A new two-dimensional (2D) material, borophene (2D boron sheet), has been grown successfully recently on single crystal Ag substrates by two parallel experiments [Mannix et al., Science, 2015, 350, 1513] [Feng et al., Nature Chemistry, 2016, advance online publication]. Three main structures have been proposed (β 12 , χ 3 and striped borophene). However, the stability of three structures is still in debate. Using first principles calculations, we examine the dynamical, thermodynamical and mechanical stability of β 12 , χ 3 and striped borophene. Free-standing β 12 and χ 3 borophene is dynamically, thermodynamically, and mechanically stable, while striped borophene is dynamically and thermodynamically unstable due to high stiffness along a direction. The origin of high stiffness and high instability in striped borophene along a direction can both be attributed to strong directional bonding.This work provides a benchmark for examining the relative stability of different structures of borophene.

Recently a stable monolayer of antimony in buckled honeycomb structure called antimonene was successfully grown on 3D topological insulator Bi 2 Te 3 and Sb 2 Te 3 , which displays semiconducting properties. By first principle calculations, we systematically investigate the phononic, electronic and optical properties of α− and β− allotropes of monolayer arsenene/antimonene. We investigate the dynamical stabilities of these four materials by considering the phonon dispersions. The obtained electronic structures reveal the direct band gap of monolayer α−As/Sb and indirect band gap of β−As/Sb. Significant absorption is observed in α−Sb, which can be used as a broad saturable absorber.

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Preparation of reliable, stable, and highly responsive gassensing devices for the detection of acetone has been considered to be a key issue for the development of accurate disease diagnosis systems via exhaled breath. In this paper, novel CeO 2 nanodot-decorated WO 3 nanowires are successfully synthesized through a sequential hydrothermal and thermolysis process. Such CeO 2 nanodot-decorated WO 3 nanowires exhibited a remarkable enhancement in acetone-sensing performance based on a miniaturized micro-electromechanical system device, which affords high response (S = 1.30−500 ppb, 1.62−2.5 ppm), low detection limit (500 ppb), and superior selectivity toward acetone. The improved performance of the acetone sensor is likely to be originated from the fast carrier transportation of WO 3 nanowires, the formation of WO 3 −CeO 2 heterojunctions, and the existence of large amounts of oxygen vacancies in CeO 2 . The improved reaction thermodynamics and sensing mechanisms have also been revealed by the specific band alignment and X-ray photoelectron spectroscopy analysis.

The superior optical and electronic properties of the two-dimensional (2D) rhenium disulfide (ReS 2 ) makes it suitable for nanoelectronic and optoelectronic applications. However, the internal defects coupled with with the low mobility and light-absorbing capability of ReS 2 impede its utilization in high-performance photodetectors. Fabrication of mixed-dimensional heterojunctions is an alternative method for designing high-performance hybrid photodetectors. This study proposes a mixed-dimensional van der Waals (vdW) heterojunction photodetector, containing high-performance onedimensional (1D) p-type tellurium (Te) and 2D n-type ReS 2 , developed by depositing Te nanowires on ReS 2 nanoflake using the dry transfer method. It can improve the injection and separation efficiency of photoexcited electron−hole pairs due to the type II p−n heterojunction formed at the ReS 2 and Te interface. The proposed heterojunction device is sensitive to visible-light sensitivity (632 nm) with an ultrafast photoresponse (5 ms), high responsivity (180 A/W), and specific detectivity (10 9 ), which is superior to the pristine Te and ReS 2 photodetectors. As compared to the ReS 2 device, the responsivity and response speed is better by an order of magnitude. These results demonstrate the fabrication and application potential of Te/ReS 2 mixed-dimensional heterojunction for highperformance optoelectronic devices and sensors.