| 1. |
- 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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| 2. |
- Xu, Chun Kai, et al.
(författare)
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Nonlinear inelastic electron scattering revealed by plasmon-enhanced electron energy-loss spectroscopy
- 2014
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Ingår i: Nature Physics. - 1745-2473 .- 1745-2481. ; 10:10, s. 753-757
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Tidskriftsartikel (refereegranskat)abstract
- Electron energy-loss spectroscopy is a powerful tool for identifying the chemical composition of materials(1-5). It relies mostly on the measurement of inelastic electrons, which carry specific atomic or molecular information. Inelastic electron scattering, however, has a very low intensity, often orders of magnitude weaker than that of elastically scattered electrons. Here, we report the observation of enhanced inelastic electron scattering from silver nanostructures, the intensity of which can reach up to 60% of its elastic counterpart. A home-made scanning probe electron energy-loss spectrometer(6) was used to produce highly localized plasmonic excitations, significantly enhancing the strength of the local electric field of silver nanostructures. The intensity of inelastic electron scattering was found to increase nonlinearly with respect to the electric field generated by the tip-sample bias, providing direct evidence of nonlinear electron scattering processes.
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| 3. |
- Gao, Bin, et al.
(författare)
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Studies of bromine modified single-walled carbon nanotubes using photoelectron spectroscopy and density-functional theory
- 2006
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Ingår i: Radiation Physics and Chemistry. - : Elsevier BV. - 0969-806X .- 1879-0895. ; 75:11, s. 1939-1942
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Tidskriftsartikel (refereegranskat)abstract
- Many applications based on single-walled carbon nanotubes (SWNTs) require chemical modification of carbon nanotube to optimize the functionalities of the device. In this contribution we discuss the properties of SWNTs immersed in a hydrobromic acid (HBr) solution. Changes of atomic and electronic structures of bromine modified SWNTs were investigated using photoelectron spectroscopy (PES). Spectra of SWNTs before and after immersion in the HBr solution exhibit different features. To understand the mechanism of interaction between SWNTs and bromine, we performed density-functional theory calculations to reveal the structural changes, adsorption energy and chemical bonding information of SWNTs interacting with bromine. In addition, based on the Gelius model, from the molecular orbitals (MOs), we calculated ultraviolet photoelectron spectra (UPS) of SWNTs with and without functionalizing and compared them with the experiment. The present study is a first step in the understanding of the functionalization mechanism of carbon nanotubes.
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| 4. |
- Hu, Wei, et al.
(författare)
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Tunable Single-Photon Emission by Defective Boron-Nitride Nanotubes for High-Precision Force Detection
- 2019
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Ingår i: The Journal of Physical Chemistry C. - : AMER CHEMICAL SOC. - 1932-7447 .- 1932-7455. ; 123:14, s. 9624-9628
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Tidskriftsartikel (refereegranskat)abstract
- Boron-nitride nanotubes (BNNTs) hold great potential for electronic, optical, and mechanical applications. By introducing a NBVN defect of removing one nitrogen atom while replacing one boron by nitrogen atom, we examined the use of defective NBVN@BNNTs as a novel type of single-photon emission (SPE) material. Using first-principles calculations to reveal the electronic structures of NBVN@BNNTs, we found that SPE with 1.45-2.29 eV energy can be generated in NBVN@BNNTs with size ranging from (5,0) to (10,0). It is also intriguing to find that their SPE responses are sensitive to the external forces, as indicated by the computed potential energy surfaces and dielectric tensors. Specifically, the (7,0) NBVN@BNNT can serve as an ideal force detector due to its sensitivity and linear response to external force. However, the (5,0) and (6,0) NBVN@BNNTs exhibit insensitive SPE with respect to force applied, and the detection ability of the (8,0), (9,0), and (10,0) NBVN@BNNTs are limited due to the emergence of new photon emissions when tensions become larger than 10 nN. These findings would open a new door for utilizing defective BNNTs for SPE and mechanical detection applications.
