Large valley Nernst effect in twisted multilayer graphene systems

Valley Nernst effect is a newly proposed and experimentally confirmed effect,which could be used to design novel thermoelectric devices.We study the valley Nernst effect in(M+N)-layer twisted multilayer graphene systems by a simple low-energy effective model.It is found that the total valley Nernst coefficient(VNC)is three orders of magnitude larger than that in monolayer group-Ⅵdichalcogenides.The total VNC increases with the increase of layer numbers.It is shown that the total VNC exhibits a structure with three peaks as a function of the Fermi energy.We identify that the central peak is always negative stemming from the flat band.Two shoulder peaks are positively induced by the conduction and valence bands,respectively.These predicted features can be tested experimentally.The present work would shed more light on valley caloritronics.

Construction of TiO_(2)-pillared multilayer graphene nanocomposites as efficient photocatalysts for ciprofloxacin degradation

We successfully constructed TiO_(2)-pillared multilayer graphene nanocomposites(T-MLGs)via a facile method as follows:dodecanediamine pre-pillaring,ion exchange(Ti4+pillaring),and interlayer in-situ formation of TiO_(2) by hydrothermal method.TiO_(2) nanoparticles were distributed uniformly on the graphene interlayer.The special structure combined the advantages of graphene and TiO_(2) nanoparticles.As a result,T-MLGs with 64.3wt%TiO_(2) showed the optimum photodegradation rate and adsorption capabilities toward ciprofloxacin.The photodegradation rate of T-MLGs with 64.3wt%TiO_(2) was 78%under light-emitting diode light irradiation for 150 min.Meanwhile,the pseudofirst-order rate constant of T-MLGs with 64.3wt%TiO_(2) was 3.89 times than that of pristine TiO_(2).The composites also exhibited high stability and reusability after five consecutive photocatalytic tests.This work provides a facile method to synthesize semiconductor-pillared graphene nanocomposites by replacing TiO_(2) nanoparticles with other nanoparticles and a feasible means for sustainable utilization of photocatalysts in wastewater control.

Ultrafine SnSSe/multilayer graphene nanosheet nanocomposite as a high-performance anode material for potassium-ion half/full batteries

Layer-structured Shsse attracts much attention as an anode material for potassium storage due to its la rge theoretical capacity.Unfortunately,their practical application is severely restrained by the dramatic volumetric variation of SnSSe.Herein,we synthesize ultrafine SnSSe/multilayer graphene nanosheet(SnSSe/MGS) by a vacuum solid-phase reaction and subsequent ball milling.Owing to the strong synergistic effect between the two components,the obtained SnSSe/MGS nanocomposite exhibits a high reversible capacity(423 mAh g^(-1) at 100 mA g^(-1)),excellent rate property(218 mAh g^(-1) at 5 A g^(-1)),and stable cycling performance(271 mAh g^(-1) after 500 cycles at 100 mA g^(-1)) in potassium-ion half batteries.Moreover,the full cell assembled by the SnSSe/MGS anode and the potassiated 3,4,9,10-perylene-tetracar boxylic aciddianhydride cathode shows excellent electrochemical performance between 0.2 and 3.3 V(209 mAh g^(-1) at 50 mA g^(-1) after 100 cycles).The presented two-step synthesis strategy of SnSSe/MGS may also provide ideas to craft other alloy-type anode materials.

Sn_(4)P_(3)nanoparticles confined in multilayer graphene sheets as a high-performance anode material for potassium-ion batteries

Phosphorus-based anodes are highly promising for potassium-ion batteries(PIBs)because of their large theoretical capacities.Nevertheless,the inferior potassium storage properties caused by the poor electronic conductivity,easy self-aggregation,and huge volumetric changes upon cycling process restrain their practical applications.Now we impregnate Sn_(4)P_(3)nanoparticles within multilayer graphene sheets(Sn_(4)P_(3)/MGS)as the anode material for PIBs,greatly improving its potassium storage performance.Specifically,the graphene sheets can efficiently suppress the aggregation of Sn_(4)P_(3)nanoparticles,enhance the electronic conductivity,and sustain the structural integrity.In addition,plenty of Sn_(4)P_(3)nanoparticles impregnated in MGS offer a large accessible area for the electrolyte,which decreases the diffusion distance for K^(+)and electrons upon K^(+)insertion/extraction,resulting in an improved rate capability.Consequently,the optimized Sn_(4)P_(3)/MGS containing 80 wt%Sn_(4)P_(3)(Sn_(4)P_(3)/MGS-80)exhibits a high reversible capacity of 378.2 and 260.2 m Ah g;at 0.1 and 1 A g^(-1),respectively,and still delivers a large capacity retention of 76.6%after the 1000th cycle at 0.5 A g^(-1).

