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arXiv 2023年

作者： Ramasubramaniam, Ashwin Naveh, Doron Department of Mechanical and Industrial Engineering University of Massachusetts Amherst AmherstMA01003 United States Materials Science and Engineering Graduate Program University of Massachusetts Amherst AmherstMA01003 United States Faculty of Engineering Bar-Ilan University Ramat Gan52900 Israel Institute for Nanotechnology and Advanced Materials Bar-Ilan University Ramat Gan52900 Israel

Modulation of electronic properties of materials by electric fields is central to the operation of modern semiconductor devices, providing access to complex electronic behaviors and greater freedom in tuning the energy bands of materials. Here, we explore one-dimensional superlattices induced by a confining electrostatic potential in monolayer MoS2, a prototypical two-dimensional semiconductor. Using first-principles calculations, we show that periodic potentials applied to monolayer MoS2 induce electrostatic superlattices in which the response is dominated by structural distortions relative to purely electronic effects. These structural distortions reduce the intrinsic band gap of the monolayer substantially while also polarizing the monolayer through piezoelectric coupling, resulting in spatial separation of charge carriers as well as Stark shifts that produce dispersive minibands. Importantly, these minibands inherit the valley-selective magnetic properties of monolayer MoS2, enabling fine control over spin-valley coupling in MoS2 and similar transition-metal dichalcogenides. Copyright © 2023, The Authors. All rights reserved.

关键词： Monolayers

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Nonlinear Self-Calibrated Spectrometer with Single GeSe-InSe Heterojunction Device

arXiv

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arXiv 2023年

作者： Darweesh, Rana Yadav, Rajesh Kumar Adler, Elior Poplinger, Michal Levi, Adi Lee, Jea-Jung Leshem, Amir Ramasubramaniam, Ashwin Xia, Fengnian Naveh, Doron Faculty of Engineering Bar-Ilan University Ramat-Gan52900 Israel Institue of Nanotechnology and Advanced Materials Bar-Ilan University Ramat-Gan52900 Israel Department of Electrical Engineering Yale University New HavenCT United States Department of Mechanical and Industrial Engineering University of Massachusetts AmherstMA01003 United States Materials Science and Engineering Graduate Program University of Massachusetts AmherstMA01003 United States

Optical spectroscopy – the measurement of electromagnetic spectra – is fundamental to various scientific domains and serves as the building block of numerous technologies.1–3 Computational spectrometry is an emerging field that employs an array of photodetectors with different spectral responses or a single photodetector device with tunable spectral response, in conjunction with numerical algorithms, for spectroscopic measurements.4–6 Compact single photodetectors made from layered materials are particularly attractive, 7–9 since they eliminate the need for bulky mechanical and optical components used in traditional spectrometers and can easily be engineered as heterostructures to optimize device performance.7,10 However, compact tunable photodetectors are typically nonlinear devices and this adds complexity to extracting optical spectra from the device response. Here, we report on the training of an artificial neural network (ANN) to recover the full nonlinear spectral photoresponse - a nonlinear problem of high dimensionality - of a single GeSe-InSe p-n heterojunction device. We demonstrate the functionality of a calibrated spectrometer in the spectral range of 400-1100 nm, with a small device footprint of ~25 × 25 μm, and we achieve a mean reconstruction error of 2 × 10-4 for the power-spectrum at a spectral resolution of 0.35 nm. Using our device, we demonstrate a solution to metamerism, an apparent matching of colors with different power spectral distributions, which is a fundamental problem in optical *** Codes Nonlinear Self-Calibrated Spectrometer, Artificial neural network, Optical imaging © 2023, CC BY.

关键词： Spectrometers

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Active modulation of valley excitons in a monolayer WSe2 via chiral metamaterials

Active modulation of valley excitons in a monolayer WSe2 via...

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2020 Frontiers in Optics Conference, FiO 2020

作者： Wu, Zilong Zheng, Yuebing Walker Department of Mechanical Engineering Materials Science and Engineering Program Texas Materials Institute University of Texas at Austin AustinTX78712 United States

Active modulation of handedness-selective valley dynamics in a monolayer WSe2 is achieved using plasmonic moiré chiral metamaterials (MCMs) with strong and dynamically tunable optical chirality. © OSA 2020 &... 详细信息

ISBN: (纸本)9781943580804

关键词： Monolayers

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Author Correction: Elastic electronics based on micromesh-structured rubbery semiconductor films (vol 5, pg 881, 2022)

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NATURE ELECTRONICS 2023年第1期6卷 86-86页

