High-Performance Broadband Floating-Base Bipolar Phototransistor Based on WSe₂/BP/MoS₂ Heterostructure

Recently, there are increasing interests in two-dimensional materials, as a result of their outstanding electrical and optical properties and numerous potential applications in optoelectronic devices. Here, we first report on a bipolar phototransistor based on WSe₂-BP-MoS₂ van der Waals heterostructure, showing its broadband photoresponse from visible to the infrared spectral regions. Broadband photoresponsivities for visible (532 nm) and the infrared (1550 nm) light waves reach up to 6.32 and 1.12 A W^1–, respectively, which are both improved by tens of times in comparison with similar photodiode devices composed of WSe₂-BP. The phototransistor also exhibits ultrasensitive shot noise limit specific detectivities which are 1.25 × 10¹¹ Jones for visible light at wavelength λ = 532 nm and 2.21 × 10¹⁰ Jones for the near-infrared light at wavelength λ = 1550 nm at room temperature. It is a promising candidate for progressive development of photodetector, with implementation of smaller sensor elements, large sensing area, super-high integration, and broadband photoresponse

Near-Infrared Photodetector Based on MoS₂/Black Phosphorus Heterojunction

Two-dimensional (2D) materials present their excellent properties in electronic and optoelectronic applications, including in ultrafast carrier dynamics, layer-dependent energy bandgap, tunable optical properties, low power dissipation, high mobility, transparency, flexibility, and the ability to confine electromagnetic energy to extremely small volumes. Herein, we demonstrate a photodetector with visible to near-infrared detection range, based on the heterojunction fabricated by van der Waals assembly between few-layer black phosphorus (BP) and few-layer molybdenum disulfide (MoS₂). The heterojunction with electrical characteristics which can be electrically tuned by a gate voltage achieves a wide range of current-rectifying behavior with a forward-to-reverse bias current ratio exceeding 10³. The photoresponsivity (<i>R</i>) of the photodetector is about 22.3 A W^–1 measured at λ = 532 nm and 153.4 mA W^–1 at λ = 1.55 μm with a microsecond response speed (15 μs). In addition, its specific detectivity <i>D</i>* is calculated to have the maximum values of 3.1 × 10¹¹ Jones at λ = 532 nm, while 2.13 × 10⁹ Jones at λ = 1550 nm at room temperature

Iridium-Catalyzed Anti-Stereoselective Asymmetric Ring-Opening Reactions of Azabenzonorbornadienes with Carboxylic Acids

The first anti-stereoselective asymmetric ring-opening reactions of azabenzonorbornadienes with carboxylic acids have been realized with an iridium catalyst assisted by ^<i>n</i>Bu₄NBr. The reaction features broad substrate scope and good functional group tolerance and allows the synthesis of chiral dihydronaphthalene derivatives with high optical purities

Facile Preparation of Superelastic and Ultralow Dielectric Boron Nitride Nanosheet Aerogels via Freeze-Casting Process

As a structural analogue of graphene, boron nitride nanosheets (BNNSs) have attracted ever-growing research interest in the past few years, due to their remarkably mechanical, electrical, and thermal properties. The preparation of BNNS aerogels is considered to be one of the most effective approaches for their practical applications. However, it has remained a great challenge to fabricate BNNS aerogels with superelasticity by a facile method. Here, we report the preparation of BNNS aerogels via a facile method involving polymer-assisted cross-linking and freeze-casting strategies. The resulting aerogels exhibit a well-ordered and anisotropic microstructure, leading to anisotropic superelasticity, high compressive strength, and excellent energy absorption ability. The unique microstructure also endows the aerogels with ultralow dielectric constant (1.24) and loss (∼0.003). The successful fabrication of such fascinating materials paves the way for application of BNNSs in energy-absorbing services, catalyst carrier, and environmental remediation, etc

High-Quality Large-Area Graphene from Dehydrogenated Polycyclic Aromatic Hydrocarbons

Recent studies show that, at the initial stage of chemical vapor deposition (CVD) of graphene, the isolated carbon monomers will form defective carbon clusters with pentagons that degrade the quality of synthesized graphene. To circumvent this problem, we demonstrate that high-quality centimeter-sized graphene sheets can be synthesized on Cu foils by a self-assembled approach from defect-free polycyclic aromatic hydrocarbons (PAHs) in a high vacuum (HV) chamber without hydrogen. Different molecular motifs, namely coronene, pentacene, and rubrene, can lead to significant difference in the quality of resulting graphene. For coronene, monolayer graphene flakes with an adequate quality can be achieved at a growth temperature as low as 550 °C. For the graphene obtained at 1000 °C, transport measurements performed on back-gated field-effect transistors (FETs) with large channel lengths (∼30 μm) exhibit a carrier mobility up to ∼5300 cm² V^–1 s^–1at room temperature. The underlying growth mechanism, which mainly involves surface-mediated nucleation process of dehydrogenated PAHs rather than segregation or precipitation process of small carbon species decomposed from the precursors, has been systematically investigated through the first-principles calculations. Our findings pave the way for optimizing selection of solid carbon precursors and open up a new route for graphene synthesis

Variable thermal transport in black, blue, and violet phosphorene from extensive atomistic simulations with a neuroevolution potential

