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Combining Cubic Spline Interpolation and Fast Fourier Transform to Extend Measuring Range of Reflectometry
Ju Cheng, Jian Lu, Hong-Chao Zhang, Feng Lei, Maryam Sardar, Xin-Tian Bian, Fen Zuo, Zhong-Hua Shen, Xiao-Wu Ni, Jin Shi
Chin. Phys. Lett. 2018, 35 (5):
050701
.
DOI: 10.1088/0256-307X/35/5/050701
The reflectometry is a common method used to measure the thickness of thin films. Using a conventional method, its measurable range is limited due to the low resolution of the current spectrometer embedded in the reflectometer. We present a simple method, using cubic spline interpolation to resample the spectrum with a high resolution, to extend the measurable transparent film thickness. A large measuring range up to 385 μm in optical thickness is achieved with the commonly used system. The numerical calculation and experimental results demonstrate that using the FFT method combined with cubic spline interpolation resampling in reflectrometry, a simple, easy-to-operate, economic measuring system can be achieved with high measuring accuracy and replicability.
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Internal Features of Fiber Fuse in a Yb-Doped Double-Clad Fiber at 3kW
Qi-Rong Xiao, Jia-Ding Tian, Yu-Sheng Huang, Xue-Jiao Wang, Ze-Hui Wang, Dan Li, Ping Yan, Ma-Li Gong
Chin. Phys. Lett. 2018, 35 (5):
054201
.
DOI: 10.1088/0256-307X/35/5/054201
We study internal features of fiber fuse in a Yb-doped double-clad fiber. The samples of fiber fuse are acquired at the power level of 3 kW in an all-fiber forward-pumped master oscillator power amplifier configuration fiber laser that is built specially for fiber fuse analyses. At this high power level, drastic refractive-index redistribution arises in an expended high refractive index area around the bullet-shaped voids of fiber fuse. Electron spin resonance analyses on post-fiber-fuse samples of the Yb-doped double-clad fiber indicate rising Frenkel defect concentration, meanwhile showing a new resonance center that is different from the ones of the Ge-doped fibers studied previously. This new resonance center probably suggests the generation of Al-oxygen hole center, a kind of defect formed during the catastrophic fuse process.
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A Flat-Gain Double-Pass Amplifier with New Hafnia-Bismuth-Erbium Codoped Fiber
Alabbas A. Al-Azzawi, Aya A. Almukhtar, P. H. Reddy, D. Dutta, S. Das, A. Dhar, M. C. Paul, U. N. Zakaria, S. W. Harun
Chin. Phys. Lett. 2018, 35 (5):
054206
.
DOI: 10.1088/0256-307X/35/5/054206
An efficient and compact double-pass optical fiber amplifier is demonstrated using a newly developed hafnia bismuth erbium co-doped fiber (HBEDF) as a gain medium. The HBEDF is fabricated using a modified chemical vapor deposition in conjunction with solution doping. The fiber has an erbium ion concentration of 12500 ppm. At the optimum length of 0.5 m, the HBEDF amplifier (HBEDFA) achieves a flat gain of 26 dB with a gain variation of less than 1.5 dB within a wavelength region from 1530 to 1560 nm when the input signal and pump power are fixed at $-$30 dBm and 140 mW, respectively. On the other hand, at the input signal power of $-$10 dBm, the HBEDFA also achieves a flat gain of 14.2 dB with a gain variation of less than 2.5 dB within a wide wavelength region from 1525 to 1570 nm. Compared with the conventional zirconia erbium co-doped fiber based amplifier, the proposed HBEDFA obtains a more efficient gain and lower noise figure. For an input signal of $-$30 dBm, the gain improvements of 6.2 dB and 4.8 dB are obtained at 1525 nm and 1540 nm, respectively.
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Improvement of Nickel-Stanogermanide Contact Properties by Platinum Interlayer
Wei-Jun Wan, Wei Ren, Xiao-Ran Meng, Yun-Xia Ping, Xing Wei, Zhong-Ying Xue, Wen-Jie Yu, Miao Zhang, Zeng-Feng Di, Bo Zhang
Chin. Phys. Lett. 2018, 35 (5):
056802
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DOI: 10.1088/0256-307X/35/5/056802
We report an effective method to improve the formation of nickel stanogermanide (NiGeSn) by the incorporation of a platinum (Pt) interlayer. After the Ni/Pt/GeSn samples are annealed we obtain uniform NiGeSn thin films, which are characterized by means of sheet resistance, atomic force microscopy, scanning electron microscopy, cross-section transmission electron microscopy, and energy dispersive x-ray spectroscopy. These results show that the presence of Pt increases the smoothness and uniform morphology of NiGeSn films.
