Electronic Instability of Kagome Metal CsV_(3)Sb_(5) in the 2×2×2 Charge Density Wave State

Recently discovered kagome metals AV_(3)Sb_(5)(A=K,Rb,and Cs)provide an ideal platform to study the correlation among nontrivial band topology,unconventional charge density wave(CDW),and superconductivity.The evolution of electronic structures associated with the change of lattice modulations is crucial for understanding of the CDW mechanism,with the combination of angle-resolved photoemission spectroscopy(ARPES)measurements and density functional theory calculations,we investigate how band dispersions change with the increase of lattice distortions.In particular,we focus on the electronic states around M point,where the van Hove singularities are expected to play crucial roles in the CDW transition.Previous ARPES studies reported a spectral weight splitting of the van Hove singularity around M point,which is associated with the 3D lattice modulations.Our studies reveal that this“splitting”can be connected to the two van Hove singularities at k_(z)=0 and k_(z)=π/c in the normal states.When the electronic system enters into the CDW state,both van Hove singularities move down.Such novel properties are important for understanding of the CDW transition.

Visible-light deposition of CrO_(x) cocatalyst on TiO_(2):Cr valence regulation for superior photocatalytic CO_(2)reduction to CH_(4)

Photodeposition is widely adopted for implanting metal/metal oxide cocatalysts on semiconductors.However,it is prerequisite that the photon energy should be sufficient to excite the host semiconductor.Here,we report a lower-energy irradiation powered deposition strategy for implanting CrO_(x) cocatalyst on TiO_(2).Excitingly,CrO_(x)-400 implanted under visible-light irradiation significantly promotes the CH4 evolution rate on TiO_(2)to 8.4μmolg·^(-1)h^(-1) with selectivity of98%from photocatalytic CO_(2)reduction,which is 15 times of that on CrO_(x)-200 implanted under UV-visible-light irradiation.Moreover,CrO_(x)-400 is identified to be composed of higher valence Cr species compared to CrO_(x)-200.This valence states regulation of Cr species is indicated to provide more active sites for CO_(2) adsorption/activation and to modulate the reaction mechanism from single Cr site to Cr-Cr dual sites,thus endowing the superior CH_(4)production.This work demonstrates an alternative strategy for constructing efficient metal oxides cocatalysts on wide bandgap semiconductor.

On the Reflected Geometric Brownian Motion with Two Barriers

In this paper, we are concerned with Re?ected Geometric Brownian Motion (RGBM) with two barriers. And the stationary distribution of RGBM is derived by Markovian in?nitesimal Generator method. Consequently the ?rst passage time of RGBM is also discussed.

Evolution hydrothermal aging resistance mechanism study of zirconium and manganese doped CeO_(2)catalysts in soot catalytic combustion based on low Miller indices crystal surface effect

The thermogravimetric analysis(TGA)experiments were carried out to reveal the mechanism of Zr and Mn doping on catalytic activity of CeO_(2)catalyst both fresh and after hydrothermal aging,and the lattice morphology and valence changes were characterized by means of Brunauer-Emmett-Teller(BET)method,X-ray diffraction(XRD),X-ray photoelectron spectroscopy(XPS),and H_(2)-temperature programmed reduction(H_(2)-TPR).Density functional theory(DFT)and molecular thermodynamics calculations were applied to investigate the change in catalytic activity,crystal surface energy and crystal morphology caused by hydrothermal aging.The maximum reaction rate temperature of fresh Mn/CeO_(2)(389℃)is similar to that of CeO_(2)(371℃)and lower than that of Zr/CeO_(2)(447℃),but the catalytic performance of CeO_(2)decreases more severely after hydrothermal aging.The catalyst crystals show different degrees of crystal surface migration after hydrothermal aging,which leads to the reduction of Ce^(3+)/Ce^(4+) ratio and the active sites shift.DFT calculations indicate that the doping of Zr and Mn reduces the surface energy of the low Miller indices surface and increases the oxygen vacancy formation energy,leading to better thermal stability and lower catalytic activity.The Zr and Mn doping also changes the adsorption energy and Gibbs free energy of H_(2)O,which dominates the migration of(111)to(110)and(100)in the vapor environment.The crystal surface migration mechanism of CeO_(2)catalysts doped with Zr and Mn induced by H_(2)O molecules at high temperature obtained in this study can provide a valuable addition to the regeneration of CeO_(2)catalysts in the after-treatment systems of diesel engines.

