VSe_(2)/V_(2)C heterocatalyst with built-in electric field for efficient lithium-sulfur batteries:Remedies polysulfide shuttle and conversion kinetics

Lithium sulfur(Li-S)battery is a kind of burgeoning energy storage system with high energy density.However,the electrolyte-soluble intermediate lithium polysulfides(Li PSs)undergo notorious shuttle effect,which seriously hinders the commercialization of Li-S batteries.Herein,a unique VSe_(2)/V_(2)C heterostructure with local built-in electric field was rationally engineered from V_(2)C parent via a facile thermal selenization process.It exquisitely synergizes the strong affinity of V_(2)C with the effective electrocatalytic activity of VSe_(2).More importantly,the local built-in electric field at the heterointerface can sufficiently promote the electron/ion transport ability and eventually boost the conversion kinetics of sulfur species.The Li-S battery equipped with VSe_(2)/V_(2)C-CNTs-PP separator achieved an outstanding initial specific capacity of 1439.1 m A h g^(-1)with a high capacity retention of 73%after 100 cycles at0.1 C.More impressively,a wonderful capacity of 571.6 mA h g^(-1)was effectively maintained after 600cycles at 2 C with a capacity decay rate of 0.07%.Even under a sulfur loading of 4.8 mg cm^(-2),areal capacity still can be up to 5.6 m A h cm^(-2).In-situ Raman tests explicitly illustrate the effectiveness of VSe_(2)/V_(2)C-CNTs modifier in restricting Li PSs shuttle.Combined with density functional theory calculations,the underlying mechanism of VSe_(2)/V_(2)C heterostructure for remedying Li PSs shuttling and conversion kinetics was deciphered.The strategy of constructing VSe_(2)/V_(2)C heterocatalyst in this work proposes a universal protocol to design metal selenide-based separator modifier for Li-S battery.Besides,it opens an efficient avenue for the separator engineering of Li-S batteries.

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.

1T-VSe_(2)@rGO复合材料的设计合成及其在镁电中的应用

本文采用简单的一步水热法合成了1T-VSe_(2)@rGO复合材料,在APC电解液环境下,并将其作为第二代可充电镁离子电池的正极材料。测试结果显示,1T-VSe_(2)@rGO复合正极材料在50 mA g^(-1)下具有263 mAh g^(-1)的高可逆容量,在50 mA g^(-1)下连续循环100次,可获得91%的初始电容的优秀循环寿命。因此,1T-VSe_(2)@rGO作为正极材料在镁离子和其他可充电电池中的应用打开了新的思路。

碘催化的2-炔基苯胺与二硒醚的亲电环化反应

研究了碘催化的2-炔基苯胺与二硒醚的亲电环化反应.结果表明,在碘单质(0.2 mmol)、2-炔基苯胺(0.2 mmol)、二硒醚(0.1 mmol)和甲苯(2 mL)共存体系中,反应温度为110℃时,2-炔基苯胺与二硒醚能发生亲电环化反应,生成相应的3-硒取代吲哚化合物,产率为中等到良好.该反应在无金属催化的条件下进行,为合成官能团吲哚提供了一种新途径.

溅射压强对WSe_(2)纳米薄膜形貌及光电性能的影响

采用射频(RF)磁控溅射技术在Si(100)衬底上制备WSe_(2)纳米薄膜,研究在不同制备压强(2.0、2.5、3.0 Pa)下WSe_(2)纳米薄膜的形貌及光电性质变化.采用扫描电子显微镜(SEM)、能谱仪(EDS)、X射线衍射仪(XRD)、光致发光谱(PL)、霍尔效应等测试对薄膜样品进行基本性质表征.SEM测试结果表明:溅射压强的改变对薄膜形貌有显著影响,随着压强的增加“蠕虫”状结构更加明显.进一步研究WSe_(2)的生长取向,XRD测试结果表明WSe_(2)薄膜在(008)晶面优先生长,证明压强的不同会改变WSe_(2)的晶体结构,提高其结晶性和光吸收特性.此外电学性能测试表明,WSe_(2)纳米薄膜的载流子浓度和霍尔系数可以通过改变压强来调节.体现了磁控溅射技术制备的WSe_(2)具有可控性好,易于重复等优点,在构建多功能WSe_(2)器件领域中具有很好的应用前景.

