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1.
Proc Natl Acad Sci U S A ; 121(23): e2400727121, 2024 Jun 04.
Artigo em Inglês | MEDLINE | ID: mdl-38819998

RESUMO

Understanding the interplay between charge, nematic, and structural ordering tendencies in cuprate superconductors is critical to unraveling their complex phase diagram. Using pump-probe time-resolved resonant X-ray scattering on the (0 0 1) Bragg peak at the Cu [Formula: see text] and O [Formula: see text] resonances, we investigate nonequilibrium dynamics of [Formula: see text] nematic order and its association with both charge density wave (CDW) order and lattice dynamics in La[Formula: see text]Eu[Formula: see text]Sr[Formula: see text]CuO[Formula: see text]. The orbital selectivity of the resonant X-ray scattering cross-section allows nematicity dynamics associated with the planar O 2[Formula: see text] and Cu 3[Formula: see text] states to be distinguished from the response of anisotropic lattice distortions. A direct time-domain comparison of CDW translational-symmetry breaking and nematic rotational-symmetry breaking reveals that these broken symmetries remain closely linked in the photoexcited state, consistent with the stability of CDW topological defects in the investigated pump fluence regime.

2.
Nat Mater ; 2024 May 03.
Artigo em Inglês | MEDLINE | ID: mdl-38702413

RESUMO

Electrochemomechanical degradation is one of the most common causes of capacity deterioration in high-energy-density cathodes, particularly intercalation-based layered oxides. Here we reveal the presence of rotational stacking faults (RSFs) in layered lithium transition-metal oxides, arising from specific stacking sequences at different angles, and demonstrate their critical role in determining structural/electrochemical stability. Our combined experiments and calculations show that RSFs facilitate oxygen dimerization and transition-metal migration in layered oxides, fostering microcrack nucleation/propagation concurrently with cumulative electrochemomechanical degradation on cycling. We further show that thermal defect annihilation as a potential solution can suppress RSFs, reducing microcracks and enhancing cyclability in lithium-rich layered cathodes. The common but previously overlooked occurrence of RSFs suggests a new synthesis guideline of high-energy-density layered oxide cathodes.

3.
Nat Commun ; 15(1): 1288, 2024 Feb 12.
Artigo em Inglês | MEDLINE | ID: mdl-38346943

RESUMO

O2-type lithium-rich layered oxides, known for mitigating irreversible transition metal migration and voltage decay, provide suitable framework for exploring the inherent properties of oxygen redox. Here, we present a series of O2-type lithium-rich layered oxides exhibiting minimal structural disordering and stable voltage retention even with high anionic redox participation based on the nominal composition. Notably, we observe a distinct asymmetric lattice breathing phenomenon within the layered framework driven by excessive oxygen redox, which includes substantial particle-level mechanical stress and the microcracks formation during cycling. This chemo-mechanical degradation can be effectively mitigated by balancing the anionic and cationic redox capabilities, securing both high discharge voltage (~ 3.43 V vs. Li/Li+) and capacity (~ 200 mAh g-1) over extended cycles. The observed correlation between the oxygen redox capability and the structural evolution of the layered framework suggests the distinct intrinsic capacity fading mechanism that differs from the previously proposed voltage fading mode.

4.
J Synchrotron Radiat ; 30(Pt 6): 1038-1047, 2023 Nov 01.
Artigo em Inglês | MEDLINE | ID: mdl-37738032

RESUMO

Self-seeded hard X-ray pulses at PAL-XFEL were used to commission a resonant X-ray emission spectroscopy experiment with a von Hamos spectrometer. The self-seeded beam, generated through forward Bragg diffraction of the [202] peak in a 100 µm-thick diamond crystal, exhibited an average bandwidth of 0.54 eV at 11.223 keV. A coordinated scanning scheme of electron bunch energy, diamond crystal angle and silicon monochromator allowed us to map the Ir Lß2 X-ray emission lines of IrO2 powder across the Ir L3-absorption edge, from 11.212 to 11.242 keV with an energy step of 0.3 eV. This work provides a reference for hard X-ray emission spectroscopy experiments utilizing self-seeded pulses with a narrow bandwidth, eventually applicable for pump-probe studies in solid-state and diluted systems.