作者： Guan, Ying-Shi Ershad, Faheem Rao, Zhoulyu Ke, Zhifan da Costa, Ernesto Curty Xiang, Qian Lu, Yuntao Wang, Xu Mei, Jianguo Vanderslice, Peter Hochman-Mendez, Camila Yu, Cunjiang Institute of Advanced Materials and School of Chemistry and Chemical Engineering Southeast University Nanjing China Department of Mechanical Engineering University of Houston Houston TX USA Department of Biomedical Engineering Pennsylvania State University University Park PA USA Department of Biomedical Engineering University of Houston Houston TX USA Department of Engineering Science and Mechanics Pennsylvania State University University Park PA USA Materials Science and Engineering Program University of Houston Houston TX USA Department of Materials Science and Engineering Materials Research Institute Pennsylvania State University University Park PA USA Department of Chemistry Purdue University West Lafayette IN USA Regenerative Medicine Research Texas Heart Institute Houston TX USA Molecular Cardiology Research Laboratory Texas Heart Institute Houston TX USA

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Ab initio study on changing behaviors of lithium-rich layered composite cathode materials

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Electrochimica Acta 2024年 500卷

作者： Chuang, Yu-cheng Tran, Ngoc Thanh Thuy Tsai, Ping-chun Lin, Shih-kang Department of Materials Science and Engineering National Cheng Kung University Tainan70101 Taiwan Research Center National Cheng Kung University Tainan70101 Taiwan Department of Mechanical Engineering National Taiwan University of Science and Technology Taipei10607 Taiwan Program on Smart and Sustainable Manufacturing Academy of Innovative Semiconductor and Sustainable Manufacturing National Cheng Kung University Tainan70101 Taiwan Core Facility Center National Cheng Kung University Tainan70101 Taiwan

The lithium-rich composite-layered oxide, xLi2MnO3•(1-x)LiM'O2, where M’ represents transition metals, is a promising cathode material with excellent capacity at high working voltage for lithium-ion batteries (LIBs). Nevertheless, an unusual charge-discharge feature is observed for this material with sloping and plateau regions during the initial charging. In this work, ab initio calculations based on density functional theory were employed to examine the stability of xLi2MnO3•(1-x)Li(Ni1/3Co1/3Mn1/3)O2 composite-layered cathode materials during the first charging. Optimized atomistic models for different compositions (x = 0.0, 0.3, 0.4, 0.5, 0.7, and 1) unveil a pseudo-rhombohedral or monoclinic-like structure within the solid solution phase, with simulated X-ray diffraction patterns closely matching experimental data. Using these atomistic models, the first charging process of the 0.4Li2MnO3•0.6Li(Ni1/3Co1/3Mn1/3)O2 cathode were investigated. There exists phase transition from a layered to a spinel structure. Additionally, Bader charge analysis reveals intriguing trends during the first delithiation process, where the valence states of Ni and Co gradual increase, while that of Mn almost remains unchanged. Simultaneously, significant oxidation of O is observed. This finding leads to further evaluations on oxygen vacancy formation in comparison to the energy required for delithiation. Defect formation energy calculations demonstrate that the plateau in charging curve is resulted from oxygen vacancy formation during the first charging. By empirical fitting oxygen chemical potential at μO = -1.200 eV, the calculated charging-discharging curves aligned well with experimental data during the first and second charging. Furthermore, the pathways of lithium and oxygen deintercalation are elucidated. This work contributes fundamental understandings on the xLi2MnO3•(1-x)LiM'O2 composite-layered oxides as cathode for LIBs, providing valuable guidance for further developments

关键词： Cathodes

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Coupling between bulk thermal defects and surface segregation dynamics

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Physical Review B 2021年第8期104卷 085408-085408页

作者： Jonathan Li Siming Zhang Chaoran Li Yaguang Zhu Jorge Anibal Boscoboinik Xiao Tong Jerzy T. Sadowski Guofeng Wang Guangwen Zhou Department of Mechanical Engineering & Materials Science and Engineering Program State University of New York Binghamton New York 13902 USA Department of Mechanical Engineering and Materials Science University of Pittsburgh Pittsburgh Pennsylvania 15261 USA Center for Functional Nanomaterials Brookhaven National Laboratory Upton New York 11973 USA

Surface segregation is a phenomenon that depends on the delicate interplay between thermodynamic driving forces and kinetic obstacles, for which elevated temperature is often needed to enhance the atom mobility and reach equilibrium. Using the classic system of Cu3Au(100) under nonisothermal conditions, herein, we show an adatom process underlying transient surface segregation dynamics through the temperature-change-driven creation and annihilation of thermal vacancies in the bulk and the resulting bulk-surface mass exchanges. This is demonstrated by monitoring the surface composition evolution of Cu3Au(100) with temperature changes between 250 and 500∘C, showing that the increase in temperature decreases monotonically the surface Au concentration as a result of the transfer of more Cu than Au from the bulk to the surface to form Cu-rich clusters of adatoms. Such a bulk thermal defect effect is expected to be universal in inducing the disparity in the bulk-surface mass exchanges of dissimilar atoms in multicomponent materials because of the inherent differences in the vacancy formation energies of the constituent atoms.

