| 1. |
- Li, Wenxiong, et al.
(författare)
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Can the Helium-detonation Model Explain the Observed Diversity of Type Ia Supernovae?
- 2021
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 906:2
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Tidskriftsartikel (refereegranskat)abstract
- We study a sample of 16 Type Ia supernovae (SNe Ia) having both spectroscopic and photometric observations within 2-3 days after the first light. The early B - V colors of such a sample tend to show a continuous distribution. For objects with normal ejecta velocity (NV), the C ii lambda 6580 feature is always visible in the early spectra, while it is absent or very weak in the high-velocity (HV) counterpart. Moreover, the velocities of the detached high-velocity features (HVFs) of the Ca II near-IR triplet (CaIR3) above the photosphere are found to be much higher in HV objects than in NV objects, with typical values exceeding 30,000 km s(-1) at 2-3 days. We further analyze the relation between the velocity shift of late-time [Fe II] lines (v([Fe II])) and host galaxy mass. We find that all HV objects have redshifted v([Fe II]), while NV objects have both blue- and redshifted v([Fe II]). It is interesting to point out that the objects with redshifted v([Fe II]) are all located in massive galaxies, implying that HV and a portion of NV objects may have similar progenitor metallicities and explosion mechanisms. We propose that, with a geometric/projected effect, the He-detonation model may account for the similarity in birthplace environment and the differences seen in some SNe Ia, including B - V colors, C II features, CaIR3 HVFs at early times, and v([Fe II]) in the nebular phase. Nevertheless, some features predicted by He-detonation simulation, such as the rapidly decreasing light curve, deviate from the observations, and some NV objects with blueshifted nebular v([Fe II]) may involve other explosion mechanisms.
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| 2. |
- Ai-Xi, Chen, et al.
(författare)
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Potential-Induced Phase Transition of N-Isobutyryl-L-cysteine Monolayers on Au(111) Surfaces
- 2017
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Ingår i: Wuli huaxue xuebao. - : PEKING UNIV PRESS. - 1000-6818. ; 33:5, s. 1010-1016
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Tidskriftsartikel (refereegranskat)abstract
- Functional solid substrates modified by self-assembled monolayers (SAMs) have potential applications in biosensors, chromatography, and biocompatible materials. The potential-induced phase transition of N-isobutyryl-L-cysteine (L-NIBC) SAMs on Au(111) surfaces was investigated by in-situ electrochemical scanning tunneling microscopy (EC-STM) in 0.1 mol.L-1 H2SO4 solution. The NIBC SAMs with two distinct structures (alpha phase and beta phase) can be prepared by immersing the Au(111) substrate in pure NIBC aqueous solution and NIBC solution controlled by phosphate buffer at pH 7, respectively. The as-prepared a phase and beta phase of NIBC SAMs show various structural changes under the control of electrochemical potentials of the Au(111) in H2SO4 solution. The a phase NIBC SAMs exhibit structural changes from ordered to disordered structures with potential changes from 0.7 V (vs saturated calomel electrode, SCE) to 0.2 V. However, the beta phase NIBC SAMs undergo structural changes from disordered structures (E < 0.3 V) to y phase (0.4 V < E < 0.5 V) and finally to the beta phase (0.5 V < E < 0.7 V). EC-STM images also indicate that the phase transition from the alpha phase NIBC SAMs to the a phase occurs at positive potential. Combined with density functional theory (DFT) calculations, the phase transition from the beta phase to the a phase is explained by the potential-induced break of bonding interactions between -COO- and the negatively charged gold surfaces.
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| 3. |
- Chang, Qingyan, et al.
(författare)
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Precursor engineering enables high-performance all-inorganic CsPbIBr2 perovskite solar cells with a record efficiency approaching 13%
- 2024
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Ingår i: Journal of Energy Chemistry. - : Elsevier BV. - 2095-4956 .- 2096-885X. ; 90, s. 16-22
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Tidskriftsartikel (refereegranskat)abstract
- All-inorganic CsPbIBr2 perovskite has attracted widespread attention in photovoltaic and other optoelectronic devices because of its superior thermal stability. However, the deposition of high-quality solution-processed CsPbIBr2 perovskite films with large thicknesses remains challenging. Here, we develop a triple-component precursor (TCP) by employing lead bromide, lead iodide, and cesium bromide, to replace the most commonly used double-component precursor (DCP) consisting of lead bromide and cesium iodide. Remarkably, the TCP system significantly increases the solution concentration to 1.3 M, leading to a larger film thickness (∼390 nm) and enhanced light absorption. The resultant CsPbIBr2 films were evaluated in planar n-i-p structured solar cells, which exhibit a considerably higher optimal photocurrent density of 11.50 mA cm−2 in comparison to that of DCP-based devices (10.69 mA cm−2). By adopting an organic surface passivator, the maximum device efficiency using TCP is further boosted to a record efficiency of 12.8% for CsPbIBr2 perovskite solar cells.
