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Sökning: WFRF:(Li Junfeng)

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1.
  • Dong, Yu, et al. (författare)
  • Observation of a Ubiquitous (π, π)-Type Nematic Superconducting Order in the Whole Superconducting Dome of Ultra-Thin BaFe2–xNixAs2 Single Crystals
  • 2021
  • Ingår i: Chinese Physics Letters. - : Institute of Physics Publishing (IOPP). - 0256-307X .- 1741-3540. ; 38:9
  • Tidskriftsartikel (refereegranskat)abstract
    • In iron-based superconductors, the (0, pi) or (pi, 0) nematicity, which describes an electronic anisotropy with a four-fold symmetry breaking, is well established and believed to be important for understanding the superconducting mechanism. However, how exactly such a nematic order observed in the normal state can be related to the superconducting pairing is still elusive. Here, by performing angular-dependent in-plane magnetoresistivity using ultra-thin flakes in the steep superconducting transition region, we unveil a nematic superconducting order along the (pi, pi) direction in electron-doped BaFe2 - x Ni x As2 from under-doped to heavily overdoped regimes with x = 0.065-0.18. It shows superconducting gap maxima along the (pi, pi) direction rotated by 45 degrees from the nematicity along (0, pi) or (pi, 0) direction observed in the normal state. A similar (pi, pi)-type nematicity is also observed in the under-doped and optimally doped hole-type Ba1 - y K y Fe2As2, with y = 0.2-0.5. These results suggest that the (pi, pi) nematic superconducting order is a universal feature that needs to be taken into account in the superconducting pairing mechanism in iron-based superconductors.
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2.
  • Li, Junjie, et al. (författare)
  • A Novel Dry Selective Isotropic Atomic Layer Etching of SiGe for Manufacturing Vertical Nanowire Array with Diameter Less than 20 nm
  • 2020
  • Ingår i: Materials. - : MDPI AG. - 1996-1944. ; 13:3
  • Tidskriftsartikel (refereegranskat)abstract
    • Semiconductor nanowires have great application prospects in field effect transistors and sensors. In this study, the process and challenges of manufacturing vertical SiGe/Si nanowire array by using the conventional lithography and novel dry atomic layer etching technology. The final results demonstrate that vertical nanowires with a diameter less than 20 nm can be obtained. The diameter of nanowires is adjustable with an accuracy error less than 0.3 nm. This technology provides a new way for advanced 3D transistors and sensors.
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3.
  • Chen, Anqi, et al. (författare)
  • Highly Sensitive Graphene Oxide-based Fabry-Perot Low-frequency Acoustic Sensor With Low-coherence Polarized Demodulation Using Three-step Phase-Shifting Arctan Algorithms
  • 2024
  • Ingår i: Journal of Lightwave Technology. - 0733-8724 .- 1558-2213. ; In Press
  • Tidskriftsartikel (refereegranskat)abstract
    • Developing low-frequency acoustic senor with high sensitivity is crucial for diverse applications, ranging from seismic monitoring, military operations, to pipeline surveillance. Here, we have proposed a high-sensitivity graphene oxide (GO)-based Fabry-Perot low-frequency sensor, in which a 170 nm thick, large-area and uniformly GO film was prepared by a vacuum filtration method. To enhance the accuracy and stability of the sensor, a low-coherence interference system based on birefringent crystal blocks was designed utilizing a three-step phase-shifting arctangent algorithm. Our sensor exhibited a sensitivity of -93.48 dB re 1 rad/μPa at 6-60 Hz with a fluctuation of 0.6 dB. The minimum detectable pressure of the sensor was measured at 0.37 μPa/Hz1/2 @20 Hz with a signal to noise ratio of 135.41 dB. Overall, this sensor offers simplicity in preparation, high sensitivity, low detectable sound pressure, making it a significant asset for low-frequency acoustic applications.
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4.
  • Xiong, Wenjuan, et al. (författare)
  • SiNx films and membranes for photonic and MEMS applications
  • 2020
  • Ingår i: Journal of materials science. Materials in electronics. - : Springer Science and Business Media LLC. - 0957-4522 .- 1573-482X. ; 31, s. 90-97
  • Tidskriftsartikel (refereegranskat)abstract
    • This work presents a novel process to form SiN x films and process for membranes with excellent mechanical properties for micro-electro-mechanical systems application as well as integration as IR waveguide for photonic application. The SiN x films were fabricated in SiNgen apparatus which is a single wafer chamber equipment compared to conventional low pressure chemical vapor deposition furnace process. The films showed low stress, good mechanical properties, but the synthesis also eradicates the issues of particle contamination. Through optimizing of the growth parameters and post annealing profile, low stress (40 Mpa) SiN x film could be finally deposited when annealing temperature rose up to 1150 °C. The stress relaxation is a result of more Si nano-crystalline which was formed during annealing, according to the FTIR results. The mechanical properties, Young’s modulus and hardness, were 210 Gpa and 20 Gpa respectively. For the waveguide application, a stack of three layers, SiO 2 /SiN x /SiO 2 was formed where the optimized layer thicknesses were used for minimum optical loss according to simulation feedback. After deposition of the first two layers in the stack, the samples were annealed in range of 900–1150 °C in order to release the stress. Chemical mechanical polish technique was applied to planarize the nitride layer prior to the oxide cladding layer. Such wafers can be used to bond to Si or Ge to manufacture advanced substrates.
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5.
  • Guo, Pengzhi, et al. (författare)
  • Twisted Alkylthiothien-2-yl Flanks and Extended Conjugation Length Synergistically Enhanced Photovoltaic Performance by Boosting Dielectric Constant and Carriers Kinetic Characteristics
  • 2021
  • Ingår i: Macromolecular Chemistry and Physics. - : Wiley. - 1022-1352 .- 1521-3935. ; 222:12
  • Tidskriftsartikel (refereegranskat)abstract
    • Alternating conjugated polymers (CPs), derived from 2-ethylhexylthiothiophen-2-yl (TS) or 2-ethylhexylthiophen-2-yl (T) flanked dithieno[3,2-d:3,2-d ']benzo[1,2-b:4,5-b ']dithiophene (DTBDT) and diketopyrrolo-pyrrole (DPP) termed as PDTBDT-TS-DPP and PDTBDT-T-DPP, are prepared and characterized. It is found that the PDTBDT-TS-DPP not only exhibits slightly deepening the highest occupied molecular orbital energy levels, and similar absorption, etc., but also presents higher dielectric constant (epsilon(r)) of 6.7 at 1 kHz in contrast to 3.2 for PDTBDT-T-DPP, which are even higher than those of 4.3 and 3.0 for PBDT-TS-DPP/PBDT-T-DPP generated from TS and T flanked benzo[1,2-b:4,5-bMODIFIER LETTER PRIME]dithiophene and DPP. Beyond that, the power conversion efficiency of 8.17% for the inverted photovoltaic devices from DPP-based CPs, is achieved from PDTBDT-TS-DPP. The alkylthio side chains are used in the DTBDT of the larger twisting angles of TS flanks and longer conjugation length, synergistically contribute to the highest dipole moments, and then lead to the enhancement of epsilon(r), thus devoted the modification exciton dissociation and charge carriers kinetic characteristics. To the authors' knowledge, it is the first time to report that epsilon(r) of the CPs is connected with the twisting angle of flanks and conjugation length of the building blocks, besides the use of functional side chains and atoms.
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6.
  • Guo, Xuewen, et al. (författare)
  • Novel small-molecule zwitterionic electrolyte with ultralow work function as cathode modifier for inverted polymer solar cells
  • 2018
  • Ingår i: Organic electronics. - : ELSEVIER SCIENCE BV. - 1566-1199 .- 1878-5530. ; 59, s. 15-20
  • Tidskriftsartikel (refereegranskat)abstract
    • Interfacial compatibility between the electrode and organic semiconductor plays a critical role in controlling the charge transport and hence efficiency of organic solar cell. Here, we introduce a novel small-molecule zwitterionic electrolyte (S1) combined with ZnO as electron transporting interlayer employed for the inverted PTB7:PC71BM bulk heterojunction solar cell. The resulting device with the S1/ZnO stacked interlayer achieves a high PCE of 8.59%, obtaining a 16.2% improvement over the control device performance of 7.4% without the S1 attributed to the significant increased short-circuit current density and fill factor. The interfacial properties are investigated. It is found that the S1/ZnO interlayer possess an ultralow work function of 3.6 eV, which originates from the interfacial double dipole step induced by the zwitterionic side chain electrostatic realignment at interface. The S1/ZnO interlayer exhibits the excellent charge extraction ability, suppresses the charge recombination loss and decreases the series resistance at the active layer/electrode contact.
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7.
