Dark-line laser.

A laser is meant to emit coherent radiation at a particular wavelength. Here, we demonstrate a laser that is prohibited to emit at a particular wavelength, called a dark line in the emission background of its gain spectrum. Specifically, we installed a 150 µm thick etalon mirror on an ytterbium-doped fiber laser. The laser suffers from 100% loss at the resonance of the etalon and generates a dark line in its emission spectrum. The interplay among the etalon resonance, homogenous gain broadening, and gain competition allows wavelength tuning and multiple-color emission from the laser.

Hollow Few-Layer Graphene-Based Structures from Parafilm Waste for Flexible Transparent Supercapacitors and Oil Spill Cleanup.

We report a versatile strategy to exploit parafilm waste as a carbon precursor for fabrication of freestanding, hollow few-layer graphene fiber mesh (HFGM) structures without use of any gaseous carriers/promoters via an annealing route. The freestanding HFGMs possess good mechanical flexibility, tailorable transparency, and high electrical conductivity, consequently qualifying them as promising electrochemical electrodes. Because of the hollow spaces, electrolyte ions can easily access into and contact with interior surfaces of the graphene fibers, accordingly increasing electrode/electrolyte interfacial area. As expected, solid-state supercapacitors based on the HFGMs exhibit a considerable enhancement in specific capacitance (20-30 fold) as compared to those employing chemical vapor deposition compact graphene films. Moreover, the parafilm waste is found to be beneficial for one-step fabrication of nanocarbon/few-layer graphene composite meshes with superior electrochemical performance, outstanding superhydrophobic property, good self-cleaning ability, and great promise for oil spill cleanup.

Layer Control of Tubular Graphene for Corrosion Inhibition of Nickel Wires.

Corrosion protection of complex surface is an active area of research due to its importance to commercial applications such as electrochemical fabrication. However, conventional coatings exhibit limited conductivity, thermal stability, and durability and are thus not suitable. Recent work has shown the potential of graphene, a two-dimensional carbon allotrope, for corrosion protection. The studies, however, limited themselves to simple planar geometries that provide limited insight in the applicability to relevant morphologies such as mesh electrodes and roughened surfaces. We here study the corrosion protection ability of tubular graphene (TG) on Ni-wires as a model system for such complex geometries. TG-covered Ni wires of approximately 50 µm diameters were produced by the annealing of cellulose acetate (CA) on Ni. The high quality of the TG coating was confirmed by Raman spectroscopy, scanning electron microscopy, and electrical measurements. We show that the graphene layer number could be controlled by adjusting the CA membrane quantity. We found a direct relation between the degree of corrosion inhibition with the variation of graphene layer number. The increase of graphene layers on a Ni surface could enhance its corrosion inhibition in acidic, basic, and marine environments, which shows the potential of our approach for future applications.

Macroscopic, freestanding, and tubular graphene architectures fabricated via thermal annealing.

Manipulation of individual graphene sheets/films into specific architectures at macroscopic scales is crucially important for practical uses of graphene. We present herein a versatile and robust method based on annealing of solid carbon precursors on nickel templates and thermo-assisted removal of poly(methyl methacrylate) under low vacuum of ∼0.6 Pa for fabrication of macroscopic, freestanding, and tubular graphene (TG) architectures. Specifically, the TG architectures can be obtained as individual and woven tubes with a diameter of ∼50 µm, a wall thickness in the range of 2.1-2.9 nm, a density of ∼1.53 mg·cm(-3), a thermal stability up to 600 °C in air, an electrical conductivity of ∼1.48 × 10(6) S·m(-1), and field emission current densities on the order of 10(4) A·cm(-2) at low applied electrical fields of 0.6-0.7 V·µm(-1). These properties show great promise for applications in flexible and lightweight electronics, electron guns, or X-ray tube sources.