5.
IUCrJ ; 10(Pt 6): 700-707, 2023 Nov 01.
Artigo em Inglês | MEDLINE | ID: mdl-37772598

RESUMO

Photoinduced nonequilibrium phase transitions have stimulated interest in the dynamic interactions between electrons and crystalline ions, which have long been overlooked within the Born-Oppenheimer approximation. Ultrafast melting before lattice thermalization prompted researchers to revisit this issue to understand ultrafast photoinduced weakening of the crystal bonding. However, the absence of direct evidence demonstrating the role of orbital dynamics in lattice disorder leaves it elusive. By performing time-resolved resonant X-ray scattering with an X-ray free-electron laser, we directly monitored the ultrafast dynamics of bonding orbitals of Ge to drive photoinduced melting. Increased photoexcitation of bonding electrons amplifies the orbital disturbance to expedite the lattice disorder approaching the sub-picosecond scale of the nonthermal regime. The lattice disorder time shows strong nonlinear dependence on the laser fluence with a crossover behavior from thermal-driven to nonthermal-dominant kinetics, which is also verified by ab initio and two-temperature molecular dynamics simulations. This study elucidates the impact of bonding orbitals on lattice stability with a unifying interpretation on photoinduced melting.

6.
Adv Mater ; 35(36): e2303032, 2023 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-37391904

RESUMO

Ultrafast optical manipulation of magnetic phenomena is an exciting achievement of mankind, expanding one's horizon of knowledge toward the functional nonequilibrium states. The dynamics acting on an extremely short timescale push the detection limits that reveal fascinating light-matter interactions for nonthermal creation of effective magnetic fields. While some cases are benchmarked by emergent transient behaviors, otherwise identifying the nonthermal effects remains challenging. Here, a femtosecond time-resolved resonant magnetic X-ray diffraction experiment is introduced, which uses an X-ray free-electron laser (XFEL) to distinguish between the effective field and the photoinduced thermal effect. It is observed that a multiferroic Y-type hexaferrite exhibits magnetic Bragg peak intensity oscillations manifesting entangled antiferromagnetic (AFM) and ferromagnetic (FM) Fourier components of a coherent AFM magnon. The magnon trajectory constructed in 3D space and time domains is decisive to evince ultrafast field formation preceding the lattice thermalization. A remarkable impact of photoexcitation across the electronic bandgap is directly unraveled, amplifying the photomagnetic coupling that is one of the highest among AFM dielectrics. Leveraging the above-bandgap photoexcitation, this energy-efficient optical process further suggests a novel photomagnetic control of ferroelectricity in multiferroics.

7.
Nat Commun ; 14(1): 4149, 2023 Jul 12.
Artigo em Inglês | MEDLINE | ID: mdl-37438468

RESUMO

Lithium-rich layered oxides, despite their potential as high-energy-density cathode materials, are impeded by electrochemical performance deterioration upon anionic redox. Although this deterioration is believed to primarily result from structural disordering, our understanding of how it is triggered and/or occurs remains incomplete. Herein, we propose a theoretical picture that clarifies the irreversible transformation and redox asymmetry of lithium-rich layered oxides by introducing a series of global and local dynamic structural evolution processes involving slab gliding and transition-metal migration. We show that slab gliding plays a key role in trigger/initiating the structural disordering and consequent degradation of the anionic redox reaction. We further reveal that the 'concerted disordering mechanism' of slab gliding and transition-metal migration produces spontaneously irreversible/asymmetric lithiation and de-lithiation pathways, causing irreversible structural deterioration and the asymmetry of the anionic redox reaction. Our findings suggest slab gliding as a crucial, yet underexplored, method for achieving a reversible anionic redox reaction.

