Exploring the role of iron in Fe_(5)Ni_(4)S_(8)toward oxygen evolution through modulation of electronic orbital occupancy

Ni-Fe-based catalysts are considered to be among the most active catalysts for the oxygen evolution reaction(OER)under alkaline conditions,with Fe playing a crucial role.However,Fe leaching occurs during the reaction due to thermodynamic instability,which has resulted in conflicting reports within the literature regarding its role.To clarify this point,we propose a strategy consisting of modulating the electronic orbital occupancy to suppress the extensive loss of Fe atoms during the OER process.Theoretical calculations,in-situ X-ray photoelectron spectroscopy,molecular dynamics simulations,and a series of characterization showed that the stable presence of Fe not only accelerates the electron transfer process but also optimizes the reaction barriers of the oxygen evolution intermediates,promoting the phase transition of Fe_(5)Ni_(4)S_(8)to highly active catalytic species.The modulated Fe_(5)Ni_(4)S_(8)-based pre-catalysts exhibit improved OER activity and long-term durability.This study provides a novel perspective for understanding the role of Fe in the OER process.

Stable Lithium-Carbon Composite Enabled by Dual-Salt Additives

Lithium metal is regarded as the ultimate negative electrode material for secondary batteries due to its high energy density.However,it suffers from poor cycling stability because of its high reactivity with liquid electrolytes.Therefore,continuous efforts have been put into improving the cycling Coulombic efficiency(CE)to extend the lifespan of the lithium metal negative electrode.Herein,we report that using dual-salt additives of LiPF_(6) and LiNO_(3) in an ether solvent-based electrolyte can significantly improve the cycling stability and rate capability of a Li-carbon(Li-CNT)composite.As a result,an average cycling CE as high as 99.30% was obtained for the Li-CNT at a current density of 2.5 mA cm^(-2) and an negative electrode to positive electrode capacity(N/P)ratio of 2.The cycling stability and rate capability enhancement of the Li-CNT negative electrode could be attributed to the formation of a better solid electrolyte interphase layer that contains both inorganic components and organic polyether.The former component mainly originates from the decomposition of the LiNO_(3) additive,while the latter comes from the LiPF_(6)-induced ring-opening polymerization of the ether solvent.This novel surface chemistry significantly improves the CE of Li negative electrode,revealing its importance for the practical application of lithium metal batteries.

Remote plasma-enhanced atomic layer deposition of gallium oxide thin films with NH_3 plasma pretreatment

High quality gallium oxide(Ga_2O_3) thin films are deposited by remote plasma-enhanced atomic layer deposition(RPEALD) with trimethylgallium(TMG) and oxygen plasma as precursors. By introducing in-situ NH3 plasma pretreatment on the substrates, the deposition rate of Ga_2O_3 films on Si and GaN are remarkably enhanced, reached to 0.53 and 0.46 ?/cycle at 250 °C,respectively. The increasing of deposition rate is attributed to more hydroxyls(–OH) generated on the substrate surfaces after NH3 pretreatment, which has no effect on the stoichiometry and surface morphology of the oxide films, but only modifies the surface states of substrates by enhancing reactive site density. Ga_2O_3 film deposited on GaN wafer is crystallized at 250 °C, with an epitaxial interface between Ga_2O_3 and GaN clearly observed. This is potentially very important for reducing the interface state density through high quality passivation.

Observation of multiple charge density wave phases in epitaxial monolayer 1T-VSe_(2) film