  • Li, Zhuwei, et al. (författare)
  • Atomically dispersed Ni active sites on covalent organic frameworks for heterogeneous metallaphotocatalytic C–N cross-coupling
  • 2024
  • Ingår i: Applied Catalysis B. - : Elsevier BV. - 0926-3373 .- 1873-3883. ; 345
  • Tidskriftsartikel (refereegranskat)abstract
    • Covalent organic frameworks (COFs) have been acknowledged as a potential platform for heterogeneous photoredox cross-coupling due to their excellent chemical stability, admirable controllability, and extremely prominent surface area. However, synthesizing COFs with bidentate ligand units and utilizing active sites remain a grand challenge. Herein, we report a promising new family of 2,6-pyridinedicarboxaldehyde-bis-(p-aminophenylimine)-based two-dimensional (2D) COFs (PP-COF) using an amine monomer and classic tri-aldehydes. On this basis, dispersed Ni single-atom sites were immobilized on three-types imine-based bi-coordinated 2D COFs (Ni SAS-PP-COF) as heterogeneous dual photoredox catalysts for photo/Ni dual-catalyzed C–N cross-coupling between aryl bromides and alkyl/sulfo amines. Under solar energy irradiation, PP-COF could absorb light to generate electrons and holes, then the photogenerated electrons are transferred to Ni sites to reduce divalent nickel to monovalent nickel. Monovalent nickel is necessary to drive the nickel catalytic cycle. Due to the increased charge separation and abundant active sites, the state-of-the-art Ni SAS-PP-COFs catalyst achieves excellent catalytic performance in comparison of pristine PP-COF. The heterogeneous Ni SAS-PP-COF catalytic system not only confirms the prospect of COFs as potential photoredox/transition-metal dual catalysts, but also provides in-depth insights into the synthesis of functional COFs toward practical metallaphotocatalytic application.
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8.
  • Lin, Qing-Fang, et al. (författare)
  • A stable aluminosilicate zeolite with intersecting three-dimensional extra-large pores
  • 2021
  • Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 374:6575, s. 1605-1608
  • Tidskriftsartikel (refereegranskat)abstract
    • Zeolites are crystalline porous materials with important industrial applications, including uses in catalytic and adsorption-separation processes. Access into and out of their inner confined space, where adsorption and reactions occur, is limited by their pore apertures. Stable multidimensional zeolites with larger pores able to process larger molecules are in demand in the fine chemical industry and for the oil processing on which the world still relies for fuels. Currently known extra-large-pore zeolites display poor stability and/or lack pore multidimensionality, limiting their usefulness. We report ZEO-1, a robust, fully connected aluminosilicate zeolite with mutually intersecting three-dimensional extra-large plus three-dimensional large pores. ZEO-1 is stable up to 1000 degrees C, has an extraordinary specific surface area (1000 square meters per gram), and shows potential as a catalytic cracking catalyst.
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9.
  • Luo, Jun, et al. (författare)
  • Effects of carbon pre-silicidation implant into Si substrate on NiSi
  • 2014
  • Ingår i: Microelectronic Engineering. - : Elsevier BV. - 0167-9317 .- 1873-5568. ; 120, s. 178-181
  • Tidskriftsartikel (refereegranskat)abstract
    • In this work, the effects of carbon pre-silicidation implant into Si(1 0 0) substrate on NiSi were investigated. NiSi films with carbon pre-silicidation implant to different doses were characterized by means of sheet resistance measurements, X-ray diffraction, scanning electron microscopy (SEM), planar view transmission electron microscopy (TEM) and second ion mass spectroscopy (SIMS). The presence of C is found to indeed significantly improve the thermal stability of NiSi as well as tends to change the preferred orientations of polycrystalline NiSi. The homogeneously distributed C at NiSi grain boundaries and C peak at NiSi/Si interface is ascribed to the improved thermal stability of NiSi. More importantly, the dose of carbon pre-silicidation implant also plays a key role in the formation of NiSi, which is suggested not to exceed a critical value about 5 x 10(15) cm(-2) in practical application in accordance with the results achieved in this work. (C) 2013 Elsevier B.V. All rights reserved.
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10.
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11.
  • Luo, Jun, et al. (författare)
  • Thermal Stability and Dopant Segregation for Schottky Diodes With Ultrathin Epitaxial NiSi(2-y)
  • 2011
  • Ingår i: IEEE Electron Device Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 0741-3106 .- 1558-0563. ; 32:8, s. 1029-1031
  • Tidskriftsartikel (refereegranskat)abstract
    • The Schottky barrier height (SBH) of an ultrathin epitaxial NiSi(2-y) film grown on Si(100) is modified significantly by means of dopant segregation (DS). The DS process begins with the NiSi(2-y) formation and is followed by dopant implantation and drive-in annealing. The rapid lattice restoration and superior morphological stability upon heat treatment up to 800 degrees C allow the epitaxial NiSi(2-y) film to take full advantage of the DS process. For drive-in annealing below 750 degrees C, the effective SBH is altered to similar to 0.9-1 eV for both electrons and holes by B-DS and As-DS, respectively, without deteriorating the integrity of the NiSi(2-y) film.
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12.
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13.
  • Luo, Jun, et al. (författare)
  • Variation of Schottky barrier height induced by dopant segregation monitored by contact resistivity measurements
  • 2014
  • Ingår i: Microelectronic Engineering. - : Elsevier BV. - 0167-9317 .- 1873-5568. ; 120, s. 174-177
  • Tidskriftsartikel (refereegranskat)abstract
    • Change of contact resistivity (rho(c)) is monitored for evaluation of Schottky barrier height (SBH) variation induced by dopant segregation (DS). This method is particularly advantageous for metal-semiconductor contacts of small SBH, as it neither requires low-temperature measurement needed in current-voltage characterization of Schottky diodes nor is affected by reverse leakage current often troubling capacitance-voltage characterization. With PtSi contact to both n- and p-type diffusion regions, and the use of opposite or alike dopants implant into pre-formed PtSi films followed by drive-in anneal at different temperatures to induce DS at PtSi/Si interface, the formation of interfacial dipole is confirmed as the responsible cause for modification of effective SBHs thus the increase or decrease of rho(c). A tentative explanation for the change of contact resistivity based on interfacial dipole theory is provided in this work. Influences and interplay of interfacial dipole and space charge on effective SBH are also discussed. (C) 2013 Elsevier B.V. All rights reserved.
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14.
  • Qin, Ning, 1990, et al. (författare)
  • Flux regulation through glycolysis and respiration is balanced by inositol pyrophosphates in yeast
  • 2023
  • Ingår i: Cell. - : Elsevier BV. - 0092-8674 .- 1097-4172. ; 186:4, s. 748-763.e15
  • Tidskriftsartikel (refereegranskat)abstract
    • Although many prokaryotes have glycolysis alternatives, it's considered as the only energy-generating glucose catabolic pathway in eukaryotes. Here, we managed to create a hybrid-glycolysis yeast. Subsequently, we identified an inositol pyrophosphatase encoded by OCA5 that could regulate glycolysis and respiration by adjusting 5-diphosphoinositol 1,2,3,4,6-pentakisphosphate (5-InsP7) levels. 5-InsP7 levels could regulate the expression of genes involved in glycolysis and respiration, representing a global mechanism that could sense ATP levels and regulate central carbon metabolism. The hybrid-glycolysis yeast did not produce ethanol during growth under excess glucose and could produce 2.68 g/L free fatty acids, which is the highest reported production in shake flask of Saccharomyces cerevisiae. This study demonstrated the significance of hybrid-glycolysis yeast and determined Oca5 as an inositol pyrophosphatase controlling the balance between glycolysis and respiration, which may shed light on the role of inositol pyrophosphates in regulating eukaryotic metabolism.
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15.
  • Qin, Ning, et al. (författare)
  • Increased CO 2 fixation enables high carbon-yield production of 3-hydroxypropionic acid in yeast
  • 2024
  • Ingår i: Nature Communications. - 2041-1723 .- 2041-1723. ; 15:1
  • Tidskriftsartikel (refereegranskat)abstract
    • CO2 fixation plays a key role to make biobased production cost competitive. Here, we use 3-hydroxypropionic acid (3-HP) to showcase how CO2 fixation enables approaching theoretical-yield production. Using genome-scale metabolic models to calculate the production envelope, we demonstrate that the provision of bicarbonate, formed from CO2, restricts previous attempts for high yield production of 3-HP. We thus develop multiple strategies for bicarbonate uptake, including the identification of Sul1 as a potential bicarbonate transporter, domain swapping of malonyl-CoA reductase, identification of Esbp6 as a potential 3-HP exporter, and deletion of Uga1 to prevent 3-HP degradation. The combined rational engineering increases 3-HP production from 0.14 g/L to 11.25 g/L in shake flask using 20 g/L glucose, approaching the maximum theoretical yield with concurrent biomass formation. The engineered yeast forms the basis for commercialization of bio-acrylic acid, while our CO2 fixation strategies pave the way for CO2 being used as the sole carbon source.
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16.
