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In-situ TEM investigation of MoS2 upon alkali metal intercalation

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Science China Chemistry 2018年第2期61卷 222-227页

作者： Qianming Huang Lifen Wang Zhi Xu Wenlong Wang xuedong bai Beijing National Laboratory for Condensed Matter Physics Institute of Physics Chinese Academy of Sciences Beijing 100190 China Collaborative Innovation Center of Quantum Matter Beijing 100190 China School of Physical Sciences University of Chinese Academy of Sciences Beijing 100190 China

Phase transition in two dimensional molybdenum disulfide (MoS_2) can be induced by several methods and has been investigated for decades. Alkali metal insertion of MoS_2 had been proved an effective method to cause phase transition early in 1970s, and has been gaining renewed interest recently, due to the possible application of MoS_2 in energy storage. The alkali metal intercalation of MoS_2 has been studied by various techniques, among which in-situ transmission electron microscopy (TEM) provides unique capability of real time resolving the structural evolution of the materials at high spatial resolutions. Here by in-situ TEM technique we investigated the structural evolution of MoS_2 upon lithium and sodium intercalation, along with transformation of the nanosheet and variation of the electron diffraction patterns. The intercalation process is accompanied by emergence of superstructures, which exist in several forms. The ion intercalation results in phase transition of MoS_2 from 2H to 1T, and the driving mechanism of the phase transition are discussed. The work provides a more comprehensive understanding of ion intercalation induced phase transition of MoS_2.

关键词： molybdenum disulfide phase transition intercalation in-situ TEM

In-situ TEM study of the dynamic behavior of the graphene-metal interface evolution under Joule heating

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Science China(Technological Sciences) 2016年第7期59卷 1080-1084页

作者： WEI JiaKe XU Zhi WANG Hao WANG WenLong bai xuedong Beijing National Laboratory for Condensed Matter Physics Institute of Physics Chinese Academy of Sciences Beijing 100190 China International Center for Quantum Materials and School of Physics Peking University Beijing 100871 China Collaborative Innovatton Center of Quantum Matter Beijing 100871 China

The dynamic behavior of the interface between few layer graphene(FLG) and tungsten metal tips under Joule heating has been studied by in-situ transmission electron microscopy(TEM) method. High-resolution and real-time observations show the tungsten tip ‘swallow' carbon atoms of the FLG and ‘spit' graphite shells at its surface. The tip was carbonized to tungsten carbide(WC, W_2 C and WC_x) after this process. A carbon diffusion mechanism has been proposed based on the diffusion of carbon atoms through the tungsten tip and separation from the surface of the tip. After Joule heating, the initial FLG-metal mechanical contact was transformed to FLG-WCx-W contact, which results in significant improvement on electrical conductivity at the interface.

关键词： In-situ TEM graphene-metal contact Joule heating carbon atoms diffusion

3D graphene foam-supported cobalt phosphate and borate electrocatalysts for high-efficiency water oxidation

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Science Bulletin 2015年第16期60卷 1426-1433页

作者： Min Zeng Hao Wang Chong Zhao Jiake Wei Wenlong Wang xuedong bai Beijing National Laboratory for Condensed Matter Physics Institute of Physics Chinese Academy of Sciences

The cobalt phosphate-/cobalt borate-based oxygen-evolving catalysts （OECs） are the important class of earth-abundant electrocatalysts that can operate with high activity for water splitting under benign conditions. This article reports the integration of cobalt phosphate （Co- Pi） and cobalt borate （Co-Bi） OECs with three-dimensional （3D） graphene foam （GF） for the electrocatalytic water oxidation reaction. The GF showed a unique advantage to serve as a highly conductive 3D support with large capacity for anchoring and loading Co-OECs, thereby facilitating mass and charge transfer due to the large amount of active sites provided by the 3D graphene scaffold. As a result, this integrated system of GF and Co-OECs exhibits synergistically enhanced catalytic activity. The overpotential （η） of Co-Pi and Co-Bi/graphene catalysts is about 0.390 and 0.315 V in neutral solutions, respectively. Besides, the integrated Co-OECs/graphene catalysts have also exhibited improved and stable oxygen evolution catalytic ability in alkaline solution.

