Xiamen University

About: Xiamen University is a education organization based out in Amoy, Fujian, China. It is known for research contribution in the topics: Catalysis & Population. The organization has 50472 authors who have published 54480 publications receiving 1058239 citations. The organization is also known as: Amoy University & Xiàmén Dàxué.

1.06 μm Q-switched ytterbium-doped fiber laser using few-layer topological insulator Bi₂Se₃ as a saturable absorber.

Abstract: Passive Q-switching of an ytterbium-doped fiber (YDF) laser with few-layer topological insulator (TI) is, to the best of our knowledge, experimentally demonstrated for the first time. The few-layer TI: Bi2Se3 (2–4 layer thickness) is firstly fabricated by the liquid-phase exfoliation method, and has a low saturable optical intensity of 53 MW/cm2 measured by the Z-scan technique. The optical deposition technique is used to induce the few-layer TI in the solution onto a fiber ferrule for successfully constructing the fiber-integrated TI-based saturable absorber (SA). By inserting this SA into the YDF laser cavity, stable Q-switching operation at 1.06 μm is achieved. The Q-switched pulses have the shortest pulse duration of 1.95 μs, the maximum pulse energy of 17.9 nJ and a tunable pulse-repetition-rate from 8.3 to 29.1 kHz. Our results indicate that the TI as a SA is also available at 1 μm waveband, revealing its potential as another broadband SA (like graphene).

A facile synthesis of highly luminescent nitrogen-doped graphene quantum dots for the detection of 2,4,6-trinitrophenol in aqueous solution

Abstract: A facile bottom-up method for the synthesis of highly fluorescent nitrogen-doped graphene quantum dots (N-GQDs) has been developed via a one-step pyrolysis of citric acid and tris(hydroxymethyl)aminomethane. The obtained N-GQDs emitted strong blue fluorescence under 365 nm UV light excitation with a high quantum yield of 59.2%. They displayed excitation-independent behavior, high resistance to photobleaching and high ionic strength. In addition to the good linear relationship between the fluorescence intensity of the N-GQDs and pH in the range 2–7, the fluorescence intensity of the N-GQDs could be greatly quenched by the addition of a small amount of 2,4,6-trinitrophenol (TNP). A sensitive approach has been developed for the detection of TNP with a detection limit of 0.30 μM, and a linearity ranging from 1 to 60 μM TNP could be obtained. The approach was highly selective and suitable for TNP analysis in natural water samples.

Synthesis and Characterization of Large-Area Graphene and Graphite Films on Commercial Cu–Ni Alloy Foils

Abstract: Controlling the thickness and uniformity during growth of multilayer graphene is an important goal. Here we report the synthesis of large-area monolayer and multilayer, particularly bilayer, graphene films on Cu–Ni alloy foils by chemical vapor deposition with methane and hydrogen gas as precursors. The dependence of the initial stages of graphene growth rate on the substrate grain orientation was observed for the first time by electron backscattered diffraction and scanning electron microscopy. The thickness and quality of the graphene and graphite films obtained on such Cu–Ni alloy foils could be controlled by varying the deposition temperature and cooling rate and were studied by optical microscopy, scanning electron microscopy, atomic force microscopy, and micro-Raman imaging spectroscopy. The optical and electrical properties of the graphene and graphite films were studied as a function of thickness.

Strain-induced direct–indirect bandgap transition and phonon modulation in monolayer WS2

Abstract: In situ strain photoluminescence (PL) and Raman spectroscopy have been employed to exploit the evolutions of the electronic band structure and lattice vibrational responses of chemical vapor deposition (CVD)-grown monolayer tungsten disulphide (WS2) under uniaxial tensile strain. Observable broadening and appearance of an extra small feature at the longer-wavelength side shoulder of the PL peak occur under 2.5% strain, which could indicate the direct-indirect bandgap transition and is further confirmed by our density-functional-theory calculations. As the strain increases further, the spectral weight of the indirect transition gradually increases. Over the entire strain range, with the increase of the strain, the light emissions corresponding to each optical transition, such as the direct bandgap transition (K-K) and indirect bandgap transition (Γ-K, ≥2.5%), exhibit a monotonous linear redshift. In addition, the binding energy of the indirect transition is found to be larger than that of the direct transition, and the slight lowering of the trion dissociation energy with increasing strain is observed. The strain was used to modulate not only the electronic band structure but also the lattice vibrations. The softening and splitting of the in-plane E’ mode is observed under uniaxial tensile strain, and polarization-dependent Raman spectroscopy confirms the observed zigzag-oriented edge of WS2 grown by CVD in previous studies. These findings enrich our understanding of the strained states of monolayer transition-metal dichalcogenide (TMD) materials and lay a foundation for developing applications exploiting their strain-dependent optical properties, including the strain detection and light-emission modulation of such emerging two-dimensional TMDs.

Synthesis of porous Cu2O/CuO cages using Cu-based metal–organic frameworks as templates and their gas-sensing properties

Abstract: Shape-controllable porous, hollow metal oxide cages are attracting more and more attention due to their widespread applications. In this paper, octahedral, truncated octahedral and cubic Cu2O/CuO cages were successfully fabricated by the thermal decomposition of the polyhedral crystals of Cu-based metal–organic frameworks (Cu-MOFs) as self-sacrificial templates at 300 °C. The morphology of the Cu-MOF polyhedral precursors was well tuned by using lauric acid as the growth modulator under solvothermal conditions. Gas-sensing measurements revealed that the octahedral Cu2O/CuO cages exhibited a gas-sensing performance far better than those exhibited by truncated octahedral and cubic cages, which is attributed to the cooperative effect of the large specific surface area (150.3 m2 g−1) and high capacity of surface-adsorbed oxygen of the octahedral Cu2O/CuO cages.