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Ultrahigh zT from strong electron-phonon interactions and a low-dimensional Fermi surface

Energy and Environmental science 2024年第5期17卷 1904-1915页

作者： Ranganayakulu, V.K. Wang, Te-Hsien Chen, Cheng-Lung Huang, Angus Ma, Ma-Hsuan Wu, Chun-Min Tsai, Wei-Han Hung, Tsu-Lien Ou, Min-Nan Jeng, Horng-Tay Lee, Chih-Hao Chen, Kuei-Hsien Li, Wen-Hsien Brod, Madison K. Snyder, G. Jeffrey Chen, Yang-Yuan Institute of Physics Academia Sinica Taipei11529 Taiwan Department of Engineering and System Science National Tsing Hua University Hsinchu30013 Taiwan Taiwan International Graduate Program Taipei11529 Taiwan Department of Physics National Chung Hsing University Taichung City40227 Taiwan Graduate School of Materials Science National Yunlin University of Science and Technology Yunlin64002 Taiwan Bachelor Program in Semiconductor Materials and Fabrication Ming Chi University of Technology New Taipei City243303 Taiwan Department of Physics National Tsing Hua University Hsinchu30013 Taiwan Center for Theory and Computation National Tsing Hua University Hsinchu30013 Taiwan Physics Division National Center for Theoretical Sciences Taipei10617 Taiwan Department of Physics National Central University Jhongli32001 Taiwan National Synchrotron Radiation Research Center Hsinchu Science Park Hsinchu30076 Taiwan Institute of Atomic and Molecular Sciences Academia Sinica Taipei10617 Taiwan Department of Materials Science and Engineering Northwestern University EvanstonIL60208 United States Graduate Institute of Applied Physics National Chengchi University Taipei11605 Taiwan

The outstanding thermoelectric performance of GeTe has attracted significant attention in the research community in recent years. However, many of the underlying physical mechanisms that contribute to GeTe's exceptionally high figure of merit (zT) remain not fully understood. In this study, an Sb-Bi codoped GeTe single crystal (Ge0.86Sb0.08Bi0.06)Te with an ultrahigh zT of 2.7 at 700 K and a record high device zT of 1.41 in the temperature range of 300-773 K was synthesized and investigated. The ultrahigh zT is attributed to the extremely low lattice thermal conductivity induced by strong electron-phonon (EP) interactions as revealed by the experimentally observed Kohn anomaly, through inelastic neutron scattering (INS) measurements. First-principles calculations further demonstrate that the remarkable EP interaction arises from the Fermi surface nesting featured in a one-dimensional (double-walled) topology. Our finding unravels the ultrahigh-zT mechanism in GeTe-based materials, serving as an inspiring guide toward high thermoelectric performance. © 2024 The Royal Society of Chemistry.

关键词： Neutron scattering

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Photoluminescence of oxygen vacancy-rich nano-TiO 2 photocatalyst for methylene blue color degradation

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materials science and engineering: B 2025年 320卷

作者： Mayer Simanjuntak I Made Joni Ferry Faizal Noto Susanto Gultom Dong-Hau Kuo Camellia Panatarani Department of Physics Faculty of Mathematic and Natural Sciences Universitas Padjadjaran Jl. Raya Bandung-Sumedang KM 21 Jatinangor Sumedang 45363 Indonesia Study Program of Biotechnology Faculty of Graduate School Universitas Padjadjaran Jl. Dipati Ukur No.35 Coblong Bandung 40132 Indonesia Functional Nano Powder University Center of Excellence Universitas Padjadjaran Jl. Raya Bandung-Sumedang KM 21 Jatinangor Sumedang 45363 Indonesia Department of Materials Science and Engineering National Taiwan University of Science and Technology No.43 Sec. 4 Keelung Road Taipei 10607 Taiwan

