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Exciton-Exciton Interactions in Van der Waals Heterobilayers

Physical Review X 2024年第3期14卷 031025-031025页

作者： Alexander Steinhoff Edith Wietek Matthias Florian Tommy Schulz Takashi Taniguchi Kenji Watanabe Shen Zhao Alexander Högele Frank Jahnke Alexey Chernikov Institut für Theoretische Physik Bremen Center for Computational Materials Science Institute of Applied Physics and Würzburg-Dresden Cluster of Excellence ct.qmat Department of Electrical Engineering and Computer Science Research Center for Materials Nanoarchitectonics Research Center for Electronic and Optical Materials Fakultät für Physik Munich Quantum Center and Center for NanoScience (CeNS) Munich Center for Quantum Science and Technology (MCQST) 80799 München Germany

Exciton-exciton interactions are key to understanding nonlinear optical and transport phenomena in van der Waals heterobilayers, which emerged as versatile platforms to study correlated electronic states. We present a combined theory-experiment study of excitonic many-body effects based on first-principle band structures and Coulomb interaction matrix elements. Key to our approach is the explicit treatment of the fermionic substructure of excitons and dynamical screening effects for density-induced energy renormalization and dissipation. We demonstrate that dipolar blueshifts are almost perfectly compensated by many-body effects, mainly by screening-induced self-energy corrections. Moreover, we identify a crossover between attractive and repulsive behavior at elevated exciton densities. Theoretical findings are supported by experimental studies of spectrally narrow, mobile interlayer excitons in atomically reconstructed, h-BN-encapsulated MoSe2/WSe2 heterobilayers. Both theory and experiment show energy renormalization on a scale of a few meV even for high injection densities in the vicinity of the Mott transition. Our results revise the established picture of dipolar repulsion dominating exciton-exciton interactions in van der Waals heterostructures and open up opportunities for their external design.

关键词： Excitons First-principles calculations Luminescence 2-dimensional systems Quantum many-body systems Many-body techniques

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Skin-like cryogel electronics from suppressed-freezing tuned polymer amorphization

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Nature Communications 2023年第1期14卷 1-10页

作者： Zhang, Xiansheng Yan, Hongwei Xu, Chongzhi Dong, Xia Wang, Yu Fu, Aiping Li, Hao Lee, Jin Yong Zhang, Sheng Ni, Jiahua Gao, Min Wang, Jing Yu, Jinpeng Ge, Shuzhi Sam Jin, Ming Liang Wang, Lili Xia, Yanzhi State Key Laboratory of Bio-Fibers and Eco-Textiles College of Textiles and Clothing Qingdao University Qingdao 266071 China Institute for Future Shandong Key Laboratory of Industrial Control Technology School of Automation Qingdao University Qingdao 266071 China College of Materials Science and Engineering Qingdao University Qingdao 266071 China CAS Key Laboratory of Engineering Plastics Institute of Chemistry Chinese Academy of Sciences Beijing 100190 China Department of Chemistry SungKyunKwan University Suwon 16419 South Korea State Key Laboratory of Fluid Power and Mechatronic Systems College of Mechanical Engineering Zhejiang University Hangzhou 310027 China College of Biological Science and Medical Engineering Donghua University Shanghai 201620 China Institute of Environmental Engineering ETH Zürich Zürich 8093 Switzerland Department of Electrical and Computer Engineering National University of Singapore Singapore 117576 Singapore

The sole situation of semi-crystalline structure induced single performance remarkably limits the green cryogels in the application of soft devices due to uncontrolled freezing field. Here, a facile strategy for achieving multifunctionality of cryogels is proposed using total amorphization of polymer. Through precisely lowering the freezing point of precursor solutions with an antifreezing salt, the suppressed growth of ice is achieved, creating an unusually weak and homogenous aggregation of polymer chains upon freezing, thereby realizing the tunable amorphization of polymer and the coexistence of free and hydrogen bonding hydroxyl groups. Such multi-scale microstructures trigger the integrated properties of tissue-like ultrasoftness (Young’s modulus <10 kPa) yet stretchability, high transparency (~92%), self-adhesion, and instantaneous self-healing (<0.3 s) for cryogels, along with superior ionic-conductivity, antifreezing (−58 °C) and water-retention abilities, pushing the development of skin-like cryogel electronics. These concepts open an attractive branch for cryogels that adopt regulated crystallization behavior for on-demand functionalities. © 2023, Springer Nature Limited.