8.
Chemosphere ; 311(Pt 1): 137074, 2023 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-36332741

RESUMO

Ibuprofen (IPF) is one of the most prescribed nonsteroidal anti-inflammatory drugs in recent times, but it is not readily removed in conventional wastewater treatments. Here, we investigate the adsorption characteristics of IPF onto calcined spherical hydrochar (CSH), which was synthesized through hydrothermal carbonization of sucrose followed by calcination. The adsorption experiments show that the equilibration time for IPF was 360 min, and a pseudo-second-order model was best fitted to the kinetic data. The isotherm data were best described by the Liu model with a theoretical maximum adsorption capacity of 95.6 mg/g. The thermodynamic data indicate the endothermic nature of the adsorption at 10-40 °C. The CSH was favorably regenerated and reused using methanol. In pH experiments, the IPF adsorption capacity declined gradually as pH rose from 2 to 8, dropped rapidly at pH 10, and became negligible at pH 12. The IPF adsorption to the CSH could occur through various adsorption mechanisms. Hydrogen-bond formation, π-π interactions, n-π* interactions, and electrostatic repulsion were explored and visualized with molecular modeling using CHEM3D. The Raman, FTIR, and XPS spectra suggest that π-π interactions could take place between the CSH and IPF. Considering the pKa value of IPF (4.91) and pHiep of the CSH (3.21), electrostatic repulsion between the negatively-charged CSH and anionic IPF could play a negative role in the adsorption. A pore-filling mechanism could contribute to the adsorption in view of the molecular size of IPF (9.43 Å × 7.75 Å × 6.23 Å) and the average pore diameter of the CSH (2.27 nm). In addition, hydrophobic interactions could be involved in the adsorption. Multi-factor adsorption experiments were executed with pH, temperature, CSH dosage, and initial IPF concentrations as input variables and IPF removal rate as an output variable, and an artificial neural network (ANN) model with a topology of 4:9:11:1 was developed to sufficiently describe the adsorption data (R > 0.99). Further analyses with additional experimental data confirm that the ANN model possessed good predictability for multi-factor adsorption.


Assuntos
Ibuprofeno , Poluentes Químicos da Água , Adsorção , Poluentes Químicos da Água/química , Concentração de Íons de Hidrogênio , Redes Neurais de Computação , Cinética , Termodinâmica
9.
Proc Natl Acad Sci U S A ; 119(15): e2119429119, 2022 04 12.
Artigo em Inglês | MEDLINE | ID: mdl-35377791

RESUMO

Charge density waves (CDWs) have been observed in nearly all families of copper-oxide superconductors. But the behavior of these phases across different families has been perplexing. In La-based cuprates, the CDW wavevector is an increasing function of doping, exhibiting the so-called Yamada behavior, while in Y- and Bi-based materials the behavior is the opposite. Here, we report a combined resonant soft X-ray scattering (RSXS) and neutron scattering study of charge and spin density waves in isotopically enriched La1.8−xEu0.2SrxCuO4 over a range of doping 0.07≤x≤0.20. We find that the CDW amplitude is temperature independent and develops well above experimentally accessible temperatures. Further, the CDW wavevector shows a nonmonotonic temperature dependence, exhibiting Yamada behavior at low temperature with a sudden change occurring near the spin ordering temperature. We describe these observations using a Landau­Ginzburg theory for an incommensurate CDW in a metallic system with a finite charge compressibility and spin-CDW coupling. Extrapolating to high temperature, where the CDW amplitude is small and spin order is absent, our analysis predicts a decreasing wavevector with doping, similar to Y and Bi cuprates. Our study suggests that CDW order in all families of cuprates forms by a common mechanism.

10.
Nat Mater ; 21(6): 664-672, 2022 06.
Artigo em Inglês | MEDLINE | ID: mdl-35301474

RESUMO

Lattice oxygen redox offers an unexplored way to access superior electrochemical properties of transition metal oxides (TMOs) for rechargeable batteries. However, the reaction is often accompanied by unfavourable structural transformations and persistent electrochemical degradation, thereby precluding the practical application of this strategy. Here we explore the close interplay between the local structural change and oxygen electrochemistry during short- and long-term battery operation for layered TMOs. The substantially distinct evolution of the oxygen-redox activity and reversibility are demonstrated to stem from the different cation-migration mechanisms during the dynamic de/intercalation process. We show that the π stabilization on the oxygen oxidation initially aids in the reversibility of the oxygen redox and is predominant in the absence of cation migrations; however, the π-interacting oxygen is gradually replaced by σ-interacting oxygen that triggers the formation of O-O dimers and structural destabilization as cycling progresses. More importantly, it is revealed that the distinct cation-migration paths available in the layered TMOs govern the conversion kinetics from π to σ interactions. These findings constitute a step forward in unravelling the correlation between the local structural evolution and the reversibility of oxygen electrochemistry and provide guidance for further development of oxygen-redox layered electrode materials.