Superconductivity in twisted multilayer graphene:A smoking gun in recent condensed matter physics

We review the recent discoveries of exotic phenomena in graphene,especially superconductivity.It has been theoretically suggested for more than one decade that superconductivity may emerge in doped graphene-based materials.For single-layer pristine graphene,there are theoretical predictions that spin-singlet d+id pairing superconductivity is present when the filling is around the Dirac point.If the Fermi level is doped to the Van Hove singularity where the density of states diverges,then unconventional superconductivity with other pairing symmetry would appear.However,the experimental perspective was a bit disappointing.Despite extensive experimental efforts,superconductivity was not found in monolayer graphene.Recently,unconventional superconductivity was found in magic-angle twisted bilayer graphene.Superconductivity was also found in ABC stacked trilayer graphene and other systems.In this article,we review the unique properties of superconducting states in graphene,experimentally controlling the superconductivity in twisted bilayer graphene,as well as a gate-tunable Mott insulator,and the superconductivity in trilayer graphene.These discoveries have attracted the attention of a large number of physicists.The study of the electronic correlated states in twisted multilayer graphene serves as a smoking gun in recent condensed matter physics.

Simulations of Tapered Channel in Multilayer Graphene as Reverse Osmosis Membrane for Desalination

Pressure-driven reverse osmosis membrane has important application in seawater desalination.Inspired by the structure of aquaporin,we established and studied the mechanism of the structure of multilayer graphene with tapered channels as reverse osmosis.The water flux of multilayer graphene with tapered channels was about 20%higher than that of parallel graphene channel.The flow resistance model was established,and the relationship between flow resistance and opening angles was clarified.The relationship between flow resistance and outlet size was also described.By means of molecular dynamics simulation,slip coefficients of multilayer graphene with tapered channel were obtained and verified by the contact angle of water.Results show that the permeability of graphene with tapered channel is about three orders of magnitude higher than that of commercial reverse osmosis membrane and the desalination rate is 100%.Temperature difference between the two sides of the tapered channel will promote the water flux positively.

Multilayer graphene refractive index tuning by optical power

Graphene’s optical absorption coefficient increases linearly with the number of layers making it more effective in the construction of optical tuning graphene-based devices. Refractive index(RI) is one of the important optical parameters of the graphene for accurately describing its optical characteristics and further applications. In view of the RI research of the multilayer graphene is lacking and existing measurement methods are complicated. Optical power tuning RI of multilayer graphene is investigated using a simple measurement and no temperature cross sensitivity all optical fiber sensing structure.Optical power tuning RI characteristics of multilayer graphene are studied by tuning the introducing broad band light power from 0.57 mW to 22.7 m W. Different thickness graphene coating shows different tuning efficiency. At 4.86-μm thickness,a 3.433-nm Bragg wavelength shift is obtained with 156.2-pm/mW wavelength versus optical power tuning sensitivity corresponding to 3.25×10~3 RI change and 0.154 URI/W(URI, unit of RI) RI optical power tuning efficiency.

Electron with arbitrary pseudo-spins in multilayer graphene

Using the low-energy effective Hamiltonian of the ABC-stacked multilayer graphene, the pseudo-spin coupling to real orbital angular momentum of electrons in multilayer graphene is investigated. We show that the electron wave function in N-layer graphene mimics the behavior of a particle with a spin of N × （n/2）, where N = {1,2,3,...}. It is said that for N 〉 1 the low-energy effective Hamiltonian for ABC-stacked graphene cannot be used to describe pseudo-spin-1/2 particles. The wave function of electrons in multilayer graphene may behave like fermionic （or bosonic） particle for N being odd （or even）. In this paper, we propose a theory of graphene serving as a host material of electrons with arbitrary pseudo-spins tunable by changing the number of graphene layers.