关键词： Self-diffusion Surface & interfacial phenomena Transition metal alloys Density functional calculations Ion beam analysis Mass spectrometry Scanning tunneling microscopy X-ray photoelectron spectroscopy

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Electronic and Optical Excitations in van der Waals materials from a Non-Empirical Wannier-Localized Optimally-Tuned Screened Range-Separated Hybrid Functional

arXiv

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arXiv 2024年

作者： Camarasa-Gómez, María Gant, Stephen E. Ohad, Guy Neaton, Jeffrey B. Ramasubramaniam, Ashwin Kronik, Leeor Department of Molecular Chemistry and Materials Science Weizmann Institute of Science Rehovoth7610001 Israel Department of Physics University of California BerkeleyCA94720 United States Materials Sciences Division Lawrence Berkeley National Laboratory BerkeleyCA94720 United States Kavli Energy NanoSciences Institute at Berkeley University of California BerkeleyCA94720 United States Department of Mechanical and Industrial Engineering University of Massachusetts Amherst AmherstMA01003 United States Materials Science and Engineering Graduate Program University of Massachusetts AmherstMA01003 United States

Accurate prediction of electronic and optical excitations in van der Waals (vdW) materials is a long-standing challenge for density functional theory. The recently proposed Wannier-localized optimally-tuned screened range-separated hybrid (WOT-SRSH) functional has proven successful in non-empirical determination of electronic band gaps and optical absorption spectra for various covalent and ionic crystals. However, for vdW materials the tuning of the material- and structure-dependent functional parameters has, until now, only been attained semi-empirically. Here, we present a non-empirical WOT-SRSH approach applicable to vdW materials, with the optimal functional parameters transferable between monolayer and bulk. We apply this methodology to prototypical vdW materials: black phosphrous, moldybdenum disulfide, and hexagonal boron nitride (in the latter case including zero-point renormalization). We show that the WOT-SRSH approach consistently achieves accuracy levels comparable to experiments and ab initio many-body perturbation theory (MBPT) calculations for band structures and optical absorption spectra, both on its own and as an optimal starting point for MBPT calculations. Copyright © 2024, The Authors. All rights reserved.

关键词： Energy gap

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Heat Transfer Coefficients of Moving Particle Beds from Flow-Dependent Particle Bed Thermal Conductivity and Near-Wall Resistance

arXiv

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arXiv 2024年

作者： Adapa, Sarath R. Zhang, Xintong Feng, Tianshi Zeng, Jian Chung, Ka Man Albrecht, Kevin J. Ho, Clifford K. Madden, Dimitri A. Chen, Renkun Department of Mechanical and Aerospace Engineering University of California La Jolla San DiegoCA92093 United States Program in Materials Science and Engineering University of California La Jolla San DiegoCA92093 United States Concentrating Solar Technologies Department Sandia National Laboratories 1515 Eubank Blvd. SE AlbuquerqueNM87123 United States

Accurate determination of heat transfer coefficients for flowing packed particle beds is essential to the design of particle heat exchangers, and other thermal and thermochemical processes. While such dense granular flows mostly fall into the well-known plug-flow regime, the discrete nature of granular materials alters the thermal transport processes in both the near-wall and bulk regions of flowing particle beds from their stationary counterparts. As a result, heat transfer correlations based on the stationary particle bed thermal conductivity could be inadequate for flowing particles in a heat exchanger. Most earlier works have achieved a reasonable agreement with experiments by treating granular heat transfer media as a plug-flow continuum with a near-wall thermal resistance in series. However, the thermophysical properties of the continuum were often obtained from measurements on stationary beds owing to the difficulty of flowing bed measurements. In this work, it was found that the properties of a stationary bed are highly sensitive to the method of particle packing and there is a decrease in the particle bed thermal conductivity and increase in the near-wall thermal resistance, measured as an effective air gap thickness, on the onset of particle flow. These variations in the thermophysical properties of stationary and flowing particle beds can lead to errors in heat transfer coefficient calculations. Therefore, the heat transfer coefficients for granular flows were calculated using experimentally determined flowing particle bed thermal conductivity and near-wall air gap for ceramic particles - CARBO CP 40/100 (mean diameter=275 µm), HSP 40/70 (404 µm) and HSP 16/30 (956 µm);at velocities of 5-15 mm·s-1;and temperatures of 300-650 ºC. The thermal conductivity and air gap values for CP 40/100 and HSP 40/70 were further used to calculate heat transfer coefficients across different particle bed temperatures and velocities for different parallel-plate heat exchange

关键词： Heat transfer coefficients

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Phonon dynamics and magnetodielectric relaxation in distorted honeycomb ferrimagnet Ni4Nb2O9: Experiment and first-principles study