As a special order of electronic correlation induced by spatial modulation, the charge density wave(CDW) phenomena in condensed matters attract enormous research interests. Here, using scanning-tunneling microscopy in various temperatures, we discover a hidden incommensurate stripe-like CDW order besides the(■) CDW phase at low-temperature of 4 K in the epitaxial monolayer 1T-VSe_(2) film. Combining the variable-temperature angle-resolved photoemission spectroscopic(ARPES) measurements, we discover a two-step transition of an anisotropic CDW gap structure that consists of two parts △_(1) and△_(2). The gap part ?1 that closes around ~ 150 K is accompanied with the vanish of the(√7×√3) CDW phase. While another momentum-dependent gap part △_(2) can survive up to ~ 340 K, and is suggested to the result of the incommensurate CDW phase. This two-step transition with anisotropic gap opening and the resulted evolution in ARPES spectra are corroborated by our theoretical calculation based on a phenomenological form for the self-energy containing a two-gap structure △_(1) +△_(2), which suggests different forming mechanisms between the(√7×√3) and the incommensurate CDW phases. Our findings provide significant information and deep understandings on the CDW phases in monolayer 1T-VSe_(2) film as a two-dimensional(2D) material.

Interfacial dynamics of GaP/Si(100) heterostructure grown by molecular beam epitaxy

The atomic structure and surface chemistry of GaP/Si(100)heterostructure with different pre-layers grown by molecu-lar beam epitaxy are studied.It is found that GaP epilayer with Ga-riched pre-layers on Si(100)substrate has regular surface mor-phology and stoichiometric abrupt heterointerfaces from atomic force microscopes(AFMs)and spherical aberration-corrected transmission electron microscopes(ACTEMs).The interfacial dynamics of GaP/Si(100)heterostructure is investigated by X-ray photoelectron spectroscopy(XPS)equipped with an Ar gas cluster ion beam,indicating that Ga pre-layers can lower the inter-face formation energy and the bond that is formed is more stable.These results suggest that Ga-riched pre-layers are more con-ducive to the GaP nucleation as well as the epitaxial growth of GaP material on Si(100)substrate.

Honeycomb Lattice in Metal-Rich Chalcogenide Fe_(2)Te

Two-dimensional honeycomb crystals have inspired intense research interest for their novel properties and great potential in electronics and optoelectronics. Here, through molecular beam epitaxy on SrTiO_3(001), we report successful epitaxial growth of metal-rich chalcogenide Fe_(2)Te, a honeycomb-structured film that has no direct bulk analogue, under Te-limited growth conditions. The structural morphology and electronic properties of Fe_(2)Te are explored with scanning tunneling microscopy and angle resolved photoemission spectroscopy, which reveal electronic bands cross the Fermi level and nearly flat bands. Moreover, we find a weak interfacial interaction between Fe_(2)Te and the underlying substrates, paving a newly developed alternative avenue for honeycomb-based electronic devices.

Molecular beam epitaxy growth of monolayer hexagonal MnTe_(2)on Si(111)substrate

Monolayer MnTe_(2)stabilized as 1 T structure has been theoretically predicted to be a two-dimensional(2 D)ferromagnetic metal and can be tuned via strain engineering.There is no naturally van der Waals(vdW)layered MnTe_(2)bulk,leaving mechanical exfoliation impossible to prepare monolayer MnTe_(2).Herein,by means of molecular beam epitaxy(MBE),we successfully prepared monolayer hexagonal MnTe_(2)on Si(111)under Te rich condition.Sharp reflection high-energy electron diffraction(RHEED)and low-energy electron diffraction(LEED)patterns suggest the monolayer is atomically flat without surface reconstruction.The valence state of Mn^(4+)and the atom ratio of([Te]:[Mn])further confirm the MnTe_(2)compound.Scanning tunneling spectroscopy(STS)shows the hexagonal MnTe_(2)monolayer is a semiconductor with a large bandgap of~2.78 eV.The valence-band maximum(VBM)locates at theΓpoint,as illustrated by angle-resolved photoemission spectroscopy(ARPES),below which three hole-type bands with parabolic dispersion can be identified.The successful synthesis of monolayer MnTe_(2)film provides a new platform to investigate the 2D magnetism.