Wastewater containing synthetic dyes poses a critical environmental hazard, necessitating the development of effective treatment techniques. Despite its promise as a photocatalyst, TiO 2 ′s inability to efficiently absorb visible light limits its practical use. To overcome this limitation, oxygen vacancy (OV) engineering was carried out in TiO 2 through solvothermal at temperatures of 150°C, 180°C, and 210°C. Comprehensive analyses confirmed a temperature-induced increase in crystallinity and OV concentration. Furthermore, photoluminescence analysis revealed mid-gap states that improve visible light absorption. Notably, the T150 sample achieved 93.43% degradation of methylene blue within 3 h under sunlight, outperforming commercial TiO 2 . The superior performance was attributed to a reduced bandgap energy, enhanced charge carrier separation, and increased generation of reactive oxygen species, all facilitated by an optimal concentration of OV. This study clarifies the interaction between photoluminescence and photocatalytic activity, highlighting OV engineering as a highly effective strategy for developing advanced TiO 2 -based materials for wastewater treatment.

关键词： Photocatalytic activity

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Magnetoelastic coupling driven magnon gap in a honeycomb antiferromagnet

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Physical Review B 2024年第10期110卷 104419页

作者： Jeongheon Choe Andrey Baydin Gaihua Ye Bowen Ma Cynthia Nnokwe Martin Rodriguez-Vega David Lujan Swati Chaudhary Fuyang Tay Jiaming He Hiroyuki Nojiri Jianshi Zhou Gregory A. Fiete Junichiro Kono Rui He Xiaoqin Li Department of Physics Center of Complex Quantum Systems Center for Dynamics and Control of Materials Department of Electrical and Computer Engineering Smalley–Curl Institute Department of Physics Applied Physics Graduate Program Smalley–Curl Institute Department of Mechanical Engineering Institute for Materials Research Department of Physics and Astronomy Department of Materials Science and NanoEngineering

Cobalt titanate, CoTiO3, is a honeycomb antiferromagnet recently confirmed experimentally to host Dirac magnons, topological spin-orbit excitons, and chiral phonons. Here, we investigate a magnon gap at the zone center which calls for a refined spin Hamiltonian. We propose a microscopic model for the magnon gap and attribute it to a lattice-distortion (phonon)-induced higher-order spin interaction. Strong magnetoelastic coupling in CoTiO3 is also evident in Raman spectra, in which the magnetic order exerts a stronger influence on phonons corresponding to in-plane ionic motions than those with out-of-plane motions. We further examine the evolution of the zone-center magnons in a high magnetic field up to 18.5 T via THz absorption spectroscopy measurements. Based on this field dependence, we propose a spin Hamiltonian that not only agrees with magnon dispersion measured by inelastic neutron scattering but also includes fewer exchange constants and a realistic anisotropy term. Our work highlights the broad implications of magnetoelastic coupling in the study of topologically protected bosonic excitations.

关键词： Magnetism Magnons Topological materials Raman spectroscopy Terahertz spectroscopy

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Temperature Dependent Fluorescence of Nanocrystalline Ce-doped Garnets For Use as Thermographic Phosphors

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MRS Online Proceedings Library 2008年第1期1076卷 1-6页

作者： Hansel, Rachael Allison, Steve Walker, Greg Interdisciplinary Graduate Program in Materials Science Vanderbilt University Nashville USA Oak Ridge National Laboratory Oak Ridge USA Department of Mechanical Engineering Vanderbilt University Nashville USA

Four samples of (Y1−xCex)3(Al1−y Gay)5O12 (where x=0.01, 0.02 and y=0, 0.5) were synthesized via the simple, efficient combustion synthesis method in order to determine the effect of substituting Ga3+ for Al3+ on the temperature-dependent fluorescent lifetime. X-ray diffraction shows that the Ga-doped samples have longer lattice constants and transmission electron microscopy data show that each sample consists of nanocrystallites which have agglomerated in micron-sized particles. Photoluminescence data reveal that the addition of gallium into the YAG:Ce matrix induces a red shift in the absorption spectra and a blue-shift in the emission spectra. The laser-induced fluorescent lifetime was determined as a function of temperature over the range of 0-125°C using two different emission filters. Increasing the amount of dopant ultimately results in a decrease of the fluorescent lifetime. The quenching temperatures for the Ga-doped samples were lower than the samples without gallium. The results of this work show that combustion synthesis is viable method for making highly luminescent, nanocrystalline TGPs. In addition, these results show that the quenching temperature of YAG:Ce can be altered by substituting ions which alter the location of the charge transfer state and by changing the morphology of the sample.