关键词： Water splitting Oxygen evolutioncatalyst Cobalt phosphate and borate Graphene foam

Electrochemical solid-state amorphization in the immiscible Cu-Li system

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Science Bulletin 2018年第18期63卷 1208-1214页

作者： Muhua Sun Jiake Wei Zhi Xu Qianming Huang Yu Zhao Wenlong Wang xuedong bai Beijing National Laboratory for Condensed Matter Physics and Institute of Physics Chinese Academy of Sciences School of Physical Sciences University of Chinese Academy of Sciences

As a typical immiscible binary system, copper (Cu) and lithium (Li) show no alloying and chemical intermixing under normal circumstances. Here we show that, when decreasing Cu nanoparticle sizes into ultrasmall range, the nanoscale size effect can play a subtle yet critical role in mediating the chemical activity of Cu and therefore its miscibility with Li, such that the electrochemical alloying and solidstate amorphization will occur in such an immiscible system. This unusual observation was accomplished by performing in-situ studies of the electrochemical lithiation processes of individual CuO nanowires inside a transmission electron microscopy (TEM). Upon lithiation, CuO nanowires are first electrochemically reduced to form discrete ultrasmall Cu nanocrystals that, unexpectedly, can in turn undergo further electrochemical lithiation to form amorphous Cu Lixnanoalloys. Real-time TEM imaging unveils that there is a critical grain size (ca. 6 nm), below which the nanocrystalline Cu particles can be continuously lithiated and amorphized. The possibility that the observed solid-state amorphization of Cu-Li might be induced by electron beam irradiation effect can be explicitly ruled out; on the contrary, it was found that electron beam irradiation will lead to the dealloying of as-formed amorphous Cu Lixnanoalloys.

关键词： Immiscible Cu-Li system Electrochemical solid-state amorphization Nanoscale size effect In-situ TEM Lithium ion battery

Photo-enhanced field electron emission of cadmium sulfide nanowires

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Science China(Physics,Mechanics & Astronomy) 2011年第11期54卷 1963-1966页

作者： ZHANG JinLing LV YingHua LIU Ning LI YanQing GAO Peng bai xuedong School of Electronic Engineering Beijing University of Posts and Telecommunications Beijing 100876 China Functional Nano ＆ Soft Materials Laboratory （FUNSOM） Soochow University Suzhou 215123 China Beijing National Laboratory for Condensed Matter Physics and Institute of Physics Chinese Academy of Sciences Beijing 100190 China

The response of field electron emission of cadmium sulfide (CdS) nanowires (NWs) to visible light has been *** is found that,upon light illumination,the turn-on voltage drops,emission current increases obviously,and the Fowler-Nordheim behavior deviates from a straight line.A process of field emission coupled with semiconducting properties of CdS NWs is ***-excited electron transition from the valence band to the conductance band of CdS nanowires increases the quantity of emitting electrons,and the photoemission decreases the effective work function of CdS emitters,which largely enhances the field emission *** response of field emission of CdS NWs to light illumination suggests an approach for tuning field emission of semiconductor emitters.

关键词： field electron emission optical coupling CdS nanowires semiconductor emitters

Real-time in situ TEM studying the fading mechanism of tin dioxide nanowire electrodes in lithium ion batteries

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Science China(Technological Sciences) 2013年第11期56卷 2630-2635页

作者： WANG LiFen XU Zhi YANG ShiZe TIAN XueZeng WEI JiaKe WANG WenLong bai xuedong Beijing National Laboratory for Condensed Matter Physics Institute of PhysicsChinese Academy of Sciences

Fading mechanism of tin dioxide （SnO2） electrodes in lithium ion batteries has attracted much attentions, which is of great importance for the battery applications. In this paper, electrochemical lithiation-delithiation cycles of individual SnO2 nanowires were conducted in situ in a high-resolution transmission electron microscopy （TEM）. Major changes in volume with expan- sions of 170%~300% on SnO2 nanowire electrodes were observed during the first lithiation process in electrochemical cycling, including conversion reaction of SnO2 precursor to Li20 matrix and active lithium host Sn, and alloying of Sn with Li to form brittle Li-Sn alloy. SnO2 nanowire electrodes were inclined to suffer from thermal runaway condition in the first two cycles. During cycling, morphology and composition evolution of SnO2 nanowire electrodes were recorded. Cyclic lithiation and del- ithiation of the electrode demonstrated the phase transition between Lii3Sn5 and Sn. Metallic Sn clusters were formed and their sizes enlarged with increasing cycle times. Detrimental aggregation of Sn clusters caused pulverization in SnO2 nanowire elec- trodes, which broke the conduction and transport path for electrons and lithium ions. The real-time in situ TEM revealed fading mechanism provides important guidelines for the viable design of the SnO2 nanowire electrodes in lithium ion batteries.

