H.M. Fu

TiZr-base Bulk Metallic Glass with over 50 mm in Diameter

Low-cost TiZr-base bulk metallic glasses (BMGs) (Ti(36.1)Zr(33.2)Ni(5.8)Be(24.9))(100-x)Cu(x) (x=5, 7 and 9) with a maximum size of over 50 mm in diameter were developed by optimizing the alloy composition. The idea is initiated by selecting a particular microstructure comprising primary beta-Ti dendrite and amorphous phase. Afterwards, based on this composition of amorphous phase, a class of TiZr-base bulk metallic glasses was designed step by step to reach the optimum composition range. The glass transition temperature (T(g)), initial crystallization temperature (T(x)) and width of supercooled region (Delta T) of (Ti(36.1)Zr(33.2)Ni(5.8)Be(24.9))(91)Cu(9) BMG are 611, 655 and 44 K, respectively. The (Ti(36.1)Zr(33.2)Ni(5.8)Be(24.9))(91)Cu(9) BMG exhibits low density of 5.541 g.cm(-3) and high compressive fracture strength of 1800 MPa, which promises the potential application as structural materials.

Stacking-dependent electronic structure of bilayer silicene

Bilayer silicene (BLS) is a class of material that possibly holds both topological and superconducting properties; however, its structure is not fully understood. By scanning stacking modes and lattice constants using first principles calculations, several meta-stable configurations are identified, including a slightly faulted-AA packing structure, named slide-2AA. Different from the metallic properties of conventional AA and AB stacking forms, band structure of slide-2AA bilayer presents a sizeable indirect energy gap of ∼1.16 eV. A metal-semiconductor phase transition along the sliding pathway with a small energy barrier is also observed, indicating its electronic properties can be easily tuned by applying small shear force along the BLS surface plane. Such unique quantitative relationship of structure and electronic properties has profound implications in nanoelectronics and electromechanical devices.

From Silicene to Half-Silicane by Hydrogenation

Graphane is graphene fully hydrogenated from both sides, forming a 1×1 structure, where all C atoms are in sp(3) configuration. In silicene, the Si atoms are in a mixed sp(2)/sp(3) configuration; it is therefore natural to imagine a silicane structure analogous to graphane. However, a monatomic silicene sheet grown on substrates generally reconstructs into different phases, and only partially hydrogenated silicene with reconstructions had been reported before. In this work, we produce half-silicane, where one Si sublattice is fully H-saturated and the other sublattice is intact, forming a perfect 1×1 structure. By hydrogenating various silicene phases on a Ag(111) substrate, we found that only the (2√3×2√3)R30° phase can produce half-silicane. Interestingly, this phase was previously considered to be a highly defective or incomplete silicene structure. Our results indicate that the structure of the (2√3×2√3)R30° phase involves a complete silicene-1×1 lattice instead of defective fragments, and the formation mechanism of half-silicane was discussed with the help of first-principles calculations.

Mg-based metallic glass/titanium interpenetrating phase composite with high mechanical performance

We report an Mg-based metallic glass/titanium interpenetrating phase composite in which constituent phases form a homogeneously interconnected network. The porous titanium constrains shear bands propagation thoroughly and promotes shear bands branching and intersection subsequently. The homogeneous phase distribution promotes regularly distributed local shear deformation and leads to a uniform deformation for the composites. Moreover, the interpenetrating phase structure introduces a mutual-reinforcement between metallic glass and titanium. Therefore, the composite exhibits excellent mechanical performance with compressive fracture strength of 1783 MPa and fracture strain of 31%.

Nonlinear Rashba spin splitting in transition metal dichalcogenide monolayers

Single-layer transition-metal dichalcogenides (TMDs) such as MoS2 and MoSe2 exhibit unique electronic band structures ideal for hosting many exotic spin-orbital orderings. It has been widely accepted that Rashba spin splitting (RSS) is linearly proportional to the external field in heterostructure interfaces or to the potential gradient in polar materials. Surprisingly, an extraordinary nonlinear dependence of RSS is found in semiconducting TMD monolayers under a gate field. In contrast to small and constant RSS in polar materials, the potential gradient in non-polar TMDs gradually increases with the gate bias, resulting in nonlinear RSS with a Rashba coefficient an order-of-magnitude larger than the linear one. Most strikingly, under a large gate field MoSe2 demonstrates the largest anisotropic spin splitting among all known semiconductors to our knowledge. Based on the k·p model via symmetry analysis, we identify that the third-order contributions are responsible for the large nonlinear Rashba splitting. The gate tunable spin splitting found in semiconducting pristine TMD monolayers promises future spintronics applications in that spin polarized electrons can be generated by external gating in an experimentally accessible way.