The Nonlinear Electronic Transport in Multilayer Graphene on Silicon-on-Insulator Substrates

We conduct a study on the superlinear transport of multilayer graphene channels that partially or completely locate on silicon which is pre-etched by inductively coupled plasma （ICP）. By fabricating a multilayer-graphene field-effect transistor on a Si/SiO2 substrate, we obtain that the superlinearity results from the interaction between the multilayer graphene sheet and the ICP-etched silicon, In addition, the observed superlinear transport of the device is found to be consistent with the prediction of Schwinger＇s mechanism. In the high bias regime, the values of a increase draxnatically from 1.02 to 1.40. The strength of the electric field corresponding to the on-start of electron-hole pair production is calculated to be 5 × 10^4 Vim. Our work provides an experimental observation of the nonlinear transport of the multilayer graphene.

In situ Preparation and Visible-light-driven Photocatalytic Degradation Performance of Nano 3C-SiC@Multilayer Graphene Oxide Heterostructure

Nano 3C-SiC@multilayer graphene oxide(NS@MGO)heterostructure was in situ prepared by carbothermal reduction of pyrolyzed precursor composed of highly dispersed cured phenolic resin and silicon dioxide derived from tetraethyl orthosilicate.The heterojunction interface,number of layers of MGO,and defect content in graphene are the three most important factors for promoting photocatalytic activity.Direct contact between 3C-SiC nanograins and MGO layers facilitates the photogenerated electrons to migrate across the heterojunction interface and avoid the formation of SiO_(2) nanolayers on the surface of SiC nanograins.The number of MGO layers is supposed to be less than ten instead of over-thick MGO.The concentrations of oxygenated components,considered the defect contents,decrease with the increase of sintering temperature for NS@MGO 0.175-T-150,and relative carbon content in the multilayer graphene increases.According to the heterostructures,properties,and photocatalytic reaction performance of the NS@MGO materials,the highest photocatalytic kinetic rate constant of 0.00891/min for NS@MGO 0.175-1500-150 shows that the significant enhancement in photocatalytic degradation activity under visible light(>420 nm)irradiation is ascribed to the advantageous synergistic effects between the nano 3C-SiC particles and the direct contact multilayer graphene oxide with appropriate layers and sufficient oxygen content of 3.51%(atomic fraction)in MGO.

Multilayer Graphene-Coated Silicon Carbide Nanowire Formation Under Defocused Laser Irradiation

Graphene-coated silicon carbide(SiC@C)core-shell nanostructures have attracted attention in the fields of energy storage and nanoelectronics.In this study,multilayer graphene-coated silicon carbide(SiC)nanowires were obtained through the laser irradiation of a mixture target of graphite powder and silicon(Si)grinding sludge discharged from Si wafer manufacturing.Laser irradiation was performed using an ytterbium(Yb)fiber pulsed laser with a pulse width of 10 ms and a wavelength of 1070 nm with various defocus distances.The effect of laser defocusing on the morphology of the generated nanostructures was investigated.Results showed that nanowires were produced under the defocused conditions,and nanoparticles were observed at the on-focus position.The products obtained under all defocused conditions showed a core-shell structure,and the SiC nanowires were covered by graphene layers.The aspect ratio of the nanowires increased with the defocus distance.Observation of the laser-induced plume using a high-speed camera showed that when the laser was defocused,the plume propagation speed slowed down,and the shape of the plume changed to a swirling vortex.The nanowire formation was closely related to the propagation speed and shape variation of the plume.This successful production of SiC@C core-shell nanowires from Si waste opens up the possibility of the sustainable development of new materials for energy storage and nanoelectronics.

