Carboxyl graphene oxide solution saturable absorber for femtosecond mode-locked erbium-doped fiber laser

The carboxyl-functionalized graphene oxide(GO-COOH) is a kind of unique two-dimensional(2 D) material and possesses excellent nonlinear saturable absorption property and high water-solubility. In this paper, we prepare saturable absorber(SA) device by depositing GO-COOH nanosheets aqueous solution on a D-shaped fiber. The modulation depth(MD) and saturable intensity of the SA are measured to be 9.6% and 19 MW/cm~2, respectively. By inserting the SA into the erbium-doped fiber(EDF) laser, a passively mode-locked EDF laser has been achieved with the spectrum center wavelength of 1562.76 nm. The pulse duration, repetition rate, and the signal-to-noise ratio(SNR) are 500 fs, 14.79 MHz, and 80 dB,respectively. The maximum average output power is measured to be 3.85 mW. These results indicate that the GO-COOH nanosheets SA can be used as a promising mode locker for the generation of ultrashort pulses.     

Ionic liquid-assisted hydrothermal synthesis of three-dimensional hierarchical CuO peachstone-like architectures

Uniform peachstone-like CuO 3D architectures consisting of single-crystal nanosheets have been successfully synthesized by using ionic liquid 1-octyl-3-methylimidazolium trifluoroacetate ([Omim]TA) as capping reagents under the ionic liquid-assisted hydrothermal condition. Detailed proofs indicated that the process of crystal growth was dominated by an oriented aggregation and self-assemble growth mechanism. The morphology of CuO evolved from nanoparticles to two-dimensional (2D) nanosheets and three-dimensional (3D) peachstone-like nanostructures. A formation process is proposed to illustrate the growth of peachstone-like CuO crystal. The influence of the ionic liquid cations on the morphology of CuO materials was studied in detail. The cations of the ionic liquids control the morphology of crystals. Additionally, it was also found that the concentration of ionic liquids and the reaction time have direct influences on the morphology of the products. Their optical absorption spectra were also studied. The synthetic strategy could be extended to assemble 3D architectures of other materials.     

Fabrication of Br doped ZnO nanosheets piezoelectric nanogenerator for pressure and position sensing applications

In this research, a unique strategy was developed to enhance the output performance of 2D ZnO nanosheets based piezoelectric nanogenerator (PENG). The Br doped 2D ZnO nanosheets were fabricated by facile hydrothermal method on nanoporous anodic aluminum oxide (AAO) template. Along with structural and optical characterization of Br doped 2D ZnO nanosheets, the electrical output performance of Br doped 2D ZnO PENG was demonstrated under external mechanical force. The corresponding output voltage of Br doped 2D ZnO nanosheets PENG reached to 8.82 V at 6HZ, which is 3 times higher than undoped ZnO nanosheets PENG. The output power density of Br doped 2D ZnO nanosheets PENG reached to 38.8962μWcm⁻² at an external load resistanec of about 2 MΩ. The Br doping in ZnO nanosheets significantly increased the sensitivity of PENG for pressure sensing and the flexibility of PENG contribute in the application of position sensing.     

Exfoliation of metal-organic framework nanosheets using surface acoustic waves

Two-dimensional (2D) metal–organic framework (MOF) nanosheets have recently received extensive attention due to their ultra-thin thickness, large specific surface area, chemical and functional designability. In this study, an unconventional method using surface acoustic wave (SAW) technology is proposed to exfoliate large quantities and uniform layers of 2D MOF-Zn₂(bim)₄ nanosheets in a microfluidic system. We successfully demonstrated that the thickness of 2D MOF is effectively and accurately controlled by optimizing the SAW parameters. The mechanisms for the efficient exfoliation of 2D MOF nanosheets is attributed to both the electric and acoustic fields generated by the SAWs in the liquid. The electric field ionizes the methanol to produce H⁺ ions, which intercalate Zn₂(bim)₄ sheets and weaken the interlayer bonding, and the strong shear force generated by SAWs separates the MOF sheets. A yield of 66% for monolayer MOFs with a maximum size of 3.5 μm is achieved under the combined effect of electric and acoustic fields. This fast, low-energy exfoliation platform has the potential to provide a simple and scalable microfluidic exfoliation method for production of large-area and quantities of 2D MOFs.     

