Search

Two-dimensional (2D) magnetic crystals have been extensively explored thanks to their potential applications in spintronics, valleytronics, and topological superconductivity. Here we report a novel monolayer magnet, namely puckered pentagonal VTe2 (PP-VTe2), intriguing atomic and electronic structures of which were firmly validated from first-principles calculations. The PP-VTe2 exhibits strong intrinsic ferromagnetism and semiconducting property distinct from the half-metallic bulk pyrite VTe2 (BP-VTe2) phase. An unusual magnetic anisotropy with large magnetic exchange energies is found. More interestingly, the multiferroic coupling between its 2D ferroelasticity and in-plane magnetization is further identified in PP-VTe2, lending it unprecedented controllability with external strains and electric fields. Serving as an emergent 2D ferromagnetic semiconductor with a novel crystal structure, monolayer PP-VTe2 provides an ideal platform for exploring exotic crystalline and spin configurations in low-dimensional systems.

With the unique properties, layered transition metal dichalcogenide (TMD) and its heterostructures exhibit great potential for applications in electronics. The electrical performance, e.g., contact barrier and resistance to electrodes, of TMD heterostructure devices can be significantly tailored by employing the functional layers, called interlayer engineering. At the interface between different TMD layers, the dangling-bond states normally exist and act as traps against charge carrier flow. In this study, we propose a technique to suppress such carrier trap that uses enhanced interlayer hybridization to saturate dangling-bond states, as demonstrated in a strongly interlayer-coupled monolayer-bilayer PtSe2 heterostructure. The hybridization between the unsaturated states and the interlayer electronic states of PtSe2 significantly reduces the depth of carrier traps at the interface, as corroborated by our scanning tunnelling spectroscopic measurements and density functional theory calculations. The suppressed interfacial trap demonstrates that interlayer saturation may offer an efficient way to relay the charge flow at the interface of TMD heterostructures. Thus, this technique provides an effective way for optimizing the interface contact, the crucial issue exists in two-dimensional electronic community.

Platinum diselenide (PtSe2) is a promising transition metal dichalcogenide (TMDC) material with unique properties. It is necessary to find a controllable fabrication method to bridge PtSe2 with other two-dimensional (2D) materials for practical applications, which has rarely been reported so far. Here, we report that the selenization of Pt(111) can be suppressed to form a Se intercalated layer, instead of a PtSe2 monolayer, by inducing confined conditions with a precoating of graphene. Experiments with graphene-island samples demonstrate that the monolayer PtSe2 can be controllably fabricated only on the bare Pt surface, while the Se intercalated layer is formed underneath graphene, as verified by atomic-resolution observations with scanning transmission electron microscopy (STEM) and scanning tunneling microscopy (STM). In addition, the orientation of the graphene island shows a negligible influence on the Se intercalated layer induced by the graphene coating. By extending the application of 2D confined reactions, this work provides a new method to control the fabrication and pattern 2D materials during the fabrication process.

Charge density wave (CDW) strongly affects the electronic properties of two-dimensional (2D) materials and can be tuned by phase engineering. Among 2D transitional metal dichalcogenides (TMDs), VTe2 was predicted to require small energy for its phase transition and shows unexpected CDW states in its T-phase. However, the CDW state of H-VTe2 has been barely reported. Here, we investigate the CDW states in monolayer (ML) H-VTe2, induced by phase-engineering from T-phase VTe2. The phase transition between T- and H-VTe2 is revealed with x-ray photoelectron spectroscopy (XPS) and scanning transmission electron microscopy (STEM) measurements. For H-VTe2, scanning tunneling microscope (STM) and low-energy electron diffraction (LEED) results show a robust 2 3 × 2 3 CDW superlattice with a transition temperature above 450 K. Our findings provide a promising way for manipulating the CDWs in 2D materials and show great potential in its application of nanoelectronics.

Creation of functional patterns in two-dimensional (2D) materials provides opportunities to extend their potential for applications. Transition-metal dichalcogenides (TMDCs) are suitable 2D materia...

Two-dimensional materials provide extraordinary opportunities for exploring phenomena arising in atomically thin crystals. Beginning with the first isolation of graphene, mechanical exfoliation has been a key to provide high-quality two-dimensional materials, but despite improvements it is still limited in yield, lateral size and contamination. Here we introduce a contamination-free, one-step and universal Au-assisted mechanical exfoliation method and demonstrate its effectiveness by isolating 40 types of single-crystalline monolayers, including elemental two-dimensional crystals, metal-dichalcogenides, magnets and superconductors. Most of them are of millimeter-size and high-quality, as shown by transfer-free measurements of electron microscopy, photo spectroscopies and electrical transport. Large suspended two-dimensional crystals and heterojunctions were also prepared with high-yield. Enhanced adhesion between the crystals and the substrates enables such efficient exfoliation, for which we identify a gold-assisted exfoliation method that underpins a universal route for producing large-area monolayers and thus supports studies of fundamental properties and potential application of two-dimensional materials.