Simulation of a CIGS Solar Cell with CIGSe2/MoSe2/Mo Rear Contact Using AFORS-HET Digital Simulation Software

In this work, the AFORS-HET digital simulation software was used to calculate the electrical characteristics of the cell/n-ZnO/i-ZnO/n-Zn (O, S)/p-CIGSe2/p + -MoSe2/Mo/SLG. When the thickness of the CIGSe2 absorber is between 3.5 and 1.5 μm, the efficiency of the cell with an interfacial layer of MoSe2 remains almost constant, with an efficiency of about 24.6%, higher to that of a conventional cell which is 23.4% for a thickness of 1.5 μm of CIGSe2. To achieve the expected results, the MoSe2 layer must be very thin less than or equal to 30 nm. In addition, a Schottky barrier height greater than 0.45 eV severely affects the fill factor and the open circuit voltage of the solar cell with MoSe2 interface layer.

Passively Q-Switched Erbium-Doped Fiber Laser with TiSe₂as Saturable Absorber

The TiSe2 nanosheets were prepared by means of ultrasound-assisted liquid phase exfoliation (LPE) and the nonlinear saturable absorption properties were experimentally investigated. The modulation depth, saturation intensity and nonsaturable absorbance of the prepared 1T-TiSe2 SA were 15.7%, 1.28 MW/cm2 and 8.2%, respectively. Taking advantage of the saturable absorption properties of TiSe2-based SA, a passively Q-switched erbium-doped fiber (EDF) laser was systematically demonstrated. The pulse repetition rates varied from 24.50 kHz up to 73.79 kHz with the increasing pump power. The obtained shortest pulse width was 1.31 μs with pulse energy of 79.28 nJ. The system presented merits of low-cost SA preparation, system compactness, superb stability and high competition.

基于SnSe_(2.37)薄膜材料的高性能近红外光电探测器

二维材料二硒化锡(SnSe_(2))具有高迁移率、高光吸收率和窄带隙的特点,被视为近红外(NIR)光电探测器的候选材料。然而SnSe_(2)在制备和生长的过程中会产生一定数量的硒空位,对SnSe_(2)近红外光电探测器的性能造成不利的影响。首先采用化学气相输运(CVT)法制备硒过量的二硒化锡(SnSe_(2.37))单晶,X射线光电子能谱(XPS)结果表明,Sn和Se的原子数比约为1∶2.37。然后通过机械剥离法从高品质的单晶上分离出横向尺寸为14μm×37μm且厚度为2 nm的SnSe_(2.37)薄膜材料。最后使用光刻图形转移法制备高性能的NIR光电探测器。经过测试,该NIR光电探测器对850 nm的近红外光表现出优异的光电探测性能,其中响应度可达2820 A·W^(-1),归一化探测率为1.02×10^(13)Jones,外量子效率为4.12×10^(5)%,响应时间为15 ms。

氢氧化铯催化二芳基二硫醚与端炔反应研究

以3-甲氧基丙炔与二苯基二硫醚的反应作为模型.探讨反应条件对反应结果的影响.实验表明以THF作溶剂,在0℃以下,不论是在空气氛中或在氮气氛中反应,都产生3-甲氧基丙炔基苯基硫醚与(Z)-1,2-二苯硫基烯的混合物,总收率约40%.在室温、空气氛中反应得上述两种生成物的混合物,总收率约80%.而在氮气保护下进行反应,则仅产生(Z)-1,2-二苯硫基烯.探讨了反应机理.在氮气保护下,进行了其他端炔与二芳基二硫醚反应,高立体选择的合成了6种(Z)-1,2-二芳硫基烯.本方法为(Z)-1,2-二芳硫基烯的合成提供了一条简便途径.

