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Large‐Area Structure‐Selective Synthesis of Symmetry‐Broken MoSe2 and Their Broadband Nonlinear Optical Responseby Joohyeon Ahn, Seongju Ha, Jungseok Choi, Dong‐Il Yeom, Youngdong YooAdvanced Optical Materials 2023, 11(12); https://doi.org/10.1002/adom.202203116AbstractTransition metal dichalcogenides (TMDCs) have various electronic and optical properties depending on their structure, so they can be used as a fascinating material in various applications including photonics, electronics, optoelectronics, and valleytronics. In particular, spiral TMDCs grown through the formation of screw dislocations exhibit novel electronic and optical properties different from layer-by-layer TMDCs. However, large-area structure-selective synthesis of TMDCs remains challenging. Here, this work reports for the first time the large-area structure-selective synthesis of monolayer MoSe2 and spiral MoSe2 using a flux-controlled chemical vapor deposition method. Under a low MoSe2 flux condition, monolayer MoSe2 is synthesized, whereas thick spiral MoSe2 is synthesized under a high flux condition. Under a medium flux condition, both monolayer and spiral MoSe2 are synthesized. In addition, through the nonlinear optical (NLO) signal analysis of monolayer MoSe2 and spiral MoSe2, the giant enhancement of NLO signals induced by the combined effect of breaking inversion symmetry and the excitonic resonance effects in the synthesized MoSe2 is confirmed. Monolayer MoSe2 and spiral MoSe2 synthesized using this method are expected to be used as advanced optical materials for novel electronics, optoelectronics, and NLO applications.
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Special Issue on Nano-Electronic Devices and Functional Applicationsby Chuljin Hwang and Sungjun Parkapplied science 2023, 13(11), 6692; https://doi.org/10.3390/app13116692Nano-electronic devices and materials hold considerable promise due to their inherent structural and material benefits, such as device miniaturization, increased integration density, and reduced power consumption. Streamlined techniques for nano-scale fabrication of these devices and materials, which are compatible with large-scale production and solution processes, help us to further understand their operational mechanisms or their respective formation processes. These advancements have resulted in significant breakthroughs in functional electronic devices, including light-emitting diodes, photodetectors, photovoltaics, transistors, and sensors. In addition, devices that feature flexibility and stretchability offer unprecedented performance for user-friendly electronic applications. This Special Issue is dedicated to discussing the most recent advancements and trends in nano-electronic devices and materials research. It includes a total of seven papers—five original research articles and two review articles as follows.
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Assessment of attenuation of varicella-zoster virus vaccines based on genomic comparisonby Jae Yun Moon, Jina Seo, Jaewoo Lee, Daechan ParkJournal of Medical Virology, 2023, 95(3); https://doi.org/10.1002/jmv.28590AbstractLive attenuated varicella-zoster virus (VZV) vaccines are used to prevent chickenpox and shingles. Single nucleotide polymorphisms (SNPs) that occur during the attenuation of parental strains are critical indicators of vaccine safety. To assess the attenuation of commercial VZV vaccines, genetic variants were comprehensively examined through high-throughput sequencing of viral DNA isolated from four VZV vaccines (Barycela, VarilRix, VariVax, and SKY Varicella). Whole-genome comparison of the four vaccines with the wild-type strain (Dumas) revealed that the sequences are highly conserved on a genome-wide scale. Among the 196 common variants across the four vaccines, 195 were already present in the genome of the parental strain (pOka), indicating that the variants occurred during the generation of the parental strain from the Dumas strain. Compared to the pOka genome, the vaccines exhibited distinct variant frequencies on a genome-wide and within an attenuation-related open reading frame. In particular, attenuation-associated 42 SNPs showed that Barycela, VarilRix, VariVax, and SKY Varicella are in ascending order regarding similarity with pOka-like genotypes, which in turn, might provide genomic evidence for the levels of attenuation. Finally, the phylogenetic network analysis demonstrated that genetic distances from the parental strain correlated with the attenuation levels of the vaccines.
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Terahertz Nondestructive Time-of-flight Imaging with a Large Depth Rangeby Hwan Sik Kim; Jangsun Kim; Yeong Hwan AhnCurrent Optics and Photonics 2022, 6(6), 619-626; https://doi.org/10.3807/COPP.2022.6.6.619 AbstractIn this study, we develop a three-dimensional (3D) terahertz time-of-flight (THz-TOF) imaging technique with a large depth range, based on asynchronous optical sampling (ASOPS) methods. THz-TOF imaging with the ASOPS technique enables rapid scanning with a time-delay span of 10 ns. This means that a depth range of 1.5 m is possible in principle, whereas in practice it is limited by the focus depth determined by the optical geometry, such as the focal length of the scan lens. We characterize the spatial resolution of objects at different vertical positions with a focal length of 5 cm. The lateral resolution varies from 0.8-1.8 mm within the vertical range of 50 mm. We obtain THz-TOF images for samples with multiple reflection layers; the horizontal and vertical locations of the objects are successfully determined from the 2D cross-sectional images, or from reconstructed 3D images. For instance, we can identify metallic objects embedded in insulating enclosures having a vertical depth range greater than 30 mm. For feasible practical use, we employ the proposed technique to locate a metallic object within a thick chocolate bar, which is not accessible via conventional transmission geometry. Keywords: Terahertz spectroscopy and imaging; Three-dimensional imaging
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Study of a deep learning-based method for improving the spectral resolution of the spectral scanning hyperspectral imaging system via synthetic spectral image databy Suhyun Kim; Sera Jung; Jonghee YoonJournal of Physics D: Applied Physics 2023, 56; https://doi.org/10.1088/1361-6463/acae31 AbstractHyperspectral imaging (HSI) techniques, measuring spatial and spectral information, have shown the ability to identify targets based on their spectral features. Among many HSI methods, a spectral scanning HSI method implemented using a tunable filter has been widely used in various applications due to wide-area HSI capability and cost-effectiveness. However, the limitation of the spectral scanning method is poor spectral resolution compared to other spectral imaging methods using dispersive materials. To overcome this limitation, we exploited a recently developed deep-learning model that retrieves multispectral information from an red, green, and blue image. Moreover, this study proposed that a color chart consisting of 18 colors could be a standard target for training the deep-learning model under various spectral scanning HSI conditions. The simulation work was performed to demonstrate the feasibility of the proposed method using synthetic hyperspectral images. Realistic synthetic data was prepared using spectral data obtained via a spectrometer (ground-truth data) and artificial filters emulating a liquid-crystal tunable filter. We found that the deep-learning model trained via a supervised learning approach using synthetic hyperspectral images successfully retrieved high-resolution spectral data. In addition, the trained deep-learning model retrieved robust spectral profiles of random colors which were not used in the training process. Collectively, the deep learning-based spectral scanning method could improve the spectral resolution of the imaging system, and the color chart would be a good and practical standard training target for the deep learning model.
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