  • Wang, Xiaolin, et al. (författare)
  • Comprehension of the Effect of a Hydroxyl Group in Ancillary Ligand on Phosphorescent Property for Heteroleptic Ir(III) Complexes : A Computational Study Using Quantitative Prediction
  • 2017
  • Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 56:15, s. 8986-8995
  • Tidskriftsartikel (refereegranskat)abstract
    • A new Ir(III) complex (dfpypya)(2)Ir(pic-OH) (2) is theoretically designed by introduction of a simple hydroxyl group into the ancillary ligand on the basis of (dfpypya)(2)Ir(pic) (1) with the aim to get the high efficiency and stable blue-emitting phosphors, where dfpypya is 3-methyl-6-(2',4'-difluoro-pyridinato)pyridazine, pic is picolinate, and pic OH is 3-hydroxypicolinic acid. The other configuration (dfpypya)(2)Ir(pic OH)' (3) is also investigated to compare with 2. The difference between 2 and 3 is whether the intramolecular hydrogen bond is formed in the (dfpypya)(2)Ir(pic OH). The quantum yield is determined by three different methods including the semiquantitative and quantitative methods. To quantitatively determine the quantum yield is still not an easy task to be completed. This work would provide some useful advices to select the suitable method to reliably evaluate the quantum yield. Complex 2 has larger quantum yield and more stability as compared with 1 and 3. The formation of intramolecular hydrogen bond would become a new method to design new phosphor with the desired properties.
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17.
  • Xu, Ke-Jun, et al. (författare)
  • Bogoliubov quasiparticle on the gossamer Fermi surface in electron-doped cuprates
  • 2023
  • Ingår i: Nature Physics. - 1745-2473 .- 1745-2481. ; 19:12, s. 1834-1840
  • Tidskriftsartikel (refereegranskat)abstract
    • Electron-doped cuprates consistently exhibit strong antiferromagnetic correlations, leading to the prevalent belief that antiferromagnetic spin fluctuations mediate Cooper pairing in these unconventional superconductors. However, early investigations showed that although antiferromagnetic spin fluctuations create the largest pseudogap at hot spots in momentum space, the superconducting gap is also maximized at these locations. This presented a paradox for spin-fluctuation-mediated pairing: Cooper pairing is strongest at momenta where the normal-state low-energy spectral weight is most suppressed. Here we investigate this paradox and find evidence that a gossamer—meaning very faint—Fermi surface can provide an explanation for these observations. We study Nd2–xCexCuO4 using angle-resolved photoemission spectroscopy and directly observe the Bogoliubov quasiparticles. First, we resolve the previously observed reconstructed main band and the states gapped by the antiferromagnetic pseudogap around the hot spots. Within the antiferromagnetic pseudogap, we also observe gossamer states with distinct dispersion, from which coherence peaks of Bogoliubov quasiparticles emerge below the superconducting critical temperature. Moreover, the direct observation of a Bogoliubov quasiparticle permits an accurate determination of the superconducting gap, yielding a maximum value an order of magnitude smaller than the pseudogap, establishing the distinct nature of these two gaps. We propose that orientation fluctuations in the antiferromagnetic order parameter are responsible for the gossamer states. 
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18.
  • Xu, Ke Jun, et al. (författare)
  • Bogoliubov quasiparticle on the gossamer Fermi surface in electron-doped cuprates
  • 2023
  • Ingår i: Nature Physics. - : Springer Nature. - 1745-2473 .- 1745-2481. ; 19:12, s. 1834-1840
  • Tidskriftsartikel (refereegranskat)abstract
    • Electron-doped cuprates consistently exhibit strong antiferromagnetic correlations, leading to the prevalent belief that antiferromagnetic spin fluctuations mediate Cooper pairing in these unconventional superconductors. However, early investigations showed that although antiferromagnetic spin fluctuations create the largest pseudogap at hot spots in momentum space, the superconducting gap is also maximized at these locations. This presented a paradox for spin-fluctuation-mediated pairing: Cooper pairing is strongest at momenta where the normal-state low-energy spectral weight is most suppressed. Here we investigate this paradox and find evidence that a gossamer—meaning very faint—Fermi surface can provide an explanation for these observations. We study Nd2–xCexCuO4 using angle-resolved photoemission spectroscopy and directly observe the Bogoliubov quasiparticles. First, we resolve the previously observed reconstructed main band and the states gapped by the antiferromagnetic pseudogap around the hot spots. Within the antiferromagnetic pseudogap, we also observe gossamer states with distinct dispersion, from which coherence peaks of Bogoliubov quasiparticles emerge below the superconducting critical temperature. Moreover, the direct observation of a Bogoliubov quasiparticle permits an accurate determination of the superconducting gap, yielding a maximum value an order of magnitude smaller than the pseudogap, establishing the distinct nature of these two gaps. We propose that orientation fluctuations in the antiferromagnetic order parameter are responsible for the gossamer states.
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19.
  • Yang, Huiqing, et al. (författare)
  • Protic Quaternary Ammonium Ionic Liquids for Catalytic Conversion of CO2 into Cyclic Carbonates : A Combined Ab Initio and MD Study
  • 2018
  • Ingår i: Industrial & Engineering Chemistry Research. - : AMER CHEMICAL SOC. - 0888-5885 .- 1520-5045. ; 57:21, s. 7121-7129
  • Tidskriftsartikel (refereegranskat)abstract
    • The mechanism of CO2 fixation catalyzed by protic hydroxyl-functionalized quaternary ammonium ionic liquids (ILs) is investigated by two different models, the Single-IL model and the Double-IL model. The relative sequence of catalytic activity calculated by the Single-IL model is contradictory with the experimental result. The situation is totally varied when the Double-IL model is utilized. In this system, ILs are not limited to the catalyst but solvent. The ILs are incorporated into the catalytic system to consider the solvent effect rather than by the existing solvent model. When the solvent effect is included, it is better to distinguish the catalytic activity of three ILs. According to the noncovalent interaction and the atoms in molecules analysis, the highest catalytic activity of tris(2-hydroxyethyl)ammonium bromide ([HTEA]Br) is attributed to its strongest nucleophilic attack and moderate hydrogen bond interaction between IL and reactant. It is necessary to consider the interaction between ILs to get a reliable result. Moreover, the solvent effect aroused by ILs should be carefully considered.
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20.
  • Berne, Olivier, et al. (författare)
  • PDRs4All : A JWST Early Release Science Program on Radiative Feedback from Massive Stars
  • 2022
  • Ingår i: Publications of the Astronomical Society of the Pacific. - : IOP Publishing. - 0004-6280 .- 1538-3873. ; 134:1035
  • Tidskriftsartikel (refereegranskat)abstract
    • Massive stars disrupt their natal molecular cloud material through radiative and mechanical feedback processes. These processes have profound effects on the evolution of interstellar matter in our Galaxy and throughout the universe, from the era of vigorous star formation at redshifts of 1-3 to the present day. The dominant feedback processes can be probed by observations of the Photo-Dissociation Regions (PDRs) where the far-ultraviolet photons of massive stars create warm regions of gas and dust in the neutral atomic and molecular gas. PDR emission provides a unique tool to study in detail the physical and chemical processes that are relevant for most of the mass in inter- and circumstellar media including diffuse clouds, proto-planetary disks, and molecular cloud surfaces, globules, planetary nebulae, and star-forming regions. PDR emission dominates the infrared (IR) spectra of star-forming galaxies. Most of the Galactic and extragalactic observations obtained with the James Webb Space Telescope (JWST) will therefore arise in PDR emission. In this paper we present an Early Release Science program using the MIRI, NIRSpec, and NIRCam instruments dedicated to the observations of an emblematic and nearby PDR: the Orion Bar. These early JWST observations will provide template data sets designed to identify key PDR characteristics in JWST observations. These data will serve to benchmark PDR models and extend them into the JWST era. We also present the Science-Enabling products that we will provide to the community. These template data sets and Science-Enabling products will guide the preparation of future proposals on star-forming regions in our Galaxy and beyond and will facilitate data analysis and interpretation of forthcoming JWST observations.
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21.
