Home > Business > Advanced functional materials: topology optimization reverse design of "heart to heart" metal structure to achieve near-field enhancement maximization

Advanced functional materials: topology optimization reverse design of "heart to heart" metal structure to achieve near-field enhancement maximization

wallpapers Business 2020-08-25 >

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Recently Professor Deng Yongxin Associate Professor Duan Yongyuan from the Institute of urban science technology of China Southern University of science technology have used the method of "he beam optimization" Nonlinear optical experiments were carried out to verify the 5 nm structure. The work is entitled "topology optimization based inverse design of plasma nanodimer with maximum near field enhancement" published in the international academic journal advanced functional materials (DOI: 10.1002 / ADFM. 202000642). Background of

the large near-field enhancement of plasmon resonance of

can greatly enhance the light matter interaction of metal nanostructures. Among them the near-field enhancement factor is the most important parameter to measure the properties of plasmon nanostructures. Therefore the design fabrication of plasmon nanostructures with the largest near-field enhancement factor has always been an important research goal in this field. In the past researchers often introduce the tip optimize the structure arrangement narrow the gap to achieve the maximum near-field enhancement such as bow structure fan structure. However this kind of empirical structural design is like looking for a needle in a haystack which limits the further improvement of near-field enhancement of plasmon nanostructures.

recently Professor Duan HuiGao's team of Hunan University together with associate professor Lei dangyuan of City University of Hong Kong associate researcher Deng Yongbo of Changchun Institute of Optics machinery of Chinese Academy of Sciences Professor Cheng Xin of Southern University of science technology used topology optimization method to reverse design the plasmon dimer structure with the largest near-field enhancement factor. Interestingly the final structure is a dimer structure of two loving hearts. Through the electromagnetic simulation analysis the maximum near-field enhancement factor can be obtained which is the performance of the maximum charge density in the gap structure. In order to carry out the experimental verification the cooperative research team successfully processed the "heart to heart" structure with a gap of 5 nm by using the high-resolution focused helium ion beam line tracing contour processing technology. Surface enhanced Raman spectroscopy (SERS) two-photon fluorescence (TPF) were used to characterize the structure.

1. The accidental generation of "heart to heart" structure topology optimization algorithm of

as a reverse design method can optimize graphics driven by data or function. According to the geometric symmetry of the dimer structure the objective function is the field enhancement factor at the center of the optimization domain. At the beginning of optimization the whole optimization domain is a vacuum homogeneous region. With the iteration of optimization calculation the dielectric constant of each grid cell changes between vacuum gold the objective function converges gradually. When the enhancement factor at the center of two adjacent structures is less than the preset error the optimization program will stop iteration output the final figure otherwise the iterative calculation will continue. Interestingly the final optimized figure is the love structure of two opposite points which truly reflects the "heart to heart" in order to maximize the field strength. Compared with the traditional simple geometry dimer structure (such as nanorod nano disk nano prism dimer etc.) the reverse design of the love dimer does show a higher near-field enhancement factor. At the same time through further simulation analysis the higher charge density at the tip is the main factor to achieve higher near-field enhancement as shown in Fig. 1 (c).

figure 1. (a) the program diagram of reverse design of near-field enhanced maximum dimer structure based on topology optimization algorithm; (b) the evolution curve of the maximum field enhancement factor with the number of iterations in the process of topology optimization with the goal of maximum near-field enhancement; (c) the evolution curve of the maximum charge density

2 The "heart to heart" structure optimized by

requires extremely high precision profile minimal nano gap which poses a great challenge to traditional nano machining. In order to solve this problem we used the high resolution helium ion microscope (him) the sketch peel lithography developed by Hunan University in 2016 to "carve" the contour of the "heart to heart" structure with high fidelity successfully obtained the 5 nm plasmon gap. As shown in Fig. 2 (a) focused helium ion beam depicts the outline of "heart to heart" structure on the pre deposited gold nano film then selectively removes the gold film outside the structure outline through tape stripping so as to retain the structure inside the outline.
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