Thickness-dependent and strain-tunable magnetism in twodimensional van der Waals VSe_(2)

Two-dimensional(2D)van der Waals(vdW)magnetic materials with reduced dimensionality often exhibit unexpected properties compared to their bulk counterparts.In particular,the mechanical flexibility of 2D structure,enhanced ferromagnetism at reduced layer thickness,as well as robust perpendicular magnetic anisotropy are quite appealing for constructing novel spintronic devices.The vdW vanadium diselenide(VSe_(2))is an attractive material whose bulk is paramagnetic while monolayer is ferromagnetic with a Curie temperature(Tc)above room temperature.To explore its possible device applications,a detailed investigation on the thickness-dependent magnetism and strain modulation behavior of VSe_(2)is highly demanded.In this article,the VSe_(2)nanoflakes were controllably prepared via chemical vapor deposition(CVD)method.The few-layer single VSe_(2)nanoflakes were found to exhibit magnetic domain structures at room temperature.Ambient magnetic force microscopy(MFM)phase images reveal a clear thickness-dependent magnetism and the MFM phase contrast is traceable for the nanoflakes of layer thickness below~6 nm.Moreover,applying strain is found efficient in modulating the magnetic moment and coercive field of 2D VSe_(2)at room temperature.These results are helpful for understanding the ferromagnetism of high temperature 2D magnets and for constructing novel straintronic devices or flexible spintronic devices.

Highly sensitive solar-blind deep ultraviolet photodetector based on graphene/PtSe_(2)/β-Ga_(2)O_(3)2D/3D Schottky junction with ultrafast speed

There is an emerging need for high-sensitivity solar-blind deep ultraviolet(DUV)photodetectors with an ultra-fast response speed.Although nanoscale devices based on Ga_(2)O_(3)nanostructures have been developed,their practical applications are greatly limited by their slow response speed as well as low specific detectivity.Here,the successful fabrication of two-/three-dimensional(2D/3D)graphene(Gr)/PtSe2/β-Ga_(2)O_(3)Schottky junction devices for high-sensitivity solar-blind DUV photodetectors is demonstrated.Benefitting from the high-quality 2D/3D Schottky junction,the vertically stacked structure,and the superior-quality transparent graphene electrode for effective carrier collection,the photodetector is highly sensitive to DUV light illumination and achieves a high responsivity of 76.2 mA/W,a large on/off current ratio of~105,along with an ultra-high ultraviolet(UV)/visible rejection ratio of 1.8×104.More importantly,it has an ultra-fast response time of 12µs and a remarkable specific detectivity of~1013 Jones.Finally,an excellent DUV imaging capability has been identified based on the Gr/PtSe2/β-Ga_(2)O_(3)Schottky junction photodetector,demonstrating its great potential application in DUV imaging systems.

Epitaxial growth of large-area and highly crystalline anisotropic ReSe2 atomic layer

The anisotropic two-dimensional （2D） layered material rhenium disulfide （ReSe2） has attracted considerable attention because of its unusual properties and promising applications in electronic and optoelectronic devices. However, because of its low lattice symmetry and interlayer decoupling, anisotropic growth and out-of-plane growth occur easily, yielding thick flakes, dendritic structure, or flower-like structure. In this stud34 we demonstrated a bottom-up method for the controlled and scalable synthesis of ReSe2 by van der Waals epitaxy. To achieve controllable growth, a micro-reactor with a confined reaction space was constructed by stacking two mica substrates in the chemical vapor deposition system. Within the confined reaction space, the nucleation density and growth rate of ReSe2 were significantly reduced, favoring the large-area synthesis of ReSe2 with a uniform monolayer thickness. The morphological evolution of ReSe2 with growth temperature indicated that the anisotropic growth was suppressed at a low growth temperature （〈600 ℃）. Field-effect transistors employing the grown ReSe2 exhibited p-type conduction with a current ON/OFF ratio up to 10s and a hole carrier mobility of 0.98 cm^2/（V·s）. Furthermore, the ReSe2 device exhibited an outstanding photoresponse to near-infrared light, with responsivity up to 8.4 and 5.1 A/W for 850- and 940-nm light, respectively. This work not only promotes the large-scale application of ReSe2 in high-performance electronic devices but also clarifies the growth mechanism of low-lattice symmetry 2D materials.