Projected Performance Advantage of Multilayer Graphene Nanoribbons as a Transistor Channel Material

The performance limits of a multilayer graphene nanoribbon(GNR)field-effect transistor(FET)are assessed and compared with those of a monolayer GNRFET and a carbon nanotube(CNT)FET.The results show that with a thin high dielectric constant(high-κ)gate insulator and reduced interlayer coupling,a multilayer GNRFET can significantly outperform its CNT counterpart with a similar gate and bandgap in terms of the ballistic on-current.In the presence of optical phonon scattering,which has a short mean free path in the graphene-derived nanostructures,the advantage of the multilayer GNRFET is even more significant.Simulation results indicate that multilayer GNRs with incommensurate non-AB stacking and weak interlayer coupling are the best candidates for high-performance GNRFETs.

Magic angles and flat Chern bands in alternating-twist multilayer graphene system

Based on the effective continuum model,we study alternating-twist multilayer graphene system and emergence of magic angles and flat band topology.All the alternating-twist multilayer graphene system(from triple layers to few layers)are found to have flat bands at magic angles where the area of AA stacking equals n-fold(n is an integer)electron cyclotron area.From the pseudo-Landau-level representation,there is always an isolated Dirac band in the alternating-twist graphene system constructed by odd number of layers.Since each pair of flat bands can be perceived as the zeroth pseudo-Landau-levels in two dimensional Dirac fermions,electron in the flat band pair can feel a pseudo-magnetic field with the same magnitude but the opposite sign.Calculated Chern number for each flat band is+1(or-1)which can be tuned by twisting in the vicinity of magic angles or by gating.The concurrent appearance of strong correlation and band topology of flat bands in the alternating-twist multilayer graphene may pave an avenue for the new understanding of superconductivity observed in triple-layered graphene,and supply a new playground for realizing(quantum)anomalous Hall effect.

Emergence of correlations in twisted monolayer-trilayer graphene heterostructures

Twisted bilayer graphene heterostructures have recently emerged as a well-established platform for studying strongly correlated phases,such as correlated insulating,superconducting,and topological states.Extending this notion to twisted multilayer graphene heterostructures has exhibited more diverse correlated phases,as some fundamental properties related to symmetry and band structures are correspondingly modified.Here,we report the observations of correlated states in twisted monolayer-trilayer(Bernal stacked)graphene heterostructures.Correlated phases at integer fillings of the moire unit cell are revealed at a high displacement field and stabilized with a moderate magnetic field on the electron-doping side at a twist angle of 1.45°,where the lift of degeneracy at the integer fillings is observed in the Landau fan diagram.Our results demonstrate the effectiveness of moire engineering in an extended structure and provide insights into electric-field tunable correlated phases.

Tunable correlation in twisted monolayer–trilayer graphene

Flat-band physics of moirésuperlattices,originally discovered in the celebrated twisted bilayer graphene,have recently been intensively explored in multilayer graphene systems that can be further controlled by electric field.In this work,we experimentally find the evidence of correlated insulators at half filling of the electron moiréband of twisted monolayer–trilayer graphene with a twist angle around 1.2°.Van Hove singularity(VHS),manifested as enhanced resistance and zero Hall voltage,is observed to be distinct in conduction and valence flat bands.It also depends on the direction and magnitude of the displacement fields,consistent with the asymmetric crystal structure.While the resistance ridges at VHS can be enhanced by magnetic fields,when they cross commensurate fillings of the moirésuperlattice in the conduction band,the enhancement is so strong that signatures of correlated insulator appear,which may further develop into an energy gap depending on the correlation strength.At last,Fermi velocity derived from temperature coefficients of resistivity is compared between conduction and valence bands with different displacement fields.It is found that electronic correlation has a negative dependence on the Fermi velocity,which in turn could be used to quantify the correlation strength.

Vibration of quadrilateral embedded multilayered graphene sheets based on nonlocal continuum models using the Galerkin method

Free vibration analysis of quadrilateral multilayered graphene sheets（MLGS） embedded in polymer matrix is carried out employing nonlocal continuum mechanics.The principle of virtual work is employed to derive the equations of motion.The Galerkin method in conjunction with the natural coordinates of the nanoplate is used as a basis for the analysis.The dependence of small scale effect on thickness,elastic modulus,polymer matrix stiffness and interaction coefficient between two adjacent sheets is illustrated.The non-dimensional natural frequencies of skew,rhombic,trapezoidal and rectangular MLGS are obtained with various geometrical parameters and mode numbers taken into account,and for each case the effects of the small length scale are investigated.