Fast-growth of single crystal monolayer graphene by CVD using methane and hydrogen has been achieved on “homemade” single crystal Cu/Ni(111) alloy foils over large area. Full coverage was achieved in 5 min or less for a particular range of composition (1.3 at.% to 8.6 at.% Ni), as compared to 60 min for a pure Cu(111) foil under identical growth conditions. These are the bulk atomic percentages of Ni, as a superstructure at the surface of these foils with stoichiometry Cu6Ni1 (for 1.3 to 7.8 bulk at.% Ni in the Cu/Ni(111) foil) was discovered by low energy electron diffraction (LEED). Complete large area monolayer graphene films are either single crystal or close to single crystal, and include folded regions that are essentially parallel and that were likely wrinkles that “fell over” to bind to the surface; these folds are separated by large, wrinkle-free regions. The folds occur due to the buildup of interfacial compressive stress (and its release) during cooling of the foils from 1075 °C to room tempera...

Recent experimental breakthroughs open up new opportunities for magnetism in few-atomic-layer two-dimensional (2D) materials, which makes fabrication of new magnetic 2D materials a fascinating issue. Here, we report the growth of monolayer VSe2 by molecular beam epitaxy (MBE) method. Electronic properties measurements by scanning tunneling spectroscopy (STS) method revealed that the as-grown monolayer VSe2 has magnetic characteristic peaks in its electronic density of states and a lower work-function at its edges. Moreover, air exposure experiments show air-stability of the monolayer VSe2. This high-quality monolayer VSe2, a very air-inert 2D material with magnetism and low edge work function, is promising for applications in developing next-generation low power-consumption, high efficiency spintronic devices and new electrocatalysts.

Hot compression tests of hot isostatic pressed (HIPped) spray formed (SF) nickel-base superalloy were carried out in the temperature range of 1050–1150 °C at strain rates of 0.001–1 s −1 , between 10–70% of engineering strain, using a Gleeble-1500 thermal simulator. Thereafter, the flow curve was developed and the constitutive equation of flow stress during hot deformation was established. The results show that the flow stress decreases by increasing deformation temperature and decreasing strain rate. Processing maps were developed based on the data obtained using the principles of dynamic materials modeling. The microstructure of deformed samples was characterized using optical and electron microscopy. The processing maps exhibit the stability domain at the temperatures of 1140–1150 °C and strain rate of 0.01 s −1 , with a peak efficiency of approximately 50%. High deformation temperature and high strain rate are conducive to the occurrence of dynamic recrystallization. The activation energy of the new Ni-Cr-Co based SF superalloy FGH100 was found to be 866.7 kJ/mol. Besides, the experimental results verify the hyperbolic sine model including strain variable, reflecting the changing law of flow stress during the hot deformation process.

Creation of functional patterns in two-dimensional (2D) materials provides opportunities to extend their potential for applications. Transition-metal dichalcogenides (TMDCs) are suitable 2D materials for pattern generation because of properties including alterable polymorphic phases, easy chalcogen-vacancy formation, metal-atom insertion, and alloying. Such patterning can be used for selective functionalization. Here we report the spontaneous formation of long-range, well-ordered 1D patterns in monolayer vanadium diselenide (VSe

Background The importance of basic surgical skills is entirely agreed among surgical educators. However, restricted by ethical issues, finance etc, the basic surgical skills training is increasingly challenged. Increasing cost gives an impetus to the development of cost-effective training models to meet the trainees' acquisition of basic surgical skills. In this situation, a cost-effective training framework was formed in our department and introduced here. Methods Each five students were assigned to a ‘training unit’. The training was implemented weekly for 18 weeks. The framework consisted of an early, a transitional, an integrative stage and a surgical skills competition. Corresponding training modules were selected and assembled scientifically at each stage. The modules comprised campus intranet databases, sponge benchtop, nonliving animal tissue, local dissection specimens and simulating reality operations. The training outcomes used direct observation of procedural skills as an assessment tool. The training data of 50 trainees who were randomly selected in each year from 2006 to 2011 year, were retrospectively analysed. Results An excellent and good rate of the surgical skills is from 82 to 88%, but there is no significant difference among 6 years (P > 0.05). The skills scores of the contestants are markedly higher than those of non-contestants (P < 0.05). The average training cost per trainee is about $21.85–34.08. Conclusion The present training framework is reliable, feasible, repeatable and cost-effective. The skills competition can promote to improve the surgical skills level of trainees.

