was extracted from C-V curves of Al/SiN/Si structures and quite different density of trap states (in the order of magnitude of 1011-1012 cm-2) was observed. It was found that the least trap states were in accordance with the lowest gate leakage current. Furthermore, the chemical bonds and the %H in Si-H and N-H were figured from FTIR measurement, demonstrating an increase in the density of Qf with the increasing %H in N-H. It reveals that the effect of SiN passivation can be improved in GaN-based HEMTs by modulating %H in Si-H and N-H, thus achieving a better Schottky characteristics.

Transport spectroscopy through dopant atom array in silicon junctionless nanowire transistors

Xiao-Song Zhao, Wei-Hua Han, Yang-Yan Guo, Ya-Mei Dou, Fu-Hua Yang
Chin. Phys. B 2018, 27 (9): 097310;  doi: 10.1088/1674-1056/27/9/097310
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We demonstrate electron transport spectroscopy through a dopant atom array in n-doped silicon junctionless nanowire transistors within a temperature range from 6 K to 250 K. Several current steps are observed at the initial stage of the transfer curves below 75 K, which result from the electron transport from Hubbard bands to one-dimensional conduction band. The current-off voltages in the transfer curves have a strikingly positive shift below 20 K and a negative shift above 20 K due to the electrostatic screening induced by the ionized dopant atoms. There exists the minimum electron mobility at a critical temperature of 20 K, resulting from the interplay between thermal activation and impurity scattering. Furthermore, electron transport behaviors change from hopping conductance to thermal activation conductance at the temperature of 30 K.

Adsorptions of metal adatoms on graphene-like BC3 and their rich electronic properties: A first-principles study

Pengfei Sui, Jiaqi Dai, Yinchang Zhao, Zhenhong Dai
Chin. Phys. B 2018, 27 (9): 097311;  doi: 10.1088/1674-1056/27/9/097311
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Density functional calculations have been performed to investigate the adsorption of twenty two different kinds of metal adatoms on graphene-like BC3. In contrast to the graphene adsorbed with adatoms, the BC3 with adatoms shows many interesting properties. (1) The interaction between the metal adatoms and the BC3 sheet is remarkably strong. The Li, Na, K, and Ca possess the binding energies larger than the cohesive energies of their corresponding bulk metals. (2) The Li, Na, and K adatoms form approximately ideal ionic bonds with BC3, while the Be, Mg, and Ca adatoms form ionic bonds with BC3 with slight hybridization of covalent bonds. The Al, Ga, In, Sn, and all transition metal adatoms form covalent bonds with BC3. (3) For all the structures studied, there exhibit metal, half-metal, semiconducting, and spin-semiconducting behaviors. Especially, the BC3 with Co adatom shows a quantum anomalous Hall (QAH) phase with a Chern number of -1 based on local density approximation calculations. (4) For Li, Na, K, Ca, Ga, In, Sn, Ti, V, Cr, Ni, Pd, and Pt, there exists a trend that the adatom species with lower ionization potential have lower work function. Our results indicate the potential applications of functionalization of BC3 with metal adatoms.

0-π transition induced by the barrier strength in spin superconductor Josephson junctions Hot!

Wen Zeng, Rui Shen
Chin. Phys. B 2018, 27 (9): 097401;  doi: 10.1088/1674-1056/27/9/097401
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The Andreev-like levels and the free energy of the spin superconductor/insulator/spin superconductor junction are obtained by using the Bogoliubov-de Gennes equation. The phase dependence of the spin supercurrents exhibits a 0-π transition by changing the barrier strength. The dependences of the critical current on the barrier strength and the temperature are also presented.

Modulational instability, quantum breathers and two-breathers in a frustrated ferromagnetic spin lattice under an external magnetic field

Wanhan Su, Jiayu Xie, Tianle Wu, Bing Tang
Chin. Phys. B 2018, 27 (9): 097501;  doi: 10.1088/1674-1056/27/9/097501
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The modulational instability, quantum breathers and two-breathers in a frustrated easy-axis ferromagnetic zig-zag chain under an external magnetic field are investigated within the Hartree approximation. By means of a linear stability analysis, we analytically study the discrete modulational instability and analyze the effect of the frustration strength on the discrete modulational instability region. Using the results from the discrete modulational instability analysis, the presence conditions of those stationary bright type localized solutions are presented. On the other hand, we obtain the analytical expressions for the stationary bright localized solutions and analyze the effect of the frustration on their emergence conditions. By taking advantage of these bright type single-magnon bound wave functions obtained, quantum breather states in the present frustrated ferromagnetic zig-zag lattice are constructed. What is more, the analytical forms for quantum two-breather states are also obtained. In particular, the energy level formulas of quantum breathers and two-breathers are derived.

