Partial Atomic Tin Nanocomplex Pillared Few-Layered Ti_(3)C_(2)Tx MXenes for Superior Lithium-Ion Storage

MXenes have attracted great interest in various fields,and pillared MXenes open a new path with larger interlayer spacing.However,the further study of pillared MXenes is blocked at multilayered state due to serious restacking phenomenon of few-layered MXene nanosheets.In this work,for the first time,we designed a facile NH4+method to fundamentally solve the restacking issues of MXene nanosheets and succeeded in achieving pillared few-layered MXene.Sn nanocomplex pillared few-layered Ti3C2Tx(STCT)composites were synthesized by introducing atomic Sn nanocomplex into interlayer of pillared few-layered Ti3C2Tx MXenes via pillaring technique.The MXene matrix can inhibit Sn nanocomplex particles agglomeration and serve as conductive network.Meanwhile,the Sn nanocomplex particles can further open the interlayer spacing of Ti3C2Tx during lithiation/delithiation processes and therefore generate extra capacity.Benefiting from the“pillar effect,”the STCT composites can maintain 1016 mAh g^?1 after 1200 cycles at 2000 mA g^?1 and deliver a stable capacity of 680 mAh g^?1 at 5 A g^?1,showing one of the best performances among MXene-based composites.This work will provide a new way for the development of pillared MXenes and their energy storage due to significant breakthrough from multilayered state to few-layered one.

Supercapacitor electrode based on few-layer h-BNNSs/rGO composite for wide-temperature-range operation with robust stable cycling performance

Currently,developing supercapacitors with robust cycle stability and suitability for wide-temperature-range operations is still a huge challenge.In the present work,few-layer hexagonal boron nitride nanosheets(h-BNNSs)with a thickness of 2−4 atomic layers were fabricated via vacuum freeze-drying and nitridation.Then,the h-BNNSs/reduced graphene oxide(rGO)composite were further prepared using a hydrothermal method.Due to the combination of two two-dimensional(2D)van der Waals-bonded materials,the as-prepared h-BNNSs/rGO electrode exhibited robustness to wide-temperature-range operations from−10 to 50℃.When the electrodes worked in a neutral aqueous electrolyte(1 M Na2SO4),they showed a great stable cycling performance with almost 107%reservation of the initial capacitance at 0℃ and 111% at 50℃ for 5000 charge−discharge cycles.

Decoration of carbon encapsulated nitrogen-rich MoxN with few-layered MoSe2 nanosheets for high-performance sodium-ion storage

Transition metal nitrides have become the focus of research in sodium ion batteries(SIBs)due to their unique metal properties and high theoretical capacity.However,the low actual capacity is still the main bottleneck for their application.Herein,using Mo-aniline frameworks as precursors,the carbon encapsulated nitrogen-rich Mo_(x)N is decorated by few-layered MoSe_(2) nanosheets(MoSe_(2)@Mo_(x)N/C-I)after the facile calcinating,selenizing,and nitriding.The carbon encapsulation can effectively strengthen the structural stability of Mo_(x)N.The nitrogen-rich Mo_(x)N and decoration of few-layered MoSe_(2) can create rich heterointerfaces and extra active sites for rapid sodium-ion storage,thus promoting reaction kinetics and improving actual capacity.The MoSe_(2)@Mo_(x)N/C-I as an anode achieves a large reversible capacity of 522.8 mAh g^(-1)at 0.1 A g^(-1),and 254.3 mAh g^(-1)capacity is obtained after 6000 cycles at 5.0 A g^(-1),showing signally improved sodium-ion storage properties.The storage mechanisms and kinetic behaviors are described systematically via the advanced testing techniques and density functional theory(DFT)calculations.It is found that the nitrogen-rich Mo_(x)N as the substrate is the basis of long cycling stability,and the few-layered MoSe_(2) are the key to improving actual capacity.This work indicates that the decoration of few-layered selenides has a broad application prospect in high-performance metal-ion batteries.

Moir patterns and step edges on few-layer graphene grown on nickel films

Few-layer graphene grown on Ni thin films has been studied by scanning tunneling microscopy. In most areas on the surfaces, moir6 patterns resulted from rotational stacking faults were observed. At a bias lower than 200 mV, only one sublattice shows up in regions without moir6 patterns while both sublattices are seen in regions with moir6 pattens. This phenomenon can be used to identify AB stacked regions. The scattering characteristics at various types of step edges are different from those of monolayer graphene edges, either armchair or zigzag.