The electronic structure and magnetic properties of SrMo1 − xCrxO3 with x of 0, 0.125, 0.25, and 0.5 have been studied using ab initio density-functional calculations with the LSDA + U method. The results suggest that light Cr doping can drive the SrMo1 − xCrxO3 system from the PM to the FM state. It is found that the spin-dependent hybridizations between Cr and Mo (via O) may induce Mo moments in Cr-doped SrMoO3. However, the effective moments of Mo ions are negligibly small for x = 0.125, 0.25. The FM behavior is contributed by the spin-polarized Cr atoms. With more increase of Cr atoms, for x = 0.5, a negative moment about 0.32 µB/Mo is induced by Cr atom which is coupled antiferromagnetically to the Cr moment. Meanwhile, the half-metallic nature is observed in which the spin-down channel has a conducting behavior, while the spin-up channel shows an isolated feature with a gap of ∼1.82 eV. The Mo 4d electrons contribute to the conducting behavior and there are practically no Cr-d states around the Fermi level.

First-principles calculations on the electronic and magnetic properties of TlNiO 3 reveal that the antiferromagnetic structure with the insulating ground state is more stable than other possible configurations in the monoclinic structure. The band gap of the antiferromagnetic insulating ground state is predicted to be 0.18 eV. The spin magnetic moments of Ni(1) and Ni(2) ions are about ±1.62 and ±0.92μ B , respectively. The differing chemical environments between the two Ni positions as well as charge disproportionation effect result in unequal magnetic moments for adjacent Ni atoms in the monoclinic TlNiO 3 .

Electronic structure and the evolution of the spin state of Co with temperature increase in YCoO3 have been investigated by using the ab initio density-functional calculations with local spin density approximation (LSDA) and LSDA+U methods. It is shown that the orthorhombic YCoO3 exhibits nonmagnetic ground state with Co ions in a low-spin state. Theoretical calculations predict the insulating ground state with a band gap of 1.84 eV due to the strong interactions with U=6.0 eV. The size of the band gap may be significantly influenced by the choice of the value of U. With temperature variation, simulation has been carried out by corresponding change of the lattice parameters based on the experimental data. The results suggest that YCoO3 has nonmagnetic (spin S=0) insulator nature in the low temperature range and semiconductor nature with an electronic transition of Co3+ ion from low-spin state to high-spin state in the high temperature range (600–1000 K).

A comparative study of the electronic structure and magnetic properties of YCoO3 and HoCoO3 has been carries out using ab initio density-functional calculations with local spin density approximation (LDSA) and LSDA + U methods. It is found that YCoO3 shows nonmagnetic (spin S=0) insulator character below 600 K and an electronic transition of Co3+ ions from a low spin (LS) state to a high-spin (HS) state above 600 K. In contrast, HoCoO3 shows nonmagnetic property with Co ions in a LS state over a wide temperature range (300-995 K). The intermediate-spin (IS) state becomes more stable than the LS state only a temperature of 1098 K in HoCoO3. We suggest that the variation of Co-O bond length induced by the unit cell expansion may play an-important role in the evolution of the spin state of Co3+ with increasing temperature in these perovskite cobalt oxides. The discrepancy of the averaged Co-O bond length in YCoO3 and HoCoO3 may be a likely reason for the difference of electronic properties between them. The decrease of the Co-O bond length could result in stabilization of the LS state. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

The magnetic properties of infinitely long monostrand Ti nanowire were investigated by using the full-potential linearized augmented plane wave method. The results show that the Ti monowires exhibit a ferromagnetic ground state. The magnetic moment is 0.61μ B per-atom at the equilibrium bond length and increases with stretching. The origin of the wire magnetism was analyzed.

Immunoglobulin light chain cDNA sequences of a perciform fish, the mandarin fish Siniperca chuatsi were amplified from head kidney mRNA by reverse transcription (RT)-PCR and RACE methods using degenerated primer and gene specific ones. In cDNA sequences of the VL region, nucleotide exchanges were present mainly within CDRs, although a lesser degree of variability was also found in FRs. Moreover, the length of CDR1 and CDR3 in the mandarin fish is shorter than in most other fish species. In the middle of S. chuatsi CL region, a microsatellite sequence (AGC)(6-8) was found, which is also present in another perciform species, the spotted wolffish (Anarhichas minor). The comparison of amino acid sequence of the mandarin fish CL domain with those of other vertebrates showed the highest degree of similarity of 94.5% to the spotted wolffish, while the similarity with rainbow trout (Oncorhynchus mykiss) Ig L1 (62.7%) and channel catfish (Ictalurus punctatus) Ig LG (55.9%) isotypes is also higher. However, there is only 50% identity in the VL regions between the mandarin fish and the wolffish. The sequence similarity of the mandarin fish CL domain with those of higher vertebrate did not readily allow it to be classified as kappa or lambda isotype. The phylogenetic analyses also demonstrated that the CL genes of the mandarin fish and most other teleost fish cluster as a separate branch out of the mammal kappa and lambda branches.

