The Role of GaN in the Heterostructure WS2/GaN for SERS Applications.

In the application of WS2 as a surface-enhanced Raman scattering (SERS) substrate, enhancing the charge transfer (CT) opportunity between WS2 and analyte is an important issue for SERS efficiency. In this study, we deposited few-layer WS2 (2-3 layers) on GaN and sapphire substrates with different bandgap characteristics to form heterojunctions using a chemical vapor deposition. Compared with sapphire, we found that using GaN as a substrate for WS2 can effectively enhance the SERS signal, with an enhancement factor of 6.45 × 104 and a limit of detection of 5 × 10-6 M for probe molecule Rhodamine 6G according to SERS measurement. Analysis of Raman, Raman mapping, atomic force microscopy, and SERS mechanism revealed that The SERS efficiency increased despite the lower quality of the WS2 films on GaN compared to those on sapphire, as a result of the increased number of transition pathways present in the interface between WS2 and GaN. These carrier transition pathways could increase the opportunity for CT, thus enhancing the SERS signal. The WS2/GaN heterostructure proposed in this study can serve as a reference for enhancing SERS efficiency.

Using Si/MoS2 Core-Shell Nanopillar Arrays Enhances SERS Signal.

Two-dimensional layered material Molybdenum disulfide (MoS2) exhibits a flat surface without dangling bonds and is expected to be a suitable surface-enhanced Raman scattering (SERS) substrate for the detection of organic molecules. However, further fabrication of nanostructures for enhancement of SERS is necessary because of the low detection efficiency of MoS2. In this paper, period-distribution Si/MoS2 core/shell nanopillar (NP) arrays were fabricated for SERS. The MoS2 thin films were formed on the surface of Si NPs by sulfurizing the MoO3 thin films coated on the Si NP arrays. Scanning electron microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy were performed to characterize Si/MoS2 core-shell nanostructure. In comparison with a bare Si substrate and MoS2 thin film, the use of Si/MoS2 core-shell NP arrays as SERS substrates enhances the intensity of each SERS signal peak for Rhodamine 6G (R6G) molecules, and especially exhibits about 75-fold and 7-fold enhancements in the 1361 cm-1 peak signal, respectively. We suggest that the Si/MoS2 core-shell NP arrays with larger area could absorb more R6G molecules and provide larger interfaces between MoS2 and R6G molecules, leading to higher opportunity of charge transfer process and exciton transitions. Therefore, the Si/MoS2 core/shell NP arrays could effectively enhance SERS signal and serve as excellent SERS substrates in biomedical detection.

Using design of experiment for parameter optimization on smart headlamp optics design.

This research focuses on the design of the optical microstructure, and the design of four kinds of light distribution for vehicles' passing beam and driving beam optical structures under the regulation ECE R123. The results show that the passing beam achieves the target light distribution with multiple light patterns superimposed by reflectors, and can meet the four segment light types under the regulations: Class C, Class V, Class E, and Class W. With the structural design method of the reflector, a cutoff line is formed under the structure without a visor to reduce the energy waste caused by the shielding structure, so that the maximum luminosity of the passing beam under the road section can reach 75,980.7 cd and the simulated maximum photometric value can reach 69,705.9 cd under Class W. The driving beam uses the total internal reflection (TIR) lens design to find the optimal 36° angle of the lens to effectively achieve the straightening and brightness enhancement of the light, and then uses the response surface methodology to optimize the optical divergence of the parameters of the microlenticular lens structure on the TIR lens to adjust the width and flatness of the light type. Among them, the radius of curvature, the thickness of the lens, and the length of the single lens are selected as the factors. Using the experimental design method of the reaction surface, the optimal solution of the driving beam design is found. The optimal solution is combined into a radius of curvature of 14.99 mm in the X direction and 25.22 mm in the Y direction, the overall thickness is 1.5 mm, and the length of a single curved surface is 2.43. Each factor is within the limit, and the maximum brightness in the center is 213,866 cd.