Monitoring dynamics of defects and single Fe atoms in N-functionalized few-layer graphene by in situ temperature programmed scanning transmission electron microscopy

In this study,we aim to contribute an understanding of the pathway of formation of Fe species during top-down synthesis of dispersed Fe on N-functionalized few layer graphene,widely used in electrocatalysis.We use X-ray absorption spectroscopy to determine the electronic structure and coordination geometry of the Fe species and in situ high angle annular dark field scanning transmission electron microscopy combined with atomic resolved electron energy loss spectroscopy to localize these,identify their chemical configuration and monitor their dynamics during thermal annealing.We show the high mobility of peripheral Fe atoms,first diffusing rapidly at the trims of the graphene layers and at temperatures as high as 573 K,diffusing from the edge planes towards in-plane locations of the graphene layers forming three-,four-coordinated metal sites and more complexes polynuclear Fe species.This process occurs via bond C-C breaking which partially reduces the extension of the graphene domains.However,the vast majority of Fe is segregated as a metal phase.This dynamic interconversion depends on the structural details of the surrounding graphitic environment in which these are formed as well as the Fe loading.N species appear stabilizing isolated and polynuclear Fe species even at temperatures as high as 873 K.The significance of our results lies on the fact that single Fe atoms in graphene are highly mobile and therefore a structural description of the electroactive sites as such is insufficient and more complex species might be more relevant,especially in the case of multielectron transfer reactions.Here we provide the experimental evidence of the formation of these polynuclear Fe-N sites and their structural characteristics.

Millimeter-sized few-layer graphene sheets with aligned channels for fast lithium-ion charging kinetics

Assembly of the top-down graphene units mostly results in 3D porous structure with randomly organized pores.The direct bottom-up synthesis of macroscopic 2D graphene sheets with organized pores are long sought in materials chemistry field,but rarely achieved.Herein,we present a self-catalysisassisted bottom-up route usingL-glutamic acid and iron chloride as starting materials for the fabrication of the millimeter-sized few-layer graphene sheets with aligned porous channels parallel to the 2D direction.The amino-and carboxyl-functional groups inL-glutamic acid can coordinate with iron cations,thus allowing an atomic dispersion of iron cations.The pyrolysis thus initiated the growth of graphene catalyzed by in-situ generated iron nanoparticles,and a dynamic flow of iron nanoparticles eventually led to the formation of millimeter-sized few-layer graphene sheets with aligned channels(60-85 nm in diameter).Used as anodes in lithium-ion batteries,these graphene sheets showed a good rate capability(142 m A h g^(-1) at 2 A g^(-1))and high capacity retention of 93%at 2 A g^(-1) after 1200 cycles.Kinetic analysis revealed that lithium ions storage was dominated by diffusion behavior and capacitive behavior together,in that graphene sheets with aligned channels could accelerate electron transfer and shorten lithium ions transport pathway.This work provides a novel approach to prepare unique porous graphene materials with specific structure for energy storage.

Performance Improvement in Hydrogenated Few-Layer Black Phosphorus Field-Effect Transistors

A capping layer for black phosphorus（BP） field-effect transistors（FETs） can provide effective isolation from the ambient air; however, this also brings inconvenience to the post-treatment for optimizing devices. We perform low-temperature hydrogenation on Al2 O3 capped BP FETs. The hydrogenated BP devices exhibit a pronounced improvement of mobility from 69.6 to 107.7 cm2 v-1 s-1, and a dramatic decrease of subthreshold swing from8.4 to 2.6 V/dec. Furthermore, high/low frequency capacitance-voltage measurements suggest reduced interface defects in hydrogenated BP FETs. This could be due to the passivation of interface traps at both Al2 O3/BP and BP/SiO2 interfaces with hydrogen revealed by secondary ion mass spectroscopy.