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Crystallization Process of Superlattice-Like Sb/SiO$_{2}$ Thin Films for Phase Change Memory Application
Xiao-Qin Zhu, Rui Zhang, Yi-Feng Hu, Tian-Shu Lai, Jian-Hao Zhang, Hua Zou, Zhi-Tang Song
Chin. Phys. Lett. 2018, 35 (5):
056803
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DOI: 10.1088/0256-307X/35/5/056803
After compositing with SiO$_{2}$ layers, it is shown that superlattice-like Sb/SiO$_{2}$ thin films have higher crystallization temperature ($\sim240^{\circ}\!$C), larger crystallization activation energy (6.22 eV), and better data retention ability (189$^{\circ}\!$C for 10 y). The crystallization of Sb in superlattice-like Sb/SiO$_{2}$thin films is restrained by the multilayer interfaces. The reversible resistance transition can be achieved by an electric pulse as short as 8 ns for the Sb(3 nm)/SiO$_{2}$(7 nm)-based phase change memory cell. A lower operation power consumption of 0.09 mW and a good endurance of $3.0\times10^{6}$ cycles are achieved. In addition, the superlattice-like Sb(3 nm)/SiO$_{2}$(7 nm) thin film shows a low thermal conductivity of 0.13 W/(m$\cdot$K).
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Atomic-Ordering-Induced Quantum Phase Transition between Topological Crystalline Insulator and $Z_{2}$ Topological Insulator
Hui-Xiong Deng, Zhi-Gang Song, Shu-Shen Li, Su-Huai Wei, Jun-Wei Luo
Chin. Phys. Lett. 2018, 35 (5):
057301
.
DOI: 10.1088/0256-307X/35/5/057301
Topological phase transition in a single material usually refers to transitions between a trivial band insulator and a topological Dirac phase, and the transition may also occur between different classes of topological Dirac phases. It is a fundamental challenge to realize quantum transition between $Z_{2}$ nontrivial topological insulator (TI) and topological crystalline insulator (TCI) in one material because $Z_{2}$ TI and TCI have different requirements on the number of band inversions. The $Z_{2}$ TIs must have an odd number of band inversions over all the time-reversal invariant momenta, whereas the newly discovered TCIs, as a distinct class of the topological Dirac materials protected by the underlying crystalline symmetry, owns an even number of band inversions. Taking PbSnTe$_{2}$ alloy as an example, here we demonstrate that the atomic-ordering is an effective way to tune the symmetry of the alloy so that we can electrically switch between TCI phase and $Z_{2}$ TI phase in a single material. Our results suggest that the atomic-ordering provides a new platform towards the realization of reversibly switching between different topological phases to explore novel applications.
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Improvement of Operation Characteristics for MONOS Charge Trapping Flash Memory with SiGe Buried Channel
Zhao-Zhao Hou, Gui-Lei Wang, Jia-Xin Yao, Qing-Zhu Zhang, Hua-Xiang Yin
Chin. Phys. Lett. 2018, 35 (5):
057302
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DOI: 10.1088/0256-307X/35/5/057302
We propose and investigate a novel metal/SiO$_{2}$/Si$_{3}$N$_{4}$/SiO$_{2}$/SiGe charge trapping flash memory structure (named as MONOS), utilizing SiGe as the buried channel. The fabricated memory device demonstrates excellent program-erasable characteristics attributed to the fact that more carriers are generated by the smaller bandgap of SiGe during program/erase operations. A flat-band voltage shift 2.8 V can be obtained by programming at +11 V for 100 μs. Meanwhile, the memory device exhibits a large memory window of $\sim$7.17 V under $\pm$12 V sweeping voltage, and a negligible charge loss of 18% after 10$^{4}$ s' retention. In addition, the leakage current density is lower than $2.52\times10^{-7}$ A$\cdot$cm$^{-2}$ below a gate breakdown voltage of 12.5 V. Investigation of leakage current-voltage indicates that the Schottky emission is the predominant conduction mechanisms for leakage current. These desirable characteristics are ascribed to the higher trap density of the Si$_{3}$N$_{4}$ charge trapping layer and the better quality of the interface between the SiO$_{2}$ tunneling layer and the SiGe buried channel. Therefore, the application of the SiGe buried channel is very promising to construct 3D charge trapping NAND flash devices with improved operation characteristics.
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Electroluminescence from the InGaN/GaN Superlattices Interlayer of Yellow LEDs with Large V-Pits Grown on Si (111)
Xi-xia Tao, Chun-lan Mo, Jun-lin Liu, Jian-li Zhang, Xiao-lan Wang, Xiao-ming Wu, Long-quan Xu, Jie Ding, Guang-xu Wang, Feng-yi Jiang
Chin. Phys. Lett. 2018, 35 (5):
057303
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DOI: 10.1088/0256-307X/35/5/057303
A blue emission originated from InGaN/GaN superlattice (SL) interlayer is observed in the yellow LEDs with V-pits embedded in the quantum wells (QWs), revealing that sufficient holes have penetrated through the QWs into SLs far away from the p-type layer. In the V-pits embedded LEDs, hole transport has two paths: via the flat $c$-plane region or via the sidewalls of V-pits. It is proved that the holes in SLs are injected from the sidewalls of V-pits, and the transportation process is significantly affected by working temperature, current density, and the size of V-pits. Four motion possibilities are discussed when the holes flow via the sidewalls. All these may contribute to a better understanding of hole transport and device design.