  • Chown, Ryan, et al. (författare)
  • PDRs4All: IV. An embarrassment of riches: Aromatic infrared bands in the Orion Bar
  • 2024
  • Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 685
  • Tidskriftsartikel (refereegranskat)abstract
    • Context. Mid-infrared observations of photodissociation regions (PDRs) are dominated by strong emission features called aromatic infrared bands (AIBs). The most prominent AIBs are found at 3.3, 6.2, 7.7, 8.6, and 11.2 µm. The most sensitive, highest-resolution infrared spectral imaging data ever taken of the prototypical PDR, the Orion Bar, have been captured by JWST. These high-quality data allow for an unprecedentedly detailed view of AIBs. Aims. We provide an inventory of the AIBs found in the Orion Bar, along with mid-IR template spectra from five distinct regions in the Bar: the molecular PDR (i.e. the three H2 dissociation fronts), the atomic PDR, and the H II region. Methods. We used JWST NIRSpec IFU and MIRI MRS observations of the Orion Bar from the JWST Early Release Science Program, PDRs4All (ID: 1288). We extracted five template spectra to represent the morphology and environment of the Orion Bar PDR. We investigated and characterised the AIBs in these template spectra. We describe the variations among them here. Results. The superb sensitivity and the spectral and spatial resolution of these JWST observations reveal many details of the AIB emission and enable an improved characterization of their detailed profile shapes and sub-components. The Orion Bar spectra are dominated by the well-known AIBs at 3.3, 6.2, 7.7, 8.6, 11.2, and 12.7 µm with well-defined profiles. In addition, the spectra display a wealth of weaker features and sub-components. The widths of many AIBs show clear and systematic variations, being narrowest in the atomic PDR template, but showing a clear broadening in the H II region template while the broadest bands are found in the three dissociation front templates. In addition, the relative strengths of AIB (sub-)components vary among the template spectra as well. All AIB profiles are characteristic of class A sources as designated by Peeters (2022, A&A, 390, 1089), except for the 11.2 µm AIB profile deep in the molecular zone, which belongs to class B11.2. Furthermore, the observations show that the sub-components that contribute to the 5.75, 7.7, and 11.2 µm AIBs become much weaker in the PDR surface layers. We attribute this to the presence of small, more labile carriers in the deeper PDR layers that are photolysed away in the harsh radiation field near the surface. The 3.3/11.2 AIB intensity ratio decreases by about 40% between the dissociation fronts and the H II region, indicating a shift in the polycyclic aromatic hydrocarbon (PAH) size distribution to larger PAHs in the PDR surface layers, also likely due to the effects of photochemistry. The observed broadening of the bands in the molecular PDR is consistent with an enhanced importance of smaller PAHs since smaller PAHs attain a higher internal excitation energy at a fixed photon energy. Conclusions. Spectral-imaging observations of the Orion Bar using JWST yield key insights into the photochemical evolution of PAHs, such as the evolution responsible for the shift of 11.2 µm AIB emission from class B11.2 in the molecular PDR to class A11.2 in the PDR surface layers. This photochemical evolution is driven by the increased importance of FUV processing in the PDR surface layers, resulting in a “weeding out” of the weakest links of the PAH family in these layers. For now, these JWST observations are consistent with a model in which the underlying PAH family is composed of a few species: the so-called ‘grandPAHs’.
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22.
  • De Putte, Dries Van, et al. (författare)
  • PDRs4All VIII. Mid-infrared emission line inventory of the Orion Bar
  • 2024
  • Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 687
  • Tidskriftsartikel (refereegranskat)abstract
    • Context . Mid-infrared emission features are important probes of the properties of ionized gas and hot or warm molecular gas, which are difficult to probe at other wavelengths. The Orion Bar photodissociation region (PDR) is a bright, nearby, and frequently studied target containing large amounts of gas under these conditions. Under the “PDRs4All” Early Release Science Program for JWST, a part of the Orion Bar was observed with MIRI integral field unit (IFU) spectroscopy, and these high-sensitivity IR spectroscopic images of very high angular resolution (0.2′′) provide a rich observational inventory of the mid-infrared (MIR) emission lines, while resolving the H II region, the ionization front, and multiple dissociation fronts. Aims . We list, identify, and measure the most prominent gas emission lines in the Orion Bar using the new MIRI IFU data. An initial analysis summarizes the physical conditions of the gas and demonstrates the potential of these new data and future IFU observations with JWST. Methods. The MIRI IFU mosaic spatially resolves the substructure of the PDR, its footprint cutting perpendicularly across the ionization front and three dissociation fronts. We performed an up-to-date data reduction, and extracted five spectra that represent the ionized, atomic, and molecular gas layers. We identified the observed lines through a comparison with theoretical line lists derived from atomic data and simulated PDR models. The identified species and transitions are summarized in the main table of this work, with measurements of the line intensities and central wavelengths. Results . We identified around 100 lines and report an additional 18 lines that remain unidentified. The majority consists of H I recombination lines arising from the ionized gas layer bordering the PDR. The H I line ratios are well matched by emissivity coefficients from H recombination theory, but deviate by up to 10% because of contamination by He I lines. We report the observed emission lines of various ionization stages of Ne, P, S, Cl, Ar, Fe, and Ni. We show how the Ne III/Ne II, S IV/S III, and Ar III/Ar II ratios trace the conditions in the ionized layer bordering the PDR, while Fe III/Fe II and Ni III/Ni II exhibit a different behavior, as there are significant contributions to Fe II and Ni II from the neutral PDR gas. We observe the pure-rotational H2 lines in the vibrational ground state from 0–0 S(1) to 0–0 S(8), and in the first vibrationally excited state from 1–1 S(5) to 1–1 S(9). We derive H2 excitation diagrams, and for the three observed dissociation fronts, the rotational excitation can be approximated with one thermal (∼700 K) component representative of an average gas temperature, and one nonthermal component (∼2700 K) probing the effect of UV pumping. We compare these results to an existing model of the Orion Bar PDR, and find that the predicted excitation matches the data qualitatively, while adjustments to the parameters of the PDR model are required to reproduce the intensity of the 0–0 S(6) to S(8) lines.
  •  
23.
  • Duan, Ningyuan, et al. (författare)
  • Reduction of NiGe/n- and p-Ge Specific Contact Resistivity by Enhanced Dopant Segregation in the Presence of Carbon During Nickel Germanidation
  • 2016
  • Ingår i: IEEE Transactions on Electron Devices. - : IEEE. - 0018-9383 .- 1557-9646. ; 63:11, s. 4546-4549
  • Tidskriftsartikel (refereegranskat)abstract
    • This brief explores the specific contact resistivity (rho(c)) of NiGe/n- and p-Ge contacts with and without carbon pregermanidation implantation. It is found that in the presence of carbon, not only the thermal stability of NiGe films is improved, but also the rho(c) of the NiGe/n- and p-Ge contacts is reduced remarkably due to enhanced phosphorus (P) and boron (B) dopant segregation (DS) at the NiGe/Ge interface after nickel germanidation. At 500 degrees C germanidation temperature, the.c values are reduced from 1.1 x 10(-4) Omega-cm(2) and 2.9 x 10(-5) Omega-cm(2) for NiGe/n- and p-Ge contacts without carbon to 7.3 x 10(-5) Omega-cm(2) and 1.4 x 10(-5) Omega-cm(2) for their counterparts with carbon, respectively.
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24.
  • Gao, Jia, et al. (författare)
  • Chemoenzymatic Synthesis of Glycopeptides Bearing Galactose-Xylose Disaccharide from the Proteoglycan Linkage Region
  • 2021
  • Ingår i: Organic Letters. - : American Chemical Society (ACS). - 1523-7060 .- 1523-7052. ; 23:5, s. 1738-1741
  • Tidskriftsartikel (refereegranskat)abstract
    • Proteoglycans have important biological activities. To improve the overall synthetic efficiency, a new chemoenzymatic route has been established for the proteoglycan linkage region bearing a galactose-xylose disaccharide. The xylosylated glycopeptides were synthesized via solid phase synthesis, which was followed by the addition of the galactose unit by the galactosyl transferase β4GalT7. This work leads to a better understanding of the acceptor preference of β4GalT7 and opens the door for expeditious synthesis of the proteoglycan linkage region.
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25.
  • Habart, Emilie, et al. (författare)
  • PDRs4All II. JWST’s NIR and MIR imaging view of the Orion Nebula
  • 2024
  • Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 685
  • Tidskriftsartikel (refereegranskat)abstract
    • Context. The James Webb Space Telescope (JWST) has captured the most detailed and sharpest infrared (IR) images ever taken of the inner region of the Orion Nebula, the nearest massive star formation region, and a prototypical highly irradiated dense photo-dissociation region (PDR). Aims. We investigate the fundamental interaction of far-ultraviolet (FUV) photons with molecular clouds. The transitions across the ionization front (IF), dissociation front (DF), and the molecular cloud are studied at high-angular resolution. These transitions are relevant to understanding the effects of radiative feedback from massive stars and the dominant physical and chemical processes that lead to the IR emission that JWST will detect in many Galactic and extragalactic environments. Methods. We utilized NIRCam and MIRI to obtain sub-arcsecond images over ∼150′′ and 42′′ in key gas phase lines (e.g., Pa α, Br α, [FeII] 1.64 µm, H2 1–0 S(1) 2.12 µm, 0–0 S(9) 4.69 µm), aromatic and aliphatic infrared bands (aromatic infrared bands at 3.3–3.4 µm, 7.7, and 11.3 µm), dust emission, and scattered light. Their emission are powerful tracers of the IF and DF, FUV radiation field and density distribution. Using NIRSpec observations the fractional contributions of lines, AIBs, and continuum emission to our NIRCam images were estimated. A very good agreement is found for the distribution and intensity of lines and AIBs between the NIRCam and NIRSpec observations. Results. Due to the proximity of the Orion Nebula and the unprecedented angular resolution of JWST, these data reveal that the molecular cloud borders are hyper structured at small angular scales of ∼0.1–1′′ (∼0.0002–0.002 pc or ∼40–400 au at 414 pc). A diverse set of features are observed such as ridges, waves, globules and photoevaporated protoplanetary disks. At the PDR atomic to molecular transition, several bright features are detected that are associated with the highly irradiated surroundings of the dense molecular condensations and embedded young star. Toward the Orion Bar PDR, a highly sculpted interface is detected with sharp edges and density increases near the IF and DF. This was predicted by previous modeling studies, but the fronts were unresolved in most tracers. The spatial distribution of the AIBs reveals that the PDR edge is steep and is followed by an extensive warm atomic layer up to the DF with multiple ridges. A complex, structured, and folded H0/H2 DF surface was traced by the H2 lines. This dataset was used to revisit the commonly adopted 2D PDR structure of the Orion Bar as our observations show that a 3D “terraced” geometry is required to explain the JWST observations. JWST provides us with a complete view of the PDR, all the way from the PDR edge to the substructured dense region, and this allowed us to determine, in detail, where the emission of the atomic and molecular lines, aromatic bands, and dust originate. Conclusions. This study offers an unprecedented dataset to benchmark and transform PDR physico-chemical and dynamical models for the JWST era. A fundamental step forward in our understanding of the interaction of FUV photons with molecular clouds and the role of FUV irradiation along the star formation sequence is provided.