Phosphorus has diverse chemical bonds, and even in its two-dimensional form, there are three stable allotropes: black phosphorene (Black-P), blue phosphorene (Blue-P), and violet phosphorene (Violet-P). Due to the complexity of these structures, no efficient and accurate classical interatomic potential has been developed for them. In this paper, we develop an efficient machine-learned neuroevolution potential model for these allotropes and apply it to study thermal transport in them via extensive molecular dynamics (MD) simulations. Based on the homogeneous nonequilibrium MD method, the thermal conductivities are predicted to be 12.5±0.2 (Black-P in armchair direction), 78.4±0.4 (Black-P in zigzag direction), 128±3 (Blue-P), and 2.36±0.05 (Violet-P) Wm−1K−1. The underlying reasons for the significantly different thermal conductivity values in these allotropes are unraveled through spectral decomposition, phonon eigenmodes, and phonon participation ratio. Under external tensile strain, the thermal conductivity in black-P and violet-P are finite, while that in blue-P appears unbounded due to the linearization of the flexural phonon dispersion that increases the phonon mean free paths in the zero-frequency limit.</p

Facile Preparation of Superelastic and Ultralow Dielectric Boron Nitride Nanosheet Aerogels via Freeze-Casting Process

As a structural analogue of graphene, boron nitride nanosheets (BNNSs) have attracted ever-growing research interest in the past few years, due to their remarkably mechanical, electrical, and thermal properties. The preparation of BNNS aerogels is considered to be one of the most effective approaches for their practical applications. However, it has remained a great challenge to fabricate BNNS aerogels with superelasticity by a facile method. Here, we report the preparation of BNNS aerogels via a facile method involving polymer-assisted cross-linking and freeze-casting strategies. The resulting aerogels exhibit a well-ordered and anisotropic microstructure, leading to anisotropic superelasticity, high compressive strength, and excellent energy absorption ability. The unique microstructure also endows the aerogels with ultralow dielectric constant (1.24) and loss (∼0.003). The successful fabrication of such fascinating materials paves the way for application of BNNSs in energy-absorbing services, catalyst carrier, and environmental remediation, etc

Rhodium-Catalyzed Asymmetric Cyclization/Addition Reactions of 1,6-Enynes and Oxa/Azabenzonorbornadienes

A mild, efficient, and novel rhodium catalyzed asymmetric cyclization–addition domino reaction of oxa/azabenzonorbornadienes and 1,6-enynes is documented. Through the use of a [Rh­(COD)₂]­BF₄-(<i>R</i>)-An-SDP catalytic system, highly enantioenriched cyclization–addition products were obtained in good yields and with excellent enantioselectivities

Enhanced Performance of Polymeric Bulk Heterojunction Solar Cells via Molecular Doping with TFSA

Organic solar cells based on bis­(trifluoromethanesulfonyl)­amide (TFSA, [CF₃SO₂]₂NH) bulk doped poly­[<i>N</i>-9′′-hepta-decanyl-2,7-carbazole-<i>alt</i>-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole) (PCDTBT):C₇₁-butyric acid methyl ester (PC₇₁BM) were fabricated to study the effect of molecular doping. By adding TFSA (0.2–0.8 wt %, TFSA to PCDTBT) in the conventional PCDTBT:PC₇₁BM blends, we found that the hole mobility was increased with the reduced series resistance in photovoltaic devices. The p-doping effect of TFSA was confirmed by photoemission spectroscopy that the Fermi level of doped PCDTBT shifts downward to the HOMO level and it results in a larger internal electrical field at the donor/acceptor interface for more efficient charge transfer. Moreover, the doping effect was also confirmed by charge modulated electroabsorption spectroscopy (CMEAS), showing that there are additional polaron signals in the sub-bandgap region in the doped thin films. With decreased series resistance, the open-circuit voltage (<i>V</i>_oc) was increased from 0.85 to 0.91 V and the fill factor (FF) was improved from 60.7% to 67.3%, resulting in a largely enhanced power conversion efficiency (PCE) from 5.39% to 6.46%. Our finding suggests the molecular doping by TFSA can be a facile approach to improve the electrical properties of organic materials for future development of organic photovoltaic devices (OPVs)

Solution-Processed Ambipolar Organic Thin-Film Transistors by Blending p- and n‑Type Semiconductors: Solid Solution versus Microphase Separation

Here, we report solid solution of p- and n-type organic semiconductors as a new type of p–n blend for solution-processed ambipolar organic thin film transistors (OTFTs). This study compares the solid-solution films of silylethynylated tetraazapentacene <b>1</b> (acceptor) and silylethynylated pentacene <b>2</b> (donor) with the microphase-separated films of <b>1</b> and <b>3</b>, a heptagon-embedded analogue of <b>2</b>. It is found that the solid solutions of (<b>1</b>)_<i>x</i>(<b>2</b>)_1–<i>x</i> function as ambipolar semiconductors, whose hole and electron mobilities are tunable by varying the ratio of <b>1</b> and <b>2</b> in the solid solution. The OTFTs of (<b>1</b>)_0.5(<b>2</b>)_0.5 exhibit relatively balanced hole and electron mobilities comparable to the highest values as reported for ambipolar OTFTs of stoichiometric donor–acceptor cocrystals and microphase-separated p-n bulk heterojunctions. The solid solution of (<b>1</b>)_0.5(<b>2</b>)_0.5 and the microphase-separated blend of <b>1:3</b> (0.5:0.5) in OTFTs exhibit different responses to light in terms of absorption and photoeffect of OTFTs because the donor and acceptor are mixed at molecular level with π–π stacking in the solid solution