Effect of particle size distribution on magnetic behavior of nanoparticles with uniaxial anisotropy

S Rizwan Ali, Farah Naz, Humaira Akber, M Naeem, S Imran Ali, S Abdul Basit, M Sarim, Sadaf Qaseem
Chin. Phys. B 2018, 27 (9): 097503;  doi: 10.1088/1674-1056/27/9/097503
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The effect of particle size distribution on the field and temperature dependence of the hysteresis loop features like coercivity (HC), remanence (MR), and blocking temperature (TB) is simulated for an ensemble of single domain ferromagnetic nanoparticles with uniaxial anisotropy. Our simulations are based on the two-state model for T<TB and the metropolis Monte-Carlo method for T>TB. It is found that the increase in the grain size significantly enhances HC and TB. The presence of interparticle exchange interaction in the system suppresses HC but causes MR to significantly increase. Our results show that the parameters associated with the particle size distribution (Dd,δ) such as the mean particle size d and standard-deviation δ play key roles in the magnetic behavior of the system.

Thickness dependent manipulation of uniaxial magnetic anisotropy in Fe-thin films by oblique deposition

Qeemat Gul, Wei He, Yan Li, Rui Sun, Na Li, Xu Yang, Yang Li, Zi-Zhao Gong, ZongKai Xie, Xiang-Qun Zhang, Zhao-Hua Cheng
Chin. Phys. B 2018, 27 (9): 097504;  doi: 10.1088/1674-1056/27/9/097504
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The uniaxial magnetic anisotropy of obliquely deposited Fe(001)/Pd film on MgO(001) substrate is investigated as a function of deposition angle and film thickness. The values of incidence angle of Fe flux relative to surface normal of the substrate are 0°, 45°, 55°, and 70°, respectively. In-situ low energy electron diffraction is employed to investigate the surface structures of the samples. The Fe film thicknesses are determined to be 50 ML, 45 ML, 32 ML, and 24 ML (1 ML=0.14 nm) by performing x-ray reflectivity on the grown samples, respectively. The normalized remanent magnetic saturation ratio and coercivity are obtained by the longitudinal surface magneto-optical Kerr effect. Here, the magnetic anisotropy constants are quantitatively determined by fitting the anisotropic magnetoresistance curves under different fields. These measurements show four-fold cubic anisotropy in a large Fe film thickness (50 ML) sample, but highly in-plane uniaxial magnetic anisotropies in thin films (24 ML and 32 ML) samples. In the obliquely deposited Fe films, the coercive fields and the uniaxial magnetic anisotropies (UMAs) increase as the deposition angle becomes more and more tilted. In addition, the UMA decreases with the increase of the Fe film thickness. Our work provides the possibility of manipulating uniaxial magnetic anisotropy, and paves the way to inducing UMA by oblique deposition with smaller film thickness.

Enhanced magneto-electric effect in manganite tricolor superlattice with artificially broken symmetry

Huanyu Pei, Shujin Guo, Hong Yan, Changle Chen, Bingcheng Luo, Kexin Jin
Chin. Phys. B 2018, 27 (9): 097701;  doi: 10.1088/1674-1056/27/9/097701
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The magneto-electric effect in magnetic materials has been widely investigated, but obtaining an enhanced magneto-electric effect is challenging. In this study, tricolor superlattices composed of manganese oxides–Pr0.9Ca0.1MnO3, La0.9Sr0.1MnO3, and La0.9Sb0.1MnO3–on (001)-oriented Nb:SrTiO3 substrates with broken space-inversion and time-reversal symmetries are designed. Regarding the electric polarization in the hysteresis loops of the superlattices at different external magnetic fields, both coercive electric field Ec and remnant polarization intensity Pr clearly show strong magnetic-field dependences. At low temperatures (<120 K), a considerable magneto-electric effect in the well-defined tricolor superlattice is observed that is absent in the single compounds. Both maxima of the magneto-electric coupling coefficients ΔEc and ΔPr appear at 30 K. The magnetic dependence of the dielectric constant further supports the magneto-electric effect. Moreover, a dependence of the magneto-electric effect on the periodicity of the superlattices with various structures is observed, which indicates the importance of interfaces. Our experimental results verify previous theoretical results regarding magneto-electric interactions, thereby paving the way for the design and development of novel magneto-electric devices based on manganite ferromagnets.