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26.
  • Huang, Shiyu, et al. (författare)
  • Single-Atom Metal Sites Anchored Hydrogen-Bonded Organic Frameworks for Superior “Two-In-One” Photocatalytic Reaction
  • 2023
  • Ingår i: Advanced Functional Materials. - : Wiley. - 1616-301X .- 1616-3028. ; 33:21
  • Tidskriftsartikel (refereegranskat)abstract
    • Photoredox catalysis is a green solution for organics transformation and CO2 conversion into valuable fuels, meeting the challenges of sustainable energy and environmental concerns. However, the regulation of single-atomic active sites in organic framework not only influences the photoredox performance, but also limits the understanding of the relationship for photocatalytic selective organic conversion with CO2 valorization into one reaction system. As a prototype, different single-atomic metal (M) sites (M2+ = Fe2+, Co2+, Ni2+, Cu2+, and Zn2+) in hydrogen-bonded organic frameworks (M-HOF) backbone with bridging structure of metal-nitrogen are constructed by a typical “two-in-one” strategy for superior photocatalytic C-N coupling reactions integrated with CO2 valorization. Remarkably, Zn-HOF achieves 100% conversion of benzylamine oxidative coupling reactions, 91% selectivity of N-benzylidenebenzylamine and CO2 conversion in one photoredox cycle. From X-ray absorption fine structure analysis and density functional theory calculations, the superior photocatalytic performance is attributed to synergic effect of atomically dispersed metal sites and HOF host, decreasing the reaction energy barriers, enhancing CO2 adsorption and forming benzylcarbamic acid intermediate to promote the redox recycle. This work not only affords the rational design strategy of single-atom active sites in functional HOF, but also facilitates the fundamental insights upon the mechanism of versatile photoredox coupling reaction systems.
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27.
  • Li, Bo, et al. (författare)
  • Boolean Gossip Networks
  • 2018
  • Ingår i: IEEE/ACM Transactions on Networking. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 1063-6692 .- 1558-2566. ; 26:1, s. 118-130
  • Tidskriftsartikel (refereegranskat)abstract
    • This paper proposes and investigates a Boolean gossip model as a simplified but non-trivial probabilistic Boolean network. With positive node interactions, in view of standard theories from Markov chains, we prove that the node states asymptotically converge to an agreement at a binary random variable, whose distribution is characterized for large-scale networks by mean-field approximation. Using combinatorial analysis, we also successfully count the number of communication classes of the positive Boolean network explicitly in terms of the topology of the underlying interaction graph, where remarkably minor variation in local structures can drastically change the number of network communication classes. With general Boolean interaction rules, emergence of absorbing network Boolean dynamics is shown to be determined by the network structure with necessary and sufficient conditions established regarding when the Boolean gossip process defines absorbing Markov chains. Particularly, it is shown that for the majority of the Boolean interaction rules, except for nine out of the total 2(16) - 1 possible nonempty sets of binary Boolean functions, whether the induced chain is absorbing has nothing to do with the topology of the underlying interaction graph, as long as connectivity is assumed. These results illustrate the possibilities of relating dynamical properties of Boolean networks to graphical properties of the underlying interactions.
  •  
28.
  • Li, Junfeng, et al. (författare)
  • A theoretical study on vibronic spectra and photo conversation process of protonated naphthalenes
  • 2018
  • Ingår i: Spectrochimica Acta Part A - Molecular and Biomolecular Spectroscopy. - : Pergamon Press. - 1386-1425 .- 1873-3557. ; 205, s. 520-527
  • Tidskriftsartikel (refereegranskat)abstract
    • The equilibrium structures and vibrational frequencies of the ground state and several singlet low-lying excited states of alpha-and beta-protonated naphthalenes (alpha-and beta-HN+) have been studied by time -dependent density -functional theory (TD-DFT). Within the Franck -Condon approximation, vibronic absorption spectra of alpha-HN+ and beta-HN+, together with the vibronic emission spectrum of alpha-HN+, have been calculated. The obtained good agreement between the theoretical and experimental spectra enables to correctly assign vibronic features in both absorption and emission spectra. Moreover, the non -radiative deactivation pathway from the low-lying excite states to the ground state in alpha-HN+ and beta-HN+, as well as the photo-induce proton transfer pathway, are investigated at the CASPT2/CASSCF/6-31G* level. Our study is helpful for understanding the photochemical behavior of these important polycyclic aromatic hydrocarbon molecules.
  •  
29.
  • Li, Junfeng, et al. (författare)
  • A time-dependent density-functional theory and complete active space self-consistent field method study of vibronic absorption and emission spectra of coumarin
  • 2014
  • Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 141:1, s. 014306-
  • Tidskriftsartikel (refereegranskat)abstract
    • Time-dependent density-functional theory (TD-DFT) and complete active space multiconfiguration self-consistent field (CASSCF) calculations have been used to determine equilibrium structures and vibrational frequencies of the ground state and several singlet low-lying excited states of coumarin. Vertical and adiabatic transition energies of S-1, S-2, and S-3 have been estimated by TD-B3LYP and CASSCF/PT2. Calculations predict that the dipole-allowed S-1 and S-3 states have a character of (1)(pi pi*), while the dipole-forbidden (1)(n pi*) state is responsible for S-2. The vibronic absorption and emission spectra of coumarin have been simulated by TD-B3LYP and CASSCF calculations within the Franck-Condon approximation, respectively. The simulated vibronic spectra show good agreement with the experimental observations available, which allow us to reasonably interpret vibronic features in the S-0 -> S-1 and S-0 -> S-3 absorption and the S-0 <- S-1 emission spectra. Based on the calculated results, activity, intensity, and density of the vibronic transitions and their contribution to the experimental spectrum profile have been discussed.
  •  
30.
  • Li, Jingyi, et al. (författare)
  • Cis-acting mutation affecting GJA5 transcription is underlying the Melanotic within-feather pigmentation pattern in chickens
  • 2021
  • Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences (PNAS). - 0027-8424 .- 1091-6490. ; 118:41
  • Tidskriftsartikel (refereegranskat)abstract
    • Melanotic (Ml) is a mutation in chickens that extends black (eumelanin) pigmentation in normally brown or red (pheomelanin) areas, thus affecting multiple within-feather patterns [J. W. Moore, J. R. Smyth Jr, J. Hered. 62, 215-219 (1971)]. In the present study, linkage mapping using a back-cross between Dark Cornish (Ml/Ml) and Partridge Plymouth Rock (ml(+)/ml(+)) chickens assigned Ml to an 820-kb region on chromosome 1. Identity-by-descent mapping, via whole-genome sequencing and diagnostic tests using a diverse set of chickens, refined the localization to the genomic region harboring GJA5 encoding gap-junction protein 5 (alias connexin 40) previously associated with pigmentation patterns in zebrafish. An insertion/deletion polymorphism located in the vicinity of the GJA5 promoter region was identified as the candidate causal mutation. Four different GJA5 transcripts were found to be expressed in feather follicles and at least two showed differential expression between genotypes. The results showed that Melanotic constitutes a cis-acting regulatory mutation affecting GJA5 expression. A recent study established the melanocortin-1 receptor (MC1R) locus and the interaction between the MC1R receptor and its antagonist agoutisignaling protein as the primary mechanism underlying variation in within-feather pigmentation patterns in chickens. The present study advances understanding the mechanisms underlying variation in plumage color in birds because it demonstrates that the activity of connexin 40/GJA5 can modulate the periodic pigmentation patterns within individual feathers.
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31.
  •  
32.
