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23 results on '"He, Yun"'

6. Effect of Cu doping on the secondary electron yield of carbon films on Ag-plated aluminum alloy

Author

Tiancun Hu, Bai He, Shukai Zhu, Jing Yang, Zhao Yanan, Chunjiang Bai, Xuan Sun, He Yun, Xinbo Wang, Meng Cao, Wanzhao Cui, Ming Liu, Huan Wei, and Zhongqiang Hu

Subjects
Materials science, Carbon film, Yield (engineering), chemistry, Chemical engineering, Aluminium, Cu doping, Alloy, engineering, General Physics and Astronomy, chemistry.chemical_element, engineering.material, Secondary electrons
Abstract

Reducing the secondary electron yield (SEY) of Ag-plated aluminum alloy is important for high-power microwave components. In this work, Cu doped carbon films are prepared and the secondary electron emission characteristics are studied systematically. The secondary electron coefficient δ max of carbon films increases with the Cu contents increasing at first, and then decreases to 1.53 at a high doping ratio of 0.645. From the viewpoint of surface structure, the higher the content of Cu is, the rougher the surface is, since more cluster particles appear on the surface due to the small solid solubility of Cu in the amorphous carbon network. However, from viewpoint of the electronic structure, the reduction of the sp2 hybrid bonds will increase the SEY effect as the content of Cu increases, due to the decreasing probability of collision with free electrons. Thus, the two mechanisms would compete and coexist to affect the SEY characteristics in Cu doped carbon films.

Published
2022

11. Analysis of secondary electron emission using the fractal method*

Author

Chunjiang Bai, Guanghui Miao, Wanzhao Cui, Rui Wang, Na Zhang, He Yun, and Tiancun Hu

Subjects
Materials science, Fractal, Secondary emission, General Physics and Astronomy, Molecular physics
Abstract

Based on the rough surface topography with fractal parameters and the Monte–Carlo simulation method for secondary electron emission properties, we analyze the secondary electron yield (SEY) of a metal with rough surface topography. The results show that when the characteristic length scale of the surface, G, is larger than 1 × 10−7, the surface roughness increases with the increasing fractal dimension D. When the surface roughness becomes larger, it is difficult for entered electrons to escape surface. As a result, more electrons are collected and then SEY decreases. When G is less than 1 × 10−7, the effect of the surface topography can be ignored, and the SEY almost has no change as the dimension D increases. Then, the multipactor thresholds of a C-band rectangular impedance transfer and an ultrahigh-frequency-band coaxial impedance transfer are predicted by the relationship between the SEY and the fractal parameters. It is verified that for practical microwave devices, the larger the parameter G is, the higher the multipactor threshold is. Also, the larger the value of D, the higher the multipactor threshold.

Published
2021

12. Magnetostriction and spin reorientation in ferromagnetic Laves phase Pr(GaxFe1–x)1.9 compounds.

Author

Zeng, Min-Yu, Tang, Qing, Mei, Zhi-Wei, Lu, Cai-Yan, Tang, Yan-Mei, Li, Xiang, He, Yun, and Guo, Ze-Ping

Subjects
NUCLEAR spin, MAGNETOSTRICTION, MAGNETIC fields, PHASE diagrams, MAGNETIZATION, GALLIUM alloys, IRON-manganese alloys
Abstract

The magnetostriction, magnetization, and spin reorientation properties in Pr(GaxFe1 – x)1.9 alloys have been investigated by high-precision x-ray diffraction (XRD) step scanning, magnetization, and Mössbauer spectra measurements. Ga substitution reduces the magnetostriction (λ||) with magnetic field H ≥ 8 kOe (1 Oe = 1.33322 × 102 Pa), but it also increases the λ|| value when H ≤ 8 kOe at 5 K. Spin-reorientations (SR) are observed in all the alloys investigated, as determined by the step scanned XRD, Mössbauer spectra, and the abnormal temperature dependence of magnetization. An increase of the spin reorientation temperature (TSR) due to Ga substitution is found in the phase diagram, which is different from the decrease one in many R(TxFe1 – x)1.9 (T = Co, Al, Mn) alloys. The present work provides a method to control the easy magnetization direction (EMD) or TSR for developing an anisotropic compensation system. [ABSTRACT FROM AUTHOR]

Published
2021
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13. Ferroelectric effect and equivalent polarization charge model of PbZr0.2Ti0.8O3 on AlGaN/GaN MIS-HEMT.