关键词： crystalline sensor dopant

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Transistor characteristics of thermal chemical vapor deposition carbon nanotubes field emission triode

Journal of Vacuum Science & Technology B: Microelectronics a...

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Journal of Vacuum science & Technology B: Microelectronics and Nanometer Structures Processing, Measurement, and Phenomena 2005年第2期23卷 868-873页

作者： Y. M. Wong W. P. Kang J. L. Davidson W. Hofmeister S. Wei J. H. Huang Department of Electrical Engineering and Computer Science Vanderbilt University Nashville Tennessee 37235 Interdisciplinary Graduate Program in Material Science Vanderbilt University Nashville Tennessee 37235 Department of Materials Science and Engineering National Tsing Hua University Hsinchu 300 Taiwan Republic of China

A study of thermal chemical vapor deposition (CVD) grown carbon nanotubes (CNTs) field emitters in a triode amplifier configuration is reported. The CNT transistor characteristics were examined by integrating gate and anode with CNT cathode in two structural forms, utilizing a TEM grid (transmission electron microscope specimen holder) as the gate electrode and a micropatterned CNT with self-aligned gate. The TEM-grid CNT triode displayed clearly gate-controlled current modulation behavior with distinct cutoff, linear, and saturation regions, and a reasonable gate turn-on field of ∼5.4V∕μm despite a large cathode-gate spacing of ∼120μm . The field emission result established the basic transistor characteristics of CNTs in a triode configuration. A CNT triode construct with a self-aligned gated fabrication technique was also developed to realize a monolithic triode structure with shorter gate-cathode spacing, lowering gate voltage, and enhancing emission current. The triode exhibited a significantly lower gate turn-on voltage of ∼40V , and gate-controlled modulation of the emission current. An anode current density of ∼30mA∕cm2 was achieved at a gate voltage of ∼80V and an anode voltage of ∼200V . The dc characteristics for both of the CNT triodes were investigated, including Ia versus Va for different Vg . Moreover, dc parameters such as transconductance, amplification factors, and anode resistance of the triode amplifier were determined. The CNT triodes exhibited useful amplification factor and high output impedance.

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Assessment of Simple Adhesive Substrates as a Method for Quantifying Microplastics and the Factors Influencing Capture

SSRN

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SSRN 2022年

作者： Rieland, Julie M. Hu, Zeyuan Deese, Julian S. Love, Brian J. Department of Materials Science and Engineering United States Department of Biomedical Engineering United States Macromolecular Science and Engineering Graduate Program 2300 Hayward St Ann ArborMI48109 United States

Microplastics are a growing environmental concern, with a large body of evidence documenting substantial distribution of plastic material in virtually all environmental compartments. Countermeasures that help to bind, aggregate, or coalesce these distributed particles might result in lower human and animal exposures. Pressure sensitive adhesives (PSAs) have been identified as a viable microplastic (MP) capture mechanism with a range of potential use conditions. As with any countermeasure, there is a need to evaluate their collection efficiency, cost, ease of installation, etc. Expanding on previous work, submerged, spray-coated PSAs were investigated as a quick and low-cost quantitative method to assess MP binding in water. Two molecular weights of poly(2-ethylhexyl acrylate) PSA (92k, 950k, and 50:50 bimodal distribution) were applied as spray-coated substrates to compare MP-adhesive interactions. Thin films of PSA (92k 6 ± 1 μm, 950k 4 ± 2 μm, 50:50 BD 6.5 ± 1 μm) were sprayed on borosilicate glass slides using a commercial air brush. Polydisperse nylon-12 particles varying in size from 15-30 µm in diameter were dispersed in aqueous solution between 0.01 and 5 mg mL -1 and agitated under ambient conditions as quantitative comparisons of adhesive wettability and net capture. Mixed assays were also performed comparing binding of common MP species including polyethylene, polystyrene, and polyester particles and fibers to understand how varying composition, size, and form factor affect adsorption. The glass slide method demonstrated linear trends associated with the MP binding to glass slides with respect both to exposure time and MP concentration. The adhesive wettability demonstrates bounding parameters under which high wettability adhesives excel at MP capture but may compromise the integrity of the adhesive film. © 2022, The Authors. All rights reserved.

