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By deviating the nanodisk from the center in the silver nanocrescent/nanodisk structure, we find that the dipole, quadrupole and octupole modes can all induce very high local electric field enhancement (LFE, more than 750) for the coupling of nanocrescent and crescent gap modes, which makes the resonant wavelengths of the non-concentric nanostructures change from the visible to near infrared regions. In addition, the LFE factor of the quadrupole mode is more than 1000, which is suitable for single molecular detection by local surface enhanced spectroscopy.

In this paper, we propose two kinds of composite structures based on the one- and two-dimensional (1D&2D) gold grating on a gold film for plasmonic refractive index sensing. The resonance modes and sensing characteristics of the composite structures are numerically simulated by the finite-difference time-domain method. The composite structure of the 1D gold semi-cylinder grating and gold film is analyzed first, and the optimized parameters of the grating period are obtained. The sensitivity and figure of merit (FOM) can reach 660RIU/nm and 169RIU−1, respectively. Then, we replace the 1D grating with the 2D gold semi-sphere particles array and find that the 2D grating composite structure can excite strong surface plasmon resonance intensity in a wider period range. The sensitivity and FOM of the improved composite structure can reach 985RIU/nm and 298 RIU−1, respectively. At last, the comparison results of the sensing performance of the two structures are discussed. The proposed structures can be used for bio-chemical refractive index sensing.

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This paper presents a theoretical demonstration of diverse microstructure fabrication by changing the angle of incidence of a six-beam laser interference lithography system. Different combinations are formed with transverse electric (TE) and transverse magnetic (TM) polarizations and various microstructures are simulated by controlling the high-reflectivity mirror group to adjust the incidence angle. This study indicates that the incidence angle has a considerable influence on the shape and period of the lattice, thereby contributing to the fabrication of microstructures with different arrangements. These structures include donut, circle, D-type, rectangular, triangular, U-type, and honeycomb lattices. The six-beam laser interference lithography technique is expected to benefit microstructure fabrication because of its simple operation, large writing area, and low cost, thereby promoting the development of micro-optics.