Assuntos
Óxidos , Oxigênio , Fontes de Energia Elétrica , Eletroquímica , Oxirredução , Oxigênio/química
11.
Sci Adv ; 8(6): eabk0832, 2022 Feb 11.
Artigo em Inglês | MEDLINE | ID: mdl-35138893

RESUMO

The normal state of high-Tc cuprates has been considered one of the essential topics in high-temperature superconductivity research. However, compared to the high magnetic field study of it, understanding a photoinduced normal state remains elusive. Here, we explore a photoinduced normal state of YBa2Cu3O6.67 through a charge density wave (CDW) with time-resolved resonant soft x-ray scattering, as well as a high magnetic field x-ray scattering. In the nonequilibrium state where people predict a quenched superconducting state based on the previous optical spectroscopies, we experimentally observed a similar analogy to the competition between superconductivity and CDW shown in the equilibrium state. We further observe that the broken pairing states in the superconducting CuO2 plane via the optical pump lead to nucleation of three-dimensional CDW precursor correlation. Ultimately, these findings provide a critical clue that the characteristics of the photoinduced normal state show a solid resemblance to those under magnetic fields in equilibrium conditions.

12.
Environ Pollut ; 267: 115583, 2020 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-33254689

RESUMO

In this study, a metal organic framework MIL-100(Fe) was synthesized for rhodamine B (RB) removal from aqueous solutions. An experimental design was conducted using a central composite design (CCD) method to obtain the RB adsorption data (n = 30) from batch experiments. In the CCD approach, solution pH, adsorbent dose, and initial RB concentration were included as input variables, whereas RB removal rate was employed as an output variable. Response surface methodology (RSM) and artificial neural network (ANN) modeling were performed using the adsorption data. In RSM modeling, the cubic regression model was developed, which was adequate to describe the RB adsorption according to analysis of variance. Meanwhile, the ANN model with the topology of 3:8:1 (three input variables, eight neurons in one hidden layer, and one output variable) was developed. In order to further compare the performance between the RSM and ANN models, additional adsorption data (n = 8) were produced under experimental conditions, which were randomly selected in the range of the input variables employed in the CCD matrix. The analysis showed that the ANN model (R2 = 0.821) had better predictability than the RSM model (R2 = 0.733) for the RB removal rate. Based on the ANN model, the optimum RB removal rate (>99.9%) was predicted at pH 5.3, adsorbent dose 2.0 g L-1, and initial RB concentration 73 mg L-1. In addition, pH was determined to be the most important input variable affecting the RB removal rate. This study demonstrated that the ANN model could be successfully employed to model and optimize RB adsorption to the MIL-100(Fe).


Assuntos
Estruturas Metalorgânicas , Adsorção , Redes Neurais de Computação , Projetos de Pesquisa
13.
Rev Sci Instrum ; 91(8): 083904, 2020 Aug 01.
Artigo em Inglês | MEDLINE | ID: mdl-32872965

RESUMO

Resonant elastic x-ray scattering has been widely employed for exploring complex electronic ordering phenomena, such as charge, spin, and orbital order, in particular, in strongly correlated electronic systems. In addition, recent developments in pump-probe x-ray scattering allow us to expand the investigation of the temporal dynamics of such orders. Here, we introduce a new time-resolved Resonant Soft X-ray Scattering (tr-RSXS) endstation developed at the Pohang Accelerator Laboratory X-ray Free Electron Laser (PAL-XFEL). This endstation has an optical laser (wavelength of 800 nm plus harmonics) as the pump source. Based on the commissioning results, the tr-RSXS at PAL-XFEL can deliver a soft x-ray probe (400 eV-1300 eV) with a time resolution of ∼100 fs without jitter correction. As an example, the temporal dynamics of a charge density wave on a high-temperature cuprate superconductor is demonstrated.

