scholarly journals Ultrafast mode-locking in highly stacked Ti3C2Tx MXenes for 1.9-μm infrared femtosecond pulsed lasers

Nanophotonics ◽  
2021 ◽  
Vol 10 (6) ◽  
pp. 1741-1751
Author(s):  
Young In Jhon ◽  
Jinho Lee ◽  
Young Min Jhon ◽  
Ju Han Lee
Keyword(s):  
High Performance ◽  
Density Functional ◽  
2D Materials ◽  
Density Functional Theory Calculations ◽  
Mode Locking ◽  
Infrared Range ◽  
Saturable Absorption ◽  
Pulsed Lasers ◽  
Saturable Absorbers ◽  
Layer Stacking

Abstract Metallic 2D materials can be promising saturable absorbers for ultrashort pulsed laser production in the long wavelength regime. However, preparing and manipulating their 2D structures without layer stacking have been nontrivial. Using a combined experimental and theoretical approach, we demonstrate here that a metallic titanium carbide (Ti3C2Tx), the most popular MXene 2D material, can have excellent nonlinear saturable absorption properties even in a highly stacked state due to its intrinsically existing surface termination, and thus can produce mode-locked femtosecond pulsed lasers in the 1.9-μm infrared range. Density functional theory calculations reveal that the electronic and optical properties of Ti3C2Tx MXene can be well preserved against significant layer stacking. Indeed, it is experimentally shown that 1.914-μm femtosecond pulsed lasers with a duration of 897 fs are readily generated within a fiber cavity using hundreds-of-layer stacked Ti3C2Tx MXene saturable absorbers, not only being much easier to manufacture than mono- or few-layered ones, but also offering character-conserved tightly-assembled 2D materials for advanced performance. This work strongly suggests that as-obtained highly stacked Ti3C2Tx MXenes can serve as superb material platforms for versatile nanophotonic applications, paving the way toward cost-effective, high-performance photonic devices based on MXenes.

scholarly journals Gallium nitride catalyzed the direct hydrogenation of carbon dioxide to dimethyl ether as primary product

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Chang Liu ◽  
Jincan Kang ◽  
Zheng-Qing Huang ◽  
Yong-Hong Song ◽  
Yong-Shan Xiao ◽  
...  
Keyword(s):  
Gallium Nitride ◽  
Dimethyl Ether ◽  
High Performance ◽  
Density Functional ◽  
Value Added ◽  
Density Functional Theory Calculations ◽  
Product Distribution ◽  
Spectroscopic Studies ◽  
Direct Hydrogenation ◽  
Hydrogenation Of Co

AbstractThe selective hydrogenation of CO2 to value-added chemicals is attractive but still challenged by the high-performance catalyst. In this work, we report that gallium nitride (GaN) catalyzes the direct hydrogenation of CO2 to dimethyl ether (DME) with a CO-free selectivity of about 80%. The activity of GaN for the hydrogenation of CO2 is much higher than that for the hydrogenation of CO although the product distribution is very similar. The steady-state and transient experimental results, spectroscopic studies, and density functional theory calculations rigorously reveal that DME is produced as the primary product via the methyl and formate intermediates, which are formed over different planes of GaN with similar activation energies. This essentially differs from the traditional DME synthesis via the methanol intermediate over a hybrid catalyst. The present work offers a different catalyst capable of the direct hydrogenation of CO2 to DME and thus enriches the chemistry for CO2 transformations.

scholarly journals Mechanism of selective benzene hydroxylation catalyzed by iron-containing zeolites

2018 ◽  
Vol 115 (48) ◽  
pp. 12124-12129 ◽  
Author(s):  
Benjamin E. R. Snyder ◽  
Max L. Bols ◽  
Hannah M. Rhoda ◽  
Pieter Vanelderen ◽  
Lars H. Böttger ◽  
...  
Keyword(s):  
High Activity ◽  
Active Site ◽  
Active Sites ◽  
High Performance ◽  
Density Functional ◽  
Catalyst Deactivation ◽  
Density Functional Theory Calculations ◽  
Oxidation Catalysis ◽  
Spectroscopic Techniques ◽  
Benzene Hydroxylation