Large-area high quality PtSe2 thin film with versatile polarity

Two-dimensional(2D)materials have attracted increasing attention for their outstanding structural and electrical properties.However,for mass-production of field effect transistors(FETs)and potential applications in integrated circuits,large-area and uniform 2D thin films with high mobility,large on-off ratio,and desired polarity are needed to synthesize firstly.Here,a transfer-free growth method for platinum diselenide(PtSe2)films has been developed.The PtSe2 films have been synthesized with various thicknesses in centimeter-sized scale.Typical FET made from a few layer PtSe2 show p-type unipolar,with a high field-effect hole mobility of 6.2 cm^(2) V^(−1) s^(−1) and an on-off ratio of 5×10^(3).The versatile semimetal-unipolar-ambipolar transition in synthesized PtSe2 films is also firstly observed as the thickness thinning.This work realizes the large-scale preparation of PtSe2 with prominent electrical properties and provides a new strategy for polarity's modulation.

Gold-vapor-assisted chemical vapor deposition of aligned monolayer WSe2 with large domain size and fast growth rate

Orientation-controlled growth of two-dimensional(2D)transition metal dichalcogenides(TMDCs)may enable many new electronic and optical applications.However,previous studies reporting aligned growth of WSe2 usually yielded very small domain sizes.Herein,we introduced gold vapor into the chemical vapor deposition(CVD)process as a catalyst to assist the growth of WSe2 and successfully achieved highly aligned monolayer WSe2 triangular flakes grown on c-plane sapphire with large domain sizes(130μm)and fast growth rate(4.3μm·s^−1).When the aligned WSe2 domains merged together,a continuous monolayer WSe2 was formed with good uniformity.After transferring to Si/SiO2 substrates,field effect transistors were fabricated on the continuous monolayer WSe2,and an average mobility of 12 cm^2·V^−1·s−1 was achieved,demonstrating the good quality of the material.This report paves the way to study the effect of catalytic metal vapor in the CVD process of TMDCs and contributes a novel approach to realize the growth of aligned TMDC flakes.

Halide vapor phase epitaxy of monolayer molybdenum diselenide single crystals

Single-crystalline transition metal dichalcogenides(TMD)films are of potential application in future electronics and optoelectronics.In this work,a halide vapor phase epitaxy(HVPE)strategy was proposed and demonstrated for the epitaxy of molybdenum diselenide(MoSe_(2))single crystals,in which metal halide vapors were in-situ produced by the chlorination of molybdenum as sources for the TMD growth.Combined with the epitaxial sapphire substrate,unidirectional domain alignment was successfully achieved and monolayer single-crystal MoSe_(2) films have been demonstrated on a 2-inch wafer for the first time.A series of characterizations ranging from centimeter to nanometer scales have been implemented to demonstrate the high quality and uniformity of the MoSe_(2).This work provides a universal strategy for the growth of TMD single-crystal films.

液态前驱体化学气相沉积法生长单层二硒化钨

化学气相沉积(CVD)是实现二维(2D)过渡金属硫族化合物(TMDs)制备的简单有效方法。晶核位置的随机分布和生长可控性差是当前实现大面积高质量制备TMDs的一项巨大挑战。本工作以单层二硒化钨的生长为例,采用液态前驱体并调控其浓度使微量金属前驱体高度均匀地分散在生长衬底表面,可有效诱导低过饱和度,从而降低成核密度,最终得到组分分布均匀、高质量的单层二硒化钨。这种液态前驱体化学气相沉积技术可以推广到其他2D材料的生长,为大面积、均匀的高质量2D材料的生长提供了一种更有效的方式。

Iodine-mediated regioselective hydroxyselenenylation of alkenes:Facile access to β-hydroxy selenides

In the presence of molecular iodine, the reaction of alkenes with diselenides proceeds efficiently under air and at room temperature in mixed solvent MeCN/H2O, which affording β-hydroxy selenides with high regioselectivity and in good to excellent yields. This iodine-mediated vicinal difunctionalization of alkenes requires mild reaction conditions and is a simple procedure, which extends the synthetic application of molecular iodine in organic synthesis.