We report the fabrication and photocarrier dynamics in graphene-MoSe₂ heterostructures. The samples were fabricated by mechanical exfoliation and manual stacking techniques. Ultrafast laser measurements were performed on the heterostructure and MoSe₂ monolayer samples. By comparing the results, we conclude that photocarriers injected in MoSe₂ of the heterostructure transfer to graphene on an ultrafast time scale. The carriers in graphene alter the optical absorption coefficient of MoSe₂. These results illustrate the potential applications of this material in optoelectronic devices.

Bi₂Se₃, as a three-dimensional topological insulator, has attracted worldwide attention for its unique surface states which are protected by time-reversal symmetry. Here we report the synthesis and characterization of high-quality single-crystalline Bi₂Se₃ nanowires. Bi₂Se₃ nanowires were synthesized by chemical vapor deposition (CVD) method via gold-catalyzed vapor-liquid-solid (VLS) mechanism. The structure and morphology were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), x-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. In magnetotransport measurements, the Aharonov-Bohm (AB) effect was observed in a nanowire-based nanodevice, suggesting the existence of surface states in Bi₂Se₃ nanowires.

We have fabricated two types of lumped-element Josephson parameter amplifiers (JPAs) by using a multilayer micro-fabrication process involving wet etching of Al films. The first type is a narrow band JPA which shows typical gain above 14 dB in a bandwidth around 35 MHz. The second type is a wideband JPA which is coupled to an input 50 Ω transmission line via an impedance transformer that changes the impedance from about 15 Ω on the non-linear resonator side to 50 Ω on the input transmission line side. The wideband JPA could operate in a 200 MHz range with a gain higher than 14 dB. The amplifiers were used for superconducting qubit readout. The results showed that the signal to noise ratio and hence the readout fidelity were improved significantly.

The effects of different coating layers on lithium metal anode formed by reacting with different controlled atmospheres (argon, CO₂-O₂ (2:1), N₂, and CO₂-O₂-N₂ (2:1:3)) have been investigated. The obtained XRD, second ion mass spectroscopy (SIMS), and scanning probe microscope (SPM) results demonstrate the formation of coating layers composed of Li₂CO₃, Li₃N, and the mixture of them on lithium tablets, respectively. The Li/Li symmetrical cell and Li/S cell are assembled to prove the advantages of the protected lithium tablet on electrochemical performance. The comparison of SEM and SIMS characterizations before/after cycles clarifies that an SEI-like composition formed on the lithium tablets could modulate the interfacial stabilization between the lithium foil and the ether electrolyte.

Here we report the thermo-controllable self-assembled structures of single-layer 4, 4"-diamino-p-terphenyl (DAT) molecules on Au (110), which are investigated by scanning tunneling microscopy (STM) combined with density functional theory (DFT) based calculations. With the deposition of monolayer DAT molecules on Au (110) and subsequent annealing at 100 ℃, all DAT molecules adsorb on a (1×5) reconstructed surface with a ladder-like structure. After annealing the sample at about 200 ℃, STM images show three distinct domains, including DAT molecules on a (1×3) reconstructed surface, dehydrogenated molecules with two hydrogen atoms detached from one amino group (-2H-DAT) on a (1×5) reconstructed surface and dehydrogenated molecules with four hydrogen atoms detached from two amino groups (-4H-DAT) on a (1×3) reconstructed surface through N-Au bonds. Furthermore, after annealing the sample to 350 ℃, STM image shows only one self-assembled structure with -4H-DAT molecules on a (1×3) reconstructed surface. Relative STM simulations of different self-assembled structures show excellent agreements with the experimental STM images at different annealing temperatures. Further DFT calculations on the dehydrogenation process of DAT molecule prove that the dehydrogenation barrier on a (1×5) reconstructed surface is lower than that on (1×3) one, which demonstrate the experimental results that the formation temperature of a (1×3) reconstructed surface is higher than that of a (1×5) one.

