Two-dimensional crystals have emerged as a class of materials that may impact future electronic technologies. Experimentally identifying and characterizing new functional two-dimensional materials is challenging, but also potentially rewarding. Here, we fabricate field-effect transistors based on few-layer black phosphorus crystals with thickness down to a few nanometres. Reliable transistor performance is achieved at room temperature in samples thinner than 7.5 nm, with drain current modulation on the order of 10(5) and well-developed current saturation in the I-V characteristics. The charge-carrier mobility is found to be thickness-dependent, with the highest values up to ∼ 1,000 cm(2) V(-1) s(-1) obtained for a thickness of ∼ 10 nm. Our results demonstrate the potential of black phosphorus thin crystals as a new two-dimensional material for applications in nanoelectronic devices.

http://absimage.aps.org/image/MAR14/MWS_MAR14-2013-005031.pdf

Black Phosphorus Field-effect Transistors

Two-dimensional (2D) materials with a moderate bandgap and high carrier mobility are useful for applications in optoelectronics. In this work, we present a systematic investigation of the mechanical, electronic and optical properties of a B2P6 monolayer using first-principles calculations. Monolayer B2P6 was estimated to be an anisotropic material from direction-dependent in-plane Young's moduli and Poisson's ratios. Also, B2P6 exhibits an ultrahigh electron mobility of ∼5888 cm2 V−1 s−1, showing advantages for application in high-speed optoelectronic devices. More importantly, for the B2P6 monolayer, a desirable transformation from an indirect to direct band gap was observed at a biaxial tensile strain of ∼4%. Increasing the biaxial strain reduces the gap and preserves the suitable band edge positions for photocatalytic water splitting in the observed strain range of 1–8%. The decreased gap also enhances the visible light absorption of the B2P6 monolayer. These findings indicate that the B2P6 monolayer has promising applications in photocatalytic and photovoltaic devices.

Mechanical, electronic and optical properties of a novel B2P6 monolayer: ultrahigh carrier mobility and strong optical absorption.

After the discovery of graphene, a lot of research has been conducted on two-dimensional (2D) materials. In order to increase the performance of 2D materials and expand their applications, two different layered materials are usually combined by van der Waals (vdW) interactions to form a heterostructure. In this work, based on first-principles calculation, some charming properties of the heterostructure constructed by Hf2CO2, AlN and GaN are addressed. The results show that Hf2CO2/AlN and Hf2CO2/GaN vdW heterostructures can keep their original band structure shape and have strong thermal stability at 300 K. In addition, the Hf2CO2/MN heterostructure has I-type band alignment structure, which can be used as a promising light-emitting device material. The charge transfer between the Hf2CO2 and AlN (or GaN) monolayers is 0.1513 (or 0.0414) |e|. The potential of Hf2CO2/AlN and Hf2CO2/GaN vdW heterostructures decreases by 6.445 eV and 3.752 eV, respectively, across the interface. Furthermore, both Hf2CO2/AlN and Hf2CO2/GaN heterostructures have remarkable optical absorption capacity, which further shows the application prospect of the Hf2CO2/MN heterostructure. The study of this work provides theoretical guidance for the design of heterostructures for use as photocatalytic and photovoltaic devices.

Electronic and Optical Properties of Atomic-Scale Heterostructure Based on MXene and MN (M = Al, Ga): A DFT Investigation.

Recently, a new two-dimensional allotrope of carbon named biphenylene has been experimentally synthesized. First-principles calculations are preformed to investigate the electronic properties of biphenylene and the doping effect is also considered to tune its electronic, magnetic, and catalytic properties. The metallic nature with an n-type Dirac cone is observed in the biphenylene. The magnetism can be induced by Fe, Cl, Cr, and Mn doping. More importantly, the doping position dependence of hydrogen evolution reaction (HER) performance of biphenylene is addressed, which can be significantly improved by atomic doping. In particular, the barrier for HER of Fe doping case is only −0.03 eV, denoting its great potential in HER catalysis.