关键词： Adhesives

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Manipulation of the nanoscale heliconical structure of a twist-bend nematic material with polarized light

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Physical Review Research 2020年第3期2卷 032004(R)-032004(R)页

作者： C. Feng J. Feng R. Saha Y. Arakawa J. Gleeson S. Sprunt C. Zhu A. Jákli Chemical Physics Interdisciplinary Program Advanced Materials and Liquid Crystal Institute Kent State University Kent Ohio 44242 USA Advanced Light Source Lawrence Berkeley National Lab Berkeley California 94720 USA Department of Physics Kent State University Kent Ohio 44242 USA Department of Applied Chemistry and Life Science Graduate School of Engineering Toyohashi University of Technology Toyohashi 441-8580 Japan

The effect of polarized violet light on the alignment and the heliconical pitch of a liquid crystal dimer containing both sulfur atoms and an azo linkage has been studied by tender resonant x-ray scattering. The results provide evidence of the manipulation of the nanoscale heliconical structure by polarized light. In addition to the bulk alignment of the heliconical nanostructure, the value of the heliconical pitch can be varied as well. After turning the light on, an increase of the pitch is observed in two steps. The increase with a subsecond timescale is attributed to the reduced heliconical order related to trans-cis photoisomerization. This is followed by a smaller increase over a 10-s timescale, which is likely related to the annihilation of defects. After turning the light off, the pitch first decreases within a few seconds to a value larger than the original (before illumination), and then relaxes further on a much longer (hours) timescale.

关键词： Chiral symmetry Dynamical phase transitions Twist deformation

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Thermomechanical Behavior Modeling of a Cr-Ni-Mo-Mn-N Austenitic Stainless Steel

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materials sciences and Applications 2016年第12期7卷 803-822页

作者： Rafael P. Ferreira Eden S. Silva Carmem C. F. Nascimento Samuel F. Rodrigues Clodualdo Aranas Jr. Valdemar S. Leal Gedeon S. Reis Graduate Program in Materials Engineering Federal Institute of Education Science and Technology of Maranh&atilde o—IFMA S&atilde o Lu&iacute s MA Brazil Engineering Coordination Universidade UNICEUMA S&atilde o Lu&iacute s MA Brazil Department of Materials Engineering McGill University Montreal Canada

The analytical approach and the thermomechanical behavior of a Cr-Ni-Mo-Mn-N austenitic stainless steel were characterized based on the parameters of work hardening (h), dynamic recovery (r) and dynamic recrystallization (n, t_0.5), considering constitutive equations (σ, ε) and deformation conditions expressed according to the Zener-Hollomon parameter (Z). The results indicated that the curves were affected by the deformation conditions and that the stress levels increased with Z under high work hardening rates. The σ_c/σ_p ratio was relatively high in the first part of the curves, indicating that softening was promoted by intense dynamic recovery (DRV). This was corroborated by the high values of r and average stacking fault energy, γ_s_fe = 66.86 mJ/m², which facilitated the thermally activated mechanisms, increasing the effectiveness of DRV and delaying the onset of dynamic recrystallization (DRX). The second part of the curves indicates that there was a delay in the kinetics of dynamic softening, with a higher value of t_0.5 and lower values of the Avrami exponent (n) due to the competing DRV-DRX mechanisms, and steady state stress (σ_ss) was achieved under higher rates of deformation.