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| 4. |
- Chen, Pan, et al.
(författare)
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Small Angle Neutron Scattering Shows Nanoscale PMMA Distribution in Transparent Wood Biocomposites
- 2021
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 21:7, s. 2883-2890
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Tidskriftsartikel (refereegranskat)abstract
- Transparent wood biocomposites based on PMMA combine high optical transmittance with excellent mechanical properties. One hypothesis is that despite poor miscibility the polymer is distributed at the nanoscale inside the cell wall. Small-angle neutron scattering (SANS) experiments are performed to test this hypothesis, using biocomposites based on deuterated PMMA and "contrast-matched" PMMA. The wood cell wall nanostructure soaked in heavy water is quantified in terms of the correlation distance d between the center of elementary cellulose fibrils. For wood/deuterated PMMA, this distance d is very similar as for wood/heavy water (correlation peaks at q approximate to 0.1 angstrom(-1)). The peak disappears when contrast-matched PMMA is used, indeed proving nanoscale polymer distribution in the cell wall. The specific processing method used for transparent wood explains the nanocomposite nature of the wood cell wall and can serve as a nanotechnology for cell wall impregnation of polymers in large wood biocomposite structures.
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| 5. |
- Duan, Sai, et al.
(författare)
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Density functional theory study on the adsorption and decomposition of the formic acid catalyzed by highly active mushroom-like Au@Pd@Pt tri-metallic nanoparticles
- 2013
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 15:13, s. 4625-4633
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Tidskriftsartikel (refereegranskat)abstract
- Local structures and adsorption energies of a formic acid molecule and its decomposed intermediates (H, O, OH, CO, HCOO, and COOH) on highly electrocatalytically active mushroom-like Au-core@Pd-shell@Pt-cluster nanoparticles with two atomic layers of the Pd shell and stoichiometric Pt coverage of around half-monolayer (Au@2 ML Pd@0.5 ML Pt) have been investigated by first principles calculations. The adsorption sites at the center (far away from the Pt cluster) and the edge (close to the Pt cluster) are considered and compared. Significant repulsive interaction between the edge sites and CO is observed. The calculated potential energy surfaces demonstrate that, with respect to the center sites, the CO2 pathway is considerably promoted in the edge area. Our results reveal that the unique edge structure of the Pt cluster is responsible for the experimentally observed high electrocatalytic activity of the Au@Pd@Pt nanoparticles toward formic acid oxidation. Such microscopic understanding should be useful for the design of new electrochemical catalysts.
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| 6. |
- Li, C. -Y, et al.
(författare)
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Observation of inhomogeneous plasmonic field distribution in a nanocavity
- 2020
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Ingår i: Nature Nanotechnology. - : Nature Research. - 1748-3387 .- 1748-3395.
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Tidskriftsartikel (refereegranskat)abstract
- The progress of plasmon-based technologies relies on an understanding of the properties of the enhanced electromagnetic fields generated by the coupling nanostrucutres1–6. Plasmon-enhanced applications include advanced spectroscopies7–10, optomechanics11, optomagnetics12 and biosensing13–17. However, precise determination of plasmon field intensity distribution within a nanogap remains challenging. Here, we demonstrate a molecular ruler made from a set of viologen-based, self-assembly monolayers with which we precisely measures field distribution within a plasmon nanocavity with ~2-Å spatial resolution. We observed an unusually large plasmon field intensity inhomogeneity that we attribute to the formation of a plasmonic comb in the nanocavity. As a consequence, we posit that the generally adopted continuous media approximation for molecular monolayers should be used carefully.
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| 7. |
- Li, Daobin, et al.