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| 5. |
- Hua, Weijie, et al.
(författare)
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Systematic Study of Soft X-ray Spectra of Poly(Dg)center dot Poly(Dc) and Poly(Da)center dot Poly(Dt) DNA Duplexes
- 2010
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 114:20, s. 7016-7021
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Tidskriftsartikel (refereegranskat)abstract
- In the present work, we have undertaken a combined experimental and theoretical study of X-ray spectroscopies for DNA base pairs, more precisely near-edge X-ray absorption, X-ray emission, and resonant inelastic X-ray scattering applied to poly(dG)center dot poly(dC) and poly(dA)center dot poly(dT) DNA duplexes. We have derived several conclusions on the nature of these X-ray spectra: the stacking of pairs has very little influence on the spectra; the spectra of a DNA composed of mixed Watson-Crick base pairs are well reproduced by linear combinations of GC and AT base pairs involved; the amine and imine nitrogens show noticeable differences as building blocks in the absorption, emission, and resonant emission spectra. The calculated spectra are in good agreement with experimental results. The ramifications of these conclusions for the use of X-ray spectroscopy for DNA are discussed.
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| 6. |
- Li, Hongbao, et al.
(författare)
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Identification of the protonation site of gaseous triglycine : the cis-peptide bond conformation as the global minimum
- 2017
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry. - 1463-9076 .- 1463-9084. ; 19:23, s. 15030-15038
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Tidskriftsartikel (refereegranskat)abstract
- Extensive ab initio investigations have been performed to characterize stable conformers of protonated triglycine (GGGH) in the gas phase. Calculations using the composite CBS-QB3 method confirmed that the most favorable site of protonation on triglycine at 298 K is still the traditional amino nitrogen, rather than the more-recently reported amide oxygen. Furthermore, a non-proline cis-peptide bond conformer is identified for the first time as the global minimum of GGGH. Further transition state calculations considering the temperature effects explained why the previous experimental infrared multiple photon dissociation (IRMPD) spectrum contains a combination of two local minima, rather than a global one. First-principles simulations have been performed for near-edge X-ray absorption fine-structure (NEXAFS) spectra and X-ray photoelectron spectra (XPS) at the C, N and O K-edges to identify the notable spectral differences that enable the unambiguous identification of different protonated forms. The calculated proton affinity (PA) and gas basicity (GB) of triglycine are in excellent agreement with the experimental values. Our study thus provides valuable insights into the protonation of short peptides and illustrates the competition between cis and trans peptide bonds.
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| 7. |
- Li-Juan, Zhang, et al.
(författare)
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A novel water layer structure inside nanobubbles at room temperature
- 2014
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Ingår i: NUCL SCI TECH. - 1001-8042. ; 25:6, s. 060503-
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Tidskriftsartikel (refereegranskat)abstract
- Molecularly thin water layer, with a hydrogen bonding network different from those in bulk water and ice, has unique properties and is generally involved in many important processes such as wetting, erosion, atmosphere chemical reaction, protein folding and biomolecular interaction. Here, we report a new water layer structure at room temperature, which is found inside nanobubbles by using synchrotron based scanning transmission soft X-ray microscopy (STXM). The three peaks 535.0, 536.8 and 540.9 eV at O K edge inside the nanobubbles show a novel characteristics of very thin water layers, which has never been observed before.
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| 8. |
- Li, Shaohan, et al.