Ultrasonic-assisted synthesis of two dimensional coral-like Pd nanosheets supported on reduced graphene oxide for enhanced electrocatalytic performance

Two dimensional (2D) Pd nanosheets supported on reduced graphene oxide (Pd/rGO) were prepared through a sonochemical routine induced by cetyltrimethylammonium bromide (CTAB). Coral-like porous Pd nanosheets (Pd/rGO-u) were obtained under the sonication condition (25 kHz, 600 W, ultrasonic transducer), while square Pd nanosheets (Pd/rGO-c) were produced via traditional chemical reduction. The size of Pd nanosheets of Pd/rGO-u and Pd/rGO-c are 69.7 nm and 59.7 nm, and the thickness are 4.6 nm and 4.4 nm, respectively. The carrier GO was proved to be partially reduced to rGO with good electrical conductivity and oxygen-containing groups facilitated a good dispersion of Pd nanosheets. The interaction between GO and CTAB made the alkyl chain assembles to a 2D lamella micelles which limit the growth of Pd atoms resulting in the formation of 2D nanosheets. A high ultrasonic power promotes the reduction and the formation of porous structure. Additionally, Pd/rGO-u exhibited a favorable electrocatalytic performance toward oxygen reduction reaction (ORR) in alkaline condition, which provided a potential synthetic strategy assisted by sonication for high-performance 2D materials.     

The rise of two-dimensional tellurium for next-generation electronics and optoelectronics

Single-element two-dimensional (2D) tellurium (Te) which possesses an unusual quasi-one-dimensional atomic chain structure is a new member in 2D materials family. 2D Te possesses high carrier mobility, wide tunable bandgap, strong light-matter interaction, better environmental stability, and strong anisotropy, making Te exhibit tremendous application potential in next-generation electronic and optoelectronic devices. However, as an emerging 2D material, the research on fundamental property and device application of Te is still in its infancy. Hence, this review summarizes the most recent research progresses about the new star 2D Te and discusses its future development direction. Firstly, the structural features, basic physical properties, and various preparation methods of 2D Te are systemically introduced. Then, we emphatically summarize the booming development of 2D Te-based electronic and optoelectronic devices including field effect transistors, photodetectors and van der Waals heterostructure photodiodes. Finally, the future challenges, opportunities, and development directions of 2D Te-based electronic and optoelectronic devices are prospected.     

1.5-MHz repetition rate passively Q-switched Nd:YVO_4 laser based on WS_2 saturable absorber

A transmission-type tungsten disulfide(WS_2)-based saturable absorber(SA) is fabricated and applied to passively Q-switched Nd:YVO_4 laser.The WS_2 nanosheets are deposited on a quartz substrate by the vertical evaporation method.By inserting the WS2 SA into the plano-concave laser cavity,we achieve 153-ns pulses with an average output power of1.19 W at 1064 nm.To the best of our knowledge,both of them are the best results among those obtained by the Q-switched solid-state lasers with WS_2-based absorbers.The repetition rate ranges from 1.176 MHz to 1.578 MHz.As far as we know,it is the first time that MHz level Q-switched pulses have been generated in all solid state lasers based on low-dimensional materials so far.     

Molecular beam epitaxy growth of monolayer hexagonal MnTe2 on Si(111) substrate

Monolayer MnTe₂ stabilized as 1T structure has been theoretically predicted to be a two-dimensional (2D) ferromagnetic metal and can be tuned via strain engineering. There is no naturally van der Waals (vdW) layered MnTe₂ bulk, leaving mechanical exfoliation impossible to prepare monolayer MnTe₂. Herein, by means of molecular beam epitaxy (MBE), we successfully prepared monolayer hexagonal MnTe₂ 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 Mn⁴⁺ and the atom ratio of ([Te]:[Mn]) further confirm the MnTe₂ compound. Scanning tunneling spectroscopy (STS) shows the hexagonal MnTe₂ monolayer is a semiconductor with a large bandgap of ~2.78 eV. The valence-band maximum (VBM) locates at the Γ point, 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 MnTe₂ film provides a new platform to investigate the 2D magnetism.     