关键词： Austenitic Stainless Steel Dynamic Recovery Dynamic Recrystallization

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Effective monitoring of environmental hazardous drug moxifloxacin hydrochloride using silver selenide on octadecyl amine modified reduced graphene oxide composite

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Journal of Environmental Chemical engineering 2024年第1期12卷

作者： Hwa, Kuo-Yuan Ganguly, Anindita Graduate Institute of Organic and Polymeric Materials National Taipei University of Technology Taipei China Department of Molecular Science and Engineering National Taipei University of Technology Taipei China International Graduate Program in Energy and Optoelectronic Materials National Taipei University of Technology China

The precise detection of antibiotics is very critical. Here, silver selenide (Ag2Se) nanorods are hydrothermally synthesized and ultrasonically treated with rGO surface modified with octadecylamine (rGO-ODA). The optical, structural, morphological, and functional analysis were performed which revealed the orthorhombic pattern of the P2221 E space group, the crystalline purity of Ag2Se, and the substantial composite formation. The morphological studies revealed nanorod like structure of the Ag2Se material and wrinkled sheets of rGO-ODA. A sensor that detects moxifloxacin hydrochloride (MOXH) antibiotic using the cyclic voltammetry (CV), differential pulse voltammetry (DPV) and UV-Vis absorbance was developed. For DPV analysis, a quite low value for detection limit 12.46 nM was exhibited with 0.199 μM – 425.16 μM linear range, and a sensitivity of 5.0439 μA M−1cm−2. For UV-Vis, the sensor demonstrated a very low limit of detection 17.42 nM over 0.12 μM – 7.7 μM working range. The use of this sensor was validated in real-time analysis with industrial waste water, fish, human blood, and urine samples. The results suggested an excellent rate of analyte recovery and enhanced efficiency for MOXH detection with a potential for commercialization in the future. © 2023

关键词： Nanorods

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Boosting Thermoelectric Performance in Nanocrystalline Ternary Skutterudite Thin Films through Metallic CoTe2 Integration

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ACS Applied materials and Interfaces 2024年第12期16卷 14770-14780页

作者： Jarwal, Bhawna Abbas, Suman Chou, Ta-Lei Vailyaveettil, Suneesh M. Kumar, Ashutosh Quadir, Shaham Ho, Thi-Thong Wong, Deniz P. Chen, Li-Chyong Chen, Kuei-Hsien Molecular Science and Technology Program Taiwan International Graduate Program Academia Sinica Taipei10617 Taiwan International Graduate Program of Molecular Science and Technology National Taiwan University Taipei10617 Taiwan Institute of Atomic and Molecular Sciences Academia Sinica Taipei10617 Taiwan Center for Condensed Matter Sciences National Taiwan University Taipei10617 Taiwan Department of Physics National Central University Taoyuan32001 Taiwan Department of Materials Science and Metallurgical Engineering Indian Institute of Technology Bhilai Chhattisgarh Durg491001 India GoldenCO80401 United States Helmholtz-Zentrum Berlin für Materialien und Energie Hahn-Meitner-Platz 1 BerlinD-14109 Germany Department of Physics National Taiwan University Taipei10617 Taiwan Center of Atomic Initiative for New Materials National Taiwan University Taipei10617 Taiwan

Metal-semiconductor nanocomposites have emerged as a viable strategy for concurrently tailoring both thermal and electronic transport properties of established thermoelectric materials, ultimately achieving synergistic performance. In this investigation, a series of nanocomposite thin films were synthesized, embedding metallic cobalt telluride (CoTe2) nanophase within the nanocrystalline ternary skutterudite (Co(Ge1.22Sb0.22)Te1.58 or CGST) matrix. Our approach harnessed composition fluctuation-induced phase separation and in situ growth during thermal annealing to seamlessly integrate the metallic phase. The distinctive band structures of both materials have developed an ohmic-type contact characteristic at the interface, which raised carrier density considerably yet negligibly affected the mobility counterpart, leading to a substantial improvement in electrical conductivity. The intricate balance in transport properties is further influenced by the metallic CoTe2 phase’s role in diminishing lattice thermal conductivity. The presence of the metallic phase instigates enhanced phonon scattering at the interface boundaries. Consequently, a 2-fold enhancement in the thermoelectric figure of merit (zT ∼ 1.30) is attained with CGST-7 wt. % CoTe2 nanocomposite film at 655 K compared to that of pristine CGST. © 2024 The Authors. Published by American Chemical Society.

关键词： Nanocomposites

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