14.
Rev Sci Instrum ; 90(11): 113101, 2019 Nov 01.
Artigo em Inglês | MEDLINE | ID: mdl-31779391

RESUMO

We present results obtained with a new soft X-ray spectrometer based on transition-edge sensors (TESs) composed of Mo/Cu bilayers coupled to bismuth absorbers. This spectrometer simultaneously provides excellent energy resolution, high detection efficiency, and broadband spectral coverage. The new spectrometer is optimized for incident X-ray energies below 2 keV. Each pixel serves as both a highly sensitive calorimeter and an X-ray absorber with near unity quantum efficiency. We have commissioned this 240-pixel TES spectrometer at the Stanford Synchrotron Radiation Lightsource beamline 10-1 (BL 10-1) and used it to probe the local electronic structure of sample materials with unprecedented sensitivity in the soft X-ray regime. As mounted, the TES spectrometer has a maximum detection solid angle of 2 × 10-3 sr. The energy resolution of all pixels combined is 1.5 eV full width at half maximum at 500 eV. We describe the performance of the TES spectrometer in terms of its energy resolution and count-rate capability and demonstrate its utility as a high throughput detector for synchrotron-based X-ray spectroscopy. Results from initial X-ray emission spectroscopy and resonant inelastic X-ray scattering experiments obtained with the spectrometer are presented.

15.
Phys Rev Lett ; 122(14): 147601, 2019 Apr 12.
Artigo em Inglês | MEDLINE | ID: mdl-31050473

RESUMO

Ba(Ni_{1-x}Co_{x})_{2}As_{2} is a structural homologue of the pnictide high temperature superconductor, Ba(Fe_{1-x}Co_{x})_{2}As_{2}, in which the Fe atoms are replaced by Ni. Superconductivity is highly suppressed in this system, reaching a maximum T_{c}=2.3 K, compared to 24 K in its iron-based cousin, and the origin of this T_{c} suppression is not known. Using x-ray scattering, we show that Ba(Ni_{1-x}Co_{x})_{2}As_{2} exhibits a unidirectional charge density wave (CDW) at its triclinic phase transition. The CDW is incommensurate, exhibits a sizable lattice distortion, and is accompanied by the appearance of α Fermi surface pockets in photoemission [B. Zhou et al., Phys. Rev. B 83, 035110 (2011)PRBMDO1098-012110.1103/PhysRevB.83.035110], suggesting it forms by an unconventional mechanism. Co doping suppresses the CDW, paralleling the behavior of antiferromagnetism in iron-based superconductors. Our study demonstrates that pnictide superconductors can exhibit competing CDW order, which may be the origin of T_{c} suppression in this system.

16.
DNA Cell Biol ; 37(10): 850-860, 2018 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-30227079

RESUMO

The role of chemotherapeutic agents in tumor immunotherapy is still controversial. In this study, we test using a TC-1 tumor model whether gemcitabine plus E7 peptide vaccine regimens (E7 peptides+CpG-ODN+anti-4-1BB Abs) may result in tumor cure in mice with large established tumors, with a focus on their effects on Ag-specific cytotoxic T lymphocyte (CTL) and myeloid-derived suppressor cell levels. Gemcitabine inhibited tumor growth by its direct cytotoxicity to tumor cells in vivo. E7 peptide vaccine regimens enhanced Ag-specific CTL lytic and antitumor therapeutic activity. Initial combination therapy using gemcitabine and E7 peptide vaccine regimens resulted in tumor regression with tumor relapse in animals with large established tumors, which appeared to result from the suppression of Ag-specific CTL activity by gemcitabine treatment. However, optimization of gemcitabine therapy by reducing its dose and frequency led to complete tumor regression without any recurring tumors in all tested mice even after discontinuation of therapy, possibly due to Ag-specific CTL responses. Thus, this study shows that the optimal dose and therapy frequency of gemcitabine are critical for achieving tumor cure in tumor-bearing animals undergoing E7 peptide vaccine regimen therapy, mainly by preventing CTL suppression. These findings may have implications for designing peptide-based therapeutic vaccines in cancer patients undergoing chemotherapy.


