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18 pages, 11211 KB

Open AccessArticle

Synthesis of MXene Composites Using Thiourea as a Nitrogen–Sulfur Precursor

by Junming Zhang, Yefeng Feng, Junhao Peng, Kaidan Wu, Zuyong Feng, Miao He, Kunhua Wen and Deping Xiong

Crystals 2025, 15(4), 353; https://doi.org/10.3390/cryst15040353 - 11 Apr 2025

Viewed by 1297

Abstract

In potassium ion electrode materials, MXenes have garnered significant attention in the energy storage field due to their high conductivity and complex surface chemistry. In this work, thiourea was used as a nitrogen–sulfur composite precursor, and a self-assembly method was employed to synthesize a material, named nitrogen–sulfur– MXene (NS-MXene). During the reaction, thiourea molecules attach to the surface and interlayers of MXene, increasing the interlayer spacing. Upon heating, thiourea molecules decompose into nitrogen (N) and sulfur (S), which then combine with the MXene material. The N and S provide additional capacity for potassium ion storage, while the increased interlayer spacing also facilitates the intercalation and deintercalation of K⁺. Use of NS-MXene as anode material for potassium-ion batteries results in a high-rate performance (final capacity of 205.2 mAhg⁻¹ at 0.1 Ag⁻¹), long-term cycling stability (128.5 mAhg⁻¹ at 0.5 Ag⁻¹), and a good specific capacity (141 mAhg⁻¹ at 0.1 Ag⁻¹). This groundbreaking discovery opens the door to investigating MXene-based energy storage materials with superior performance and creates a new standard for MXene derivatives. Full article

(This article belongs to the Section Hybrid and Composite Crystalline Materials)

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16 pages, 13674 KB

Open AccessArticle

Quadruple Plasmon-Induced Transparency and Dynamic Tuning Based on Bilayer Graphene Terahertz Metamaterial

by Jiayu Zhang, Junyi Li, Shuxian Chen, Kunhua Wen and Wenjie Liu

Nanomaterials 2023, 13(17), 2474; https://doi.org/10.3390/nano13172474 - 1 Sep 2023

Cited by 3 | Viewed by 1854

Abstract

This study proposes a terahertz metamaterial structure composed of a silicon–graphene–silicon sandwich, aiming to achieve quadruple plasmon-induced transparency (PIT). This phenomenon arises from the interaction coupling of bright–dark modes within the structure. The results obtained from the coupled mode theory (CMT) calculations align with the simulations ones using the finite difference time domain (FDTD) method. Based on the electric field distributions at the resonant frequencies of the five bright modes, it is found that the energy localizations of the original five bright modes undergo diffusion and transfer under the influence of the dark mode. Additionally, the impact of the Fermi level of graphene on the transmission spectrum is discussed. The results reveal that the modulation depths (MDs) of 94.0%, 92.48%, 93.54%, 96.54%, 97.51%, 92.86%, 94.82%, and 88.20%, with corresponding insertion losses (ILs) of 0.52 dB, 0.98 dB, 1.37 dB, 0.70 dB, 0.43 dB, 0.63 dB, 0.16 dB, and 0.17 dB at the specific frequencies, are obtained, achieving multiple switching effects. This model holds significant potential for applications in versatile modulators and optical switches in the terahertz range. Full article

(This article belongs to the Special Issue Advanced Nanostructure in Terahertz Technology and Applications)

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15 pages, 3884 KB

Open AccessReview

Principles and Applications of Seismic Monitoring Based on Submarine Optical Cable

by Junzhe Yu, Pengbai Xu, Zhangjun Yu, Kunhua Wen, Jun Yang, Yuncai Wang and Yuwen Qin

Sensors 2023, 23(12), 5600; https://doi.org/10.3390/s23125600 - 15 Jun 2023

Cited by 16 | Viewed by 6843

Abstract

Submarine optical cables, utilized as fiber-optic sensors for seismic monitoring, are gaining increasing interest because of their advantages of extending the detection coverage, improving the detection quality, and enhancing long-term stability. The fiber-optic seismic monitoring sensors are mainly composed of the optical interferometer, fiber Bragg grating, optical polarimeter, and distributed acoustic sensing, respectively. This paper reviews the principles of the four optical seismic sensors, as well as their applications of submarine seismology over submarine optical cables. The advantages and disadvantages are discussed, and the current technical requirements are concluded, respectively. This review can provide a reference for studying submarine cable-based seismic monitoring. Full article