通过调控范霍夫奇点在外延单层VSe_(2)中诱导出巡游铁磁性

处在费米能级处的范霍夫奇点(van Hove singularity)由于具有发散的态密度特征可以诱导出巡游铁磁性.本文在SrTiO_(3)(111)衬底上外延生长单层VSe_(2)薄膜,并通过调控范霍夫奇点诱导出巡游铁磁性.作者通过角分辨光电子能谱技术直接观测到了单层VSe_(2)中的范霍夫奇点能带结构.理论计算表明,当该范霍夫奇异点靠近费米能级时,可通过斯通纳(Stoner)不稳定性产生巡游铁磁性.实验上,作者利用SrTiO_(3)(111)在低温下极大增强的介电常数εr,通过界面电荷转移效应调控范霍夫奇点向费米能级处移动,并通过电输运测量观测到了3.3 K的巡游铁磁性转变.此外,通过改变薄膜层厚和更换衬底的方式,作者可以进一步调控界面电荷转移效果和范霍夫奇点的能量位置,并对巡游铁磁性进行调控.这项研究证明了范霍夫奇点可以成为巡游铁磁性的调控自由度,并拓展了二维磁体在未来电子信息技术的应用潜力.

Regulating Li transport in Li-magnesium alloy for dendrite free Li metal anode

Li metal has become a strong candidate for anode due to its high theoretical specific capacity and lowest electrochemical potential.However,the poor reversibility caused by continuous chemical and electrochemical degradation hinders the practical application of Li metal.Solid-solution-based metal alloy phases have been proposed as hosts for regulating the non-dendrite electrodeposition,but the fundamental understanding remains unclear due to the drastically different deposition behaviors of Li on them.Here we found the difference in the diffusion coefficient of Li atoms on solid-solution-based metal alloy phases(Li-Mg and Li-Ag alloys)was a major contributor to the different deposition behaviors.The low Li atom diffusion coefficient of Li-Mg alloy showed a preferential Li accumulation on the upper surface rather than the inward-growth plating of Li atoms into alloy foil in Li-Ag alloy.By the process of secondary recrystallization,we improved the diffusion coefficient of Li atoms in Li-Mg alloy that facilitates the inward transfer rather than surface plating of Li atoms.In this case,the recrystallized Li-Mg alloy underwent a solidsolution phase change in the delithiation-lithiation cycles which yielded a high Coulombic efficiency of 99.3%with a reversible gravimetric capacity of 2,874 mAh·g−1 and superior cycling stability over 5,000 h without dendrite growth.

手性晶体CoSi中拓扑费米弧的电荷不稳定性

拓扑边界态出现在拓扑非平庸态和平庸态之间的边界上,通常是无间隙的或被称为金属态.例如,拓扑绝缘体的表面态是无间隙的狄拉克态.这些金属拓扑边界态往往可以被近自由费米子很好的描述.如果拓扑边界态具有显著的电子-电子相互作用的行为,无间隙的边界态会转变为有间隙的有序态,例如密度波态或超导态,这在理论上是非常有趣的,但目前还缺少相关的实验证据.本文报道了在Co Si(001)表面观察到了电子-电子相互作用驱动的、在拓扑边界态上形成的非公度电荷密度波(CDW). CDW的波矢随温度的变化而变化,这与拓扑表面费米弧随温度的演化相吻合. CDW相的取向由费米弧的手性决定,这暗示了CDW与费米弧之间存在直接的联系.该发现将促进在拓扑材料边界上寻找更多相互作用驱动的有序态,例如超导和磁性.

High-performance solar-blind photodetector arrays constructed from Sn-doped Ga_(2)O_(3)microwires via patterned electrodes

Ga_(2)O_(3)has been regarded as a promising material for solar-blind detection due to its ultrawide bandgap and low growth cost.Although semiconductor microwires(MWs)possess unique optical and electronic characteristics,the performances of photodetectors developed from Ga_(2)O_(3)MWs are still less than satisfactory.Herein,we demonstrate high-performance solar-blind photodetectors based on Sn-doped Ga_(2)O_(3)MWs,possessing a light/dark current ratio of 107 and a responsivity of 2,409 A/W at 40 V.Moreover,a 1×10 solar-blind photodetector linear array is developed based on the Sn-doped Ga_(2)O_(3)MWs via a patternedelectrodes method.And clear solar-blind images are obtained by using the photodetector array as the imaging unit of a solarblind imaging system.The results provide a convenient way to construct high-performance solar-blind photodetector arrays based on Ga_(2)O_(3)MWs,and thus may push forward their future applications.