关键词： Gels and hydrogels Polymers

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57 GHz Acoustic Resonator with k2 of 7.3 % and Q of 56 in Thin-Film Lithium Niobate

57 GHz Acoustic Resonator with k2 of 7.3 % and Q of 56 in Th...

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International Electron Devices Meeting (IEDM)

作者： Jack Kramer Sinwoo Cho Michael E. Liao Kenny Huynh Omar Barrera Lezli Matto Mark S. Goorsky Ruochen Lu Department of Electrical and Computer Engineering The University of Texas at Austin Austin TX USA Department of Materials Science & Engineering University of California Los Angeles CA USA

ISBN: (纸本)9781665489607

This paper reports an acoustic resonator at 57 GHz with a high electromechanical coupling $(k^{2})$ of 7.3% and 3-dB quality factor (Q) of 56, collectively enabling a record-breaking Figure of merit $(\mathrm{F}\mathrm{o}\mathrm{M},\ Q\cdot k^{2})$ of 4.1, an order of magnitude higher than the state-of-the-art acoustic resonators. The device leverages the third-order antisymmetric (A3) Lamb mode in 110 nm 128°Y-cut lithium niobate (LiNbO 3 ) piezoelectric thin film. A new film stack, namely transferred thin-film LiNbO 3 on sapphire substrate with an intermediate amorphous silicon (Si) layer, facilitates the record-breaking performance at millimeter-wave (mmWave). The acoustic resonator features a compact footprint of 0.006 $\mathrm{m}\mathrm{m}^{2}$. Acoustic design consideration is reported. The thickness of the $\mathrm{L}\mathrm{i}\mathrm{N}\mathrm{b}\mathrm{O}_{3}$ was measured with X-ray diffraction and verified with cross-sectional electron microscopy images. Triple-axis rocking curves confirm the $\mathrm{L}\mathrm{i}\mathrm{N}\mathrm{b}\mathrm{O}_{3}$ crystalline quality is higher than prior transferred $\mathrm{L}\mathrm{i}\mathrm{N}\mathrm{b}\mathrm{O}_{3}$ layers on Si. Upon further development, the reported platform can enable various signal processing functions at mmWave.

关键词： Radio frequency Q-factor Lithium niobate Resonator filters Resonant frequency X-ray diffraction Acoustics

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Deep Learning Approach for Classifying Contamination Levels with Limited Samples 27

Deep Learning Approach for Classifying Contamination Levels ...

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IS and T International Symposium on Electronic Imaging: 27th Color Imaging: Displaying, Processing, Hardcopy, and Applications, COLOR 2022

作者： Zhao, Min Diaz-Amaya, Susana Deering, Amanda J. Stanciu, Lia Chiu, George T.-C. Allebach, Jan P. School of Electrical and Computer Engineering Purdue University West LafayetteIN United States R&D|Sustainability & Outreach - Bayer at Convergence - Bayer Crop Science West LafayetteIN United States Department of Food Science Purdue University West LafayetteIN United States School of Materials Engineering Purdue University West LafayetteIN United States School of Mechanical Engineering Purdue University West LafayetteIN United States

The detection of the contaminants in daily food and drinking water is crucial for global public health. For heavy metals detection of Mercury (Hg) and Arsenic (As), our group has proposed a novel paper-based and microfluidic device integrated with a mobile phone and an image analysis pipeline to capture and analyze the sensor images on-site. Still, the detection of lower contamination levels remains challenging due to the small number of available data samples and large intra-class variance of our application. To overcome this challenge, we explore traditional data augmentation and GAN-based augmentation techniques for synthesizing realistic colorimetric images;and we propose a CNN classifier for five-contamination-levels classification. Our proposed system is trained and evaluated on a limited dataset of 126 phone captured images of five contamination levels. Our system yields 88.1% classification accuracy and 91.92% precision, demonstrating the feasibility of this approach. We believe that this approach of training deep learning models on limited detection images datasets presents a clear path toward phone-based contamination-levels detection. © 2022, Society for Imaging science and Technology.

