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4. Nonvolatile infrared memory in MoS2/PbS van der Waals heterostructures.

Author

Wang, Qisheng, Wen, Yao, Cai, Kaiming, Cheng, Ruiqing, Yin, Lei, Zhang, Yu, Li, Jie, Wang, Zhenxing, Wang, Feng, Wang, Fengmei, Shifa, Tofik Ahmed, Jiang, Chao, Yang, Hyunsoo, and He, Jun

Abstract

Optoelectronic devices for information storage and processing are at the heart of optical communication technology due to their significant applications in optical recording and computing. The infrared radiations of 850, 1310, and 1550 nm with low energy dissipation in optical fibers are typical optical communication wavebands. However, optoelectronic devices that could convert and store the infrared data into electrical signals, thereby enabling optical data communications, have not yet been realized. We report an infrared memory device using MoS2/PbS van der Waals heterostructures, in which the infrared pulse intrigues a persistent resistance state that hardly relaxes within our experimental time scales (more than 104 s). The device fully retrieves the memory state even after powering off for 3 hours, indicating its potential for nonvolatile storage devices. Furthermore, the device presents a reconfigurable switch of 2000 stable cycles. Supported by a theoretical model with quantitative analysis, we propose that the optical memory and the electrical erasing phenomenon, respectively, originate from the localization of infrared-induced holes in PbS and gate voltage pulse-enhanced tunneling of electrons from MoS2 to PbS. The demonstrated MoS2 heterostructure-based memory devices open up an exciting field for optoelectronic infrared memory and programmable logic devices.

Published
2018

12. Facile Electron Transfer in Atomically Coupled Heterointerface for Accelerated Oxygen Evolution

Author

Ibrahim, Kassa Belay, Shifa, Tofik Ahmed, Moras, Paolo, Moretti, Elisa, Vomiero, Alberto, Ibrahim, Kassa Belay, Shifa, Tofik Ahmed, Moras, Paolo, Moretti, Elisa, and Vomiero, Alberto

Abstract

An efficient and cost-effective approach for the development of advanced catalysts has been regarded as a sustainable way for green energy utilization. The general guideline to design active and efficient catalysts for oxygen evolution reaction (OER) is to achieve high intrinsic activity and the exposure of more density of the interfacial active sites. The heterointerface is one of the most attractive ways that plays a key role in electrochemical water oxidation. Herein, atomically cluster-based heterointerface catalysts with strong metal support interaction (SMSI) between WMn2O4 and TiO2 are designed. In this case, the WMn2O4 nanoflakes are uniformly decorated by TiO2 particles to create electronic effect on WMn2O4 nanoflakes as confirmed by X-ray absorption near edge fine structure. As a result, the engineered heterointerface requires an OER onset overpotential as low as 200 mV versus reversible hydrogen electrode, which is stable for up to 30 h of test. The outstanding performance and long-term durability are due to SMSI, the exposure of interfacial active sites, and accelerated reaction kinetics. To confirm the synergistic interaction between WMn2O4 and TiO2, and the modification of the electronic structure, high-resolution transmission electron microscopy (HR-TEM), X-ray photoemission spectroscopy (XPS), and X-ray absorption spectroscopy (XAS) are used., Validerad;2023;Nivå 2;2023-03-08 (joosat);Licens fulltext: CC BY License

Published
2023
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13. Confinement Accelerates Water Oxidation Catalysis : Evidence from In Situ Studies

Author

Ibrahim, Kassa Belay, Shifa, Tofik Ahmed, Bordin, Matteo, Moretti, Elisa, Wu, Heng-Liang, Vomiero, Alberto, Ibrahim, Kassa Belay, Shifa, Tofik Ahmed, Bordin, Matteo, Moretti, Elisa, Wu, Heng-Liang, and Vomiero, Alberto

