Laser crystallization for large-area electronics

Laser crystallization is reviewed for the purpose of fabrication of polycrystalline silicon thin film transistors (poly-Si TFTs). Laser-induced rapid heating is important for formation of crystalline films with a low thermal budget. Reduction of electrically active defects located at grain boundaries is essential for improving electrical properties of poly-Si films and achieving poly-Si TFTs with high performances. The internal film stress is attractive to increase the carrier mobility. Recent developments in laser crystallization methods with pulsed and continuous-wave lasers are also reviewed. Control of heat flow results in crystalline grain growth in the lateral direction, which is important for fabrication of large crystalline grains. We also report an annealing method using a high-power infrared semiconductor laser. High-power lasers will be attractive for rapid formation of crystalline films over a large area and activation of silicon with impurity atoms.     

Spin depolarization dynamics of WSe_2 bilayer

In this work, the spin dynamics of a centrosymmetric WSe_2 bilayer has been investigated by the two-color timeresolved Kerr rotation together with helicity-resolved transient reflectance techniques. Two depolarization processes associated with the direct transition are discovered at a low temperature of 10 K, with the characteristic decaying time of～3.8 ps and ～20 ps, respectively. The short decay time of ～3.8 ps is suggested to be the exciton spin lifetime of the WSe_2 bilayer, which is limited by the short exciton lifetime of the WSe_2 bilayer and the rapid intervalley electron–hole exchange interaction between K+and K-valley in the same layer as that of monolayer. The long decay time of ～20 ps is suggested to be the spin lifetime of photo-excited electrons, whose spin relaxation is governed by the rapid intervalley scattering from the K valley to the global minimum Σ valley and the subsequent interlayer charge transfer in WSe_2 bilayer.Our experimental results prove the existence of the spin-polarized excitons and carriers even in centrosymmetric transition metal dichalcogenides(TMDCs) bilayers, suggesting their potential valleytronic and spintronic device applications.     

Surface Modification for WSe_2 Based Complementary Electronics

High-performance WSe₂ complementary transistors are demonstrated on an individual flake by ozone exposure,which relies on the charge transfer mechanism. This technology is readily feasible for modulating the conductivity type in WSe₂, and the p–n junction presents a high on-off ratio of 10⁴. Based on robust p-type transistors and matched output current of n-type WSe₂ transistors, the complementary inverter achieves a high voltage gain of 19.9. Therefor...     

Substrate pre-treatment of flexible material for printed electronics with carbon nanotube based ink

In this work, an innovative solution was developed in order to make paper-based material, used traditionally in the packaging and labelling industries, compatible with the printing of functional conductive inks. In order to avoid the deterioration of the ink functionalities due to different paper properties, a UV-curing inkjettable primer layer was developed. This pre-treatment enables homogeneous surface properties such as smoothness, absorption capacity and surface energy to be obtained, for almost all the examined substrates. To confirm the positive impact of such pre-treatment, conductivity has been measured when using a new conductive ink, combining the processability of the PEDOT-PSS conductive polymer with the high electrical properties of carbon nanotubes (CNTs). Significant improvement has been measured for all paper materials and similar conductivity (close to reference PET film) has been obtained whatever the substrate involved. This pre-treatment now makes it possible to consider paper-based material as a potential substrate for printed electronics. In this case, the substrate adaptation technique offers an innovative solution to produce low-cost and flexible electronics.     

One-step preparation of water-soluble single-walled carbon nanotubes

A novel one-step process using potassium persulfate (KPS) as oxidant is proposed in this paper to prepare water-soluble single-walled carbon nanotubes (SWNTs). The process without the need for organic solvents and acids is a low-cost, eco-friendly, facile method. Morphology observation by atomic force microscopy (AFM) indicates that the KPS-treated SWNTs were effectively debundled without obvious shortening in their length. The functional groups and thermal stability of the treated SWNTs were analyzed by Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and thermogravimetric analysis (TGA). XPS results show that several functional groups such as potassium carboxylate (-COOK), carbonyl (-CO) and hydroxyl (-C-OH) groups were formed on the surfaces of the SWNTs, while the TGA results reveal that the quantity of the functional groups can reach to approximately 20%.     