Scaling up the fabrication of wafer-scale Ni-MoS2/WS2 nanocomposite moulds using novel intermittent ultrasonic-assisted dual-bath micro-electroforming

In the scale-up fabrication process for electroformed Ni-MoS₂/WS₂ composite moulds, the formulation of nanosheets is critical, since the size, charge, and their distribution can largely affect the hardness, surface morphology and tribological properties of the moulds. Additionally, the long-term dispersion of hydrophobic MoS₂/WS₂ nanosheets in a nickel sulphamate solution is problematic. In this work, we studied the effect of ultrasonic power, processing time, surfactant types and concentrations on the properties of nanosheets to elaborate their dispersion mechanism and control their size and surface charge in divalent nickel electrolyte. The formulation of MoS₂/WS₂ nanosheets was optimized for effective electrodeposition along with nickel ions. A novel strategy of intermittent ultrasonication in the dual bath was proposed to resolve the problem of long-term dispersion, overheating, and deterioration of 2D material deposition under direct ultrasonication. Such strategy was then validated by electroforming 4-inch wafer-scale Ni-MoS₂/WS₂ nanocomposite moulds. The results indicated that the 2D materials were successfully co-deposited into composite moulds without any defects, along with the mould microhardness increasing by ∼2.8 times, the coefficient of friction reducing by two times against polymer materials, and the tool life increasing up to 8 times. This novel strategy will contribute to the industrial manufacturing of 2D material nanocomposites under ultrasonication process.     

Structural features and electronic properties of Group-IIIB pnictides nanosheets and nanoribbons

Two-dimensional (2D) materials exhibit unique electronic properties compared with their bulks. A systematical study of new type 2D tetragonal materials of MPn (M = Sc and Y; Pn = P, As and Sb) nanosheets and the corresponding nanoribbons are proposed by density functional theory calculations. Several thermodynamically stable 2D tetragonal structures were firstly determined, and such novel tetragonal structures bilayer MPn(100) exhibit extraordinary Weyl semimetal electronic structures, while monolayer MPn(110) are semiconductors. Moreover, bilayer MPn(100) nanoribbons with zigzag edges show metallic behavior, whereas those with linear edges show semiconducting properties. The band gaps for bilayer MPn(100) nanoribbons with linear edges can be significantly tuned by their widths. The zero-gap semiconducting behaviors of 2D tetragonal MPn nanosheets and the tunable band gaps of 1D MPn nanoribbons provide these MPn nanosheets and nanoribbons with promising applications in nanoscale electronic devices.     

Scalable preparation of water-soluble ink of few-layered WSe_2 nanosheets for large-area electronics

Few-layer two-dimensional(2 D) semiconductor nanosheets with a layer-dependent band gap are attractive building blocks for large-area thin-film electronics. A general approach is developed to fast prepare uniform and phase-pure 2 HWSe2 semiconducting nanosheets at a large scale, which involves the supercritical carbon dioxide(SC-CO2) treatment and a mild sonication-assisted exfoliation process in aqueous solution. The as-prepared 2 H-WSe2 nanosheets preserve the intrinsic physical properties and intact crystal structures, as confirmed by Raman, x-ray photoelectron spectroscopy(XPS),and scanning transmission electron microscope(STEM). The uniform 2 H-WSe2 nanosheets can disperse well in water for over six months. Such good dispersivity and uniformity enable these nanosheets to self-assembly into thickness-controlled thin films for scalable fabrication of large-area arrays of thin-film electronics. The electronic transport and photoelectronic properties of the field-effect transistor based on the self-assembly 2 H-WSe2 thin film have also been explored.     

Epitaxial fabrication of AgTe monolayer on Ag(111) and the sequential growth of Te film

Transition-metal chalcogenides (TMCs) materials have attracted increasing interest both for fundamental research and industrial applications. Among all these materials, two-dimensional (2D) compounds with honeycomb-like structure possess exotic electronic structures. Here, we report a systematic study of TMC monolayer AgTe fabricated by direct depositing Te on the surface of Ag(111) and annealing. Few intrinsic defects are observed and studied by scanning tunneling microscopy, indicating that there are two kinds of AgTe domains and they can form gliding twin-boundary. Then, the monolayer AgTe can serve as the template for the following growth of Te film. Meanwhile, some Te atoms are observed in the form of chains on the top of the bottom Te film. Our findings in this work might provide insightful guide for the epitaxial growth of 2D materials for study of novel physical properties and for future quantum devices.     