Abstract

Basic insight into the structural evolution of electrocatalysts under operating conditions is of substantial importance for designing water oxidation catalysts. The first-row transition metal-based catalysts present state-of-the-art oxygen evolution reaction (OER) performance under alkaline conditions. Apparently, confinement has become an exciting strategy to boost the performance of these catalysts. The van der Waals (vdW) gaps of transition metal dichalcogenides are acknowledged to serve as a suitable platform to confine the first-row transition metal catalysts. This study focuses on confining Ni(OH)2 nanoparticle in the vdW gaps of 2D exfoliated SnS2 (Ex-SnS2) to accelerate water oxidation and to guarantee long term durability in alkaline solutions. The trends in oxidation states of Ni are probed during OER catalysis. The in situ studies confirm that the confined system produces a favorable environment for accelerated oxygen gas evolution, whereas the un-confined system proceeds with a relatively slower kinetics. The outstanding OER activity and excellent stability, with an overpotential of 300 mV at 100 mA cm−2 and Tafel slope as low as 93 mV dec−1 results from the confinement effect. This study sheds light on the OER mechanism of confined catalysis and opens up a way to develop efficient and low-cost electrocatalysts., Validerad;2023;Nivå 2;2023-11-02 (joosat);Funder: MOST (Ministry of Science and Technology) Taiwan (Contract nos. 110-2113-M-002 -019 -MY3)Licens fulltext: CC BY-NC License

Published
2023
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15. Kinetics, isotherm, mechanism, and recyclability of novel nano-sized Ce4+-doped Ni–Al layered double hydroxide for defluoridation of aqueous solutions.

Author

Wagassa, Ararso Nagari, Shifa, Tofik Ahmed, Bansiwal, Amit, and Zereffa, Enyew Amare

Subjects
LAYERED double hydroxides, WASTE recycling, AQUEOUS solutions, ADSORPTION isotherms, ADSORPTION capacity, HYDROGEN bonding
Abstract

Excessive fluoride removal from aqueous solutions is of utmost importance as it has an adverse impact on human health. This study investigates the defluoridation efficiency of a novel nano-sized Ce+4-doped Ni/Al layered double hydroxide (Ni–Al-Ce LDH) for aqueous solutions. The synthesized Ni–Al-Ce LDH exhibited a well-defined nanoscale plate-like morphology and a high surface area with an average size of 11.51 nm, which contributed to its enhanced fluoride adsorption capacity. XRD, SEM, HRTEM, and BET studies confirmed these characteristics. XPS analysis confirmed the presence of Ce4+ ions within the Ni–Al LDH. The experimental results indicated that the process of defluoridation followed a pseudo-second-order model of kinetics, suggesting a chemisorption mechanism. The fluoride adsorption isotherms demonstrated well fits to the Freundlich, Langmuir, and Jovanovic models, indicating both monolayer and multilayer fluoride adsorption on the Ce-doped Ni–Al LDH. The maximum adsorption capacity was found to be 238.27 mg/g (Langmuir) and 130.73 mg/g (Jovanovic) at pH 6.0 and 25 °C. The proposed mechanisms for fluoride adsorption on the LDH include ion exchange, surface complexation, hydrogen bonding, and ligand exchange. The Ni–Al-Ce LDH nanomaterial exhibited good recyclability, maintaining 71% of the fluoride adsorption efficiency even after four consecutive cycles. This study highlights the significant role of Ce doping in improving the performance of Ni–Al LDH as a defluoridation adsorbent. [ABSTRACT FROM AUTHOR]

Published
2023
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26. Ultrathin Magnetic 2D Single‐Crystal CrSe

Author

Zhang, Yu, primary, Chu, Junwei, additional, Yin, Lei, additional, Shifa, Tofik Ahmed, additional, Cheng, Zhongzhou, additional, Cheng, Ruiqing, additional, Wang, Feng, additional, Wen, Yao, additional, Zhan, Xueying, additional, Wang, Zhenxing, additional, and He, Jun, additional

Published
2019
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29. Few-layered CuInP2S6 nanosheet with sulfur vacancy boosting photocatalytic hydrogen evolution.

