To improve the drawback of surface-enhanced Raman scattering (SERS) sensors that are sensitive to excitation angles and realize the monitoring of contaminants in complex environments, we have proposed and prepared a cascaded wire-in-cavity-in-bowl (WICIB) structure on flexible polydimethysiloxane, with feasibility for plasmonic coupling. We demonstrated that the WICIB structure can serve as a highly sensitive, homogeneous, and stable SERS substrate for conventional detection. The plasmonic coupling and distribution of the enhanced electromagnetic field were evidently proven by finite element simulations, and the strong electromagnetic field was regulated around the wire and inside the cavity, which is very beneficial for the polydirectional and in situ detection. By virtue of the triple synergistic enhancement effect and unique optical properties, we successfully achieved the in situ detection of the residual pollutant molecules, ziram and 2-naphthalenethiol, in microdroplets of apple juice and lake water. Accordingly, such a flexible SERS sensor exhibits great potential in on-site environmental monitoring.
Micro-structural characteristics and electrical properties of an n-type GaN epilayer on Al2O3 irradiated by 290-MeV 238U32+ ions to various fluences were investigated using atomic force microscopy (AFM), scanning electron microscopy (SEM), high-resolution X-ray diffraction (HRXRD), and Raman scattering spectroscopy. AFM images show that the nano-hillocks generated, and the diameter and density of the nano-hillocks, increase obviously with increasing ion fluence, accompanied by an increase in surface roughness. SEM images display that the Al, O, and C elements appear on the GaN surface, along with a spiral-like, layered volcanic-cone structure formed at the highest-fluence irradiation. HRXRD reveals that the dislocation density increases, as the lattices gradually expand, and that Ga2O3 was produced with increasing ion fluence. Raman scattering spectra show that no N and Ga vacancies were produced, the free-carrier concentration decreases, while its mobility first increases and then exhibits a significant reduction with increasing ion fluence.
The effect of temperature on the evolution of loops in nickel was investigated under 30 keV He+ irradiation. The size, Burgers vector, and nature of loops were analyzed by a transmission electron microscope (TEM). In addition, the Weibull statistical analysis was introduced to analyze the size distributions of the loops. The TEM results indicate that the sizes of loops increase with increasing irradiation temperature, where they are mainly in the range of 10–30, 20–50, and 30–80 nm at 300, 400, and 500 °C, respectively. In the irradiation temperature range of 300–500 °C, the size distributions of loops fit Weibull distribution very well, which suggests that the loops tend to grow larger and/or be merged. In addition, almost all the loops formed under He+ irradiation are the interstitial loops with Burgers vectors b = a2⟨110⟩, which is ascribed to the assistance of the He atom on the formation process of loops.
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