Crystal growth and spectral properties of Tb: Lu2O3

Jiaojiao Shi, Bin Liu, Qingguo Wang, Huili Tang, Feng Wu, Dongzhen Li, Hengyu Zhao, Zhanshan Wang, Wen Deng, Xu Zian, Xu Jiayue, Xiaodong Xu, Jun Xu
Chin. Phys. B 2018, 27 (9): 097801;  doi: 10.1088/1674-1056/27/9/097801
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The crystal growth, x-ray diffraction pattern, absorption spectrum, emission spectrum, and fluorescence lifetime of a Tb:Lu2O3 single crystal were studied. Excited at 483 nm, the peak absorption cross-section was calculated to be 3.5×10-22 cm2, and the full width at half maximum was found to be 2.85 nm. The Judd-Ofelt (J-O) intensity parameters Ω2, Ω4, and Ω6 were computed to be 3.79×10-20 cm2, 1.30×10-20 cm2, and 1.08×10-20 cm2, with a spectroscopic quality factor Ω4/Ω6 being 1.20. The emission cross-sections of green emission around 543 nm and yellow emission around 584 nm were calculated to be 9.43×10-22 cm2 and 1.32×10-22 cm2, respectively. The fluorescence lifetime τexp of 5D4 was fitted to be 1.13 ms. The data suggest that the Tb:Lu2O3 crystal could be a potential candidate for green and yellow laser operation.

Quantum frequency down-conversion of single photons at 1552 nm from single InAs quantum dot

Ben Ma, Si-Hang Wei, Ze-Sheng Chen, Xiang-Jun Shang, Hai-Qiao Ni, Zhi-Chuan Niu
Chin. Phys. B 2018, 27 (9): 097802;  doi: 10.1088/1674-1056/27/9/097802
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Near-infrared single photon sources in telecommunication bands, especially at 1550 nm, are required for long-distance quantum communication. Here a down-conversion quantum interface is implemented, where the single photons emitted from single InAs quantum dot at 864 nm is down converted to 1552 nm by using a fiber-coupled periodically poled lithium niobate (PPLN) waveguide and a 1.95 μm pump laser, and the frequency conversion efficiency is~40%. The single-photon purity of quantum dot emission is preserved during the down-conversion process, i.e., g(2)(0), only 0.22 at 1552 nm. This present technique advances the Ⅲ-V semiconductor quantum dots as a promising platform for long-distance quantum communication.

INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

Dynamically tunable terahertz passband filter based on metamaterials integrated with a graphene middle layer

MaoSheng Yang, LanJu Liang, DeQuan Wei, Zhang Zhang, Xin Yan, Meng Wang, JianQuan Yao
Chin. Phys. B 2018, 27 (9): 098101;  doi: 10.1088/1674-1056/27/9/098101
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The dynamic tunability of a terahertz (THz) passband filter was realized by changing the Fermi energy (EF) of graphene based on the sandwiched structure of metal-graphene-metal metamaterials (MGMs). By using plane wave simulation, we demonstrated that the central frequency (f0) of the proposed filter can shift from 5.04 THz to 5.71 THz; this shift is accompanied by a 3 dB bandwidth (Δf) decrease from 1.82 THz to 0.01 THz as the EF increases from 0 to 0.75 eV. Additionally, in order to select a suitable control equation for the proposed filter, the curves of Δf and f0 under different graphene EF were fitted using five different mathematical models. The fitting results demonstrate that the DoseResp model offers accurate predictions of the change in the 3 dB bandwidth, and the Quartic model can successfully describe the variation in the center frequency of the proposed filter. Moreover, the electric field and current density analyses show that the dynamic tuning property of the proposed filter is mainly caused by the competition of two coupling effects at different graphene EF, i.e., graphene-polyimide coupling and graphene-metal coupling. This study shows that the proposed structures are promising for realizing dynamically tunable filters in innovative THz communication systems.