Event-triggered adaptive tracking control of a class of nonlinear systems with asymmetric time-varying output constraints

This article investigates the event-triggered adaptive neural network(NN)tracking control problem with deferred asymmetric time-varying(DATV)output constraints.To deal with the DATV output constraints,an asymmetric time-varying barrier Lyapunov function(ATBLF)is first built to make the stability analysis and the controller construction simpler.Second,an event-triggered adaptive NN tracking controller is constructed by incorporating an error-shifting function,which ensures that the tracking error converges to an arbitrarily small neighborhood of the origin within a predetermined settling time,consequently optimizing the utilization of network resources.It is theoretically proven that all signals in the closed-loop system are semi-globally uniformly ultimately bounded(SGUUB),while the initial value is outside the constraint boundary.Finally,a single-link robotic arm(SLRA)application example is employed to verify the viability of the acquired control algorithm.

Confinement synergy at the heterointerface for enhanced oxygen evolution

Two-dimensional transition metal hydroxides with abundant reserves and low prices have played an indispensable role in energy catalytic applications.Recent reports indicated that the incorporation of Fe species into Co-based catalysts can synergistically enhance oxygen evolution reaction(OER)activity.Constructing a heterointerface on the surface of Co-based catalysts can provide a platform to investigate the role of heterointerface in reaction kinetics.Herein,we constructed a Fe-O-Co heterointerface without electronic effect by depositing FeO_(x)clusters on the oxygen vacancies of CoOOH surface.FeO_(x)/CoOOH exhibited excellent OER intrinsic activity,which can deliver the turnover frequency(TOF)of 4.56 s^(-1)at the overpotentials of 300 mV and the Tafel slope of 33 mV·dec^(-1).In-situ electrochemical impedance spectroscopy(EIS)and density functional theory(DFT)calculations demonstrated that the synergistic effect between Fe sites and Co sites confined at the Fe-O-Co heterointerface accelerated the charge transfer during OER and optimized the adsorption of oxygen intermediates,consequently enhancing OER.

Demonstration of epitaxial growth of strain-relaxed GaN films on graphene/SiC substrates for long wavelength light-emitting diodes

Strain modulation is crucial for heteroepitaxy such as GaN on foreign substrates.Here,the epitaxy of strain-relaxed GaN films on graphene/SiC substrates by metal-organic chemical vapor deposition is demonstrated.Graphene was directly prepared on SiC substrates by thermal decomposition.Its pre-treatment with nitrogen-plasma can introduce C–N dangling bonds,which provides nucleation sites for subsequent epitaxial growth.The scanning transmission electron microscopy measurements confirm that part of graphene surface was etched by nitrogen-plasma.We study the growth behavior on different areas of graphene surface after pre-treatment,and propose a growth model to explain the epitaxial growth mechanism of GaN films on graphene.Significantly,graphene is found to be effective to reduce the biaxial stress in GaN films and the strain relaxation improves indium-atom incorporation in InGaN/GaN multiple quantum wells(MQWs)active region,which results in the obvious red-shift of light-emitting wavelength of InGaN/GaN MQWs.This work opens up a new way for the fabrication of GaN-based long wavelength light-emitting diodes.