关键词： lithium ion battery tin dioxide nanowire electrode fading mechanism tin aggregation in situ TEM

Towards the controlled CVD growth of graphitic B-C-N atomic layer films： The key role of B-C delivery molecular precursor

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Nano Research 2016年第5期9卷 1221-1235页

作者： Hao Wang Chong Zhao Lei Liu Zhi Xu Jiake Wei Wenlong Wang xuedong bai Enge Wang In ternational Center for Quantum Materials School of Physics Peking University Beijing 100871 China Beijing National Laboratory for Condensed Matter Physics Institute of Physics Chinese Academy of Sciences Beijing 100190 China Collaborative Innovation Center of Quantum Matter Beijing 100871 China

Graphene-like, ternary system B-C-N atomic layer materials promise highly tunable electronic properties and a plethora of potential applications. However, thus far, experimental synthesis of the B-C-N atomic layers normally yields a microscopic phase-segregated structure consisting of pure C and BN domains. Further, growing the truly ternary B-C-N phase layers with homogenous atomic arrangements has proven to be very challenging. Here, in designing a better- controlled process for the chemical vapor deposition （CVD） growth of B-C-N atomic layer films with the minimized C and BN phase segregation, we selected trimethyl borane （TMB）, a gaseous organoboron compound with pre-existing B--C bonds, as the molecular precursor to react with ammonia （NH3） gas that serves as the nitrification agent. The use of this unique B-C delivery precursor allows for the successful synthesis of high-quality and large-area B-C-N atomic layer films. Moreover, the TMB/NH3 reactant combination can offer a high level of tunability and control of the overall chemical composition of B-C-N atomic layers by regulating the relative partial pressure of two gaseous reactants. Electrical transport measurements show that a finite energy gap can be opened in the as-grown B-C-N atomic layers and its tunability is essentially dependent on the relative C to BN atomic compositions. On the basis of carefully controlled experiments, we show that the pre-existing B-C bonds in the TMB molecular precursor have played a crucial role in effectively reducing the C and BN phase segregation problem, thereby facilitating the formation of truly ternary B-C-N phase atomic layers.

关键词： graphitic B-C-N atomic layer chemical vapor deposition B-C delivery precursor minimized phase segregation

Filament growth dynamics in solid electrolyte-based resistive memories revealed by in situ TEM

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Nano Research 2014年第7期7卷 1065-1072页

作者： Xuezeng Tian Lifen Wang Jiake Wei Shize Yang Wenlong Wang Zhi Xu xuedong bai Beijing National Laboratory for Condensed Matter Physics Institute of Physics Chinese Academy of Sciences Beijing 7 O0190 China

Solid electrolyte based-resistive memories have been considered to be a potential candidate for future information technology with applications in non-volatile memory, logic circuits and neuromorphic computing. A conductive filament model has been generally accepted to be the underlying mechanism for the resistive switching. However, the growth dynamics of such conductive filaments is still not fully understood. Here, we explore the controllability of filament growth by correlating observations of the filament growth with the electric field distribution and several other factors. The filament growth behavior has been recorded using in situ transmission electron microscopy. By studying the real- time recorded filament growth behavior and morphologies, we have been able to simulate the electric field distribution in accordance with our observations. Other factors have also been shown to affect the filament growth, such as Joule heating and electrolyte infrastructure. This work provides insight into the controllable growth of conductive filaments and will help guide research into further functionalities of nanoionic resistive memories.

关键词： resistive switching conductive filaments in situ transmissionelectron microscope real-time observation computer simulation

The Rise of Two‑Dimensional‑Material‑Based Filters for Airborne Particulate Matter Removal

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Advanced Fiber Materials 2023年第2期5卷 461-483页

作者： Jun Liu Enze Tian Shaolin Zhang Deyu Kong Kehai Liu xuedong bai Kaihui Liu School of Physics and Materials Science Guangzhou UniversityGuangzhou 510006China Research Center for Advanced Information Materials(CAIM) Huangpu Research and Graduate School of Guangzhou UniversityGuangzhou 510555China Songshan Lake Materials Laboratory Dongguan 523808China Institute of Physics Chinese Academy of SciencesBeijing 100190China State Key Laboratory for Mesoscopic Physics School of PhysicsPeking UniversityBeijing 100871China

Airborne particulate matter(PM)has been the leading contributor to air pollution,posing a substantial risk to human health,and effective filtration technologies are ***-dimensional(2D)materials,such as graphene,graphitic carbon nitride(g-C3N4),molybdenum disulfide(MoS2),and MXenes have emerged in recent years for PM filtration due to their exception-ally large specific surface area and unique electrical ***,the most extensively used 2D materials for PM filtration followed by a summary of their fabrication methods and corresponding morphologies were *** them,the coating is the most cost-effective technique for achieving large-scale and quick *** can effectively enhance filtration efficiency and reduce pressure drop by upgrading electrostatic force and lowering the fiber *** initial and long-term performance of 2D-material-based filters was *** all 2D materials,GO is the most studied and shows the best performance by upgrading the dipole–dipole and electrostatic interaction between filters and *** study is expected to explore various 2D materials beyond GO,to evaluate filtration efficiency for submicron PM at m/s level air velocity,and to extend the service life for potential applications.

关键词： Two-dimensional material Graphene PM filtration Fabrication Electrospinning Coating