Two-dimensional (2D) Van der Waals heterostructures have aroused extensive concerns in recent years. Their fabrication calls for facile and efficient transfer techniques for achieving well-defined structures. In this work, we report a simple and effective dry transfer method to fabricate 2D heterostructures with a clean interface. Using Propylene Carbonate (PC) films as stamps, we are able to pick up various 2D materials flakes from the substrates and unload them to the receiving substrates at an elevated temperature. Various multilayer heterostructures with ultra-clean interfaces were fabricated by this technique. Furthermore, the 2D materials can be pre-patterned before transfer so as to fabricate desired device structures, demonstrating a facile way to promote the development of 2D heterostructures.

We report comprehensive angle-resolved photoemission investigations on the electronic structure of single crystal multiple-layer FeSe films grown on CaF₂ substrate by pulsed laser deposition (PLD) method. Measurements on FeSe/CaF₂ samples with different superconducting transition temperatures T_c of 4 K, 9 K, and 14 K reveal electronic difference in their Fermi surface and band structure. Indication of the nematic phase transition is observed from temperature-dependent measurements of these samples; the nematic transition temperature is 140–160 K, much higher than~90 K for the bulk FeSe. Potassium deposition is applied onto the surface of these samples; the nematic phase is suppressed by potassium deposition which introduces electrons to these FeSe films and causes a pronounced electronic structure change. We compared and discussed the electronic structure and superconductivity of the FeSe/CaF₂ films by PLD method with the FeSe/SrTiO₃ films by molecular beam epitaxy (MBE) method and bulk FeSe. The PLD-grown multilayer FeSe/CaF₂ is more hole-doped than that in MBE-grown multiple-layer FeSe films. Our results on FeSe/CaF₂ films by PLD method establish a link between bulk FeSe single crystal and FeSe/SrTiO₃ films by MBE method, and provide important information to understand superconductivity in FeSe-related systems.

Asymmetrical graphene plasmon reflection patterns are found in infrared near-field images of tapered graphene ribbons epitaxially grown on silicon carbon substrates. Comparing experimental data with numerical simulations, the asymmetry of these patterns is attributed to reflection of plasmons by wrinkled edges naturally grown in the graphene. These graphene wrinkles are additional plasmon reflectors with varying optical conductivity, which act as nanometer scale plasmonic modulators and thus have potential applications in photoelectric information detectors, transmitters, and modulators.

Directed networks such as gene regulation networks and neural networks are connected by arcs (directed links). The nodes in a directed network are often strongly interwound by a huge number of directed cycles, which leads to complex information-processing dynamics in the network and makes it highly challenging to infer the intrinsic direction of information flow. In this theoretical paper, based on the principle of minimum-feedback, we explore the node hierarchy of directed networks and distinguish feedforward and feedback arcs. Nearly optimal node hierarchy solutions, which minimize the number of feedback arcs from lower-level nodes to higher-level nodes, are constructed by belief-propagation and simulated-annealing methods. For real-world networks, we quantify the extent of feedback scarcity by comparison with the ensemble of direction-randomized networks and identify the most important feedback arcs. Our methods are also useful for visualizing directed networks.

The composite quasi solid state electrolytes (CQSE) is firstly synthesized with quasi solid state electrolytes (QSE) and lithium-ion-conducting material Li_1.4Al_0.4Ti_1.6(PO₄)₃ (LATP), and the QSE consists of[LiG4][TFSI] with fumed silica nanoparticles. Compared with LATP, CQSE greatly improves the interface conductance of solid electrolytes. In addition,it has lower liquid volume relative to QSE. Although the liquid volume fraction of CQSE drops to 60%, its conductivity can also reach 1.39×10^-4 s/cm at 20℃. Linear sweep voltammetry (LSV) is conducted on each composite electrolyte. The results show the possibility that CQSE has superior electrochemical stability up to 5.0 V versus Li/Li⁺¹. TG curves also show that composite electrolytes have higher thermal stability. In addition, the performance of Li/QSE/LiMn₂O₄ cells and Li/CQSE/LiMn₂O₄ is evaluated and shows good electrochemical characteristics at 60℃.

