Arrayed van der Waals Vertical Heterostructures based on 2D GaSe Grown by Molecular Beam Epitaxy

Vertically stacking two dimensional (2D) materials can enable the design of novel electronic and optoelectronic devices and realize complex functionality. However, the fabrication of such artificial heterostructures in wafer scale with an atomically-sharp interface poses an unprecedented challenge. Here, we demonstrate a convenient and controllable approach for the production of wafer-scale 2D GaSe thin films by molecular beam epitaxy. In-situ reflection high-energy electron diffraction oscillations and Raman spectroscopy reveal a layer-by-layer van der Waals epitaxial growth mode. Highly-efficient photodetector arrays were fabricated based on few-layer GaSe on Si. These photodiodes show steady rectifying characteristics and a relatively high external quantum efficiency of 23.6%. The resultant photoresponse is super-fast and robust with a response time of 60 us. Importantly, the device shows no sign of degradation after 1 million cycles of operation. Our study establishes a new approach to produce controllable, robust and large-area 2D heterostructures and presents a crucial step for further practical applications

Magnetic-field-induced nonlinear transport in HfTe5

The interplay of electron correlations and topological phases gives rise to various exotic phenomena including fractionalization, excitonic instability, and axionic excitation. Recently-discovered transition-metal pentatellurides can reach the ultra-quantum limit in low magnetic fields and serve as good candidates for achieving such a combination. Here, we report evidences of density wave and metal-insulator transition in HfTe5 induced by intense magnetic fields. Using the nonlinear transport technique, we detect a distinct nonlinear conduction behavior in the longitudinal resistivity within the a-c plane, corresponding to the formation of a density wave induced by magnetic fields. In high fields, the onset of the nonlinear conduction in the Hall resistivity indicates an impurity-pinned magnetic freeze-out as the possible origin of the insulating behavior. These frozen electrons can be gradually re-activated into mobile states above a threshold electric field. These experimental evidences call for further investigations into the underlying mechanism for the bulk quantum Hall effect and field-induced phase transtions in pentatellurides.Comment: 13 pages, 4 figure

Periplaneta americana extract attenuates hepatic fibrosis progression by inhibiting collagen synthesis and regulating the TGF-β1/Smad signaling pathway

Introduction. Liver fibrosis is the damage repair response following chronic liver diseases. Activated hepatic stellate cells (HSCs) are the main extracellular matrix (ECM)-producing cells and key regulators in liver fibrosis. Periplaneta americana shows prominent antifibrotic effects in liver fibrosis; however, the underlying mechanisms remain undetermined. This study aimed to elucidate the therapeutic effects of P. americana extract (PA-B) on liver fibrosis based on the regulation of the TGF-β1/Smad signal pathway. Material and methods. HSCs and Sprague Dawley rats were treated with TGF-β1 and CCl4, respectively, to establish the hepatic fibrosis model in vitro and in vivo. The effect of PA-B on liver rat fibrosis was evaluated by biochemical (serum aspartate aminotransferase (AST), alanine aminotransferase (ALT), hyaluronic acid (HA), laminin (LN), collagen type Ⅳ (Col-Ⅳ), pro-collagen type Ⅲ (PC-Ⅲ)) and histological examinations. Further, fibrogenic markers expression of alpha smooth muscle actin (α-SMA), collagen type I (Col-I), and collagen type III (Col-III), and the TGF-β1/Smad pathway-related factors were assessed by immunofluorescence (IF), real time quantitative polymerase chain reaction (RT-qPCR), and western blotting (WB). Results. Treatment of HSC-T6 cells with PA-B suppressed the expression of α-SMA, Col-I, and Col-III, downregulated the expression of TGF-β1 receptors I and II (TβR I and TβR II, respectively), Smad2, and Smad3, and upregulated Smad7 expression. PA-B mitigates pathologic changes in the rat model of liver fibrosis, thus alleviating liver index, and improving liver function and fibrosis indices. The effects of PA-B on the expression of α-SMA, Col-I, Col-III, TβR I, TβR II, Smad2, Smad3, and Smad7 were consistent with the in vitro results, including reduced TGF-β1 expression. Conclusions. The therapeutic effect of PA-B on liver fibrosis might involve suppression of the secretion and expression of TGF-β1, regulation of the TGF-β1/Smad signaling pathway, and inhibition of collagen production and secretion

Wafer-scale arrayed p-n junctions based on few-layer epitaxial GaTe

Two-dimensional (2D) materials have attracted substantial attention in electronic and optoelectronic applications with superior advantages of being flexible, transparent and highly tunable. Gapless graphene exhibits ultra-broadband and fast photoresponse while the 2D semiconducting MoS2 and GaTe unveil high sensitivity and tunable responsivity to visible light. However, the device yield and the repeatability call for a further improvement of the 2D materials to render large-scale uniformity. Here we report a layer-by-layer growth of wafer-scale GaTe with a hole mobility of 28.4 cm2/Vs by molecular beam epitaxy. The arrayed p-n junctions were developed by growing few-layer GaTe directly on three-inch Si wafers. The resultant diodes reveal good rectifying characteristics, photoresponse with a maximum photoresponsivity of 2.74 A/W and a high photovoltaic external quantum efficiency up to 62%. The photocurrent reaches saturation fast enough to capture a time constant of 22 {\mu}s and shows no sign of device degradation after 1.37 million cycles of operation. Most strikingly, such high performance has been achieved across the entire wafer, making the volume production of devices accessible. Finally, several photo-images were acquired by the GaTe/Si photodiodes with a reasonable contrast and spatial resolution, demonstrating for the first time the potential of integrating the 2D materials with the silicon technology for novel optoelectronic devices