  • Li, Junfeng, et al. (författare)
  • The correct assignment of vibrationally-resolved absorption spectra of protonated anthracene isomers
  • 2021
  • Ingår i: Spectrochimica Acta Part A - Molecular and Biomolecular Spectroscopy. - : Elsevier. - 1386-1425 .- 1873-3557. ; 244
  • Tidskriftsartikel (refereegranskat)abstract
    • The assignment of experimental optical absorption spectra of protonated anthracene has been under debate for years. It is complicated by the presence of rich vibronic spectral features and the possible co-occurrence of two isomers, 9H-An(+) and 1H-An(+). In this study, the vibrationally resolved absorption spectra of 9H-An(+) and 1H-An(+) have been calculated using time-dependent density functional theory. The calculated vibronic spectra profiles of 9H-An(+) and 1H-An(+) are in excellent agreementwith the corresponding experimental results and provide unambiguously spectra assignments. It shows that the previously reported assignments based on vertical excitation energy are largelywrong. The onset located at 493.8 nmof the experimental spectrumcan be assigned to the S-0 -> S-1 transition of 9H-An(+), while the origin band located at 453.5 nmcorresponds to the S-0 -> S-2 transition of 1H-An(+).
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33.
  • Li, JunFeng, et al. (författare)
  • Theoretical studies on the vibrationally-resolved absorption and fluorescence spectra of H-Pyrene(+) and H-Coronene(+)
  • 2015
  • Ingår i: Chemical Physics Letters. - : Elsevier. - 0009-2614 .- 1873-4448. ; 641, s. 57-61
  • Tidskriftsartikel (refereegranskat)abstract
    • H-Pyrene and H-Coronene are important carrier candidates for the diffuse interstellar band. In order to understand the observed absorption and fluorescence emission spectra of H-Pyrene and H-Coronene, time-dependent density functional theory (TD-DFT) method and Franck-Condon approximation have been employed to simulate the corresponding vibrationally-resolved optical spectra. For H-Pyrene, the calculated absorption, emission and 0-0 band energies are in good agreement with the experimental values. The strong absorption and emission vibrational peaks near the 0-0 band match well with the experiment peaks. A noticeable deviation for several weak peaks far away from the origin band is observed, as a result of the vibronic coupling with other excited states. For H-Coronene, the predicted vibrationally resolved electronic absorption and emission spectra resemble very well their experimental counterparts spectra, allowing to fully assign the observed vibronic peaks.
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34.
  • Li, Junfeng, 1982- (författare)
  • Theoretical Studies on Vibrationally Resolved Optical Spectra of Polycyclic Aromatic Molecules
  • 2019
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Polycyclic aromatic molecules are of great interest owing to their many important applications in chemistry and have therefore been the focus of investigations for over half a century with spectroscopic techniques. This thesis is devoted to the modeling of vibrationally resolved optical spectra of polycyclic aromatic molecules. The general goal is to demonstrate the importance of nuclear motion on the electronic spectra and provide reliable spectral assignments and spectral fingerprints to distinguish different molecular isomers that are often not possible to be identified by experiments alone. In this thesis, four sets of polycyclic aromatic molecules have been systematically studied by using quantum chemistry methods. The simulated vibronic spectra are in good agreement with their experimental counterparts, which enables to provide correct reassignments for the electronic spectra.
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35.
  • Li, Xiaodong, et al. (författare)
  • Critical role of the external bias in improving the performance of polymer solar cells with a small molecule electrolyte interlayer
  • 2015
  • Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry. - 2050-7488 .- 2050-7496. ; 3:2, s. 504-508
  • Tidskriftsartikel (refereegranskat)abstract
    • A small-molecule electrolyte based on the popular ethylene diamine tetraacetic acid (EDTA-N) is introduced as an efficient cathode interlayer in inverted polymer solar cells, helping to deliver power conversion efficiency over 9%. The strong dependence of device performance on the external bias suggests that the ion motion plays a critical role in improving the performance of devices with electrolyte interlayers.
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36.
  • Li, Xiaodong, et al. (författare)
  • Disodium Edetate As a Promising Interfacial Material for Inverted Organic Solar Cells and the Device Performance Optimization
  • 2014
  • Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society. - 1944-8244 .- 1944-8252. ; 6:23, s. 20569-20573
  • Tidskriftsartikel (refereegranskat)abstract
    • Disodium edetate (EDTA-Na), a popular hexadentate ligand in analytical chemistry, was successfully introduced in organic solar cells (OSCs) as cathode interfacial layer. The inverted OSCs with EDTA-Na showed superior performance both in power conversion efficiency and devices stability compared with conventional devices. Interestingly, we found that the performance of devices with EDTA-Na could be optimized through external bias treatment. After optimization, the efficiency of inverted OSCs with device structure of ITO/EDTA-Na/polymer thieno[3,4-b]thiophene/benzodithiophene (PTB7):PC71BM/MoO3/Al was significantly increased to 8.33% from an initial value of 6.75%. This work introduces a new class of interlayer materials, small molecule electrolytes, for organic solar cells.
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37.
  • Li, Xiaodong, et al. (författare)
  • The effect of external electric field on the performance of perovskite solar cells
  • 2015
  • Ingår i: Organic electronics. - : Elsevier. - 1566-1199 .- 1878-5530. ; 18, s. 107-112
  • Tidskriftsartikel (refereegranskat)abstract
    • Planar heterojunction perovskite solar cells were fabricated through a low temperature approach. We find that the device performance significantly depends on the external bias before and during measurements. By appropriate optimization of the bias conditions, we could achieve an 8-fold increase in the power conversion efficiency. The significant improvement in device performance might be caused by the ion motion in the perovskite under the external electric field.
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38.
  • Li, Zhuwei, et al. (författare)
  • Engineering single-atom active sites anchored covalent organic frameworks for efficient metallaphotoredox C-N cross-coupling reactions
  • 2022
  • Ingår i: Science Bulletin. - : Elsevier BV. - 2095-9273. ; 67:19, s. 1971-1981
  • Tidskriftsartikel (refereegranskat)abstract
    • Photoredox catalysis has become an indispensable solution for the synthesis of small organic molecules. However, the precise construction of single-atomic active sites not only determines the catalytic performance, but also avails the understanding of structure-activity relationship. Herein, we develop a facile approach to immobilize single-atom Ni sites anchored porous covalent organic framework (COF) by use of 4,40,400-(1,3,5-triazine-2,4,6-triyl)trianiline and 2,6-diformylpyridine (Ni SAS/TD-COF). Ni SAS/TDCOF catalyst achieves excellent catalytic performance in visible-light-driven catalytic carbon-nitrogen cross-coupling reaction between aryl bromides and amines under mild conditions. The reaction provides amine products in excellent yields (71%-97%) with a wide range of substrates, including aryl and heteroaryl bromides with electron-deficient, electron-rich and neutral groups. Notably, Ni SAS/TD-COF could be recovered from the reaction mixture, corresponding to the negligible loss of photoredox performance after several cycles. This work provides a promising opportunity upon rational design of single-atomic active sites on COFs and the fundamental insight of photoredox mechanism for sustainable organic transformation.
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39.
  • Liu, Jinbiao, et al. (författare)
  • Study of n-type doping in germanium by temperature based PF+ implantation
  • 2020
  • Ingår i: Journal of materials science. Materials in electronics. - : Springer Science and Business Media LLC. - 0957-4522 .- 1573-482X. ; 31, s. 161-166
  • Tidskriftsartikel (refereegranskat)abstract
    • Incorporation of P in germanium was studied by using PF+ molecular implantation in a range from room temperature to 400 °C. The presence of F acted as a barrier for P in-diffusion and resulted in higher activation of P at room temperature. In addition, it is found that when the implantation is performed at 400 °C, the residual defects are stable and the diffusion of P can be blocked during activation annealing. Therefore, the final junction depth could be well controlled by the implantation process itself. This method is meaningful for the shallow junction formation in sub 14-nm Ge-based FinFETs or high-performance photodetectors. 
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40.
  • Liu, Yi, et al. (författare)
  • Effect of fluorine atoms on optoelectronic, aggregation and dielectric constants of 2,1,3-benzothiadiazole-based alternating conjugated polymers
  • 2021
  • Ingår i: Dyes and Pigments. - : Elsevier BV. - 0143-7208 .- 1873-3743. ; 193
  • Tidskriftsartikel (refereegranskat)abstract
    • Three 2,1,3-benzothiadiazole-based conjugated copolymers named PBDT-0F-BTs, PBDT-2F-BTs and PBDT-6F-FBTs, which were derived from 4,8-bis(4,5-dioctylthiophen-2-yl)benzo[1,2-b:4,5-b′]dithiophene and (3,4′-bis(2-hexyl- decyl)-2,2′-dithiophene-5-yl) substituted 2,1,3-benzothiadiazole and/or 5,6-difluoro- 2,1,3-benzothiadiazole derivatives with 2,2′-dithiophene and/or 3,3′-difluoro- 2,2′-dithiophene as π-linkers, were prepared and characterized. The copolymers PBDT-0F-BTs, PBDT-2F-BTs and PBDT-6F-FBTs exhibited the highest occupied molecular orbital (HOMO) and lowest unoccupied orbital (LUMO) energy levels of −5.38 eV/−3.57 eV, −5.45 eV/−3.65 eV and −5.55 eV/−3.78 eV, with the light response from 300 nm to 720–750 nm, alongside with the similar aggregation, except that the charge transporting mobilities were successively increased, and the dielectric constants were gradually improved from 3.3 to 4.8 to 5.9 at 1 KHz, while the fluorine atoms in the each repeat unit of polymers were varied from 0 to 2 and then up to 6, respectively. Beyond that, it has also been found that the power conversion efficiencies and exciton dissociation probability (P(E,T)) of the bulk heterojunction organic photovoltaic cells (BHJ-OPVs) from the blend films of polymers paired with Y6 (2,2'-((2Z,2'Z)-((12,13-bis(2-ethylhexyl)-3,9-diundecyl12,13-dihydro[1,2,5]thia- diazolo[3,4-e]thieno[2'',3'':4',5']thieno[2',3':4,5]pyrrolo[3,2-g]thieno[2',3':4,5]thieno[3,2-b]indole-2,10-diyl)bis(methanylylidene))bis(5,6-difluoro-3-oxo-2,3-dihydro-1H-ind-ene-2,1-diylidene))dimalononitrile), were varied from 7.83% and 85.9%, to 9.22% and 90.2% and then up to 12.34% and 91.4%. The results indicated that the continuous insertion of the fluorine atoms into the repeat units of the conjugated polymers would result in the consecutively deepening the HOMO energy levels, increase dielectric constants and charge mobilities, thus devote to the enhancement of the P(E,T) and the performance of the BHJ-OPVs.