Angle-resolved polarized Raman (ARPR) spectroscopy can be utilized to assign the Raman modes based on crystal symmetry and Raman selection rules and also to characterize the crystallographic orientation of anisotropic materials. However, polarized Raman measurements can be implemented by several different configurations and thus lead to different results. In this work, we systematically analyze three typical polarization configurations:1) to change the polarization of the incident laser, 2) to rotate the sample, and 3) to set a half-wave plate in the common optical path of incident laser and scattered Raman signal to simultaneously vary their polarization directions. We provide a general approach of polarization analysis on the Raman intensity under the three polarization configurations and demonstrate that the latter two cases are equivalent to each other. Because the basal plane of highly ordered pyrolytic graphite (HOPG) exhibits isotropic feature and its edge plane is highly anisotropic, HOPG can be treated as a modelling system to study ARPR spectroscopy of two-dimensional materials on their basal and edge planes. Therefore, we verify the ARPR behaviors of HOPG on its basal and edge planes at three different polarization configurations. The orientation direction of HOPG edge plane can be accurately determined by the angle-resolved polarization-dependent G mode intensity without rotating sample, which shows potential application for orientation determination of other anisotropic and vertically standing two-dimensional materials and other materials.

Using scanning tunneling spectroscopy, we studied the transition from tunneling regime to local point contact on the iron-based superconductor Ba_0.6K_0.4Fe₂As₂. By gradually reducing the junction resistance, a series of spectra were obtained with the characteristics evolving from single-particle tunneling into Andreev reflection. The spectra can be well fitted to the modified Blonder-Tinkham-Klapwijk (BTK) model and exhibit significant changes of both spectral broadening and orbital selection due to the formation of point contact. The spatial resolution of the point contact was estimated to be several nanometers, providing a unique way to study the inhomogeneity of unconventional superconductors on such a scale.

We report the success in introducing Mn into (Li_1-xFe_x)OHFe_1-ySe superconducting crystals by applying two different hydrothermal routes, ion exchange (1-step) and ion release/introduction (2-step). The micro-region x-ray diffraction and energy dispersive x-ray spectroscopy analyses indicate that Mn has been doped into the lattice, and its content in the 1-step fabricated sample is higher than that in the 2-step one. Magnetic susceptibility and electric transport properties reveal that Mn doping influences little on the superconducting transition, regardless of 1-step or 2-step routes. By contrast, the characteristic temperature T^*, at which the negative Hall coefficient reaches its minimum, is significantly reduced by Mn doping. This implies that the hole carriers contribution is obviously modified, and hence the hole band might have no direct relationship with the superconductivity in (Li_1-xFe_x)OHFe_1-ySe superconductors. Our present hydrothermal methods of ion exchange and ion release/introduction provide an efficient way for elements substitution/doping into (Li_1-xFe_x)OHFe_1-ySe superconductors, which will promote the in-depth investigations on the role of multiple electron and hole bands and their interplay with the high-temperature superconductivity in the FeSe-based superconductors.

A bow shock is formed in the interaction of a high-speed laser-driven plasma cloud with a cylinder obstacle. Its temporal and spatial structures are observed by shadowgraphy and interferometry. The width of the shock transition region is ～ 50 μm, comparable to the ion-ion collision mean free path, which indicates that collision is dominated in the shock probably. The Mach-number of the ablating plasma cloud is ～ 15 at first, and decreases with time resulting in a changing shock structure. A two-dimension hydrodynamics code, USim, is used to simulate the interaction process. The simulated shocks can well reproduce the observed.