Assuntos
Adenocarcinoma/terapia , Antimetabólitos Antineoplásicos/farmacologia , Vacinas Anticâncer/administração & dosagem , Terapia Combinada/métodos , Desoxicitidina/análogos & derivados , Linfócitos T Citotóxicos/efeitos dos fármacos , Adenocarcinoma/genética , Adenocarcinoma/imunologia , Adenocarcinoma/patologia , Animais , Anticorpos/farmacologia , Antígenos de Neoplasias/administração & dosagem , Antígenos de Neoplasias/química , Vacinas Anticâncer/química , Linhagem Celular Tumoral , Citotoxicidade Imunológica/efeitos dos fármacos , Desoxicitidina/farmacologia , Tratamento Farmacológico/métodos , Células Epiteliais/efeitos dos fármacos , Células Epiteliais/imunologia , Células Epiteliais/patologia , Feminino , Humanos , Imunização , Imunoterapia/métodos , Camundongos , Camundongos Endogâmicos C57BL , Transplante de Neoplasias , Oligodesoxirribonucleotídeos/administração & dosagem , Oligodesoxirribonucleotídeos/síntese química , Peptídeos/administração & dosagem , Peptídeos/síntese química , Linfócitos T Citotóxicos/imunologia , Linfócitos T Citotóxicos/patologia , Carga Tumoral/efeitos dos fármacos , Membro 9 da Superfamília de Receptores de Fatores de Necrose Tumoral/antagonistas & inibidores , Membro 9 da Superfamília de Receptores de Fatores de Necrose Tumoral/genética , Membro 9 da Superfamília de Receptores de Fatores de Necrose Tumoral/imunologia , Gencitabina
17.
Clin Exp Vaccine Res ; 7(2): 119-128, 2018 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-30112351

RESUMO

PURPOSE: The goal of this study was to purify and characterize Ebola virus glycoprotein (GP)-specific IgG antibodies from hybridoma clones. MATERIALS AND METHODS: For hybridoma production, mice were injected by intramuscular-electroporation with GP DNA vaccines, and boosted with GP vaccines. The spleen cells were used for producing GP-specific hybridoma. Enzyme-linked immunosorbent assay, Western blot assay, flow cytometry, and virus-neutralizing assay were used to test the ability of monoclonal IgG antibodies to recognize GP and neutralize Ebola virus. RESULTS: Twelve hybridomas, the cell supernatants of which displayed GP-binding activity by enzyme-linked immunosorbent assay and the presence of both IgG heavy and light chains by Western blot assay, were chosen as a possible IgG producer. Among these, five clones (C36-1, D11-3, D12-1, D34-2, and E140-2) were identified to secrete monoclonal IgG antibodies. When the monoclonal IgG antibodies from the 5 clones were tested for their antigen specificity, they recognized GP in an antigen-specific and IgG dose-dependent manner. They remained reactive to GP at the lowest tested concentrations (1.953-7.8 ng/mL). In particular, IgG antibodies from clones D11-3, D12-1, and E140-2 recognized the native forms of GP expressed on the cell surface. These antibodies were identified as IgG1, IgG2a, or IgG2b kappa types and appeared to recognize the native forms of GP, but not the denatured forms of GP, as determined by Western blot assay. Despite their GP-binding activity, none of the IgG antibodies neutralized Ebola virus infection in vitro, suggesting that these antibodies are unable to neutralize Ebola virus infection. CONCLUSION: This study shows that the purified IgG antibodies from 5 clones (C36-1, D11-3, D12-1, D34-2, and E140-2) possess GP-binding activity but not Ebola virus-neutralizing activity.