Synthesis and compressive properties of Al–Ni–Y metallic glass

An Al-based metallic glass rod with 0.75 mm diameter was prepared successfully using the copper-mould casting technique together with the proper melt treatment of the liquid alloy. The compressive properties of this Al–Ni–Y metallic glass were experimentally examined. The results showed that the amorphous alloy has a high yield strength of 1090 MPa and a compressive fracture strength of 1150 MPa. Its fracture surface presented typical vein patterns and melting phenomena characteristic of a monolithic metallic glass.

Interlayer‐State‐Coupling Dependent Ultrafast Charge Transfer in MoS2/WS2 Bilayers

Light‐induced interlayer ultrafast charge transfer in 2D heterostructures provides a new platform for optoelectronic and photovoltaic applications. The charge separation process is generally hypothesized to be dependent on the interlayer stackings and interactions, however, the quantitative characteristic and detailed mechanism remain elusive. Here, a systematical study on the interlayer charge transfer in model MoS2/WS2 bilayer system with variable stacking configurations by time‐dependent density functional theory methods is demonstrated. The results show that the slight change of interlayer geometry can significantly modulate the charge transfer time from 100 fs to 1 ps scale. Detailed analysis further reveals that the transfer rate in MoS2/WS2 bilayers is governed by the electronic coupling between specific interlayer states, rather than the interlayer distances, and follows a universal dependence on the state‐coupling strength. The results establish the interlayer stacking as an effective freedom to control ultrafast charge transfer dynamics in 2D heterostructures and facilitate their future applications in optoelectronics and light harvesting.

Direct Observation on the Evolution of Shear Banding and Buckling in Tungsten Fiber Reinforced Zr-Based Bulk Metallic Glass Composite

The evolution of micro-damage and deformation of each phase in the composite plays a pivotal role in the clarification of deformation mechanism of composite. However, limited model and mechanical experiments were conducted to reveal the evolution of the deformation of the two phases in the tungsten fiber reinforced Zr-based bulk metallic glass composite. In this study, quasi-static compressive tests were performed on this composite. For the first time, the evolution of micro-damage and deformation of the two phases in this composite, i.e., shear banding of the metallic glass matrix and buckling deformation of the tungsten fiber, were investigated systematically by controlling the loading process at different degrees of deformation. It is found that under uniaxial compression, buckling of the tungsten fiber occurs first, while the metallic glass matrix deforms homogeneously. Upon further loading, shear bands initiate from the fiber/matrix interface and propagate in the metallic glass matrix. Finally, the composite fractures in a mixed mode, with splitting in the tungsten fiber, along with shear fracture in the metallic glass matrix. Through the analysis on the stress state in the composite and resistance to shear banding of the two phases during compressive deformation, the possible deformation mechanism of the composite is unveiled. The deformation map of the composite, which covers from elastic deformation to final fracture, is obtained as well.

Size dependent melting behaviors of nanocrystalline in particles embedded in amorphous matrix

The composites of In nanoparticles embedded in Al-based amorphous matrix were synthesized. As the content of In increases, the average size of In nanoparticles increases. The melting behaviors of embedded In nanoparticles were investigated, indicating that the melting temperature is suppressed, and the smaller the size is, the lower the melting temperature is. It is confirmed by comparing the differential scanning calorimetry curves with those of the size distribution. The size dependent melting behaviors of nanoparticles were discussed with the thermodynamic model.

Tuning magnetic splitting of zigzag graphene nanoribbons by edge functionalization with hydroxyl groups

The electronic properties and relative stability of zigzag graphene nanoribbons are studied by varying the percentage of hydroxyl radicals for edge saturation using first principle calculations. The passivated structures of zigzag graphene nanoribbon have spin-polarized ground state with antiferromagnetic exchange coupling across the edge and ferromagnetic coupling along the edges. When the edges are specially passivated by hydroxyl, the potentials of spin exchange interaction across the two edges shift accordingly, resulting into a spin-semiconductor. Varying the concentration of hydroxyl groups can alter the maximum magnetization splitting. When the percentage of asymmetrically adsorbed hydroxyl reaches 50%, the magnetization splitting can reach a value as high as 275meV due to the asymmetrical potential across the nanoribbon edges. These results would favor spintronic device applications based on zigzag graphene nanoribbons. V C 2015 AIP Publishing LLC .[ http://dx.doi.org/10.1063/1.4915337]