In order to study the basic superconductivity properties of Pr₂Pt₃Ge₅, we synthesized the single crystalline samples by the Pt-Ge self-flux method. R₂Pt₃Ge₅ (R = La, Ce) were also grown for a systematic study. Zero-resistivity was observed in both the La- and Pr-based samples below the reported superconducting transition temperatures. However, magnetic susceptibility measurements showed low superconductivity volume fractions in both La₂Pt₃Ge₅ and Pr₂Pt₃Ge₅ (less than 2%). Ce₂Pt₃Ge₅ did not show any signature of superconductivity. From the specific heat measurements, we did not observe a superconducting transition peak in Pr₂Pt₃Ge₅, suggesting that it is not a bulk superconductor. The magnetic susceptibility and heat capacity measurements revealed two antiferromagnetic (AFM) orders in Pr₂Pt₃Ge₅ at T_N1 = 4.2 K and T_N2=3.5 K, as well as a single AFM transition at T_N = 3.8 K in Ce₂Pt₃Ge₅.

Two-dimensional (2D) organic nanomaterials are fascinating because of their unique properties and pentential applications in future optoelectronic devices. Polyaniline (PANI) has attracted much attention for its high conductivity, good environmental stability and unusual doping chemistry. We report on liquid-phase exfoliation of layered PANI films grown by electrochemical polymerization. Atomic force microscopy images demonstrate that few- or even mono-layer PANI nanosheets can be fabricated. The PANI nanosheets can be transferred onto a variety of surfaces, providing a promising route to their incorporation into a variety of devices for further studies and various applications.

In this paper, granular segregation in a two-compartment cell in zero gravity is studied numerically by DEM simulation. In the simulation using a virtual window method we find a non-monotonic flux, a function which governs the segregation. A parameter is used to quantify the segregation. The effect of three parameters: the total number of particles N, the excitation strength Γ, and the position of the window coupling the two compartments, on the segregation and the waiting time τ are investigated. It is found that the segregation observed in zero gravity exists and does not depend on the excitation strength Γ. The waiting time τ, however, depends strongly on Γ: the higher the Γ, the lower the waiting time τ. The simulation results are important in guiding the SJ-10 satellite microgravity experiments.

We experimentally demonstrated a diode-pumped Kerr-lens mode-locked femtosecond (fs) laser with a self-frequency doubling Yb:YCa₄O(BO₃)₃ crystal. Sub-40 fs laser pulses were directly generated from the oscillator without extracavity compression. The central wavelength was tunable from 1039 nm to 1049 nm with a typical bandwidth of 35 nm and an average output power of 53 mW. For the first time, a self-frequency doubled second harmonic green laser with tunable range from 519 nm to 525 nm was observed.

We demonstrate the direct loading of cold atoms into a microchip 2-mm Z-trap, where the evaporative cooling can be performed efficiently, from a macroscopic quadrupole magnetic trap with a high loading efficiency. The macroscopic quadrupole magnetic trap potential is designed to be moveable by controlling the currents of the two pairs of anti-Helmholtz coils. The cold atoms are initially prepared in a standard six-beam magneto-optical trap and loaded into the macroscopic quadrupole magnetic trap, and then transported to the atom chip surface by moving the macroscopic trap potential. By means of a three-dimensional absorption imaging system, we are able to optimize the position alignment of the atom cloud in the macroscopic trap and the microchip Z-shaped wire. Consequently, with a proper magnetic transfer scheme, we load the cold atoms into the microchip Z-trap directly and efficiently. The loading efficiency is measured to be about 50%. This approach can be used to generate appropriate ultracold atoms sources, for example, for a magnetically guided atom interferometer based on atom chip.

The application of transparent conducting indium-tin-oxide (ITO) film as full front electrode replacing the conventional bus-bar metal electrode in III-V compound GaInP solar cell was proposed. A high-quality, non-rectifying contact between ITO and 10 nm N⁺-GaAs contact layer was formed, which is benefiting from a high carrier concentration of the terrilium-doped N⁺-GaAs layer, up to 2×10¹⁹ cm^-3. A good device performance of the GaInP solar cell with the ITO electrode was observed. This result indicates a great potential of transparent conducting films in the future fabrication of larger area flexible III-V solar cell.