萃取/反相萃取分离富集-氢化物无色散原子荧光法测定复杂地质样品中的痕量碲

采用MIBK萃取/反相萃取分离富集的方法,建立了氢化物无色散原子荧光法测定复杂地质样品中的痕量碲的新方法。实验了HCl-NaBr-MIBK体系萃取Te(Ⅳ)的能力,研究了Te(Ⅳ)在KMnO₄-HCl-MIBK体系中的反相萃取行为。当萃取条件为3.6 mol·L-1HCl-100 g·L-1NaBr时,Te(Ⅳ)可被MIBK完全萃取;用HCl-KMnO₄氧化MIBK相中的Te(Ⅳ),水相反相萃取Te(Ⅵ),成功分离了氢化物原子荧光法测定Te的Au,Ag,Pt,Pd,Cu,Pb,Co,Ni,Cd,As,Sb,Bi,Hg,Tl和Se等干扰元素,方法检出限为1.14×10-4 μg·g-1,相对标准偏差为6.84%,对国家标准物质样品分析的结果与所给参考值吻合,可用于复杂地质样品中痕量Te的测定。     

One-step synthesis of flower-like Au-ZnO microstructures at room temperature and their photocatalytic properties

In this paper, 3D flower-like Au-ZnO microstructures with controlled morphology and dimensions were synthesized by a facile one-step aqueous solution route at room temperature, and the photocatalytic properties of these structures were investigated. The as-prepared flower-like Au-ZnO structures with a diameter of about 3 μm consisted of many ZnO nanosheets which interacted with each other. These nanosheets, which were successfully decorated by Au NPs, showed an average thickness of 10 nm and a single-crystalline structure with {2-1-10} planar surfaces. The growth process of Au-ZnO structures and the effects of trisodium citrate on the nucleation and growth of ZnO were investigated. The formation of Au NPs in this experiment was discussed too. The Au-ZnO structures showed higher photocatalytic activity than that of pure ZnO.     

Facile fabrication of manganese phosphate nanosheets for supercapacitor applications

Ionics - Manganese phosphate (Mn3(PO4)2·3H2O) nanosheets are successfully fabricated via a facile chemical precipitation method. The Mn3(PO4)2·3H2O nanosheets synthesized at...     

分子筛组装单质半导体碲的拉曼光谱

无机介孔材料MCM41是高有序,直孔道介孔分子筛,具有孔径约4nm的一维均匀孔道,孔壁厚约1nm,介孔体积可达40%,是一种很理想的组装材料主体。半导体碲位于第Ⅵ族,其六方相的晶格排列呈螺旋链状结构。本文采用固相合成反应方法,将单质半导体碲成功地组装在MCM41介孔分子筛中。在组装体中,单质半导体碲保持着六方相的晶体结构,其拉曼晶体振动表现出纳米晶体的结构特征。真空热处理实验表明,组装体具有良好的热稳定性。Te的六方相和所具有的独特的螺旋链状结构使Te分子很容易进入MCM41的直孔道内,同时MCM41均匀而规则的直孔道限制了Te螺旋链的随机排列,因而被组装在直孔道内的Te能螺旋链式生长,形成一维半导体纳米晶体,排列均匀,尺寸单一,具有稳定的空间构型     

Tunable passively Q-switched ytterbium-doped fiber laser using MoWS2/rGO nanocomposite saturable absorber

