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120. Catalytic performance of binary transition metal sulfide FeCoS2/rGO for lithium–sulfur batteries.

Author

Gan, Tian, Wang, Jin, Liao, Yunlong, Lin, Zhiping, and Wu, Fugen

Subjects
METAL sulfides, TRANSITION metals, TRANSITION metal oxides, LITHIUM sulfur batteries, ELECTRON density, BINDING energy, CATALYTIC activity
Abstract

The FeCoS2/rGO was synthesized by a one-step hydrothermal method, which has the advantages of environmental friendliness and low cost. Dense and homogeneous FeCoS2 nanodots are dispersed in the reduced graphene oxide flakes, which is beneficial to improve catalytic activity. Compared with FeS2/rGO, FeCoS2/rGO exhibits much higher initial discharge capacity and much better capacity retention ratio. The lower activation energy and the relatively narrow peak shape and small reduction/oxidation peak spacing show that FeCoS2/rGO have better catalytic activity than FeS2/rGO. It can be also confirmed by first-principles calculation that the adsorption energy of the Fe site (− 1.8334 eV) and the Co site (− 1.7539 eV) on the FeCoS2 surface is better than that of FeS2. So, the synergistic reaction of Fe and Co will adjust microregional electron density and change binding energy to polysulfides. [ABSTRACT FROM AUTHOR]

Published
2023
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121. Prediction of the hardest BiFeO3 from first-principles calculations.

Author

Zhang, Runqing, Bai, Lingling, Xie, Xing, Hu, Peiju, Wu, Ziqiao, Dong, Huafeng, Wen, Minru, and Wu, Fugen

Abstract

BiFeO3 is the only material with ferroelectric Curie temperature and Néel temperature higher than room temperature, making it one of the most well-studied multiferroic materials. Based on an ab initio evolutionary algorithm, we predicted a new cubic C-type antiferromagnetic structure (Fd3¯m-BiFeO3) at ambient pressure. It was found that Fd3¯m-BiFeO3 is the hardest BiFeO3 (Vickers hardness ∼ 9.12 GPa), about 78% harder than R3c-BiFeO3 (the well-known multiferroic material), which contributes to extending the life of BiFeO3 devices. In addition, Fd3¯m-BiFeO3 has the largest shear modulus (83.74 GPa) and the largest Young's modulus (214.72 GPa). Besides, we found an interesting phenomenon that among the common multiferroic materials (BiFeO3, BaTiO3, PbTiO3, SrRuO3, KNbO3, and BiMnO3), Pnma-BiMnO3 has the largest bulk modulus, and its bulk modulus is about 15% larger than that of Fd3¯m-BiFeO3. However, its Vickers hardness (4.47 GPa) is much smaller than that of Fd3¯m-BiFeO3. This is because the Vickers hardness is proportional to the shear modulus and the shear modulus of Fd3¯m-BiFeO3 is larger than that of Pnma-BiMnO3. This work provides a deeper and more comprehensive understanding of BiFeO3. [ABSTRACT FROM AUTHOR]

Published
2023
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127. New multiferroic BiFeO3 with large polarization

Author

Zhang, Runqing, primary, Hu, Peiju, additional, Bai, Lingling, additional, Xie, Xing, additional, Dong, Huafeng, additional, Wen, Minru, additional, Mu, Zhongfei, additional, Zhang, Xin, additional, and Wu, Fugen, additional

Published
2022
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138. Robust Deposition of Sub‐Millimeter WSe2 Drive Ultrasensitive Gate‐Tunable 2D Material Photodetectors.

Author

Yang, Mengmeng, Luo, Zhongtong, Gao, Wei, Zhang, Menglong, Huang, Le, Zhao, Yu, Yao, Jiandong, Wu, Fugen, Li, Jingbo, and Zheng, Zhaoqiang

Subjects
PHOTODETECTORS, OPTOELECTRONIC devices, PHOTOSENSITIVITY, OPTOELECTRONICS, PASSIVATION
Abstract