Tuning electronic, magnetic and catalytic behaviors of biphenylene network by atomic doping

Two-dimensional PtSe2/hBN vdW heterojunction as photoelectrocatalyst for the solar-driven oxygen evolution reaction: A first principles study

Possessing long-range FM order and tunable interlayer magnetic coupling, extensive investigations of monolayered ferromagnetic chromium triiodide (CrI3) have been developed. In this work, by means of first-principles simulation, we systematically calculated the electronic and magnetic characteristic of two-dimensional (2D) CrI3 adsorbed by gas molecules, CO, H2, H2O and N2, which can provide theoretical guidance to modulate the desired properties of this layered material. The results show that the adsorption of those gas molecules can significantly enhance FM couplings of monolayer CrI3. In particular, the N2 adsorption can remarkably improve the Curie temperatures of the pristine CrI3 monolayer by about 2.6 times. We also hope that our findings can provide more interest around the recently studied 2D FM semiconductors.

Remarkably improved Curie temperature for two-dimensional CrI3 by gas molecular adsorption: a DFT study

Two-dimensional materials have opened up extensive applications for traditional materials. In particular, heterostructures can further create fantastic performances. In this investigation, the lateral heterostructure was constructed using Janus MoSSe and WSSe monolayers with armchair and zigzag interfaces. Performing first-principles calculations and molecular dynamics simulation method, the thermal stability and the semiconductor characteristics with the type-II band structure to separate the photogenerated charges of such Janus MoSSe/WSSe heterostructure are presented, which suggests the potential application of acting as a photocatalyst for water splitting. Importantly, the asymmetric interface of the Janus MoSSe/WSSe heterostructure can result in natural bending, which limits the heat flow transport. Smaller heat flow and the interfacial thermal resistance of the lateral MoSSe/WSSe heterostructure with a zigzag edge interface are mainly due to suppressed acoustic branches. These structural symmetry and interface-dependent properties show the future applications in photovoltaic and thermoelectric devices.

/pdf/the-thermal-and-electronic-properties-of-the-lateral-janus-2f0dvgf5.pdf

The Thermal and Electronic Properties of the Lateral Janus MoSSe/WSSe Heterostructure

This study reports the simulation and experiments of a MEMS-based igniter for a semiconductor bridge (SCB), which is fabricated using complementary metal oxide semiconductor technology. The finite-element method was first employed to simulate the ultrafast temperature response of the ignition process of SCB under conditions of an electro-exploding ignition, electro-thermal ignition, and no-ignition and to conduct a capacitor discharge stimulation. The recorded voltage from an oscilloscope was used as the initial condition, and conductivity values based on experimental data were taken as a key parameter for the polysilicon material to ensure the accuracy of the heat source loaded into the model. Under the electro-exploding ignition, the SCB was initially ignited at the sharp corners at the valley of the first voltage peak instead of the secondary peak. The maximum temperature of the SCB was no more than the melting point of the polysilicon material (except for the sharp corners) and only at 1369 ​K under the electro-thermal ignition and no-ignition conditions, respectively. The optical testing and ablation results of the bridge area demonstrate that the numerically simulated temperature is quite accurate. This method can be easily extended to other MEMS-based igniters for temperature prediction applications. 

An ultrafast temperature response analysis of a MEMS-based igniter using the finite-element method

Optimization of blade geometry by neural network in natural convection and entropy generation of nanofluids within an oblique square cavity with the effects of volumetric radiation with LB method

A low‐profile dual‐band metasurface antenna is demonstrated for 4G LTE and 5G Sub‐6GHz applications. Based on the characteristic mode analysis, a wideband metasurface with stable radiation pattern is proposed by introducing Minkowski fractal structure in the edge patches and scaling the corner patches. The metasurface is operating in Sub‐6GHz band and excited by a Vivaldi bowtie slot antenna, which also serves as the radiator in LTE band. To validate the concept, a prototype with an overall size of 1.05λ0 × 1.05λ0 × 0.045λ0 (λ0 is the free‐space wavelength at 2.3 GHz) is fabricated. The experiment results show that the −10 dB impedance bandwidths in two bands are 1.7–2.78 (48.2%) and 3.2–5.01 GHz (44.1%), respectively. Moreover, broadside radiation performances in two bands are obtained.

Zijun Zheng

Papers

Remarkably improved Curie temperature for two-dimensional CrI3 by gas molecular adsorption: a DFT study

The Thermal and Electronic Properties of the Lateral Janus MoSSe/WSSe Heterostructure

An ultrafast temperature response analysis of a MEMS-based igniter using the finite-element method

Optimization of blade geometry by neural network in natural convection and entropy generation of nanofluids within an oblique square cavity with the effects of volumetric radiation with LB method

A low‐profile dual‐band antenna using fractal‐based wideband metasurface with stable radiation pattern