A direct, catalytic conversion of benzene to phenol would have wide-reaching economic impacts. Fe zeolites exhibit a remarkable combination of high activity and selectivity in this conversion, leading to their past implementation at the pilot plant level. There were, however, issues related to catalyst deactivation for this process. Mechanistic insight could resolve these issues, and also provide a blueprint for achieving high performance in selective oxidation catalysis. Recently, we demonstrated that the active site of selective hydrocarbon oxidation in Fe zeolites, named α-O, is an unusually reactive Fe(IV)=O species. Here, we apply advanced spectroscopic techniques to determine that the reaction of this Fe(IV)=O intermediate with benzene in fact regenerates the reduced Fe(II) active site, enabling catalytic turnover. At the same time, a small fraction of Fe(III)-phenolate poisoned active sites form, defining a mechanism for catalyst deactivation. Density-functional theory calculations provide further insight into the experimentally defined mechanism. The extreme reactivity of α-O significantly tunes down (eliminates) the rate-limiting barrier for aromatic hydroxylation, leading to a diffusion-limited reaction coordinate. This favors hydroxylation of the rapidly diffusing benzene substrate over the slowly diffusing (but more reactive) oxygenated product, thereby enhancing selectivity. This defines a mechanism to simultaneously attain high activity (conversion) and selectivity, enabling the efficient oxidative upgrading of inert hydrocarbon substrates.

scholarly journals Time-Resolved X-ray Operando Observations of Lithiation Gradients across the Cathode Matrix and Individual Oxide Particles during Fast Cycling of a Li-Ion Cell

2021 ◽  
Author(s):  
Tianlong Zheng ◽  
Jing He ◽  
Pingwei Cai ◽  
Xi Liu ◽  
Duojie Wu ◽  
...  
Keyword(s):  
Electronic Structure ◽  
Specific Surface ◽  
Surface Area ◽  
Specific Surface Area ◽  
High Performance ◽  
Density Functional ◽  
Density Functional Theory Calculations ◽  
Carbon Paper ◽  
Free Energy Barrier ◽  
Active Components

Abstract Self-supporting three-dimensional (3D) transition metal electrodes have been considered for designing high-performance non-noble metal oxygen evolution reaction (OER) catalysts owing to their advantages such as binder-free, good mass transfer, and large specific surface area. However, the poor conductivity of ((oxy)hydr)oxides and the difficulty in adjusting their electronic structure limit their application. As an alternative strategy, instead of constituting the array electrode by the active components themselves, we herein report 3D Co(OH)2@MnO2 heterostructure decorated carbon nanoarrays grown directly on carbon paper (Co(OH)2@MnO2-CNAs). This unique structure can not only enhance electrical conductivity but also provide a larger specific surface area, and facilitate electrolyte diffusion and ion transport. The core-shell heterostructured Co(OH)2@MnO2 formed via incorporation with MnO2 facilitates the transition of CoII to CoIII in Co(OH)2 and it increases the storage of oxidative charge in the catalyst, leading to an OER activity with benchmark RuO2 and good stability. Density functional theory calculations suggest that the improved OER performance can be attributed to the formation of the heterojunction structure, resulting in the modulation of the electronic structure of Co atoms and the reduction of the free energy barrier of the rate-determining step for the OER.

scholarly journals Nitrogen-rich covalent organic frameworks with multiple carbonyls for high-performance sodium batteries

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
Ruijuan Shi ◽  
Luojia Liu ◽  
Yong Lu ◽  
Chenchen Wang ◽  
Yixin Li ◽  
...  
Keyword(s):  
High Performance ◽  
Density Functional ◽  
Specific Capacity ◽  
Density Functional Theory Calculations ◽  
Rechargeable Batteries ◽  
High Rate ◽  
Ex Situ ◽  
Covalent Organic Frameworks ◽  
Rate Performance ◽  
Practical Applications

AbstractCovalent organic frameworks with designable periodic skeletons and ordered nanopores have attracted increasing attention as promising cathode materials for rechargeable batteries. However, the reported cathodes are plagued by limited capacity and unsatisfying rate performance. Here we report a honeycomb-like nitrogen-rich covalent organic framework with multiple carbonyls. The sodium storage ability of pyrazines and carbonyls and the up-to twelve sodium-ion redox chemistry mechanism for each repetitive unit have been demonstrated by in/ex-situ Fourier transform infrared spectra and density functional theory calculations. The insoluble electrode exhibits a remarkably high specific capacity of 452.0 mAh g−1, excellent cycling stability (~96% capacity retention after 1000 cycles) and high rate performance (134.3 mAh g−1 at 10.0 A g−1). Furthermore, a pouch-type battery is assembled, displaying the gravimetric and volumetric energy density of 101.1 Wh kg−1cell and 78.5 Wh L−1cell, respectively, indicating potentially practical applications of conjugated polymers in rechargeable batteries.