Highly stable lithium anode enabled by self-assembled monolayer of dihexadecanoalkyl phosphate

Li has been considered as the ultimate anode material for high energy density secondary Li batteries.However,its practical application has been limited due to its low Coulombic efficiency(CE)and the formation of lithium dendrites.Recently,we have developed a microspherical Li-carbon nanotube(Li-CNT)composite material passivated with octadecylphosphonic acid(OPA)self-assembled monolayer(SAM)exhibiting suppressed lithium dendrite formation and improved environmental/electrochemical stability.In this work,we demonstrated the significantly enhanced passivation effects of a SAM using dihexadecanoalkyl phosphate(DHP),a molecule that is comprised of double hydrophobic alkyl chains and forms a denser SAM on surfaces with large curvature.As a result,the DHP SAM delivers superior environmental and electrochemical stability to the OPA passivated Li-CNT material.In specific,the DHP passivated Li-CNT composite(DHP-Li-CNT)delivers a high CE of 99.25%under a 33.3%depth of discharge(DOD)at 1 C,when it is paired with a LiFePO4 cathode.The evolution of the SAM during cycling and the effects of DOD and current density on the CE of the DHP-Li-CNT anode have also been investigated.The improved SAM passivation constitutes an important step in achieving the goal of practically applicable Li anodes.

Modulation of electronic state in copper-intercalated 1T-TaS_(2)

Intercalation is an effective method to modify physical properties and induce novel electronic states of transition metal dichalcogenide(TMD)materials.However,it is difficult to reveal the microscopic electronic state evolution in the intercalated TMDs.Here we successfully synthesize the copper-intercalated 1T-TaS_(2) and characterize the structural and electronic modification combining resistivity measurements,atomic-resolution scanning transmission electron microscopy(ADF-STEM),and scanning tunneling microscopy(STM).The intercalated Cu atom is determined to be directly below the Ta atom and suppresses the commensurate charge density wave(CCDW)phase.Two specific electronic modulations are discovered in the near-commensurate(NC)CDW phase:the electron doping state near the defective star of Davids(SDs)in metallic domains and the spatial evolution of the Mott gap in insulating domains.Both modulations reveal that intercalated Cu atoms act as a medium to enhance the interaction between intralayer SDs,in addition to the general charge transfer effect.It also solidifies the Mott foundation of the insulating gap in pristine samples.The intriguing electronic evolution in Cu-intercalated 1T-TaS_(2) will motivate further exploration of novel electronic states in the intercalated TMD materials.

Epitaxial growth ofβ-Ga_(2)O_(3)thin films on Ga_(2)O_(3)and Al_(2)O_(3)substrates by using pulsed laser deposition

In this work,we have successfully grown high quality epitaxialβ-Ga_(2)O_(3)thin films onβ-Ga_(2)O_(3)(100)and Al_(2)O_(3)(0001)substrates using pulsed laser deposition(PLD).By optimizing temperature and oxygen pressure,the best conditions were found to be 650-700℃and 0.5 Pa.To further improve the quality of hetero-epitaxialβ-Ga_(2)O_(3),the sapphire substrates were pretreated for atomic terraced surface by chemical cleaning and high temperature annealing.From the optical transmittance measurements,the films grown at 600-750℃exhibit a clear absorption edge at deep ultraviolet region around 250-275 nm wavelength.High resolution transmission electron microscope(HRTEM)images and X-ray diffraction(XRD)patterns demonstrate thatβ-Ga_(2)O_(3)(-201)//Al_(2)O_(3)(0001)epitaxial texture dominated the epitaxial oxide films on sapphire substrate,which opens up the possibilities of high power electric devices.