Heterostructured CuO@ZnO@Ag biomimetic setaria as wettability-switchable difunctional SERS substrate for trace pesticide and DNA detections

Wettability modification is an effective way in tailoring hotspots in surface Raman scattering (SERS) nowadays. However, due to the theoretical contradiction between hydrophobic and hydrophilic strategies, opposite views are usually put forward in building SERS structures. To realize the integration of hydrophobicity and hydrophilia in the same substrate, a wettability-switchable SERS architecture composed of heterostructured CuO@ZnO@Ag biomimetic nano Setaria (NS) has been designed and prepared in this paper. Experimentally, the structure shows impressive SERS performance under both hydrophobic and hydrophilic states. The limit of detection approaches even to single-molecule level and the lowest relative standard deviation is only ca 9.8%. Finite-different time-domain simulations and experimental analyses were systemically made to unearth the mechanism deep behind. Besides, owing to fine quantifiability, the CuO@ZnO@Ag NS shows promising potential in the detection of trace pesticide and deoxyribonucleic acid. This work provides a new idea for integrating the strategies of ‘concentration’ and ‘decentralization’, endowing SERS structure with wider application, and is also meaningful for other surface sciences.

The Application of Two Dimensional Numerical Simulation Method of Ground Penetrating Radar in Concrete Dam Nondestructive Testing

electromagnetic wave theory was used by ground penetrating radar, the defects in concrete dams were judged according to the measured concrete reflection waveform, frequency and wave velocity. The working principle of ground penetrating radar and numerical simulation process based on the finite different time domain method were studied, cracks, voids images in concrete was forward simulated by the above method. It was important to determine the quality defects in concrete.

FROZEN MODE IN PHOTONIC CRYSTAL WAVEGUIDE

We propose a structure of 2D photonic crystal waveguide composed of hexagonal lattices of air holes in high index materials. Frozen mode regime can be observed within the photonic band gap. Light incident into the waveguide is coupled into two modes. One mode has enhanced amplitude and the other one has slow group velocity. Finite-different time-domain (FDTD) simulation is used to demonstrate the propagation of the slow mode.

Research on the 1.06 μm Reflectivity of Subwavelength Surface-Relief Structure via Finite Different Time Domain Method

In this paper, setting 1.06 μm Gaussian modulated pulse electromagnetic wave as irradiation sources, the influences of structural parameters on reflectivity are analyzed by finite different time domain (FDTD) method. The results show that the filled factor and height are key factors for circular tube relief structure with non absorption. The optimal height could be set to 0.2 μm, which is one odd time of the ratio of incident wavelength λ and four equivalent refractive index 4N, then the best filled factor is between 0.7 and 0.9, the ratio of inner and outer diameter could be set between 0.4 and 0.6, and the structure period has little significant influence. Compared with cylinder solid structure, it has been discovered that circular tube hollow structure could weaken the backward energy of electromagnetic wave, and it would be more suitable for antireflection structure than solid cylinder structure. Moreover, we design two another circular tube relief structures simulations with different extinction coefficients, it is found that the reflectivities are lower up to 0.00016% than the non absorption one.