2D semiconductors are regarded as the potential channel materials for high‐performance integrated optoelectronics. However, the absence of an effective photoconductive gain mechanism and the adverse effects from traditional SiO2 substrate prevent the further breakthrough of the photosensitivity of 2D semiconductors‐based photodetectors. Here, an ingenious out‐of‐plane heterostructure is proposed for boosting the photosensitivity. Sub‐millimeter scale (>700 µm) tri‐layer WSe2 with high quality and uniformity is robustly deposited and integrated with 2D photosensitive channels for gate‐tunable photodetection. The WSe2 with naturally passivated surface can not only serve as a substrate passivation layer to mitigate the detrimental substrate effects, but also introduces vertical built‐in fields, which efficiently separates the photogenerated carriers and produces high photoconductive gain. Under gate voltage modulation, the proposed InSe photodetector exhibits a series of excellent performances, including responsivity of 112 A W−1, detectivity of 8.6 × 1012 Jones, light on/off ratio of 1.3 × 104 and rise/decay time of 29.1/15.3 ms. More inspiringly, this heterostructure scheme is universally applicable to 2D WS2 photodetector and also significantly improves its photosensitivity, demonstrating broad applicability. This research will provide helpful guidance for the design and optimization of customizable optoelectronic devices based on 2D semiconductors. [ABSTRACT FROM AUTHOR]

Published
2022
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139. A Cost-Effective Long-Wave Infrared Detector Material Based on Graphene@PtSe 2 /HfSe 2 Bidirectional Heterostructure: A First-Principles Study.

Author

Zhang, Jianzhi, Huang, Hongfu, Peng, Junhao, Li, Chuyu, Dong, Huafeng, Kong, Sifan, Xie, Yiyuan, Wu, Runqian, Wen, Minru, and Wu, Fugen

Subjects
BAND gaps, INFRARED detectors, LIGHT absorption, HETEROSTRUCTURES, INFRARED absorption, OPTICAL properties
Abstract

The Graphene@PtSe2 heterostructure is an excellent long-wave infrared detection material. However, the expensive cost of PtSe2 prevents its widespread use in infrared detection. In this paper, Hf was used to partially replace Pt to form Graphene@(PtSe2)n(HfSe2)4−n (n = 1, 2, and 3) bidirectional heterostructures consisting of graphene and lateral PtSe2/HfSe2 composites based on first-principles calculations. Then, the new bidirectional heterostructures were compared with heterostructures formed by graphene with pure MSe2 (M = Pt, Hf). It was found that the band gaps of the bidirectional heterostructures were between those of Graphene@PtSe2 and Graphene@HfSe2. Among these heterostructures, the Graphene@(PtSe2)3(HfSe2)1 bidirectional heterostructure has almost the same optical absorption properties in the infrared wavelength region of 1.33~40 µm as the Graphene@PtSe2 heterostructure, and it improves the absorption in the near-infrared wavelength region of 0.75~1.33 µm. Such a designment may bring the material costs down (since PtSe2 costs approximately five times more than HfSe2). This study on the designment of the bidirectional Graphene@(PtSe2)3(HfSe2)1 heterostructure also illustrates a cost-effective design method for Pt-based IR detectors. [ABSTRACT FROM AUTHOR]

Published
2022
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145. SiC IGBT degradation mechanism investigation under HV-H3TRB tests

Author

Wu, Ziming, Dai, Zongbei, Zhou, Jian, Dong, Huafeng, Wang, Wencan, Xie, Feiwan, Wang, Haoran, Yan, Jiahui, Chen, Xiyu, Yang, Shaohua, and Wu, Fugen

Abstract

The high voltage–high humidity–high temperature reverse bias (HV-H3TRB) test was utilized to evaluate the reliability of silicon carbide insulated gate bipolar transistors (SiC IGBTs). Moisture invasion often induces termination/passivation and metal corrosion. Therefore, the HV-H3TRB test is generally used to assess termination / passivation robustness. However, under the HV-H3TRB test conditions, gate quality degradation may occur. In this study, the dominant degradation mechanism of SiC IGBTs was investigated. The changes of the most sensitive static characteristics (e.g., threshold voltage, breakdown voltage, and leakage current) were recorded. The threshold voltage decreased and leakage current increased substantially after > 1000 h of HV-H3TRB tests under 85 ℃/85% RH climate conditions. Capacitance–voltage (C–V) curve measurements indicated that the mobile ions at the SiC/SiO2interface or in the gate oxide likely caused the threshold-voltage instability in the SiC IGBTs after the HV-H3TRB tests. This instability can be recovered by applying a negative gate bias. Subsequent failure analysis confirmed no corrosion of metals or termination/passivation in the device, which indicates the robustness of the passivation (consisting of phosphor-silicate glass and Si3N4). Therefore, the gate quality appears to be a significant reliability risk for SiC IGBTs under high humidity, high temperature, and high voltage conditions.

Published
2023
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