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Coexistence of Polaronic States and Superconductivity in Iron-Pnictide Compound Ba$_{2}$Ti$_{2}$Fe$_{2}$As$_{4}$O
Li-Yuan Rong, Xun Shi, Pierre Richard, Yun-Lei Sun, Guang-Han Cao, Xiang-Zhi Zhang, Jun-Zhang Ma, Ming Shi, Yao-Bo Huang, Tian Qian, Hong Ding, Ren-Zhong Tai
Chin. Phys. Lett. 2018, 35 (5):
057401
.
DOI: 10.1088/0256-307X/35/5/057401
The electronic structure of iron-pnictide compound superconductor Ba$_{2}$Ti$_{2}$Fe$_{2}$As$_{4}$O, which has metallic intermediate Ti$_{2}$O layers, is studied using angle-resolved photoemission spectroscopy. The Ti-related bands show a 'peak-dip-hump' line shape with two branches of dispersion associated with the polaronic states at temperatures below around 120 K. This change in the spectra occurs along with the resistivity anomaly that was not clearly understood in a previous study. Moreover, an energy gap induced by the superconducting proximity effect opens in the polaronic bands at temperatures below $T_{\rm c}$ ($\sim$21 K). Our study provides the spectroscopic evidence that superconductivity coexists with polarons in the same bands near the Fermi level, which provides a suitable platform to study interactions between charge, lattice and spin freedoms in a correlated system.
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Electronic Phase Separation in Iron Selenide (Li,Fe)OHFeSe Superconductor System
Yiyuan Mao, Jun Li, Yulong Huan, Jie Yuan, Zi-an Li, Ke Chai, Mingwei Ma, Shunli Ni, Jinpeng Tian, Shaobo Liu, Huaxue Zhou, Fang Zhou, Jianqi Li, Guangming Zhang, Kui Jin, Xiaoli Dong, Zhongxian Zhao
Chin. Phys. Lett. 2018, 35 (5):
057402
.
DOI: 10.1088/0256-307X/35/5/057402
The phenomenon of phase separation into antiferromagnetic (AFM) and superconducting (SC) or normal-state regions has great implication for the origin of high-temperature (high-$T_{\rm c}$) superconductivity. However, the occurrence of an intrinsic antiferromagnetism above the $T_{\rm c}$ of (Li,Fe)OHFeSe superconductor is questioned. Here we report a systematic study on a series of (Li,Fe)OHFeSe single crystal samples with $T_{\rm c}$ up to $\sim$41 K. We observe an evident drop in the static magnetization at $T_{\rm afm} \sim 125$ K, in some of the SC ($T_{\rm c} \lesssim 38$ K, cell parameter $c \lesssim 9.27$ Å) and non-SC samples. We verify that this AFM signal is intrinsic to (Li,Fe)OHFeSe. Thus, our observations indicate mesoscopic-to-macroscopic coexistence of an AFM state with the normal (below $T_{\rm afm}$) or SC (below $T_{\rm c}$) state in (Li,Fe)OHFeSe. We explain such coexistence by electronic phase separation, similar to that in high-$T_{\rm c}$ cuprates and iron arsenides. However, such an AFM signal can be absent in some other samples of (Li,Fe)OHFeSe, particularly it is never observed in the SC samples of $T_{\rm c} \gtrsim 38$ K, owing to a spatial scale of the phase separation too small for the macroscopic magnetic probe. For this case, we propose a microscopic electronic phase separation. The occurrence of two-dimensional AFM spin fluctuations below nearly the same temperature as $T_{\rm afm}$, reported previously for a (Li,Fe)OHFeSe ($T_{\rm c} \sim 42$ K) single crystal, suggests that the microscopic static phase separation reaches vanishing point in high-$T_{\rm c}$ (Li,Fe)OHFeSe. A complete phase diagram is thus established. Our study provides key information of the underlying physics for high-$T_{\rm c}$ superconductivity.
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Shape Anisotropy and Resonance Mode Guided Reliable Interconnect Design for In-plane Magnetic Logic
Xiao-Kuo Yang, Bin Zhang, Jia-Hao Liu, Ming-Liang Zhang, Wei-Wei Li, Huan-Qing Cui, Bo Wei
Chin. Phys. Lett. 2018, 35 (5):
057501
.