(This article belongs to the Special Issue Optic Fiber Sensing Technology for Marine Environment)

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8 pages, 4226 KB

Open AccessCommunication

Facile Preparation of Au–Ag Composite Nanostructure for High-Sensitive and Uniform Surface-Enhanced Raman Spectroscopy

by Wenjie Liu, Zhonghua Yan, Weina Zhang, Kunhua Wen, Bo Sun, Xiaolong Hu and Yuwen Qin

Photonics 2023, 10(4), 354; https://doi.org/10.3390/photonics10040354 - 23 Mar 2023

Cited by 1 | Viewed by 2008

Abstract

Preparation of a high-sensitive and uniform surface-enhanced Raman spectroscopy (SERS) active substrate structure usually faces complex processes and high costs. Here, porous Au–Ag composite nanostructures that are conventional fabricated by the deposition of a multilayer Au–Ag, annealing, and dealloying process are proposed for high-performance SERS. By annealing at a suitable temperature, nanopores could be firmly distributed on the surface, which serves as hot spots. The electric field distribution was also performed by the finite difference time domain. The experiment results exhibited excellent uniformity and high sensitivity of SERS detection. The enhancement factor of the R6G molecules detected by the SERS substrate reached 1.37 × 10⁷, and the relative standard deviation was as low as 4.9%. The minimum detection concentration of R6G molecules by the Au–Ag composite nanostructures with bottom Au mirror could reach 10⁻¹³ M. The proposed Au–Ag composite nanostructures and the fabrication process have great potential in preparation of a high-sensitive and uniform SERS substrate. Full article

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10 pages, 2461 KB

Open AccessArticle

A Plasmonic Chip-Scale Refractive Index Sensor Design Based on Multiple Fano Resonances

by Kunhua Wen, Li Chen, Jinyun Zhou, Liang Lei and Yihong Fang

Sensors 2018, 18(10), 3181; https://doi.org/10.3390/s18103181 - 20 Sep 2018

Cited by 36 | Viewed by 3745

Abstract

In this paper, multiple Fano resonances preferred in the refractive index sensing area are achieved based on sub-wavelength metal-insulator-metal (MIM) waveguides. Two slot cavities, which are placed between or above the MIM waveguides, can support the bright modes or the dark modes, respectively. Owing to the mode interferences, dual Fano resonances with obvious asymmetrical spectral responses are achieved. High sensitivity and high figure of merit are investigated by using the finite-difference time-domain (FDTD) method. In view of the development of chip-scale integrated photonics, two extra slot cavities are successively added to the structure, and consequently, three and four ultra-sharp Fano peaks with considerable performances are obtained, respectively. It is believed that this proposed structure can find important applications in the on-chip optical sensing and optical communication areas. Full article

(This article belongs to the Section Physical Sensors)

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9 pages, 2871 KB

Open AccessArticle

Plasmonic Multichannel Refractive Index Sensor Based on Subwavelength Tangent-Ring Metal–Insulator–Metal Waveguide

by Zicong Guo, Kunhua Wen, Qinyang Hu, Wenhui Lai, Jiyan Lin and Yihong Fang

Sensors 2018, 18(5), 1348; https://doi.org/10.3390/s18051348 - 26 Apr 2018

Cited by 86 | Viewed by 5002

Abstract

In this paper, a multichannel refractive index sensor based on a subwavelength metal–insulator–metal (MIM) waveguide coupled with tangent-ring resonators is proposed. When two tangent-ring resonators were placed above the MIM waveguide, Fano resonance with asymmetrical line shape appeared in the transmission spectrum due to the interference between the light–dark resonant modes. The sensitivity and figure of merit were as high as 880 nm/RIU and 964, respectively. Through adding more tangent-ring resonators, multiple Fano resonances with ultrasharp peaks/dips were achieved in the wavelength range of 800–2000 nm. Besides, negative group delays were also observed in the Fano resonant dips. Two-dimensional finite-difference time-domain (FDTD) method was used to simulate and analyze the performances of the proposed structures. These kinds of multiring structures can find important applications in the on-chip optical sensing and optical communication areas. Full article

(This article belongs to the Section Physical Sensors)

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