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Two-dimensional (2D) intrinsic ferromagnetic semiconductors are expected to stand out in the spintronic field. Recently, the monolayer VI 3 has been experimentally synthesized but the weak ferromagnetism and low Curie temperature (T C ) limit its potential application. Here we report that the Janus structure can elevate the T C to 240 K. And it is discussed that the reason for high T C in Janus structure originates from the lower virtual exchange gap between t 2g and e g states of nearest-neighbor V atoms. Besides, T C can be further substantially enhanced by tensile strain due to the increasing ferromagnetism driven by rapidly quenched direct exchange interaction. Our work supports a feasible approach to enhance Curie temperature of monolayer VI 3 and unveils novel stable intrinsic FM semiconductors for realistic applications in spintronics.

As a typical two-dimensional (2D) semiconducting material, layered transition metal dichalcogenides (TMDCs) show promise in electronics and optoelectronics. To fully realize their potential, cost-effective large-area and layer-number modulated synthesis is highly desired. Here, taking MoS2 as an example, we demonstrate a layer-by-layer scalable growth of coalesced TMDC films on a moving sapphire substrate by local-feeding atmospheric-pressure chemical vapor deposition. By linear moving of the substrate across the cone-shaped diffusion concentration gradient of Mo-containing species and controlling the moving cycles, continuous MoS2 films with the thickness from a monolayer up to ~30 layers can be obtained. Compared with the growth on a stationary substrate, the monolayer film grown on a moving substrate shows preferable 2D epitaxial growth with much smoother surface morphology. We believe this can be attributed to the spatial separation of the initial nucleation step and the following 2D ripening process during substrate moving, which is the key to promoting the 2D lateral growth. The results shed light on developing new synthetic strategies toward atomic-thickness-controlled growth of 2D TMDC films in a scalable and efficient process that is suitable for large-area device fabrication.

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Silicon wafer with a nanostructured porous layer on top surface was obtained with Cu(NO 3 ) 2 -HF-H 2 O 2 aqueous solution treatment in a low Cu 2+ concentration region (0.001 M-0.02 M). The influences of different recipes concentrations on silicon surface morphology and the average etching rate were investigated. Craters and pores structures are successfully formed on the silicon surface layer. No copper particles are observed from the SEM images of as-prepared silicon surface with pores. The mechanism of forming nanostructured porous layer on silicon surface without metal nanoparticles was discussed. The morphology evolution of Si surface and the transition from craters to pores in the low Cu 2+ concentration region were investigated.

Abstract-We present a novel optical flip-flop configuration that consists of two unidirectional ring lasers with separate cavities but sharing the same active element unidirectionally. We show that in such a configuration light in the lasing cavity can suppress lasing in the other cavity so that this system forms an optical bistable element. Essential for obtaining the bistability is the presence of an additional feedback circuit that is shared by both lasers. We show experimentally that the flip-flop can be optically set and reset, has a contrast ratio of 40 dB and allows low optical power operation. We also present a model based on roundtrip equations. Good agreement between theory and experiments is obtained.

In this paper, we demonstrate a wavelength widely tunable gain-switched Er³⁺-doped ZBLAN fiber laser around 2.8 μm. The laser can be tuned over 170 nm (2699 nm~2869.9 nm) for various pump power levels, while maintaining stable μs-level single-pulse gain-switched operation with controllable output pulse duration at a selectable repetition rate. To the best of our knowledge, this is the first wavelength tunable gain-switched fiber laser in the 3 μm spectral region with the broadest tuning range (doubling the record tuning range) of the pulsed fiber lasers around 3 μm. Influences of pump energy and power on the output gain-switched laser performances are investigated in detail. This robust, simple, and versatile mid-infrared pulsed fiber laser source is highly suitable for many applications including laser surgery, material processing, sensing, spectroscopy, as well as serving as a practical seed source in master oscillator power amplifiers.