DOI: 10.1088/0256-307X/35/5/057501
Dipole coupled nanomagnets controlled by the static Zeeman field can form various magnetic logic interconnects. However, the corner wire interconnect is often unreliable and error-prone at room temperature. In this study, we address this problem by making it into a reliable type with trapezoid-shaped nanomagnets, the shape anisotropy of which helps to offer the robustness. The building method of the proposed corner wire interconnect is discussed, and both its static and dynamic magnetization properties are investigated. Static micromagnetic simulation demonstrates that it can work correctly and reliably. Dynamic response results are reached by imposing an ac microwave field on the proposed corner wire. It is found that strong ferromagnetic resonance absorption appears at a low frequency. With the help of a very small ac field with the peak resonance frequency, the required static Zeeman field to switch the corner wire is significantly decreased by $\sim$21 mT. This novel interconnect would pave the way for the realization of reliable and low power nanomagnetic logic circuits.
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Curbing Charging Currents in Pulsed Field Emission by Prolonging Pulse Edges
Jin-Di Wei, Yun-Hui Li, Geng-Min Zhang, Jin Yang, Ying-Jie Xing, Wen-Sheng Zhou
Chin. Phys. Lett. 2018, 35 (5):
057901
.
DOI: 10.1088/0256-307X/35/5/057901
In field emission under a non-dc voltage, a displacement current is inevitable due to charging the cathode–anode condenser. Under an often-used square voltage pulse, in which the voltage rises from zero to a certain value abruptly, the charging current in the circuit is very large at the rising and falling edges. This large charging current makes measurement of the actual emissive current from the cathode difficult, constitutes a threat to the components in the circuit and causes attenuation of the emissive current within the pulse. To alleviate these drawbacks, trapezoid voltage pulses, whose rising edges are extended dramatically in comparison with square voltage pulses, are employed to extract the field emission. Under a trapezoid voltage pulse, the charging current is clearly lowered as expected. Furthermore, the heat generated by the charging current under the trapezoid voltage pulse is much smaller than that under the square voltage pulse. Hence the emissive current does not show any attenuation within the pulse. Finally, the average emissive currents are found to decrease with the repetition frequency of the pulses.
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Growth of $\beta$-Ga$_{2}$O$_{3}$ Films on Sapphire by Hydride Vapor Phase Epitaxy
Ze-Ning XIONG, Xiang-Qian XIU, Yue-Wen LI, Xue-Mei HUA, Zi-Li XIE, Peng CHEN, Bin LIU, Ping HAN, Rong ZHANG, You-Dou ZHENG
Chin. Phys. Lett. 2018, 35 (5):
058101
.
DOI: 10.1088/0256-307X/35/5/058101
Two-inch Ga$_{2}$O$_{3}$ films with ($\bar{2}$01)-orientation are grown on $c$-sapphire at 850–1050$^{\circ}\!$C by hydride vapor phase epitaxy. High-resolution x-ray diffraction shows that pure $\beta$-Ga$_{2}$O$_{3}$ with a smooth surface has a higher crystal quality, and the Raman spectra reveal a very small residual strain in $\beta$-Ga$_{2}$O$_{3}$ grown by hydride vapor phase epitaxy compared with bulk single crystal. The optical transmittance is higher than 80% in the visible and near-UV regions, and the optical bandgap energy is calculated to be 4.9 eV.
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Anomaly Detection of Complex Networks Based on Intuitionistic Fuzzy Set Ensemble
Jin-Fa Wang, Xiao Liu, Hai Zhao, Xing-Chi Chen
Chin. Phys. Lett. 2018, 35 (5):
058901
.
DOI: 10.1088/0256-307X/35/5/058901
Ensemble learning for anomaly detection of data structured into a complex network has been barely studied due to the inconsistent performance of complex network characteristics and the lack of inherent objective function. We propose the intuitionistic fuzzy set (IFS)-based anomaly detection, a new two-phase ensemble method for anomaly detection based on IFS, and apply it to the abnormal behavior detection problem in temporal complex networks. Firstly, it constructs the IFS of a single network characteristic, which quantifies the degree of membership, non-membership and hesitation of each network characteristic to the defined linguistic variables so that makes the unuseful or noise characteristics become part of the detection. To build an objective intuitionistic fuzzy relationship, we propose a Gaussian distribution-based membership function which gives a variable hesitation degree. Then, for the fuzzification of multiple network characteristics, the intuitionistic fuzzy weighted geometric operator is adopted to fuse multiple IFSs and to avoid the inconsistence of multiple characteristics. Finally, the score function and precision function are used to sort the fused IFS. Finally, we carry out extensive experiments on several complex network datasets for anomaly detection, and the results demonstrate the superiority of our method to state-of-the-art approaches, validating the effectiveness of our method.
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36 articles
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