scholarly journals Cross-plane transport in a single-molecule two-dimensional van der Waals heterojunction

2020 ◽  
Vol 6 (22) ◽  
pp. eaba6714 ◽  
Author(s):  
Shiqiang Zhao ◽  
Qingqing Wu ◽  
Jiuchan Pi ◽  
Junyang Liu ◽  
Jueting Zheng ◽  
...  
Keyword(s):  
Charge Transport ◽  
Single Molecule ◽  
Density Functional ◽  
Electronic Materials ◽  
2D Materials ◽  
Molecular Layer ◽  
Van Der Waals ◽  
Density Functional Theory Calculations ◽  
Two Dimensional ◽  
Guest Molecules

Two-dimensional van der Waals heterojunctions (2D-vdWHs) stacked from atomically thick 2D materials are predicted to be a diverse class of electronic materials with unique electronic properties. These properties can be further tuned by sandwiching monolayers of planar organic molecules between 2D materials to form molecular 2D-vdWHs (M-2D-vdWHs), in which electricity flows in a cross-plane way from one 2D layer to the other via a single molecular layer. Using a newly developed cross-plane break junction technique, combined with density functional theory calculations, we show that M-2D-vdWHs can be created and that cross-plane charge transport can be tuned by incorporating guest molecules. The M-2D-vdWHs exhibit distinct cross-plane charge transport signatures, which differ from those of molecules undergoing in-plane charge transport.

scholarly journals Tracking structural evolution: operando regenerative CeOx/Bi interface structure for high-performance CO2 electroreduction

2020 ◽  
Author(s):  
Ruichao Pang ◽  
Pengfei Tian ◽  
Hongliang Jiang ◽  
Minghui Zhu ◽  
Xiaozhi Su ◽  
...  
Keyword(s):  
High Performance ◽  
Density Functional ◽  
Structural Evolution ◽  
Density Functional Theory Calculations ◽  
Active Phase ◽  
Interface Structure ◽  
Operating Conditions ◽  
Faradaic Efficiency ◽  
Co2 Electroreduction ◽  
Water Activation

Abstract Unveiling the structural evolution and working mechanism of catalysts under realistic operating conditions is crucial for the design of efficient electrocatalysts for CO2 electroreduction, yet remains highly challenging. Here, by virtue of operando structural measurements at multiscale levels, it is identified under CO2 electroreduction conditions that an as-prepared CeO2/BiOCl precatalyst gradually evolves into CeOx/Bi interface structure with enriched Ce3+ species, which serves as the real catalytically active phase. The derived CeOx/Bi interface structure compared to pure Bi counterpart delivers substantially enhanced performance with a formate Faradaic efficiency approaching 90% for 24 hours in a wide potential window. The formate Faradaic efficiency can be further increased by using isotope D2O instead of H2O. Density functional theory calculations suggest that the regenerative CeOx/Bi interfacial sites can not only promote water activation to increase local *H species for CO2 protonation appropriately, but also stabilize the key intermediate *OCHO in formate pathway.

scholarly journals Influence of Ce, Nd, Eu and Tm Dopants on the Properties of InSe Monolayer: A First-Principles Study

Nanomaterials ◽  
2021 ◽  
Vol 11 (10) ◽  
pp. 2707
Author(s):  
Zhi Xie ◽  
Limin Chen
Keyword(s):  
Density Functional ◽  
Diluted Magnetic Semiconductors ◽  
Magnetic Semiconductors ◽  
Magnetic Moments ◽  
Density Functional Theory Calculations ◽  
Infrared Range ◽  
Type Conductivity ◽  
Substitutional Doping ◽  
Low Dimension ◽  
Lanthanide Atoms