Microsized SnS/Few-Layer Graphene Composite with Interconnected Nanosized Building Blocks for Superior Volumetric Lithium and Sodium Storage

To develop anode materials with superior volumetric storage is crucial for practical application of lithium/sodium-ion batteries.Here,we have developed a micro/nanostructured Sn S/few-layer graphene(Sn S/FLG)composite by facile scalable plasma milling.Inside the hybrid,SnS nanoparticles are tightly supported by FLG,forming nanosized primary particles as building blocks and assembling to microsized secondary granules.With this unique micro/nanostructure,the Sn S/FLG composite possesses a high tap density of 1.98 g cm^(-3)and thus ensures a high volumetric storage.The combination of Sn S nanoparticles and FLG nanosheets can not only enhance the overall electrical conductivity and facilitate the ion diffusion greatly,but alleviate the large volume expansion of Sn S effectively and maintain the electrode integrity during cycling.Thus,the densely compacted Sn S/FLG composite exhibits superior volumetric lithium and sodium storage,including high volumetric capacities of 1926.5/1051.4 m Ah cm^(-3)at 0.2 A g^(-1),and high retained capacities of 1754.3/760.3 m Ah cm^(-3)after 500cycles at 1.0 A g^(-1).With superior volumetric storage performance and facile scalable synthesis,the Sn S/FLG composite can be a promising anode for practical batteries application.

Synthesized few-layers hexagonal boron nitride nanosheets

The hexagonal boron nitrides （BNs） with different morphologies are synthesized on a large scale by a simple route using a two-step synthetic process. The morphology of h-BN can be easily controlled by changing the heat-treatment atmosphere. The whiskers with 0.5-10 μm in diameter and 50-100 μm in length consist of few-layers nanosheets in the NH3 gas. The BN nanosheets can be dissociated from the whiskers by ultrasonic treatment, which are less than 5 nm in thickness and even only two layers thick. The concentration and activity of N play an important rule, and abundant N and higher activity are conducive for refining grain in reaction. The H3BO3 and C3N6H6 molecules form a layer-like morphology with the interlinked planar triangle by a hydrogen-bonded structure.

Few-layered graphene via gas-driven exfoliation for enhanced supercapacitive performance

High-quality graphene flakes have long been desirable for numerous applications including energy stor- age, printable electronics, and catalysis. In this contribution, we report a green, efficient, facile gas-driven exfoliation process for the preparation of high-quality graphene in large scale. The gas exfoliation process was realized by the interplay between the expansion of interlayer at high temperature and the gasifi- cation of liquid nitrogen within the interlayer. Detailed experiments demonstrated that the higher tem- perature was critical to the formation of fewer layers. The exfoliated graphene was proved to be of high quality. We further investigated the electrochemical behavior of this exfoliated graphene. As a result, this few-layered graphene demonstrated an enhanced capability as a supercapacitor, much higher than its counterpart parent material.

Visible-infrared-terahertz optical modulation of few-layer graphene through lithium intercalation

Optical modulation is significant and ubiquitous to telecommunication technologies,smart windows,and military devices.However,due to the limited tunability of traditional doping,achieving broadband optical property change is a tough problem.Here,we demonstrate a remarkable transformation of optical transmittance in few-layer graphene(FLG)covering the electromagnetic spectra from the visible to the terahertz wave after lithium(Li)intercalation.It results in the transmittance being higher than 90%from the wavelengths of 480 to 1040 nm,and it increases most from 86.4%to 94.1%at 600 nm,reduces from∼80%to∼68%in the wavelength range from 2.5 to 11μm,has∼20%reduction over a wavelength range from 0.4 to 1.2 THz,and reduces from 97.2%to 68.2%at the wavelength of 1.2 THz.The optical modification of lithiated FLG is attributed to the increase of Fermi energy(Ef)due to the charge transfer from Li to graphene layers.Our results may provide a new strategy for the design of broadband optical modulation devices.

Few-layered MoS_(2)anchored on 2D porous C_(3)N_(4)nanosheets for Ptfree photocatalytic hydrogen evolution