Electronic structure and magnetic properties of perovskite EuZrO 3 have been investigated using the ab initio density-functional calculations with local spin density approximation (LSDA) and LSDA+U methods. The results that are obtained reveal that the antiferromagnetic G-type arrangement is more stable than other possible configurations. The ground G-AFM state shows the insulator property with an energy gap of about 0.27 eV at U =0 eV. It is found that the energy gap strongly depends on the correction potential parameter of U due to the strong interaction of the f electrons of Eu in EuZrO 3 . The spin magnetic moment of Eu ions is predited to be 6.82 μ B , which is in well agreement with the experimental result of 6.87 μ B.

The importance of basic surgical skills is entirely agreed among surgical educators. However, restricted by ethical issues, finance etc, the basic surgical skills training is increasingly challenged. Increasing cost gives an impetus to the development of cost-effective training models to meet the trainees' acquisition of basic surgical skills. In this situation, a cost-effective training framework was formed in our department and introduced here.Each five students were assigned to a 'training unit'. The training was implemented weekly for 18 weeks. The framework consisted of an early, a transitional, an integrative stage and a surgical skills competition. Corresponding training modules were selected and assembled scientifically at each stage. The modules comprised campus intranet databases, sponge benchtop, nonliving animal tissue, local dissection specimens and simulating reality operations. The training outcomes used direct observation of procedural skills as an assessment tool. The training data of 50 trainees who were randomly selected in each year from 2006 to 2011 year, were retrospectively analysed.An excellent and good rate of the surgical skills is from 82 to 88%, but there is no significant difference among 6 years (P0.05). The skills scores of the contestants are markedly higher than those of non-contestants (P0.05). The average training cost per trainee is about $21.85-34.08.The present training framework is reliable, feasible, repeatable and cost-effective. The skills competition can promote to improve the surgical skills level of trainees.

The present paper focuses on the Inlet/TBCC/Nozzle integration concept design for the hypersonic civic aircraft. Firstly, several basic principles were put forward for the Inlet/TBCC/Nozzle integration concept design .Secondly. A set of fast, versatile, and trusted analysis tool was developed which could analyze the design constraints and the matching relationship between the various components among a wide flight range. Assisted by this tool, the design issues of Inlet/TBCC/Nozzle, the multiple-variable control law for an optimized TBCC propulsion system were analyzed .Then a solution for the inlet/TBCC/Nozzle integration concept design was presented. The result shows that, to meet the conflict requirements in the long range from take-off to Mach 5, the turbine based combine cycle propulsion system should apply a variable cycle engine concept via the modulation of 11 variable geometries. It can also be concluded that the solution for the TBCC propulsion system concept could meet the basic mission requirements for the hypersonic airplane.

[Abstract] The geometry-variable hypersonic intake plays an important role in the next generation air-breathing propulsion system operating across a wide Mach spectrum. Among them, the turbine based combined cycle (TBCC) engine which operates in Mach regime ranging from zero to five, typically require a geometry-variable hypersonic intake capable of sucking high quality air with adaptive mass flow rate under different flight conditions. A trivariable adjustable rectangle hypersonic intake concept was derived in this paper from integrated multi-level performance analysis of TBCC propulsion system. The design process of the intake firstly worked out its configuration in design-point based on integration of intake with turbofan/ramjet hybrid engine by means of one-dimensional shock wave theory. Whereafter, the intake’s geometry-viable scheme and its control laws in off-design points were acquired using a multi-object optimization algorithm based on intake and TBCC engine iterative interaction. Result of simulation demonstrated that the geometry-variable intake matched well with the turbofan/ramjet hybrid engine in the given Mach regime.

[Abstract] As one of the most challenging technologies for the turbine based combined cycle engine concept with the tandem layout for a hypersonic cruise vehicle, turbofan/ram mode transition study was carried out based on a tested nonlinear combined cycle engine models. Five steps were divided in the transition process to investigate the law on the combined modulation of the five variable geometries and the fuel flow to guarantee stable mode transition. Methods such as adjustment of single geometry, tandem optimization and Latin orthogonal experiment were applied separately or together to accelerate the search for Pareto solutions considering the characteristic difference of the multiple objects optimization problems in the steps. Based on the summarized rules, a new set of transition control law was designed for a new configuration with a more promising set of cycle parameters. The transient simulation shows stable mode transition could also be acquired through proper control of the variables.

A simple and feasible method to retrieve directional fraction of vegetation cover is presented. A digital camera is adopted to capture multi-angle images for a wheat field and trees. The viewing angles are controlled by an automatic multi-angle observation device. After image processing, directional fraction cover and gap probability can be obtained.