(författare)
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Pushing the limit of thermal conductivity of MAX borides and MABs
- 2022
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Ingår i: Journal of Materials Science & Technology. - : Elsevier. - 1005-0302. ; 97, s. 79-88
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Tidskriftsartikel (refereegranskat)abstract
- The emergence of MAX borides as well as MAB phases attracted great attention because of the renewable developments of ternary ceramics and offering great opportunities in potential applications. However, the number of borides remains limited, and further fundamental descriptions and detailed investigations on various properties are still lacking. In this report, we employ an integrated computational scheme that combines density functional theory with the evolutional algorithm to search for the favorable structures of P- and S-glued ternary borides terminated by Nb metal. We discover that the structures of 212-type, as e.g. Nb2PB2 and Nb2SB2, belong to the P‾6m2 space group, while those of 211-type, as e.g. Nb2PB and Nb2SB, prefer to crystallize in the P63/mmc space group, and the corresponding carbides Nb2PC and Nb2SC are also considered for the sake of completeness and comparative analsys. The predicted Nb2PB2, Nb2PB, Nb2SB, Nb2PC and Nb2SC are energetically stable, as revealed by the negative formation energies and by the proposed reaction paths with respect to the most competing phases, as well as dynamically stable, as suggested by the non-imaginary phonon spectra. The thermal conductivities of the six materials show unusual behaviors, particularly for the acoustic and optical contributions, and are accompanied by a strong anisotropy. Most importantly, Nb2PB2 is found to be an excellent thermal conductor with a total thermal conductivity of ~65 W/(m K), while Nb2SC is found to be an ultra-low thermal conductor, with a total thermal conductivity of ~5 W/(m K). These values are clearly outside the currently reported range of thermal conductivities, which makes Nb2PB2 and Nb2SC extremely interesting for fundamental research as well as prospective applications with the aid of artificial tunings on the almost independent MB block and the A layer. The discovery of these novel materials is expected to contribute substantially to the rapid development of ternary ceramics and to accelerate attempts in the applicability of MAX phases for heat conduction.
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| 9. |
- Li, Xiao-Fei, et al.
(författare)
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Unraveling the formation mechanism of graphitic nitrogen-doping in thermally treated graphene with ammonia
- 2016
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Ingår i: Scientific Reports. - : Nature Publishing Group. - 2045-2322. ; 6
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Tidskriftsartikel (refereegranskat)abstract
- Nitrogen-doped graphene (N-graphene) has attractive properties that has been widely studied over the years. However, its possible formation process still remains unclear. Here, we propose a highly feasible formation mechanism of the graphitic-N doing in thermally treated graphene with ammonia by performing ab initio molecular dynamic simulations at experimental conditions. Results show that among the commonly native point defects in graphene, only the single vacancy 5-9 and divacancy 555-777 have the desirable electronic structures to trap N-containing groups and to mediate the subsequent dehydrogenation processes. The local structure of the defective graphene in combining with the thermodynamic and kinetic effect plays a crucial role in dominating the complex atomic rearrangement to form graphitic-N which heals the corresponding defect perfectly. The importance of the symmetry, the localized force field, the interaction of multiple trapped N-containing groups, as well as the catalytic effect of the temporarily formed bridge-N are emphasized, and the predicted doping configuration agrees well with the experimental observation. Hence, the revealed mechanism will be helpful for realizing the targeted synthesis of N-graphene with reduced defects and desired properties.
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| 10. |
- Lian, Ke-Yan, et al.
(författare)
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Big Bandgap in Highly Reduced Graphene Oxides
- 2013
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 117:12, s. 6049-6054
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Tidskriftsartikel (refereegranskat)abstract
- It is generally believed that the bandgap of the graphene oxide is proportional to the concentration of the oxygen atoms and a highly reduced graphene oxide (rGO) without vacancy defects should be gapless. We show here from first principles calculations that the bandgap can be effectively opened even in low oxidation level with the absorption of oxygen atoms either symmetrically or asymmetrically. The properly arranged absorption can induce a bandgap up to 1.19 eV for a C/O ratio of 16/1 in a symmetric system and a bandgap up to 1.58 eV for a C/O ratio of 32/3 in an asymmetric system, at generalized gradient approximation (GGA) level. The hybridization between the in-plane p(xy) orbitals of oxygen atoms and the out-of-plane p(z) frontier orbital of graphene is responsible for the opening of the bandgap. This finding sheds new light on the bandgap engineering of graphene.
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