Author

Yu, Peng, Wang, Fengmei, Meng, Jun, Shifa, Tofik Ahmed, Sendeku, Marshet Getaye, Fang, Ju, Li, Shuxian, Cheng, Zhongzhou, Lou, Xiaoding, and He, Jun

Subjects
HYDROGEN evolution reactions, SULFUR, SOLAR energy conversion, INTERSTITIAL hydrogen generation, HYDROGEN, LIGHT absorption
Abstract

Photochemical water splitting offers an economic and sustainable approach for solar energy conversion into hydrogen fuel to mitigate the problem of greenhouse gas emissions. To this end, exploring novel semiconductor photocatalysts, which have efficient light absorption and thermodynamically favorable band alignment for water splitting, is crucial. Here, we rationally develop a new photocatalyst of CuInP2S6 nanosheets to generate hydrogen gas under light illumination. The CuInP2S6 nanosheet (with a thickness of around 4–7 nm) photocatalyst exhibits a high hydrogen production rate of 804 μmol g−1 h−1, eight times higher than that of the microsheet counterpart, due to the introduced abundant sulfur vacancies. Experimental characterization and theoretical calculations verify that the prolonged carrier lifetime and optimized band alignment in ultrathin CuInP2S6 nanosheets boost photocatalytic hydrogen evolution. This work opens a new avenue for photocatalysis via using novel layered binary metal phosphorous trichalcogenides. [ABSTRACT FROM AUTHOR]

Published
2021
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34. Nonvolatile infrared memory in MoS 2 /PbS van der Waals heterostructures

Author

Wang, Qisheng, primary, Wen, Yao, additional, Cai, Kaiming, additional, Cheng, Ruiqing, additional, Yin, Lei, additional, Zhang, Yu, additional, Li, Jie, additional, Wang, Zhenxing, additional, Wang, Feng, additional, Wang, Fengmei, additional, Shifa, Tofik Ahmed, additional, Jiang, Chao, additional, Yang, Hyunsoo, additional, and He, Jun, additional

Published
2018
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41. Strongly coupled van der Waals heterostructures for high-performance infrared phototransistor.

Author

Wang, Zhenxing, He, Jun, Cheng, Ruiqing, Yin, Lei, Wang, Feng, Li, Jie, Shifa, Tofik Ahmed, Li, Ningning, Wen, Yao, and Feng, Liping

Subjects
VAN der Waals forces, HETEROSTRUCTURES, PHOTOTRANSISTORS, RAMAN effect, PHOTOLUMINESCENCE
Abstract

The interfacial coupling in van der Waals (vdWs) heterostructures can effectively modulate the device performance. In this study, we demonstrate a high performance infrared detector fabricated by direct epitaxial growth of Te nanowires onto a MoS2 monolayer. Such directly grown Te/MoS2 heterostructures show much stronger interfacial coupling than artificially transferred Te/MoS2 hybrids, as evidenced from their Raman and photoluminescence spectra. The strong vdWs interfacial coupling leads to a high performance infrared detector with both ultrahigh photoresponsivity (>103 A/W) and rapid response time (τrising = 15 ms) at the telecommunication wavelength of 1550 nm. The anti-bipolar and rectification behaviors observed in the strongly coupled grown Te-MoS2 heterojunction further confirm the effective interfacial coupling. In contrast, the weakly coupled transferred Te-MoS2 heterojunction that is obtained by artificial transfer exhibits negligible anti-bipolar behavior and slight rectification behavior. These findings indicate that the coupled vdWs hybrid structures have great potential for achieving high performance photodetectors. [ABSTRACT FROM AUTHOR]

Published
2019
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48. Integrated High-Performance Infrared Phototransistor Arrays Composed of Nonlayered PbS–MoS2 Heterostructures with Edge Contacts

Author

Wen, Yao, primary, Yin, Lei, additional, He, Peng, additional, Wang, Zhenxing, additional, Zhang, XianKun, additional, Wang, Qisheng, additional, Shifa, Tofik Ahmed, additional, Xu, Kai, additional, Wang, Fengmei, additional, Zhan, Xueying, additional, Wang, Feng, additional, Jiang, Chao, additional, and He, Jun, additional

Published
2016
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50. Epitaxial 2D PbS Nanoplates Arrays with Highly Efficient Infrared Response

Author

Wen, Yao, primary, Wang, Qisheng, additional, Yin, Lei, additional, Liu, Qi, additional, Wang, Feng, additional, Wang, Fengmei, additional, Wang, Zhenxing, additional, Liu, Kaili, additional, Xu, Kai, additional, Huang, Yun, additional, Shifa, Tofik Ahmed, additional, Jiang, Chao, additional, Xiong, Jie, additional, and He, Jun, additional

Published
2016
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