Microwave-assisted Hydrothermal Synthesis of Carbon Materials with Tunable Microstructure

A facile microwave-assisted hydrothermal route has been developed for a synthesis of versatile carbon materials. The monosaccharide fructose aqueous solution was adopted as the starting material, and the p H of the solution was adjusted to be in acidic（pH 4）, neutral（pH 7） and basic（pH 10.5） conditions. The p H buffered fructose solutions were treated at different temperatures by a microwave-assisted hydrothermal technique. As-prepared carbon materials displayed p H and temperature dependent multi-morphologies（porous, spherical or core-shell）, which were determined by transmission and scanning electron microscopic analyses（TEM and SEM）. And the hypothesis of dehydration mechanism of hydrothermal synthesis was analyzed by ultraviolet extinction and Fourier transform infrared spectroscopy. It was found that as compared with normal hydrothermal synthesis, microwave assistance could efficiently increase the production yield and improve the spherical geometry of the carbon particles in neutral condition. By changing the p H of the system, acidic p H induces aggregation of the spheres, while basic p H produces more trends toward core-shell or sponge-like porous structure. The study opens a novel route to the production of polytropic carbon materials and suggests a potential niche market established from the green synthesis.

Tunable near-infrared plasmonic perfect absorber based on phase-change materials

A tunable plasmonic perfect absorber with a tuning range of 650 nm is realized by introducing a 20 nm thick phase-change material Ge2Sb2Te5 layer into the metal–dielectric–metal configuration.The absorption at the plasmonic resonance is kept above 0.96 across the whole tuning range.In this work we study this extraordinary optical response numerically and reveal the geometric conditions which support this phenomenon.This work shows a promising route to achieve tunable plasmonic devices for multi-band optical modulation,communication,and thermal imaging.

Controllable optical activity of non-spherical Ag and Co SERS substrate with different magnetic field

We experimentally fabricate a non-spherical Ag and Co surface-enhanced Raman scattering（SERS） substrate, which not only retains the metallic plasmon resonant effect, but also possesses the magnetic field controllable characteristics.Raman detections are carried out with the test crystal violet（CV） and rhodamine 6G（R6G） molecules with the initiation of different magnitudes of external magnetic field. Experimental results indicate that our prepared substrate shows a higher SERS activity and magnetic controllability, where non-spherical Ag nanoparticles are driven to aggregate effectively by the magnetized Co and plenty of hot-spots are built around the metallic Ag nanoparticles, thereby leading to the enhancement of local electromagnetic field. Moreover, when the external magnetic field is increased, our prepared substrate demonstrates excellent SERS enhancement. With the 2500 Gs and 3500 Gs（1 Gs = 10^（-4）T） magnetic fields, SERS signal can also be obtained with the detection limit lowering down to 10^（-9）M. These results indicate that our proposed magnetic field controlled substrate enables us to freely achieve the enhanced and controllable SERS effect, which can be widely used in the optical sensing, single molecule detection and bio-medical applications.