Facile preparation of magnetically functionalized graphite nanosheets for porcine pancreatic lipase immobilization

We report that silicon nanoparticles (SiNPs) with typical sizes from 5 to 50 nm prepared by grinding of porous silicon can act as efficient scavengers of human immunodeficiency virus (HIV) and respiratory syncytial virus (RSV). In vitro studies have revealed a strong suppression of the viral activity in the presence of SiNPs with concentration above 0.1 and 0.01 mg/mL for HIV and RSV, respectively. The observed effect is explained by binding of the virions with SiNPs that is supposed to be universal for different enveloped viruses. Because of the cytotoxic concentration of SiNPs is of the order of 1 mg/mL, SiNPs can be proposed for applications in new harmless methods of antiviral treatment.     

Biaxial strain-induced enhancement in the thermoelectric performance of monolayer WSe_2

The effects of biaxial strain on the electronic structure and thermoelectric properties of monolayer WSe_2 have been investigated by using first-principles calculations and the semi-classical Boltzmann transport theory. The electronic band gap decreases under strain, and the band structure near the Fermi level of monolayer WSe_2 is modified by the applied biaxial strain. Furthermore, the doping dependence of the thermoelectric properties of n-and p-doped monolayer WSe_2 under biaxial strain is estimated. The obtained results show that the power factor of n-doped monolayer WSe_2 can be increased by compressive strain while that of p-doping can be increased with tensile strain. Strain engineering thus provides a direct method to control the electronic and thermoelectric properties in these two-dimensional transition metal dichalcogenides materials.     

First-principles analysis of phonon thermal transport properties of two-dimensional WS_2/WSe_2 heterostructures

The van der Waals(vdW)heterostructures of bilayer transition metal dichalcogenide obtained by vertically stacking have drawn increasing attention for their enormous potential applications in semiconductors and insulators.Here,by using the first-principles calculations and the phonon Boltzmann transport equation(BTE),we studied the phonon transport properties of WS2/WSe2 bilayer heterostructures(WS2/WSe2-BHs).The lattice thermal conductivity of the ideal WS2/WSe2-BHs crystals at room temperature(RT)was 62.98 W/mK,which was clearly lower than the average lattice thermal conductivity of WS2 and WSe2 single layers.Another interesting finding is that the optical branches below 4.73 THz and acoustic branches have powerful coupling,mainly dominating the lattice thermal conductivity.Further,we also noticed that the phonon mean free path(MFP)of the WS2/WSe2-BHs(233 nm)was remarkably attenuated by the free-standing monolayer WS2(526 nm)and WSe2(1720 nm),leading to a small significant size effect of the WS2/WSe2-BHs.Our results systematically demonstrate the low optical and acoustic phonon modes-dominated phonon thermal transport in heterostructures and give a few important guidelines for the synthesis of van der Waals heterostructures with excellent phonon transport properties.     

WSe_2 as a saturable absorber for multi-gigahertz Q-switched mode-locked waveguide lasers [Invited]

Graphene and other extraordinary two-dimensional materials together with recent advances in optical modulators have set the foundations for the widespread applications of next-generation optoelectronic devices. In this work, we report on the high-performance fundamentally mode-locked waveguide laser modulated by chemicalvapor-deposition-grown WSe2 as a saturable absorber. By incorporating a WSe2 sample into a monolithic Nd:YVO4 waveguide platform, 6.526 GHz picosecond pulsed laser generation has been achieved at the wavelength of 1 μm with pulse duration of 47 ps.     

n型透明导电薄膜CdIn2O4电学性质的研究和大面积制备的最佳条件

在Ar+O2气氛中,采用射频反应溅射Cd-In靶制备CdIn2O4薄膜.制得的薄膜经x射线衍射(XRD)检测为CdIn2O2和CdO相组成的多晶.从理论上分析了热处理前后氧空位、掺杂点缺陷和富氧电子陷阱在影响膜的载流子浓度和电子散射中所起的重要作用.同时,对样品进行Hall效应、Seebeck效应测试并得出不同载流子浓度下的迁移率、有效质量、弛豫时间以及它们之间的相互关系,特别强调了弛豫时间的重要性.为了提高导电膜的透射率,还分析了Burstein-Moss漂移和带隙收缩对光带隙的影响,并在薄膜制备时选择了合适的衬底温度T8≈280℃.实验表明,在氧分压为8％左右时制备的薄膜质量较好,热处理后的指标大约为迁移率μH=31×10-4m2/V·s,电阻率ρ=1.89×10-5Ω·m.     