We demonstrated a tunable Q-switched ytterbium-doped fiber laser (YDFL) using MoWS₂/rGO nanocomposite as passive saturable absorber. Further, the Mo_1?xW_xS₂/rGO nanosheets, with x proportion of 0.2, are synthesized using hydrothermal exfoliation technique. The proposed nanocomposite-PVA based thin film is fabricated by mixing the MoWS₂/rGO nanosheets with polyvinyl alcohol (PVA). The fabricated thin film is sandwiched between two fiber ferrules to realize the proposed saturable absorber (SA). Further, the proposed MoWS₂/rGO-PVA based thin film SA exhibits a fast relaxation time and a high damage threshold which are suitable to realize a Q-switched pulsed laser with a tunable wavelength range of 10?nm that extends from 1028?nm to 1038?nm. For the highest pump power of 267.4?mW, the generated Q-switched pulses exhibit a narrow pulse width of 1.22 μs, the pulse repetition rate of 90.4?kHz, the highest pulse energy of 2.13?nJ and its corresponding average power of 0.193?mW. To the best of author’s knowledge, this is the first realization of a tunable Q-switching fiber laser in a 1?μm wavelength using MoWS₂/rGO nanocomposite saturable absorber.     

Construction of GQDs-Decorated Ultrathin Bi2WO6 Nanosheets Hydrogel: a Recyclable-Flexible Platform with Excellent Piezo-Photocatalytic Activity for High-Performance Water Decontamination and its Theoretical Interpretation

It is demonstrated that, by using the electronic reconstruction of ultrathin Bi₂WO₆ (BWO) nanosheets with graphene quantum dots (GQDs) upon a unique process of laser irradiation in liquid (LAL), a kind of GQDs modified BWO nanosheets under metastable state were synthesized, which performed excellent visible-light piezo-photocatalytic organics degradation. Furthermore, using commercial cpolyacrylamids (PAM) as the additional materials, a kind of electronic reconstruction GQDs-BWO nanosheets hydrogel was achieved by dispersed the functionalized powders into a super absorbent polymers (SAPs) system upon in situ polymerization method, which showed that it is a bracing idea to use SAPs for water decontamination reactors to enable full use of vibration energy synergistic with light of nature to driven pollution degradation. First-principles calculation was also simultanously performed in this study. This study may provide a new enlightenment on fabricating novel 2D nanomaterials hydrogel for efficient effluent purification and potentially other environmental or energy applications.     

Ultrathin nanosheets of Mn<Subscript>3</Subscript>O<Subscript>4</Subscript>: A new two-dimensional ferromagnetic material with strong magnetocrystalline anisotropy

Two-dimensional (2D) materials with robust ferromagnetism have played a key role in realizing nextgeneration spin-electronic devices, but many challenges remain, especially the lack of intrinsic ferromagnetic behavior in almost all 2D materials. Here, we highlight ultrathin Mn₃O₄ nanosheets as a new 2D ferromagnetic material with strong magnetocrystalline anisotropy. Magnetic measurements along the in-plane and out-of-plane directions confirm that the out-of-plane direction is the easy axis. The 2D-confined environment and Rashba-type spin-orbit coupling are thought to be responsible for the magnetocrystalline anisotropy. The robust ferromagnetism in 2D Mn₃O₄ nanosheets with magnetocrystalline anisotropy not only paves a new way for realizing the intrinsic ferromagnetic behavior in 2D materials but also provides a novel candidate for building next-generation spin-electronic devices.     

Harmonic Mode-Locked Er-Doped Fiber Laser by Evanescent Field-Based MXene Ti3C2Tx (T = F,O, or OH) Saturable Absorber

MXenes, as a legendary family of 2D van der Waals nanosheets materials, are extensively studied due to their unique characteristics of broadband nonlinear optical response. In particular, MXenes have excellent nonlinear optical properties of very large nonlinear absorption coefficients and very large nonlinear refractive indexes, which have attracted people's great attentions to study the application of MXenes in photonics, electronics, and optoelectronics in recent years. However, the high-repetition-rate (HRR) ultrafast pulses are not explored based on these kinds of materials. MXene Ti₃C₂T_x saturable absorber (SA) based on micro-fiber is fabricated by optical deposition method. Here, MXene Ti₃C₂T_x SA is used to achieve 36th harmonic mode-locking with a repetition rate of 218.4 MHz, a central wavelength of 1566.9 nm, the pulse width of 850 fs, and the spectral width of 3.51 nm. The maximum average output power and pulse energy are 6.95 mW and 0.032 nJ, respectively. This research based on MXene Ti₃C₂T_x light modulator opens a bright avenue for advanced nonlinear photonics.