Ultra-broadband and polarization-independent planar absorber based on multilayered graphene

We propose an ultra-broadband and polarization independent planar absorber comprising multilayered graphene. The bandwidth of the proposed absorber is extended by increasing the number of layers of graphene, and it is polarization independent due to its symmetrical unit structure. The full wave simulation results show that an absorber with three graphenebased layers can efficiently harvest an electromagnetic wave with random polarization from 17.9 GHz to 188.7 GHz（i.e.,covering frequency regimes from K to D bands and relative bandwidth of - 165%）. The physical absorption mechanism of ultra-broadband absorption has been elaborated upon using the destructive interference method and multiple resonances approach in a multilayered medium. The proposed absorber can be used in many applications such as medical treatment,electromagnetic compatibility, and stealth technique.

VARIATIONAL PRINCIPLES FOR NONLOCAL CONTINUUM MODEL OF ORTHOTROPIC GRAPHENE SHEETS EMBEDDED IN AN ELASTIC MEDIUM

Equations governing the vibrations and buckling of multilayered orthotropic graphene sheets can be expressed as a system of n partial differential equations where n refers to the number of sheets. This description is based on the continuum model of the graphene sheets which can also take the small scale effects into account by employing a nonlocal theory. In the present article a variational principle is derived for the nonlocal elastic theory of rectangular graphene sheets embedded in an elastic medium and undergo- ing transverse vibrations. Moreover the graphene sheets are subject to biaxial compression. Rayleigh quotients are obtained for the frequencies of freely vibrating graphene sheets and for the buckling load. The influence of small scale effects on the frequencies and the buckling load can be observed qualiatively from the expressions of the Rayleigh quotients. Elastic medium is modeled as a combination of Winkler and Pasternak foundations acting on the top and bottom layers of the mutilayered nano-structure. Natural boundary con- ditions of the problem are derived using the variational principle formulated in the study. It is observed that free boundaries lead to coupled boundary conditions due to nonlocal theory used in the continuum formulation while the local （classical） elasticity theory leads to uncoupled boundary conditions. The mathematical methods used in the study involve calculus of variations and the semi-inverse method for deriving the variational integrals.

Characteristic modification by inserted metal layer and interface graphene layer in ZnO-based resistive switching structures

ZnO-based resistive switching device Ag/ZnO/TiN, and its modified structure Ag/ZnO/Zn/ZnO/TiN and Ag/graphene/ZnO/TiN, were prepared. The effects of inserted Zn layers in ZnO matrix and an interface graphene layer on resistive switching characteristics were studied. It is found that metal ions, oxygen vacancies, and interface are involved in the RS process. A thin inserted Zn layer can increase the resistance of HRS and enhance the resistance ratio. A graphene interface layer between ZnO layer and top electrode can block the carrier transport and enhance the resistance ratio to several times. The results suggest feasible routes to tailor the resistive switching performance of ZnO-based structure.

Improving comprehensive properties of Cu-11.9Al-2.5Mn shape memory alloy by adding multi-layer graphene carried by Cu_(51)Zr_(14)inoculant particles

In order to improve the comprehensive properties of the Cu-11.9Al-2.5Mn shape memory alloy(SMA),multilayer graphene(MLG)carried by Cu_(51)Zr_(14)inoculant particles was incorporated and dispersed into this alloy through preparing the preform of the cold-pressed MLG-Cu_(51)Zr_(14)composite powders.In the resultant novel MLG/Cu-Al-Mn composites,MLG in fragmented or flocculent form has a good bonding with the Cu-Al-Mn matrix.MLG can prevent the coarsening of grains of the Cu-Al-Mn SMA and cause thermal mismatch dislocations near the MLG/Cu-Al-Mn interfaces.The damping and mechanical properties of the MLG/Cu-Al-Mn composites are significantly improved.When the content of MLG reaches 0.2 wt.%,the highest room temperature damping of 0.0558,tensile strength of 801.5 MPa,elongation of 10.8%,and hardness of HV 308 can be obtained.On the basis of in-depth observation of microstructures,combined with the theory of internal friction and strengthening and toughening theories of metals,the relevant mechanisms are discussed.