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41.
  • Peeters, Els, et al. (författare)
  • PDRs4All: III. JWST's NIR spectroscopic view of the Orion Bar
  • 2024
  • Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 685
  • Tidskriftsartikel (refereegranskat)abstract
    • Context. JWST has taken the sharpest and most sensitive infrared (IR) spectral imaging observations ever of the Orion Bar photodis-sociation region (PDR), which is part of the nearest massive star-forming region the Orion Nebula, and often considered to be the 'prototypical'strongly illuminated PDR. Aims. We investigate the impact of radiative feedback from massive stars on their natal cloud and focus on the transition from the H II region to the atomic PDR -crossing the ionisation front (IF) -, and the subsequent transition to the molecular PDR -crossing the dissociation front (DF). Given the prevalence of PDRs in the interstellar medium and their dominant contribution to IR radiation, understanding the response of the PDR gas to far-ultraviolet (FUV) photons and the associated physical and chemical processes is fundamental to our understanding of star and planet formation and for the interpretation of any unresolved PDR as seen by JWST. Methods. We used high-resolution near-IR integral field spectroscopic data from NIRSpec on JWST to observe the Orion Bar PDR as part of the PDRs4All JWST Early Release Science programme. We constructed a 3″ × 25″ spatio-spectral mosaic covering 0.97-5.27 μm at a spectral resolution R of ~2700 and an angular resolution of 0.075″-0.173″. To study the properties of key regions captured in this mosaic, we extracted five template spectra in apertures centred on the three H2 dissociation fronts, the atomic PDR, and the H II region. This wealth of detailed spatial-spectral information was analysed in terms of variations in the physical conditions-incident UV field, density, and temperature -of the PDR gas. Results. The NIRSpec data reveal a forest of lines including, but not limited to, He I, H I, and C I recombination lines; ionic lines (e.g. Fe III and Fe II); O I and N I fluorescence lines; aromatic infrared bands (AIBs, including aromatic CH, aliphatic CH, and their CD counterparts); pure rotational and ro-vibrational lines from H2; and ro-vibrational lines from HD, CO, and CH+, with most of them having been detected for the first time towards a PDR. Their spatial distribution resolves the H and He ionisation structure in the Huygens region, gives insight into the geometry of the Bar, and confirms the large-scale stratification of PDRs. In addition, we observed numerous smaller-scale structures whose typical size decreases with distance from θ1 Ori C and IR lines from C I, if solely arising from radiative recombination and cascade, reveal very high gas temperatures (a few 1000 K) consistent with the hot irradiated surface of small-scale dense clumps inside the PDR. The morphology of the Bar, in particular that of the H2 lines, reveals multiple prominent filaments that exhibit different characteristics. This leaves the impression of a 'terraced'transition from the predominantly atomic surface region to the CO-rich molecular zone deeper in. We attribute the different characteristics of the H2 filaments to their varying depth into the PDR and, in some cases, not reaching the C+/C/CO transition. These observations thus reveal what local conditions are required to drive the physical and chemical processes needed to explain the different characteristics of the DFs and the photochemical evolution of the AIB carriers. Conclusions. This study showcases the discovery space created by JWST to further our understanding of the impact radiation from young stars has on their natal molecular cloud and proto-planetary disk, which touches on star and planet formation as well as galaxy evolution.
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42.
  • Qin, Changliang, et al. (författare)
  • Impact of pattern dependency of SiGe layers grown selectively in source/drain on the performance of 14 nm node FinFETs
  • 2016
  • Ingår i: Solid-State Electronics. - : Elsevier. - 0038-1101 .- 1879-2405. ; 124, s. 10-15
  • Tidskriftsartikel (refereegranskat)abstract
    • A complete mapping of 14 nm FinFETs performance over 200 mm wafers was performed and the pattern dependency of SiGe selective growth was calculated using an empirical kinetic molecule model for the reactant precursors. The transistor structures were analyzed by conventional characterization tools and their performance was simulated by considering the process related variations. The applied model presents for the first time a powerful tool for transistor community to predict the SiGe profile and strain modulating over a processed wafer, independent of wafer size.
  •  
43.
  • Qin, Changliang, et al. (författare)
  • Process optimizations to recessed e-SiGe source/drain for performance enhancement in 22 nm all-last high-k/metal-gate pMOSFETs
  • 2016
  • Ingår i: Solid-State Electronics. - : Elsevier. - 0038-1101 .- 1879-2405. ; 123, s. 38-43
  • Tidskriftsartikel (refereegranskat)abstract
    • In this paper, the technology of recessed embedded SiGe (e-SiGe) source/drain (S/D) module is optimized for the performance enhancement in 22 nm all-last high-k/metal-gate (HK/MG) pMOSFETs. Different Si recess-etch techniques were applied in S/D regions to increase the strain in the channel and subsequently, improve the performance of transistors. A new recess-etch method consists of a two-step etch method is proposed. This process is an initial anisotropic etch for the formation of shallow trench followed by a final isotropic etch. By introducing the definition of the upper edge distance (D) between the recessed S/D region and the channel region, the process advantage of the new approach is clearly presented. It decreases the value of D than those by conventional one-step isotropic or anisotropic etch of Si. Therefore, the series resistance is reduced and the channel strain is increased, which confirmed by the simulation results. The physical reason of D reducing is analyzed in brief. Applying this recess design, the implant conditions for S/D extension (SDE) are also optimized by using a two-step implantation of BF2 in SiGe layers. The overlap space between doping junction and channel region has great effect on the device's performance. The designed implantation profile decreases the overlap space while keeps a shallow junction depth for a controllable short channel effect. The channel resistance as well as the transfer ID-VG curves varying with different process conditions are demonstrated. It shows the drive current of the device with the optimized SDE implant condition and Si recess-etch process is obviously improved. The change trend of on-off current distributions extracted from a series of devices confirmed the conclusions. This study provides a useful guideline for developing high performance strained PMOS SiGe technology.
  •  
44.
  • Shao, Teng, et al. (författare)
  • A chemically bonded and plasmonic Z-scheme junction for high-performance artificial photosynthesis of hydrogen peroxide
  • 2022
  • Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry (RSC). - 2050-7488 .- 2050-7496. ; 11:3, s. 1199-1207
  • Tidskriftsartikel (refereegranskat)abstract
    • Artificial photosynthesis has been regarded as a promising solution for the clean, sustainable, and efficient production of hydrogen peroxide (H2O2). However, rigorous regulation of light absorption, charge transfer, and surface kinetics is significant for catalytic performance. As a proof of concept, we report a chemically bonded and plasmonic Z-scheme junction as a model material prepared by the in situ assembly of nonstoichiometric W18O49 (WO) onto two-dimensional carbon nitride nanosheets (CNs) for high-performance artificial photosynthesis of H2O2. Notably, this typical Z-scheme photocatalyst exhibits the highest H2O2 generation rate of 732.4 μmol g−1 h−1, higher than that of individual catalysts, even maintaining 140.5 μmol g−1 h−1 under broad-spectrum response irradiation (λ > 700 nm). From the analysis of experimental characterization and density functional theory calculations, the superior performance of CN/WO heterostructures is ascribed to an intense localized surface plasmon resonance absorption, appropriate band alignment, and strong internal electric field. This work not only elucidates the key role of chemically bonded and plasmonic heterostructures but also paves an avenue for the rational design and construction of Z-scheme photocatalysts for solar energy conversion.
  •  
45.