Effect of intramolecular and intermolecular hydrogen bonding on the ESIPT process in DEAHB molecule

Hui Li, Lina Ma, Hang Yin, Ying Shi
Chin. Phys. B 2018, 27 (9): 098201;  doi: 10.1088/1674-1056/27/9/098201
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Density functional theory (DFT) and time-dependent density functional theory (TDDFT) methods are used to investigate the influences of intramolecular and intermolecular hydrogen bonding on excited-state intramolecular proton transfer (ESIPT) for the 4-N,N'-(diethylamino)-2-hydroxybenzaldehyde (DEAHB). The structures of DEAHB and its hydrogen-bonded complex in the ground-state and the excited-state are optimized. In addition, the detailed descriptions of frontier molecular orbitals of the DEAHB monomer and DEAHB-DMSO complex are presented. Moreover, the transition density matrix is worked out to gain deeper insight into the orbitals change. It is hoped that the present work not only elaborates different influence mechanisms between intramolecular and intermolecular hydrogen bonding interactions on the ESIPT process for DEAHB, but also may be helpful to design and develop new materials and applications involved DEAHB systems in the future.

Heavy ion induced upset errors in 90-nm 64 Mb NOR-type floating-gate Flash memory

Jin-Shun Bi, Kai Xi, Bo Li, Hai-Bin Wang, Lan-Long Ji, Jin Li, Ming Liu
Chin. Phys. B 2018, 27 (9): 098501;  doi: 10.1088/1674-1056/27/9/098501
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Upset errors in 90-nm 64 Mb NOR-type floating-gate Flash memory induced by accelerated 129Xe and 209Bi ions are investigated in detail. The linear energy transfer covers the range from 50 to 99.8 MeV/(mg/cm2). When the memory chips are powered off during heavy ions irradiation, single-event-latch-up and single-event-function-interruption are excluded, and only 0->1 upset errors in the memory array are observed. These error bit rates seem very difficult to achieve and cannot be simply recovered based on the power cycle. The number of error bits shows a strong dependence on the linear energy transfer (LET). Under room-temperature annealing conditions, the upset errors can be reduced by about two orders of magnitude using rewrite/reprogram operations, but they subsequently increase once again in a few minutes after the power cycle. High-temperature annealing can diminish almost all error bits, which are affected by the lower LET 129Xe ions. The percolation path between the floating-gate (FG) and the substrate contributes to the radiation-induced leakage current, and has been identified as the root cause of the upset errors of the Flash memory array in this work.

Efficiency-enhanced AlGaInP light-emitting diodes using transparent plasmonic silver nanowires

Xia Guo, Qiao-Li Liu, Hui-Jun Tian, Chun-Wei Guo, Chong Li, An-Qi Hu, Xiao-Ying He, Hua Wu
Chin. Phys. B 2018, 27 (9): 098502;  doi: 10.1088/1674-1056/27/9/098502
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Silver nanowire (AgNW) networks have been demonstrated to exhibit superior transparent and conductive performance over that of indium-doped tin oxide (ITO) and have been proposed to replace ITO, which is currently widely used in optoelectronic devices despite the scarcity of indium on Earth. In this paper, the current spreading and enhanced transmittance induced by AgNWs, which are two important factors influencing the light output power, were analyzed. The enhanced transmittance was studied by finite-difference time-domain simulation and verified by cathodoluminescence measurements. The enhancement ratio of the light output power decreased as the GaP layer thickness increased, with enhancement ratio values of 79%, 52%, and 15% for GaP layer thicknesses of 0.5 μ, 1 μ, and 8 μ, respectively, when an AgNW network was included in AlGaInP light-emitting diodes. This was because of the decreased current distribution tunability of the AgNW network with the increase of the GaP layer thickness. The large enhancement of the light output power was caused by the AgNWs increasing carrier spread out of the electrode and the enhanced transmittance induced by the plasmonic AgNWs. Further decreasing the sheet resistance of AgNW networks could raise their light output power enhancement ratio.

Modeling and identification of magnetostrictive hysteresis with a modified rate-independent Prandtl-Ishlinskii model

Wei Wang, Jun-en Yao
Chin. Phys. B 2018, 27 (9): 098503;  doi: 10.1088/1674-1056/27/9/098503
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This paper presents a modified rate-independent Prandtl-Ishlinskii (MRIPI) model based on the Fermi-Dirac distribution for the asymmetric hysteresis description of magnetostrictive actuators. Generally, the classical Prandtl-Ishlinskii (CPI) model can hardly describe the asymmetric hysteresis. To overcome this limitation, various complex operators have been developed to replace the classical operator. In this study, the proposed MRIPI model maintains the classical operator while a modified input function based on the Fermi-Dirac distribution is presented to replace the classical input function. With this method, the MRIPI model can describe the asymmetric hysteresis of magnetostrictive actuators in a relatively simple mathematic format and has fewer parameters to be identified. A velocity-based sine cosine algorithm (VSCA) is also proposed for the parameter identification of the MRIPI model. To verify the validity of the MRIPI model, experiments are performed and the results are compared with those of the existing modeling methods.