Geochronological Framework of Paleoproterozoic Intrusive Rocks and Its Constraints on Tectonic Evolution of the Liao-Ji Belt,Sino-Korean Craton

The Liao-Ji belt(LJB)is one of the Paleoproterozoic tectonic belts located in the North China Craton.A large number of Paleoproterozoic meta-volcanic-sedimentary rock and intrusive rocks are preserved in the LJB,which provide reliable carriers for the study of the Paleoproterozoic tectonic evolution of the North China Craton.The Paleoproterozoic intrusive rock in the LJB can be divided into the following seven types:syenogranite,quartz diorite,porphyry granite,migmatitic granite,sye-nite,metamorphic plutonic rock,and granitic pegmatite and metagabbro(metamorphic diabase).Zir-con U-Pb dating of 15 samples from intrusive rocks was carried out in this study.The chronology framework of the Paleoproterozoic intrusive rock in the LJB was established,and the magmatism of intrusive rocks can be divided into three stages:2200 to 2110,2010 to 1937,1900 to 1820 Ma.The chronological framework supported the evolution model of subduction accretionary arc-continent colli-sion in the LJB effectively.Combined with previous geochemical work,it was a passive continental margin environment at approximately 2200 Ma,and then transformed into and active continental margin.The bimodal intrusive rocks between 2180 and 2150 Ma indicated a back-arc tension envi-ronment which lasted until approximately 2110 Ma with a large number of basic intrusive rocks.And then the back-arc basin began to contract and the magmatic activities were reduced,with only a small number of intrusive rock activities occurring at approximately 2040,2010 and 1937 Ma.After the orogenic activities,there was a post-orogenic extension stage from 1900 to 1820 Ma.Magmatic activi-ties caused by the environmental extension started to occur more frequently and subsequently resulted in the large-scale intrusive rocks in eastern Liaoning.

Molecular movements of trehalose inside a single network enabling a rapidly-recoverable tough hydrogel

It remains a challenge to achieve rapidly recoverable hydrogels by molecular hydrogen-bonding interaction because of its slow inter-action kinetics.This work for the first time reports a trehalose(Tre)-based molecular movement mechanism inside a single network of polyacrylamide(PAM)that accelerates the kinetics of hydrogenbonding interaction,and thereby endows the hydrogel with high toughness and rapid shape and mechanical recoverability.The resultant PAM@Tre hydrogel is capable of full shape recovery after 10,000 loading/unloading cycles at a strain of 500%.Even after being stretched at a strain of 2500%,it can recover to its original shape within 10 seconds.Moreover,the molecular movement of trehalose also endows the PAM@Tre hydrogel with fracture energy and toughness as high as~9000 J m^(-2) and~1600 kJ m^(-3),respec-tively,leading to strong resistance to both static and dynamic piercing.The PAM@Tre hydrogel is thus believed to have enormous potentials in protection devices,bionic skin,soft actuator,and stretchable electronics.

Disentangling the electron-lattice dichotomy of the excitonic insulating phase in Ta_(2)Ni(Se_(1-x)S_(x))_(5)with sulfur substitution and potassium deposition

Ta_(2)NiSe_(5)is a promising candidate for hosting an excitonic insulator(EI)phase,a novel electronic state driven by electron-hole Coulomb attraction.However,the role of electron-lattice coupling in the formation of the EI phase remains controversial.Here,we use angle-resolved photoemission spectroscopy(ARPES)to study the band structure evolution of Ta_(2)Ni(Se_(1-x)S_(x))_(5)with sulfur substitution and potassium deposition,which modulate the band gap and the carrier concentration,respectively.We find that the Ta 5d states originating from the bottom of the conduction band persist at the top of the valence band in the low-temperature monoclinic phase,indicating the importance of exciton condensation in opening the gap in the semi-metallic band structure.We also observe that the characteristic overlap between the conduction and valence bands can be restored in the monoclinic lattice by mild carrier injection,suggesting that the lattice distortion in the monoclinic phase is not the main factor for producing the insulating gap,but rather the exciton condensation in the electronic system is the dominant driving force.Our results shed light on the electron-lattice decoupling and the origin of the EI phase in Ta_(2)Ni(Se_(1-x)Sx)_(5).