The Pt-free photocatalytic hydrogen evolution(PHE)has been the focus in the photocatalytic field.The catalytic system with the large accessible surface and good mass-transfer ability,as well as the intimate combination of co-catalyst with semiconductor is promising for the promotion of the application.Here,we have reported the design of the two-dimensional(2D)porous C_(3)N_(4)nanosheets(PCN NS)intimately combined with few-layered MoS_(2)for the high-effective Pt-free PHE.The PCN NS were synthesized based on peeling the melamine–cyanuric acid precursor(MC precursor)by the triphenylphosphine(TP)molecular followed by the calcination,mainly due to the matched size of the(100)plane distance of the precursor(0.8 nm)and the height of TP molecular.The porous structure is favorable for the mass-transfer and the 2D structure having large accessible surface,both of which are positive to promote the photocatalytic ability.The few-layered MoS_(2)are grown on PCN to give 2D MoS_(2)/PCN composites based on anchoring phosphomolybdic acid(PMo_(12))cluster on polyetherimide(PEI)-modified PCN followed by the vulcanization.The few-layered MoS_(2)have abundant edge active sites,and its intimate combination with porous PCN NS is favorable for the faster transfer and separation of the electrons.The characterization together with the advantage of 2D porous structure can largely promote the photocatalytic ability.The MoS_(2)/PCN showed good PHE activity with the high hydrogen production activity of 4,270.8μmol·h^(−1)·g^(−1)under the simulated sunlight condition(AM1.5),which was 7.9 times of the corresponding MoS_(2)/bulk C_(3)N_(4)and 12.7 times of the 1 wt.%Pt/bulk C_(3)N_(4).The study is potentially meaningful for the synthesis of PCN-based catalytic systems.

Moiréflat bands of twisted few-layer graphite

We report that the twisted few layer graphite(tFL-graphite)is a new family of moiréheterostructures(MHSs),which has richer and highly tunable moiréflat band structures entirely distinct from all the known MHSs.A tFL-graphite is composed of two few-layer graphite(Bernal stacked multilayer graphene),which are stacked on each other with a small twisted angle.The moiréband structure of the tFL-graphite strongly depends on the layer number of its composed two van der Waals layers.Near the magic angle,a tFL-graphite always has two nearly flat bands coexisting with a few pairs of narrowed dispersive(parabolic or linear)bands at the Fermi level,thus,enhances the DOS at EF.This coexistence property may also enhance the possible superconductivity as been demonstrated in other multiband superconductivity systems.Therefore,we expect strong multiband correlation effects in tFL-graphite.Meanwhile,a proper perpendicular electric field can induce several isolated nearly flat bands with nonzero valley Chern number in some simple tFL-graphites,indicating that tFL-graphite is also a novel topological flat band system.

Natural overlaying behaviors push the limit of planar cyclic deformation performance in few-layer MoS_(2) nanosheets

As a typical two-dimensional(2D)transition metal dichalcogenides(TMDCs)material with nonzero band gap,MoS_(2)has a wide range of potential applications as building blocks in the field of nanoelectronics.The stability and reliability of the corresponding nanoelectronic devices depend critically on the mechanical performance and cyclic reliability of 2D MoS_(2).Although an in situ technique has been used to analyze the mechanical properties of 2D materials,the cyclic mechanical behavior,that is,fatigue,remains a major challenge in the practical application of the devices.This study was aimed at analyzing the planar cyclic performance and deformation behavior of three-layer MoS_(2)nanosheets(NSs)using an in situ transmission electron microscopy(TEM)variable-amplitude uniaxial low-frequency and cyclic loading-unloading tensile acceleration test.We also elucidated the strengthening effect of the natural overlaying affix fragments(other external NSs)or wrinkle folds(internal folds from the NS itself)on cycling performances and service life of MoS_(2)NSs by delaying the whole process of fatigue crack initiation,propagation,and fracture.The results have been confirmed by molecular dynamics(MDs)simulations.The overlaying enhancement effect effectively ensures the long-term reliability and stability of nanoelectronic devices made of few-layer 2D materials.

Resistive-type sensors based on few-layer MXene and SnO_(2)hollow spheres heterojunctions:Facile synthesis,ethanol sensing performances

High-performance and low-cost gas sensors are highly desirable and involved in industrial production and environmental detection.The combination of highly conductive MXene and metal oxide materials is a promising strategy to further improve the sensing performances.In this study,the hollow SnO_(2)nanospheres and few-layer MXene are assembled rationally via facile electrostatic synthesis processes,then the SnO_(2)/Ti_(3)C_(2)T_(x)nanocomposites were obtained.Compared with that based on either pure SnO_(2)nanoparticles or hollow nanospheres of SnO_(2),the SnO_(2)/Ti_(3)C_(2)T_(x)composite-based sensor exhibits much better sensing performances such as higher response(36.979),faster response time(5 s),and much improved selectivity as well as stability(15 days)to 100ppm C2H5OH at low working temperature(200°C).The improved sensing performances are mainly attributed to the large specific surface area and significantly increased oxygen vacancy concentration,which provides a large number of active sites for gas adsorption and surface catalytic reaction.In addition,the heterostructure interfaces between SnO_(2)hollow spheres and MXene layers are beneficial to gas sensing behaviors due to the synergistic effect.