Dependence of switching process on the perpendicular magnetic anisotropy constant in P-MTJ

Mao-Sen Yang, Liang Fang, Ya-Qing Chi
Chin. Phys. B 2018, 27 (9): 098504;  doi: 10.1088/1674-1056/27/9/098504
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We investigate the dependence of the switching process on the perpendicular magnetic anisotropy (PMA) constant in perpendicular spin transfer torque magnetic tunnel junctions (P-MTJs) using micromagnetic simulations. It is found that the final stable states of the magnetization distribution of the free layer after switching can be divided into three different states based on different PMA constants:vortex, uniform, and steady. Different magnetic states can be attributed to a trade-off among demagnetization, exchange, and PMA energies. The generation of the vortex state is also related to the non-uniform stray field from the polarizer, and the final stable magnetization is sensitive to the PMA constant. The vortex and uniform states have different switching processes, and the switching time of the vortex state is longer than that of the uniform state due to hindrance by the vortex.

Potentials of classical force fields for interactions between Na+ and carbon nanotubes Hot!

De-Yuan Li, Guo-Sheng Shi, Feng Hong, Hai-Ping Fang
Chin. Phys. B 2018, 27 (9): 098801;  doi: 10.1088/1674-1056/27/9/098801
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Carbon nanotubes (CNTs) have long been expected to be excellent nanochannels for use in desalination membranes and other bio-inspired human-made channels owing to their experimentally confirmed ultrafast water flow and theoretically predicted ion rejection. The correct classical force field potential for the interactions between cations and CNTs plays a crucial role in understanding the transport behaviors of ions near and inside the CNT, which is key to these expectations. Here, using density functional theory calculations, we provide classical force field potentials for the interactions of Na+/hydrated Na+ with (7,7), (8,8), (9,9), and (10,10)-type CNTs. These potentials can be directly used in current popular classical software such as nanoscale molecular dynamics (NAMD) by employing the tclBC interface. By incorporating the potential of hydrated cation-π interactions to classical all-atom force fields, we show that the ions will move inside the CNT and accumulate, which will block the water flow in wide CNTs. This blockage of water flow in wide CNTs is consistent with recent experimental observations. These results will be helpful for the understanding and design of desalination membranes, new types of nanofluidic channels, nanosensors, and nanoreactors based on CNT platforms.

Cascading failure in multilayer networks with dynamic dependency groups

Lei Jin, Xiaojuan Wang, Yong Zhang, Jingwen You
Chin. Phys. B 2018, 27 (9): 098901;  doi: 10.1088/1674-1056/27/9/098901
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The cascading failure often occurs in real networks. It is significant to analyze the cascading failure in the complex network research. The dependency relation can change over time. Therefore, in this study, we investigate the cascading failure in multilayer networks with dynamic dependency groups. We construct a model considering the recovery mechanism. In our model, two effects between layers are defined. Under Effect 1, the dependent nodes in other layers will be disabled as long as one node does not belong to the largest connected component in one layer. Under Effect 2, the dependent nodes in other layers will recover when one node belongs to the largest connected component. The theoretical solution of the largest component is deduced and the simulation results verify our theoretical solution. In the simulation, we analyze the influence factors of the network robustness, including the fraction of dependent nodes and the group size, in our model. It shows that increasing the fraction of dependent nodes and the group size will enhance the network robustness under Effect 1. On the contrary, these will reduce the network robustness under Effect 2. Meanwhile, we find that the tightness of the network connection will affect the robustness of networks. Furthermore, setting the average degree of network as 8 is enough to keep the network robust.

RETRACTION

Retraction: Detection of finger interruptions in silicon solar cells using photoluminescence imaging(Chinese Physics B, 2018, Vol. 27, No. 6, 068801)

Lei Zhang, Peng Liang, Hui-Shi Zhu, Pei-De Han
Chin. Phys. B 2018, 27 (9): 099901;  doi: 10.1088/1674-1056/27/9/099901
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Since publication, it has been brought to the attention of the Editorial Office of Chinese Physics B that parts of this paper showed strong similarities to the following article (including one equation, some analyses, the motivation and the conclusion) without citation:“Detection of Finger Interruptions in Silicon Solar Cells Using Line Scan Photoluminescence Imaging,” IEEE Journal of Photovoltaics, 2017, vol. 7, No. 6, pp. 1496-1502.
Following our investigation, this article has been retracted by the Editorial Office of Chinese Physics B.
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