Clock distribution for BaF_2 readout electronics at CSNS-WNS

A BaF_2(Barium Fluoride) detector array is designed to precisely measure the(n, γ) cross section at the CSNS-WNS(white neutron source at China Spallation Neutron Source). It is a 4π solid angle-shaped detector array consisting of 92 BaF_2 crystal elements. To discriminate signals from the BaF_2 detector, a pulse shape discrimination method is used, supported by a waveform digitization technique. There are 92 channels for digitizing. The precision and synchronization of clock distribution restricts the performance of waveform digitizing. In this paper, a clock prototype for the BaF_2 readout electronics at CSNS-WNS is introduced. It is based on the PXIe platform and has a twin-stage tree topology. In the first stage, clock is synchronously distributed from the tree root to each PXIe crate through a coaxial cable over a long distance, while in the second stage, the clock is further distributed to each electronic module through a PXIe dedicated differential star bus. With the help of this topology, each tree node can fan out up to 20 clocks with 3U size. Test results show the clock jitter is less than 20 ps, which meets the requirements of the BaF_2 readout electronics. Besides, this clock system has the advantages of high density, simplicity, scalability and cost saving, so it can be useful for other clock distribution applications.     

X-ray source for irradiation of large-area objects

The results of experiments with a three-ring large-area diode that were conducted on an MIG pulse generator are reported. The MIG generator makes it possible to produce in a matched load electrical pulses up to 2 TW in power with an FWHM of 50–60 ns (1.2–1.4 TW and 80–90 ns in our experiments). In the operating mode of the generator, the current amplitude through the load is 2 MA (the current of a relativistic electron beam) at a diode voltage of ≈ 500 kV. As a load, a large-area vacuum diode with three ring-shaped cathodes is used. It is shown that about 20% of the energy stored in the capacitor bank can be converted to the energy of a relativistic electron beam by matching the output resistance of the MIG generator to the load resistance. When the beam slows down on a condensed foil target, the parameters of the resulting source are the following: the mean energy of X-ray quanta is ≈ 70 keV; irradiated area, 500 cm²; pulse FWHM, 65 ns; energy flux in the spectrum, 2 J/cm²; and percentage of X-ray radiation (10–100 keV) in the flux, ≈ 50%.     

Influence of Polar Pressure Transmission Medium on the Pressure Coefficient of Excitonic Interband Transitions in Monolayer WSe_2

The influence of the pressure transmission medium(PTM)on the excitonic interband transitions in monolayer tungsten diselenide(WSe_2)is investigated using photoluminescence(PL)spectra under hydrostatic pressure up to 5GPa.Three kinds of PTMs,condensed argon(Ar),1:1 n-pentane and isopentane mixture(PM),and4:1 methanol and ethanol mixture(MEM,a PTM with polarity),are used.It is found that when either Ar or PM is used as the PTM,the PL peak of exciton related to the direct K-K interband transition shows a pressure-induced blue-shift at a rate of 32±4 or 32±1 meV/GPa,while it turns to be 50±9meV/GPa when MEM is used as the PTM.The indirect A-K interband transition presents almost no shift with increasing pressure up to approximatel.y 5 GPa when Ar and PM are used as the PTM,while it shows a red-shift at the rate of-17±7meV/GPa by using MEM as the PTM.These results reveal that the optical interband transitions of monolayer WSe_2 are very sensitive to the polarity of the PTM.The anomalous pressure coefficient obtained using the polar PTM of MEM is ascribed to the existence of hydrogen-like bonds between hydroxyl in MEM and Se atoms under hydrostatic pressure.     

Scalable preparation of three-atom and four-atom W states via atom-cavity-laser interaction

We propose the optical generation of W states for three atomic and four atomic qubits, with each qubit trapped in a separate cavity and coupled to the cavity laser. A single-photon source and two classical fields are employed in the present scheme. By encoding the quantum information of each qubit on the degenerate ground states of the atom, we obtain the atomic entanglement that is relatively stable against spontaneous emission. It is demonstrated that the three- and four-atomic W states can be produced deterministically via a proper manipulation of the atom-cavity interaction sequence and time. Generalization of the present scheme to prepare multi-atomic W states is also discussed.     

Sonication of chitin-glucan, preparation of water-soluble fractions and characterization by HPLC

A water-insoluble chitin-glucan complex, isolated from the mycelium of Aspergillus niger, was swollen in various aqueous media and treated subsequently by high-energy sonication. The concentration of the resulting water-soluble polysaccharide fractions was dependent on the swelling medium, the amount of the chitin-glucan complex in the suspension, and on the time of sonication. The yields of water-soluble chitin-glucan were within the range 13.6 to 24.4% relative to the mass of the original chitin-glucan. The nitrogen content obtained for the samples of water-soluble chitin-glucan indicated a higher content of chitin (3.45% of nitrogen in high-molecular fraction) than in the original water-insoluble chitin-glucan sample (1.8%). The distribution of the molecular weights of the water-soluble fractions prepared was determined by high-performance liquid chromatography.     