关键词： Potable water

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Integration of fullerenes and carbon nanotubes with aggressively scaled CMOS gate stacks

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MRS Online Proceedings Library 2021年第1期789卷 205-210页

作者： Udayan Ganguly Chungho Lee Edwin C. Kan Department of Materials Science and Engineering Cornell University USA School of Electrical and Computer Engineering Cornell University USA

Here we report the first study towards the integration of fullerenes and carbon nanotubes (CNT) in the gate stack of CMOS technology, which is a promising hybrid approach of top-down and bottom-up fabrication process. Prospective processes for C60 and CNT deposition over an aggressively scaled 2 nm gate oxide in the MOS capacitor structure have been monitored. CV measurements show minimal silicon contamination and interface states. Step charging at a specific voltage that corresponds to a fixed number density of C60 is used to establish the structural integrity and size-mono-dispersion of C60. The CV method can be further used to probe the charge injection into C60 and its anions to establish fundamental understanding of their molecular orbital (MO) structure.

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Purcell-enhanced X-ray Imaging in Ultra-thin Scintillators

Purcell-enhanced X-ray Imaging in Ultra-thin Scintillators

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Conference on Lasers and Electro-Optics (CLEO)

作者： Roman Schuetz Yaniv Kurman Neta Lahav Avner Shultzman Charles Roques-Carmes Alon Lifshits Segev Zaken Rotem Strassberg Orr Be’Er Yehonadav Bekenstein Ido Kaminer Department of Electrical and Computer Engineering Technion - Israel Institute of Technology Haifa Israel Department of Materials Science and Engineering Technion - Israel Institute of Technology Haifa Israel Research Laboratory of Electronics Massachusetts Institute of Technology Cambridge MA USA

We demonstrate improved X-ray imaging using nanophotonic scintillators. Our scintillators rely on Purcell enhancement for brighter and faster emission. Applying this concept in radiology and nuclear medicine could ena... 详细信息

ISBN: (纸本)9781957171258

关键词： Positron emission tomography Purcell effect Spatial frequency Spontaneous emission X ray imaging X rays

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Accelerating Wireless Federated Learning via Nesterov's Momentum and Distributed Principle Component Analysis

arXiv

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arXiv 2023年

作者： Dong, Yanjie Wang, Luya Chi, Yuanfang Wang, Jia Zhang, Haijun Yu, Fei Richard Leung, Victor C.M. Hu, Xiping The Faculty of Engineering Shenzhen MSU-BIT University Shenzhen China The College of Computer Science and Software Engineering Shenzhen University Shenzhen China Beijing Advanced Innovation Center for Materials Genome Engineering Beijing Engineering and Technology Research Center for Convergence Networks and Ubiquitous Services Institute of Artificial Intelligence University of Science and Technology Beijing Beijing China The Department of Systems and Computer Engineering Carleton University Ottawa Canada The Department of Electrical and Computer Engineering The University of British Columbia Vancouver Canada

A wireless federated learning system is investigated by allowing a server and workers to exchange uncoded information via orthogonal wireless channels. Since the workers frequently upload local gradients to the server via bandwidth-limited channels, the uplink transmission from the workers to the server becomes a communication bottleneck. Therefore, a one-shot distributed principle component analysis (PCA) is leveraged to reduce the dimension of uploaded gradients such that the communication bottleneck is relieved. A PCA-based wireless federated learning (PCA-WFL) algorithm and its accelerated version (i.e., PCA-AWFL) are proposed based on the low-dimensional gradients and the Nesterov's momentum. For the non-convex loss functions, a finite-time analysis is performed to quantify the impacts of system hyper-parameters on the convergence of the PCA-WFL and PCA-AWFL algorithms. The PCA-AWFL algorithm is theoretically certified to converge faster than the PCA-WFL algorithm. Besides, the convergence rates of PCA-WFL and PCA-AWFL algorithms quantitatively reveal the linear speedup with respect to the number of workers over the vanilla gradient descent algorithm. Numerical results are used to demonstrate the improved convergence rates of the proposed PCA-WFL and PCA-AWFL algorithms over the benchmarks. © 2023, CC BY.