(författare)
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Atomically dispersed platinum supported on curved carbon supports for efficient electrocatalytic hydrogen evolution
- 2019
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Ingår i: Nature Energy. - : Nature Publishing Group. - 2058-7546. ; 4:6, s. 512-518
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Tidskriftsartikel (refereegranskat)abstract
- Dispersing catalytically active metals as single atoms on supports represents the ultimate in metal utilization efficiency and is increasingly being used as a strategy to design hydrogen evolution reaction (HER) electrocatalysts. Although platinum (Pt) is highly active for HER, given its high cost it is desirable to find ways to improve performance further while minimizing the Pt loading. Here, we use onion-like nanospheres of carbon (OLC) to anchor stable atomically dispersed Pt to act as a catalyst (Pt-1/OLC) for the HER. In acidic media, the performance of the Pt-1/OLC catalyst (0.27 wt% Pt) in terms of a low overpotential (38 mV at 10 mA cm(-2)) and high turnover frequencies (40.78 H-2 s(-1) at 100 mV) is better than that of a graphene-supported single-atom catalyst with a similar Pt loading, and comparable to a commercial Pt/C catalyst with 20 wt% Pt. First-principle calculations suggest that a tip-enhanced local electric field at the Pt site on the curved support promotes the reaction kinetics for hydrogen evolution.
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| 8. |
- Li, Xiyu, et al.
(författare)
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On the Mechanism for the Extremely Efficient Sensitization of Yb3+ Luminescence in CsPbCl3 Nanocrystals
- 2019
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Ingår i: Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185 .- 1948-7185. ; 10:3, s. 487-492
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Tidskriftsartikel (refereegranskat)abstract
- Rare earth ion (RE3+)-doped inorganic CsPbX3 (X = Cl or Cl/Br) nanocrystals have been presented as promising materials for applications in solar-energy conversion technology. An extremely efficient sensitization of Yb3+ luminescence in CsPbCl3 nanoparticles (NCs) was very recently demonstrated where quantum cutting is responsible for the performance of photoluminescence quantum yields over 100% (T. J. Milstein, et al. Nano Letters 2018, 18, 3792). In the present work, based on the cubic phase of inorganic perovskite, we seek to obtain atom-level insight into the basic mechanisms behind these observations in order to boost the further development of RE3+-doped CsPbX3 NCs for optoelectronics. In our calculations of cubic crystal structure, we do not find any energy level formed in the middle of the band gap, which disfavors a mechanism of stepwise energy transfer from the perovskite host to two Yb3+ ions. Our work indicates that the configuration with "right-angle" Yb3+-V-Pb-Yb3+ couple is most likely to form in Yb3+-doped CsPbCl3. Associated with this "right-angle" couple, the "right-angle" Pb atom with trapped excited states would localize the photogenerated electrons and act as the energy donor in a quantum cutting process, which achieves simultaneous sensitization of two neighboring Yb3+ ions.
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| 9. |
- Liu, Zhu, et al.
(författare)
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Targeted opportunities to address the climate-trade dilemma in China
- 2016
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Ingår i: Nature Climate Change. - : Nature Publishing Group. - 1758-678X .- 1758-6798. ; 6:2, s. 201-
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Tidskriftsartikel (refereegranskat)abstract
- International trade has become the fastest growing driver of global carbon emissions, with large quantities of emissions embodied in exports from emerging economies. International trade with emerging economies poses a dilemma for climate and trade policy: to the extent emerging markets have comparative advantages in manufacturing, such trade is economically efficient and desirable. However, if carbon-intensive manufacturing in emerging countries such as China entails drastically more CO2 emissions than making the same product elsewhere, then trade increases global CO2 emissions. Here we show that the emissions embodied in Chinese exports, which are larger than the annual emissions of Japan or Germany, are primarily the result of China's coal-based energy mix and the very high emissions intensity (emission per unit of economic value) in a few provinces and industry sectors. Exports from these provinces and sectors therefore represent targeted opportunities to address the climate-trade dilemma by either improving production technologies and decarbonizing the underlying energy systems or else reducing trade volumes.
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| 10. |
- Zhang, Qun, et al.
(författare)
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The Realistic Domain Structure of As-Synthesized Graphene Oxide from Ultrafast Spectroscopy
- 2013
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 135:33, s. 12468-12474
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Tidskriftsartikel (refereegranskat)abstract
- Graphene oxide (GO) is an attractive alternative for large-scale production of graphene, but its general structure is still under debate due to its complicated nonstoichiometric nature. Here we perform a set of femto-second pump-probe experiments on as-synthesized GO to extrapolate structural information in situ. Remarkably, it is observed that, in these highly oxidized GO samples, the ultrafast graphene-like dynamics intrinsic to pristine graphene is completely dominant over a wide energy region and can be modified by the localized impurity states and the electron-phonon coupling under certain conditions. These observations, combined with the X-ray photoelectron spectroscopy analysis and control experiments, lead to an important conclusion that GO consists of two types of domain, namely the carbon-rich graphene-like domain and the oxygen-rich domain. This study creates a new understanding of the realistic domain structure and properties of as-synthesized GO, offering useful guidance for future applications based on chemically modified/functionalized graphenes.
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