  • Wang, Guilei, et al. (författare)
  • Growth of SiGe layers in source and drain regions for 10 nm node complementary metal-oxide semiconductor (CMOS)
  • 2020
  • Ingår i: Journal of materials science. Materials in electronics. - : Springer Science and Business Media LLC. - 0957-4522 .- 1573-482X. ; 31, s. 26-33
  • Tidskriftsartikel (refereegranskat)abstract
    • In this study, the integration of Si 1−x Ge x (50% ≤ x ≤ 60%) selective epitaxy on source/drain regions in 10 nm node FinFET has been presented. One of the major process issues was the sensitivity of Si-fins’ shape to ex- and in-situ cleaning prior to epitaxy. For example, the sharpness of Si-fins could easily be damaged during the wafer washing. The results showed that a DHF dip before the normal cleaning, was essential to clean the Si-fins while in-situ annealing in range of 780–800 °C was needed to remove the native oxide for high epitaxial quality. Because of smallness of fins, the induced strain by SiGe could not be directly measured by X-ray beam in a typical XRD tool in the lab or even in a Synchrotron facility. Further analysis using nano-beam diffraction technique in high-resolution transmission electron microscope also failed to provide information about strain in the FinFET structure. Therefore, the induced strain by SiGe was simulated by technology computer-aided design program and the Ge content was measured by using energy dispersive spectroscopy. Simulation results showed 0.8, 1 and 1.3 GPa for Ge content of 40%, 50% and 60%, respectively. A kinetic gas model was also introduced to predict the SiGe profile on Si-fins with sharp triangular shape. The input parameters in the model includes growth temperature, partial pressure of the reactant gases and the exposed Si coverage in the chip area.
  •  
46.
  • Wang, Guilei, et al. (författare)
  • Integration of Highly Strained SiGe in Source and Drain with HK and MG for 22 nm Bulk PMOS Transistors
  • 2017
  • Ingår i: Nanoscale Research Letters. - : Springer. - 1931-7573 .- 1556-276X. ; 12
  • Tidskriftsartikel (refereegranskat)abstract
    • In this study, the integration of SiGe selective epitaxy on source/drain regions and high-k and metal gate for 22 nm node bulk pMOS transistors has been presented. Selective Si1-xGex growth (0.35 <= x <= 0.40) with boron concentration of 1-3 x 10(20) cm(-3) was used to elevate the source/drain. The main focus was optimization of the growth parameters to improve the epitaxial quality where the high-resolution x-ray diffraction (HRXRD) and energy dispersive spectrometer (EDS) measurement data provided the key information about Ge profile in the transistor structure. The induced strain by SiGe layers was directly measured by x-ray on the array of transistors. In these measurements, the boron concentration was determined from the strain compensation of intrinsic and boron-doped SiGe layers. Finally, the characteristic of transistors were measured and discussed showing good device performance.
  •  
47.
  • Wang, Guilei, et al. (författare)
  • Integration of highly-strained SiGe materials in 14 nm and beyond nodes FinFET technology
  • 2015
  • Ingår i: Solid-State Electronics. - : Elsevier BV. - 0038-1101 .- 1879-2405. ; 103, s. 222-228
  • Tidskriftsartikel (refereegranskat)abstract
    • SiGe has been widely used as stressors in source/drain (S/D) regions of Metal-Oxide-Semiconductor Field Effect Transistor (MOSFET) to enhance the channel mobility. In this study, selectively grown Si1-xGex (0.33 <= x <= 0.35) with boron concentration of 1 x 10(20) cm(-3) was used to elevate the S/D regions on bulk FinFETs in 14 nm technology node. The epitaxial quality of SiGe layers, SiGe profile and the strain amount of the SiGe layers were investigated. In order to in-situ clean the Si-fins before SiGe epitaxy, a series of prebaking experiments at temperature ranging from 740 to 825 degrees C were performed. The results showed that the thermal budget needs to be limited to 780-800 degrees C in order to avoid any damage to the shape of Si-fins but to remove the native oxide which is essential for high epitaxial quality. In this study, a kinetic gas niodel was also applied to predict the SiGe growth profile on Si-fins with trapezoidal shape. The input parameters for the model include growth temperature, partial pressures of reactant gases and the chip layout. By knowing the epitaxial profile, the strain to the Si-fins exerted by SiGe layers can be calculated. This is important in understanding the carrier transport in the FinFETs. The other benefit of the modeling is that it provides a cost-effective alternative for epitaxy process development as the SiGe profile can be readily predicted for any chip layout in advance.
  •  
48.
  • Wang, Guilei, et al. (författare)
  • pMOSFETs Featuring ALD W Filling Metal Using SiH4 and B2H6 Precursors in 22 nm Node CMOS Technology
  • 2017
  • Ingår i: Nanoscale Research Letters. - : SPRINGER. - 1931-7573 .- 1556-276X. ; 12
  • Tidskriftsartikel (refereegranskat)abstract
    • In this paper, pMOSFETs featuring atomic layer deposition (ALD) tungsten (W) using SiH4 and B2H6 precursors in 22 nm node CMOS technology were investigated. It is found that, in terms of threshold voltage, driving capability, carrier mobility, and the control of short-channel effects, the performance of devices featuring ALD W using SiH4 is superior to that of devices featuring ALD W using B2H6. This disparity in device performance results from different metal gate-induced strain from ALD W using SiH4 and B2H6 precursors, i.e. tensile stresses for SiH4 (similar to 2.4 GPa) and for B2H6 (similar to 0.9 GPa).
  •  
49.
  • Wang, Guilei, et al. (författare)
  • Study of SiGe selective epitaxial process integration with high-k and metal gate for 16/14 nm nodes FinFET technology
  • 2016
  • Ingår i: Microelectronic Engineering. - : Elsevier. - 0167-9317 .- 1873-5568. ; 163, s. 49-54
  • Tidskriftsartikel (refereegranskat)abstract
    • In this study, the process integration of SiGe selective epitaxy on source/drain regions, for 16/14 nm nodes FinFET with high-k & metal gate has been presented. Selectively grown Si1-xGex (0.35 <= x <= 0.40) with boron concentration of 1 x 10(20) cm(-3) was used to elevate the source/drain of the transistors. The epi-quality, layer profile and strain amount of the selectively grown SiGe layers were also investigated by means of various characterizations. A series of prebaking experiments were performed for temperatures ranging from 740 to 825 degrees C in order to in situ clean the Si fins prior to the epitaxy. The results showed that the thermal budget needs to be limited to 780-800 degrees C in order to avoid any damages to the shape of Si fins but to remove the native oxide effectively which is essential for high epitaxial quality. The Ge content in SiGe layers on Si fins was determined from the strain measured directly by reciprocal space mappings using synchrotron radiation. Atomic layer deposition technique was applied to fill the gate trench with W using WF6 and B2H6 precursors. By such an AID approach, decent growth rate, low resistivity and excellent gap filling capability of W in pretty high aspect-ratio gate trench was realized. The as-fabricated FinFETs demonstrated decent electrical characteristics.
  •  
50.
  • Yao, Yao, et al. (författare)
  • The effect of China's Clean Air Act on cognitive function in older adults : a population-based, quasi-experimental study
  • 2022
  • Ingår i: Lancet Healthy Longevity. - 2666-7568. ; 3:2, s. e98-e108
  • Tidskriftsartikel (refereegranskat)abstract
    • Background Air pollution might accelerate cognitive ageing; it is unclear whether large-scale interventions, such as China's Clean Air Act (CCAA), can mitigate cognitive deterioration. We aimed to evaluate the effect of CCAA on changes in cognitive function in older adults.Methods In this population-based, quasi-experimental study, we did a difference-in-differences analysis of the data collected during the 2014 and 2018 waves of the Chinese Longitudinal Healthy Longevity Survey (CLHLS). The study design used a counterfactual analysis feature by dividing CLHLS participants into two groups. The intervention group included participants who lived in areas where the provincial government set a target of reducing particulate matter (PM) by at least 5% annually from 2014 onward, whereas the control group consisted of individuals who lived in areas without a PM reduction target. Global cognitive function was measured using the Mini-Mental State Examination (MMSE). We used fixed-effects models to examine the between-group differences in MMSE score changes before and after CCAA implementation. We associated longitudinal changes in MMSE scores with changes in concentrations of PM with a diameter of less than 2·5 μm (PM2·5) concentration and other regulated pollutants. We used alternative models and sensitivity analyses to evaluate the robustness of the results from the main models.Findings 2812 individuals participated in the 2014 and 2018 surveys (mean age 81·0 years [SD 9·3] in 2014; 1408 [50·1%] female and 1404 [49·9%] male). 2251 (80·0%) were included in the intervention group and 561 (20·0%) in the control group. After controlling for potential confounders, the intervention group had a significantly smaller decline in MMSE scores from 2014 to 2018 compared with the control group: the mean between-group difference was 2·45 points (95% CI 1·32–3·57). Interquartile increases in PM2·5 were associated with a significant MMSE score decline of 0·83 points (95% CI 0·24–1·42); similarly, increases in SO2 were also associated with a significant MMSE score decline of 0·80 points (0·32–1·29).Interpretation Implementing stringent clean air policies might mitigate the risk of air pollutant-associated cognitive ageing in older people.
  •  
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