For the first time, large-area, vertically oriented few-layered hafnium disulfide (V-HfS 2 ) nanosheets have been grown by chemical vapor deposition. The individual HfS 2 nanosheets are well [001] oriented, with highly crystalline quality. Far different from conventional van der Waals epitaxial growth mechanism for two-dimensional transition metal dichalcogenides, a novel dangling-bondassisted self-seeding growth mechanism is proposed to describe the growth of V-HfS 2 nanosheets: difficult migration of HfS 2 adatoms on substrate surface results in HfS 2 seeds growing perpendicularly to the substrate; V-HfS 2 nanosheets inherit the growth direction of HfS 2 seeds; V-HfS 2 nanosheets further expand in the in-plane direction with time evolution. Moreover, the V-HfS 2 nanosheets show strong and broadened photons absorption from near infrared to ultraviolet; the V-HfS 2 -based photodetector exhibits an ultrafast photoresponse time of 24 ms, and a high photosensitivity ca. 10 3 for 405 nm laser.

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The ability to detect the full-Stokes polarization of light is vital for a variety of applications that often require complex and bulky optical systems. Here, we report an on-chip polarimeter comprising four metasurface-integrated graphene–silicon photodetectors. The geometric chirality and anisotropy of the metasurfaces result in circular and linear polarization-resolved photoresponses, from which the full-Stokes parameters, including the intensity, orientation, and ellipticity of arbitrarily polarized incident infrared light (1550 nm), can be obtained. The design presents an ultracompact architecture while excluding the standard bulky optical components and structural redundancy. Computational extraction of full-Stokes parameters from mutual information among four detectors eliminates the need for a large absorption contrast between different polarization states. Our monolithic plasmonic metasurface integrated polarimeter is ideal for a variety of polarization-based applications including biological sensing, quantum information processing, and polarization photography.

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Hierarchical MoSe2–CoSe2 nanotubes (MS–CS NTs) are in situ converted from the CoMoO4 nanowires (NWs) via a facile hydrothermal selenization method.

Abstract:For the first time, a facile, ultrafast, ammoniadriven microwave-assisted synthesis of high-quality nitrogen-doped graphene quantum dots (NGQDs) at room temperature and atmospheric pressure is presented. This one-step method is very cheap, environment friendly, and suitable for large-scale production. The as-synthesized NGQDs consisting of one to three graphene monolayers exhibit highly crystalline quality with an average size of 5.3 nm. A new fluorescence (FL) emission peak at 390 nm is observed, which might be attributed to the doped nitrogen atoms into the GQDs. An interesting red-shift is observed by comparing the FL excitation spectra to the UV-visible absorption spectra. Based on the optical properties, the detailed Jablonski diagram representing the energy level structure of NGQDs is derived.

In this article, single-crystalline tetrahedral Ag 3 PO 4 microcrystals with exposed {111} facets was successfully synthesized via a facile wet chemical method. The tetrahedral Ag 3 PO 4 with exposed {111} facets showed the highest photocatalytic activity in visible light irradiation among the {111}, {110} and {100} facets. By DFT calculations, it is demonstrated that the surface energy of the {111} facets is higher than that of the {110} and {100} facets. It was found that the largest band gap of the Ag 3 PO 4 {111} surface is likely to suppress the recombination of electron-hole pairs by exploring the electronic structures of the different surfaces of Ag 3 PO 4 . Meanwhile, the dispersion between the valence bands and conduction bands of the {111} surface is beneficial for the separation of photogenerated electrons and holes on the {111} surface, which further improves the photocatalytic activity of the {111} surface.

For the first time, a porous and conductive CoSe/graphene network (CSGN), constructed by CoSe nanocrystals being tightly connected with each other and homogeneously anchored on few-layered graphene nanosheets, has been synthesized by a facile one-pot solvothermal method. Compared to unhybridized CoSe, CSGN exhibits much faster kinetics and better electrocatalytic behavior for hydrogen evolution reaction (HER). The HER mechanism of CSGN is improved to Volmer-Tafel combination, instead of Volmer-Heyrovsky combination, for CoSe. CSGN has a very low Tafel slope of 34.4 mV/dec, which is much lower than that of unhybridized CoSe (41.8 mV/dec) and is the lowest ever reported for CoSe-based electrocatalysts. CSGN delivers a current density of 55 mA/cm at 250 mV overpotential, much larger than that of CoSe (33 mA/cm). Furthermore, CSGN shows superior electrocatalytic stability even after 1500 cycles. The excellent HER performance of CSGN is attributed to the unique porous and conductive network, which can not only guarantee interconnected conductive paths in the whole electrode but also provide abundant catalytic active sites, thereby facilitating charge transportation between the electrocatalyst and electrolyte. This work provides insight into rational design and low-cost synthesis of nonprecious transition-metal chalcogenide-based electrocatalysts with high efficiency and excellent stability for HER.