关键词： Momentum

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Temperature-dependent perpendicular anisotropy and Gilbert damping of L10−FePd films: Role of noble-metal buffer layers

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Physical Review materials 2022年第11期6卷 113402-113402页

作者： Dingbin Huang Deyuan Lyu Xinjun Wang Michael B. Katz Delin Zhang Jian-Ping Wang Daniel B. Gopman Xiaojia Wang Department of Mechanical Engineering University of Minnesota Minneapolis Minnesota 55455 USA Minnesota Institute for Ultrafast Science University of Minnesota Minneapolis Minnesota 55455 USA Department of Electrical and Computer Engineering University of Minnesota Minneapolis Minnesota 55455 USA Department of Materials Science and Engineering University of Maryland College Park Maryland 20742 USA Materials Science and Engineering Division National Institute of Standards and Technology Gaithersburg Maryland 20899 USA

The moderate bulk perpendicular magnetic anisotropy (PMA, Ku≈1MJ/m3) and low Gilbert damping (α < 0.01) make L10-FePd a promising candidate for energy-efficient and nonvolatile spintronic devices with large areal densities (down to 5-nm pitch sizes or even lower). Existing applications subject spintronic devices to a wide range of operating temperatures (e.g., −55 to 150 °C). To better address the technological viability of FePd for spintronic applications, it is of utmost importance to evaluate the material performance of L10-FePd (e.g., anisotropy strength and Gilbert damping) at elevated temperatures. In this work, we systematically investigate the effect of buffer layers (Cr/Pt, Cr/Ru, Cr/Rh, Cr/Ir, and Ir) on the PMA and Gilbert damping of L10-FePd from room temperature (RT, 25 °C) to 150 °C using the time-resolved magneto-optical Kerr effect metrology. It is found that the effective anisotropy field (Hk,eff) of FePd decreases with the testing temperature (Ttest) and the ratio of Hk,eff(150 °C)/Hk,eff(25 °C) is positively correlated to the degree of L10 phase ordering. The Gilbert damping of L10-FePd either increases with Ttest or stays nearly constant over the Ttest range. We attribute the temperature dependence of Gilbert damping to the spin diffusion length of the metallic buffer layer (λ), presumably through the spin pumping effect. Results of this work provide guidance to tailor L10-FePd properties through buffer layer engineering for applications in spintronic devices over wide operating temperature ranges.

关键词： Magnetic anisotropy Magnetism Magnetization dynamics Spin pumping Spintronics

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Heterogeneous Cathode Work Function Measurement and Interpretation: A case Study with SrVO3

Heterogeneous Cathode Work Function Measurement and Interpre...

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International Conference on Vacuum Electronics

作者： Lin Lin Ryan Jacobs Dane Morgan John Booske Department of Materials Science and Engineering University of Wisconsin-Madison Madison WI USA Department of Electrical and Computer Engineering University of Wisconsin-Madison Madison WI USA

Work function is a key electron emission property. However, questions remain on how to unambiguously measure and interpret the work function. In this proceeding, using polycrystalline SrVO 3 perovskite as an example, we clarify a few key issues in work function characterization. We show that the vacuum level, which is significantly affected by the patch and external electric fields, needs to be carefully selected to obtain a clear work function interpretation.

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Purcell enhancement of X-ray scintillation

Purcell enhancement of X-ray scintillation

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Conference on Lasers and Electro-Optics (CLEO)

作者： Neta Lahav Yaniv Kurman Roman Schuetz Alon Lifshits Segev Zaken Orr Be’er Yehonadav Bekenstein Ido Kaminer Department of Electrical and Computer Engineering Technion - Israel Institute of Technology Haifa Israel Department of Materials Science and Engineering Technion - Israel Institute of Technology Haifa Israel

We demonstrate nanophotonic enhancement of the intrinsic spontaneous emission of X-ray-driven scintillation. By designing a 16-layers nanophotonic scintillator structure, we present the first observation of Purcell-en... 详细信息

ISBN: (数字)9781957171050

ISBN: (纸本)9781665466660

关键词： Scintillators Spontaneous emission X-ray lasers Nanostructures Electrooptical waveguides

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