Author

Zhao, Yao-Peng, Wang, Chong, Zheng, Xue-Feng, Ma, Xiao-Hua, Li, Ang, Liu, Kai, He, Yun-Long, Lu, Xiao-Li, and Hao, Yue

Subjects
MODULATION-doped field-effect transistors, FERROELECTRICITY, GALLIUM nitride, INDIUM gallium zinc oxide, TWO-dimensional electron gas, PULSED laser deposition, THRESHOLD voltage
Abstract

PbZr0.2Ti0.8O3 (PZT) gate insulator with the thickness of 30 nm is grown by pulsed laser deposition (PLD) in AlGaN/GaN metal–insulator–semiconductor high electron mobility transistors (MIS-HEMTs). The ferroelectric effect of PZT AlGaN/GaN MIS-HEMT is demonstrated. The polarization charge in PZT varies with different gate voltages. The equivalent polarization charge model (EPCM) is proposed for calculating the polarization charge and the concentration of two-dimensional electron gas (2DEG). The threshold voltage (Vth) and output current density (IDS) can also be obtained by the EPCM. The theoretical values are in good agreement with the experimental results and the model can provide a guide for the design of the PZT MIS-HEMT. The polarization charges of PZT can be modulated by different gate-voltage stresses and the Vth has a regulation range of 4.0 V. The polarization charge changes after the stress of gate voltage for several seconds. When the gate voltage is stable or changes at high frequency, the output characteristics and the current collapse of the device remain stable. [ABSTRACT FROM AUTHOR]

Published
2021
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16. Comparative study on characteristics of Si-based AlGaN/GaN recessed MIS-HEMTs with HfO2 and Al2O3 gate insulators.

Author

Zhao, Yao-Peng, Wang, Chong, Zheng, Xue-Feng, Ma, Xiao-Hua, Liu, Kai, Li, Ang, He, Yun-Long, and Hao, Yue

Subjects
MODULATION-doped field-effect transistors, ATOMIC layer deposition, ELECTRON mobility, THRESHOLD voltage, BREAKDOWN voltage, CHEMICAL stability
Abstract

Two types of enhancement-mode (E-mode) AlGaN/GaN metal–insulator–semiconductor high-electron-mobility transistors (MIS-HEMTs) with different gate insulators are fabricated on Si substrates. The HfO2 gate insulator and the Al2O3 gate insulator each with a thickness of 30 nm are grown by the plasma-enhanced atomic layer deposition (PEALD). The energy band diagrams of two types of dielectric MIS-HEMTs are compared. The breakdown voltage (VBR) of HfO2 dielectric layer and Al2O3 dielectric layer are 9.4 V and 15.9 V, respectively. With the same barrier thickness, the transconductance of MIS-HEMT with HfO2 is larger. The threshold voltage (Vth) of the HfO2 and Al2O3 MIS-HEMT are 2.0 V and 2.4 V, respectively, when the barrier layer thickness is 0 nm. The C–V characteristics are in good agreement with the Vth's transfer characteristics. As the barrier layer becomes thinner, the drain current density decreases sharply. Due to the dielectric/AlGaN interface is very close to the channel, the scattering of interface states will lead the electron mobility to decrease. The current collapse and the Ron of Al2O3 MIS-HEMT are smaller at the maximum gate voltage. As Al2O3 has excellent thermal stability and chemical stability, the interface state density of Al2O3/AlGaN is less than that of HfO2/AlGaN. [ABSTRACT FROM AUTHOR]

Published
2020
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