Ultrasonic preparation and nanosheets supported binary metal oxide nanocomposite for the effective application towards the electrochemical sensor

Binary metal oxides (La₂O₃@SnO₂) decorated reduced graphene oxide nanocomposite was synthesized by ultrasound process in an environmentally benign solvent with a working frequency of 25 and 40 kHz (6.5 l200 H, Dakshin, India and maximum input power 210 W). Further, to enhance the electrocatalytic activity, the reduced graphene oxide (rGO) was prepared from graphene oxide by ultrasonication method. As prepared La₂O₃@SnO₂/rGO was scrutinized using XRD, TEM, EDX and quantitative test for the structural and morphology properties. As modified La₂O₃@SnO₂/rGO nanocomposite exhibits better electrochemical activity towards the oxidation of methyl nicotinate with higher anodic current compared to other modified and unmodified electrode for the detection of methyl nicotinate with larger linear range (0.035–522.9 µM) and lower limit of detection (0.0197 µM). In addition, the practical feasibility of the sensor was inspected with biological samples, reveals the acceptable recovery of the sensor in real samples.     

High-efficiency preparation of oil-dispersible MoS<Subscript>2</Subscript> nanosheets with superior anti-wear property in ultralow concentration

Molybdenum disulfide (MoS₂) nanosheets are a promising lubricant additive for enhanced engine efficiency in cars. However, high-cost production methods and poor dispersion have limited their application in industry. In this study, the ball milling process is demonstrated as a low-cost and high-efficient method for fabrication of oil-dispersible MoS₂ nanosheet, and the ball milling parameters are optimized. Moreover, the lubrication effectiveness of ball-milled MoS₂ nanosheet was also evaluated. Results indicated that well-dispersed MoS₂ nanosheets with a size of 250 nm can be manufactured with optimized surfactants of zinc dialkyldithiphosphates (ZDDP) and polyisobutylene succinimide (PIBS) after being ball milled for 36 h. Tribological results revealed that a friction coefficient of white oil with 0.25% MoS₂ nanosheets reached 0.075, much lower than that of lubricant without nanosheets (0.16). The wear scar radius of 0.015% MoS₂ nanosheets was similar with that of Hertz contact, and the wear scar radius reduction reached 20% compared with that of 1% ZDDP. In addition, EDS and XPS results indicated the formation of a MoS₂ and FeS tribofilm on the wear surface.     

Engineering birnessite-type MnO2 nanosheets on fiberglass for pH-dependent degradation of methylene blue

We construct hierarchical MnO₂ nanosheets @ fiberglass nanostructures via one-pot hydrothermal method without any surfactants. The morphology and structure of MnO₂-modified fiberglass composites are examined by focus ion beam scanning electron microscopy (FIB/SEM), X-Ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR). The birnessite-type MnO₂ nanosheets are observed to grow vertically on the surface of fiberglass. Furthermore, the birnessite-type MnO₂-fiberglass composites exhibit good ability for degradation of methylene blue (MB) in different pH levels. In neutral solution (pH 6.5–7.0), it achieves a high removal rate of 96.1% (2 h, at 60 °C) in the presence of H₂O₂; and in acidic environment (pH 1.5), 96.8% of MB solution (20 mg/L, 100 mL) is decomposed by oxidation within only 5 min. In principles, the rational design of MnO₂ nanosheets-decorated fiberglass architectures demonstrated the suitability of the low-cost MnO₂-modified fiberglass nanostructure for water treatment.     

Development of large-area quadrant silicon detector for charged particles

The quadrant silicon detector, a kind of passivated implanted planar silicon detector with quadrant structure on the junction side, gained its wide application in charged particle detection. In this paper, the manufacturing procedure, performance test and results of the quadrant silicon detector developed recently at the China Institute of Atomic Energy are presented. The detector is about 300 μm thick with a 48 mm×48 mm active area. The leakage current under the full depletion bias voltage of -16 V is about 2.5 nA, and the rise time is better than 160 ns. The energy resolution for a 5.157 MeV α-particle is around the level of 1%. Charge sharing effects between the neighboring quads, leading to complicated correlations between two quads, were observed when α particles illuminated on the junction side. It is explained as a result of distortion of the electric field of the inter-quad region. Such an event is only about 0.6% of all events and can be neglected in an actual application.