18.
Nanomaterials (Basel) ; 8(8)2018 Aug 01.
Artigo em Inglês | MEDLINE | ID: mdl-30071684

RESUMO

The production of a large amount of high-quality transition metal dichalcogenides is critical for their use in industrial applications. Here, we demonstrate the scalable exfoliation of bulk molybdenum disulfide (MoS2) powders into single- or few-layer nanosheets using the Taylor-Couette flow. The toroidal Taylor vortices generated in the Taylor-Couette flow provide efficient mixing and high shear stresses on the surfaces of materials, resulting in a more efficient exfoliation of the layered materials. The bulk MoS2 powders dispersed in N-methyl-2-pyrrolidone (NMP) were exfoliated with the Taylor-Couette flow by varying the process parameters, including the initial concentration of MoS2 in the NMP, rotation speed of the reactor, reaction time, and temperature. With a batch process at an optimal condition, half of the exfoliated MoS2 nanosheets were thinner than ~3 nm, corresponding to single to ~4 layers. The spectroscopic and microscopic analysis revealed that the exfoliated MoS2 nanosheets contained the same quality as the bulk powders without any contamination or modification. Furthermore, the continuous exfoliation of MoS2 was demonstrated by the Taylor-Couette flow reactor, which produced an exfoliated MoS2 solution with a concentration of ~0.102 mg/mL. This technique is a promising way for the scalable production of single- or few-layer MoS2 nanosheets without using hazardous intercalation materials.

19.
J Am Chem Soc ; 140(34): 10710-10720, 2018 08 29.
Artigo em Inglês | MEDLINE | ID: mdl-30028604

RESUMO

Non-noble-metal, thin-film oxides are widely investigated as promising catalysts for oxygen evolution reactions (OER). Amorphous cobalt oxide films electrochemically formed in the presence of borate (CoBi) and phosphate (CoPi) share a common cobaltate domain building block, but differ significantly in OER performance that derives from different electron-proton charge transport properties. Here, we use a combination of L edge synchrotron X-ray absorption (XAS), resonant X-ray emission (RXES), resonant inelastic X-ray scattering (RIXS), resonant Raman (RR) scattering, and high-energy X-ray pair distribution function (PDF) analyses that identify electronic and structural factors correlated to the charge transport differences for CoPi and CoBi. The analyses show that CoBi is composed primarily of cobalt in octahedral coordination, whereas CoPi contains approximately 17% tetrahedral Co(II), with the remainder in octahedral coordination. Oxygen-mediated 4 p-3 d hybridization through Co-O-Co bonding was detected by RXES and the intersite dd excitation was observed by RIXS in CoBi, but not in CoPi. RR shows that CoBi resembles a disordered layered LiCoO2-like structure, whereas CoPi is amorphous. Distinct domain models in the nanometer range for CoBi and CoPi have been proposed on the basis of the PDF analysis coupled to XAS data. The observed differences provide information on electronic and structural factors that enhance oxygen evolving catalysis performance.

20.
Polymers (Basel) ; 10(6)2018 Jun 10.
Artigo em Inglês | MEDLINE | ID: mdl-30966683

RESUMO

A simple and cost-effective fabrication method for plasmonic nanolens arrays (PNA) with a narrow gap has been proposed for fabricating enhanced fluorescence substrates, in which the fluorophores interacting with the enhanced electromagnetic field generated by localized surface plasmons provide a higher fluorescence signal. The PNA was fabricated by the sequential depositions of the SiO2 and Ag layers on a UV-nanoimprinted nanodot array with a pitch of 500 nm, a diameter of 250 nm, and a height of 100 nm. During the deposition processes, the shape of the nanodots changed to that of nanolenses, and the gap between the nanolenses was decreased via sidewall deposition. To examine the feasibility of the fabricated PNA for enhanced fluorescence application, a streptavidin-Cy5 (SA-Cy5) conjugate dissolved in a saline buffer solution was spotted on the PNA, and the fluorescence signals of the SA-Cy5 were measured and compared with those on a bare glass substrate. The enhancement factor was affected by the gap between the nanolenses, and the maximum enhancement factor of ~128 was obtained from the PNA with a SiO2 layer thickness of 150 nm and an Ag layer thickness of 100 nm. Finally, an electromagnetic field analysis was used to examine the fluorescence signal enhancement, and was conducted using rigorous coupled wave analysis.

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