Naifei Ren

Broadband visible-light absorber via hybridization of propagating surface plasmon.

We demonstrate a broadband visible-light absorber based on excitation of multiple propagating surface plasmon (PSP) resonances. The simple structure is constructed of continuous gold/silica multi-layers covered by a one-dimensional gold grating. The broadening of bandwidth arises from the inter-layer hybridization and spectral superposition of PSPs, which is predicted with the analytical coupled oscillator model and validated using the RCWA simulation. The average absorption increases with the number of gold/silica pairs and exceeds 95% over the whole visible spectrum when only five pairs are included. Moreover, results show that the absorption can be further enhanced by grading the thickness of silica layers. The presented design might enable promising applications in the fields of photovoltaic cells and thermal emitters, owing to its advantages of wideband, near-unity absorption and simple fabrication simultaneously.

Reducing the pump power of optically controlled terahertz metamaterial via tailoring the resistance of the silicon gap region

Optically tunable metamaterials provide an ultrafast and active manipulation of terahertz wave. We demonstrate a strategy to alleviate the tradeoff between the requirement of low optical pump power and the achievement of significant resonance modulation in the photoexcited metamaterials. We have shown that the resonance strength of split-ring resonator metamaterial is determined by the resistance of its silicon gaps. By reducing the resistance through geometry adjustment of the gap region, the needed photoconductivity and hence the pump power can be substantially reduced without deteriorating the resonance tuning effect. The presented design rule may offer an avenue to realize low-power optically tunable terahertz devices.

Initial dislocation density effect on strain hardening in FCC aluminium alloy under laser shock peening

Abstract The effect of initial dislocation density on subsequent dislocation evolution and strain hardening in FCC aluminium alloy under laser shock peening (LSP) was investigated by using three-dimension discrete dislocation dynamics (DD) simulation. Initial dislocations were randomly generated and distributed on slip planes for three different dislocation densities of 4.21 × 1012, 8.12 × 1012 and 1.26 × 1013 m−2. Besides, variable densities of prismatic loops were introduced into the DD cells as nanoprecipitates to study the dislocation pinning effect. The flow stresses as a function of strain rate obtained by DD simulation are compared with relevant experimental data. The results show a significant dislocation density accumulation in the form of dislocation band-like structures under LSP. The overall yield strength in FCC aluminium alloy decreases with increasing initial dislocation density and forest dislocation strengthening becomes negligible under laser induced ultra-high strain rate deformation. In addition, yield strength is enhanced by increasing the nanoprecipitate density due to dislocation pinning effect.

Broadening of absorption band by coupled gap plasmon resonances in a near-infrared metamaterial absorber

We propose a strategy to broaden the absorption band of the conventional metamaterial absorber by incorporating alternating metal/dielectric films. Up to 7-fold increase in bandwidth and ~95% average absorption are achieved arising from the coupling of induced multiple gap plasmon resonances. The resonance coupling is analytically demonstrated using the coupled oscillator model, which reveals that both the optimal coupling strength and the resonance wavelength matching are required for the enhancement of absorption bandwidth. The presented multilayer design is easily fabricated and readily implanted to other absorber configurations, offering a practical avenue for applications in photovoltaic cells and thermal emitters.

SUNKEN HOLLOW CARBON SPHERES SUPPORTED Pt ELECTROCATALYST FOR EFFICIENT METHANOL OXIDATION AND OXYGEN REDUCTION REACTION

Sunken hollow carbon spheres (SHCs) are prepared by using glucose as carbon source and polystyrene spheres (PSs) as templates. Pt particles are then loaded on the SHCs as electrocatalyst and used for catalyzing both methanol oxidation and oxygen reduction reaction (ORR) in acidic media. Physical measurements show that the SHCs are formed due to sinking of hollow carbon spheres. It can be imagined that the SHCs have the similar specific surface area as hollow carbon spheres with reduced volume. Moreover, the SHCs have high surface area (786.3 m2 ⋅ g-1) with hollow and sunken structure are beneficial for the uniform dispersion of the noble metal particles and efficiently improve the mass transfer in catalytic reactions. The cyclic voltammogram measurements show that the current densities on Pt/SHC electrocatalyst are 2.1 times ) that on commercial Pt/C for methanol oxidation and 1.5 times () that on Pt/C for ORR at the same Pt loadings, being promising candidate for fuel cell electrocatalyst.