Doping of foreign atoms may substantially alter the properties of the host materials, in particular low-dimension materials, leading to many potential functional applications. Here, we perform density functional theory calculations of two-dimensional InSe materials with substitutional doping of lanthanide atoms (Ce, Nd, Eu, Tm) and investigate systematically their structural, magnetic, electronic and optical properties. The calculated formation energy shows that the substitutional doping of these lanthanide atoms is feasible in the InSe monolayer, and such doping is more favorable under Se-rich than In-rich conditions. As for the structure, doping of lanthanide atoms induces visible outward movement of the lanthanide atom and its surrounding Se atoms. The calculated total magnetic moments are 0.973, 2.948, 7.528 and 1.945 μB for the Ce-, Nd-, Eu-, and Tm-doped systems, respectively, which are mainly derived from lanthanide atoms. Further band structure calculations reveal that the Ce-doped InSe monolayer has n-type conductivity, while the Nd-doped InSe monolayer has p-type conductivity. The Eu- and Tm-doped systems are found to be diluted magnetic semiconductors. The calculated optical response of absorption in the four doping cases shows redshift to lower energy within the infrared range compared with the host InSe monolayer. These findings suggest that doping of lanthanide atoms may open up a new way of manipulating functionalities of InSe materials for low-dimension optoelectronics and spintronics applications.

scholarly journals Nonlinear plasmonic metasurfaces assisted laser mode locking

2020 ◽  
Vol 243 ◽  
pp. 14001
Author(s):  
Lei Zhang ◽  
Jiyong Wang ◽  
Aurelien Coillet ◽  
Philippe Grelu ◽  
Benoit Cluzel ◽  
...  
Keyword(s):  
Transfer Functions ◽  
Incident Light ◽  
Mode Locking ◽  
Pulse Generation ◽  
Nonlinear Regime ◽  
Practical Implementation ◽  
Saturable Absorption ◽  
Geometrical Parameters ◽  
Neuromorphic Circuits ◽  
Saturable Absorbers

Plasmonic metasurfaces are artificial 2D layers made of subwavelength elementary cells, which give rise to novel wave properties that do not exist in nature. In the linear regime, their applications have been extensively studied, especially in wavefront manipulation for lensing, holography or polarization control. Interests in metasurfaces operating in nonlinear regime have also increased due to their ability to efficiently convert the fundamental light into harmonic frequencies and multiphoton emissions. Nevertheless, practical applications in the nonlinear regime have been rarely reported. In this study, we report that plasmonic metasurfaces with well-controlled polarimetric nonlinear transfer functions perform as saturable absorbers with modulation performances superior to that of other 2D materials. We employ planar nanotechnologies to fabricate 2D plasmonic metasurfaces with precise size, gap and orientation. We quantify the relationship between saturable absorption and the plasmonic resonances of the unit cell by altering the excitation power of pumping laser, the polarization of incident light and the geometrical parameters of the plasmonic metasurfaces. Finally, we provide a practical implementation by integrating the saturable metasurfaces into a fiber laser cavity and realize a stable self-starting ultrashort laser pulse generation. As such, this work sheds light on ultrathin nonlinear saturable absorbers for applications where nonlinear functions are required, such as in ultrafast laser or neuromorphic circuits.

scholarly journals Resonant Ta Doping for Enhanced Mobility in Transparent Conducting SnO2

2019 ◽  
Author(s):  
Benjamin Williamson ◽  
Thomas Featherstone ◽  
Sanjayan Sathasivam ◽  
Jack Swallow ◽  
Huw Shiel ◽  
...  
Keyword(s):  
Photoelectron Spectroscopy ◽  
High Performance ◽  
Density Functional ◽  
Density Functional Theory Calculations ◽  
Consumer Electronics ◽  
Electron Effective Mass ◽  
Conducting Oxides ◽  
Transparent Conducting ◽  
Earth Abundant ◽  
Sb Doping

<div>Transparent conducting oxides (TCOs) are ubiquitous in modern consumer electronics. SnO<sub>2</sub> is an earth abundant, cheaper alternative to In<sub>2</sub>O<sub>3</sub> as a TCO however, its performance in terms of electrical properties lags behind that of In<sub>2</sub>O<sub>3</sub>. Based on the recent discovery of mobility and conductivity enhancements in In<sub>2</sub>O<sub>3</sub> from resonant dopants, we use a combination of state-of-the-art hybrid density functional theory calculations, high resolution photoelectron spectroscopy and semiconductor statistics modelling to understand what the optimal dopant is to maximise performance of SnO<sub>2</sub>-based TCOs. We demonstrate that Ta is the optimal dopant for high performance SnO<sub>2</sub>, as it is a resonant dopant which is readily incorporated into SnO<sub>2</sub> with the Ta 5d states sitting ~1.4 eV above the conduction band minimum. Experimentally, the electron effective mass of Ta doped SnO<sub>2</sub> was shown to be 0.23m<sub>0</sub>, compared to 0.29m<sub>0</sub> seen with conventional Sb doping, explaining its ability to yield higher mobilities and conductivities.</div><div><br></div>

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