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Physical Review materials 2025年第4期9卷 045202-045202页

作者： Harshita Singh Sobhit Singh Sayandeep Ghosh Prativa Pramanik Vasant Sathe Roland Mathieu Wilfrid Prellier Subhash Thota Department of Physics Indian Institute of Technology Guwahati Assam 781039 India Department of Mechanical Engineering University of Rochester Rochester New York 14627 USA Materials Science Program University of Rochester Rochester New York 14627 USA Department of Physics Chungnam National University Daejeon 34134 Republic of Korea Department of Physics Kunsan National University Gunsan 54150 Republic of Korea Department of Materials Science and Engineering Uppsala University Uppsala SE-75103 Sweden UGC DAE Consortium for Scientific Research Indore 452 001 India Laboratoire CRISMAT ENSICAEN CNRS Université de Caen Normandie Université Caen France

We present the experimental and theoretical studies of lattice dynamics, electronic structure, and magnetodielectric relaxation in the ferrimagnetic (FiM) Ni4Nb2O9. This system exhibits a distorted honeycomb lattice with the space group Pbcn (no. 60) and undergoes FiM ordering below 76 K (TFN), accompanied by a magnetic compensation at 33 K (TCOM). By employing density-functional theory (DFT+U) calculations and vibrational spectroscopy, we study all the allowed Raman and infrared phonon modes in Ni4Nb2O9. Temperature-dependent analysis of Raman-active phonon frequencies provides evidence of spin-phonon coupling in Ni4Nb2O9. Interestingly, we observe a nonlinear mode softening phenomenon in both frequencies ω(T) and their linewidths δωF(T), which can be described using three-phonon anharmonic processes. Contrary to the behavior of the remaining modes, 510 cm−1 mode shows a blue shift and effectively acts as a breathing mode for Ni atoms of two sublattices, and hence plays a crucial role in stabilizing the FiM ground state, thus explaining the strong sensitivity of this Ag mode to temperature. Our investigation of the temperature- and field-dependent relative dielectric permittivity and loss-tangent data reveals the absence of magnetodielectric coupling and the presence of dipole relaxation behavior in Ni4Nb2O9. Additionally, the theoretically determined indirect band gap is about 2.7 eV. Overall, our study helps to fill the existing knowledge gap and provides valuable insights into the electronic, vibrational, and magnetodielectric properties of Ni4Nb2O9, shedding light on its potential applications in dielectric-ceramic resonators and electrochemical sensors.

关键词： Local density approximation

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Electrochemical Control of Copper Foam Synthesis for Critical Heat Flux Enhancement During Boiling

SSRN

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SSRN 2023年

作者： Pandey, Hari Mehrabi, Hamed Williams, Amanda Mira-Hernández, Carolina Coridan, Robert H. Hu, Han Department of Mechanical Engineering University of Arkansas FayettevilleAR72701 United States Materials Science and Engineering Program University of Arkansas FayettevilleAR72701 United States Universidad Pontificia Bolivariana Medellín Colombia Department of Chemistry and Biochemistry University of Arkansas FayettevilleAR72701 United States

Nano-engineered structured boiling surfaces have shown great promise in the improvement of heat dissipation performance in thermal management applications. Electrodeposited copper foams have attracted lots of scientific and engineering interest owing to their multi-tier structures. In this study, hierarchical copper foams with ultra-wicking properties were fabricated using cathodic deposition at different pH, including both acidic (pH 0) and basic (pH 10 and 12) solutions. Pendant droplet wicking tests and pool boiling experiments were performed to characterize the wicking flux and the critical heat flux (CHF) of the fabricated copper foams, respectively. The results show that base deposited copper foams (pH 10 and 12) yield higher wicking flux and higher boiling CHF than acid deposited copper foam (pH 0) due to smaller dendrites and crystallites. The effect of the surface structures on bubble dynamics is probed by analyzing the maximum bubble size, bubble count, and the power and dominant frequency of vapor fraction at varying heat fluxes from high-speed videos. The results reveal no significant differences between tested surfaces (flat copper and copper foams deposited at pH 0, 10, and 12) when the heat flux is kept the same. On the other hand, acoustic emissions (AE) are used to characterize the copper foam structures in both wicking and boiling tests. The results show consistent acoustic signatures between wicking and boiling that smaller AE amplitude is observed for higher wicking flux and higher CHF. Combing the optical and acoustic analysis, it is concluded that the main role of surface structures play in CHF enhancement is through improving capillary wicking underneath the bubbles rather than affecting the dynamics of the apparent liquid-vapor interfaces. This study not only explores the relationship between electrochemical control and wicking properties but also demonstrates the role of wicking in structure-enhanced boiling CHF through acoustic emission ana

关键词： Heat flux

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