Inverse opal manganese dioxide constructed by few-layered ultrathin nanosheets as high-performance cathodes for aqueous zinc-ion batteries

Considering the high safety,low-cost and high capacity,aqueous zinc ion batteries have been a potential candidate for energy storage ensuring smooth electricity supply.Herein,we have synthesized inverse opal manganese dioxide constructed by few-layered ultrathin nanosheets by a solution template method at mild temperature.The ultrathin nanosheets with the thickness as small as 1 nm are well separated without obvious aggregation.Used as cathode material for aqueous zinc ion batteries,the few-layered ultrathin nanosheets combined with the inverse opal structure guarantee excellent performance.A high specific discharge capacity of 262.9 mAh·g^-1 is retained for the 100th cycle at a current density of 300 mA·g^-1 with a high capacity retention of 95.6%.A high specific discharge capacity of 121 mAh·g^-1 at a high current density of 2,000 mA·g^-1 is achieved even after 5,000 long-term cycles.The ex-situ X-ray diffraction (XRD) patterns,selected-area electron diffraction (SAED) patterns and high-resolution transmission electron microscopy (HRTEM) results demonstrate that the discharge/charge processes involve the reversible formation of zinc sulfate hydroxide hydrate on the cathode while in-plane crystal structure of the layered bimessite MnO2 could be maintained.This unique structured MnO2 is a promising candidate as cathode material for high capacity,high rate capability and long-term aqueous zinc-ion batteries.

Carbon and few-layer MoS2 nanosheets co-modified TiO2 nanosheets with enhanced electrochemical properties for lithium storage

Carbon and few-layer MoS2 nanosheets co- modified TiO2 nanocomposites （defined as MoS2-C@TiO2） were prepared through a facile one-step pyrolysis reaction technique. In this unique nanostructure, the TiO2 nanosh- eets with stable structure serve as the backbones, and carbon coating and few-layer MoS2 tightly adhere onto the surface of the TiO2. It needs to be pointed out that the carbon coating improves the overall electronic conductivity and the few-layer MoS2 facilitates the diffusion of lithium ions and offers more active sites for lithium-ion storage. As a result, when evaluated as lithium-ion battery anodes, the MoS2-C@TiO2 nanocomposites exhibit markedly enhanced lithium storage capability compared with pure TiO2. A high specific capacity of 180 mA.h.g-1 has been achieved during the preliminary cycles, and the specific capacity can maintain 160 mA.h.g-1 at a high current density of 1C （1C=167 mA.g-1） even after 300 discharge/ charge cycles, indicating the great potential of the MoS2- C@TiO2 on energy storage.

Efficient and Large-Scale Synthesis of Few-Layered Graphene Using an Arc-Discharge Method and Conductivity Studies of the Resulting Films

An arc-discharge method using a buffer gas containing carbon dioxide has been developed for the efficient and large-scale synthesis of few-layered graphene.The resulting samples of few-layered graphene,well-dispersed in organic solvents such as N,N-dimethylformamide(DMF)and 1,2-dichlorobenzene(o-DCB),were examined by transmission electron microscopy(TEM),X-ray diffraction(XRD),Raman spectroscopy,atomic force microscopy(AFM),and thermal gravimetric analysis(TGA).The electrical conductivity and transparency of flexible films prepared using a direct solution process have also been studied.

Few-layer MoS2 saturable absorbers for short-pulse laser technology: current status and future perspectives [Invited]

Few-layer molybdenum disulfide（MoS2） is emerging as a promising quasi-two-dimensional material for photonics and optoelectronics, further extending the library of suitable layered nanomaterials with exceptional optical properties for use in saturable absorber devices that enable short-pulse generation in laser systems. In this work, we catalog and review the nonlinear optical properties of few-layer MoS2, summarize recent progress in processing and integration into saturable absorber devices, and comment on the current status and future perspectives of MoS2-based pulsed lasers.