Ultra-wideband UV Absorber Based on Rhodium Metal and Silica Materials

Objective The principal method currently employed by researchers to prevent damage to the human body and materials from ultraviolet (UV) radiation involves chemical protection strategies. With the development of metamaterials and nanotechnology, physical methods have been developed for protection against ultraviolet radiation. UV absorbers based on artificial microstructures can be used to absorb UV radiation and exhibit important applications in UV detection, sensing, and protection. Owing to limitations in materials and manufacturing processes, research on UV absorbers is relatively slow. Therefore, improved surface plasma materials and processes are sought to improve the absorption of UV absorbers. Metallic rhodium (Rh) is an excellent surface plasmon material. Compared with other noble metals, the surface of Rh can excite surface plasmon polaritons (SPPs) and exhibits a strong surface plasmon response in the UV band. Rh exhibits excellent stability in various environments. In this study, a UV absorber is designed using Rh metal and dioxide (SiO2) material to absorb ultraviolet radiation.Methods The unit structure of the UV absorber designed in this study consists of a Rh substrate, SiO2 dielectric layer, and Rh pattern layer. The finite element method (FEM) is used to analyze the dependence of the absorption characteristics of the absorber on the incident wavelength, incidence angle, azimuth angle, and geometrical structure parameters. Using the Comsol Multiphysics 5.4 software for modeling, the incident/reflection ports are set above the unit structure, the transmission ports are set below the unit structure, and the periodic boundary conditions are set in the horizontal direction of the unit structure. The field distribution is obtained by simulating the interaction between the incident ultraviolet radiation and absorber. The absorptivity and relative impedance are obtained from the reflection and transmission coefficients, respectively.Results and Discussions The optimal structural parameters of the absorber designed in this study are as follows: the unit period p=340 nm, the height of the Rh metal substrate h1=150 nm, the height of the SiO2 dielectric h2=30 nm, the height of the upper Rh pattern h3=90 nm, the distance between the Rh pattern layer and boundary of the unit structure t=60 nm, the spacing between the Rh pattern layers s=50 nm, the radius of the large cylindrical cavity R=90 nm, the radius of the small cylindrical cavity r=18 nm, and the distance between the axis of symmetry of the small cylindrical cavity and the axis of symmetry of the unit structure d=120 nm. As shown in Fig. 3, the absorber can realize an absorptivity exceeding 90% in the wavelength range of 200 -400 nm. In the wavelength ranges of 250-300 nm and 325-400 nm, the absorptivity exceeds 95%. Broadband absorption can be realized from the near -UV to the far -UV band. Figure 4 shows contour plots of the absorptivity as a function of the incident angle and incident wavelength, with Fig. 4(a) and (b) showing the transverse -magnetic (TM) and transverse electric (TE) waves, respectively. As shown in Fig. 4(a), when the incident angle is in the range of 0 degrees-45 degrees and wavelength in the range of 200-400 nm, the average absorptivity of the TM wave after incidence can reach approximately 90%. As shown in Fig. 4(b), the TE wave can realize the absorptivity of approximately 90% on average when the incident angle range is 0 degrees-45 degrees and wavelength range is 200-400 nm. As shown in Fig. 4(c), the absorption of the absorber is largely unaffected by the azimuth angle of the input wave. The electric and magnetic field distributions in the x- y, x- z, and y- z planes for the TM and TE waves incident vertically at the peak wavelengths are shown in Figs. 5 and 6, respectively. Figure 7 shows the relative impedance of the absorber as a function of the wavelength. This indicates that the relative impedance of the absorber matches the value of the relative wave impedance in free space. Furthermore, Fig. 8 shows the effects of the structural parameters on the absorptivity of the TM waves when the incidence angle is 0 degrees.Conclusions In this study, an ultraviolet ultra -broadband absorber based on Rh metal and SiO2 dielectric materials is designed. The cell structure comprises a Rh metal substrate, SiO2 dielectric plate, and Rh metal pattern layer. The finite element method analysis results show that the UV absorber realizes absorption via the surface plasmon resonance effect. The absorption characteristics of the absorber can be adjusted by varying the individual parameters of the cell structure. Owing to the rotational symmetry of the structure, the absorber is polarization insensitive. With the optimized structural parameters corresponding to p=340 nm, t=60 nm, s=50 nm, R=90 nm, r=18 nm, d=120 nm, h1=150 nm, h2=30 nm, and h3=90 nm, an average absorptivity exceeding 90% can be realized in the incident angle range of 0 degrees-45 degrees and wavelength range of 200-400 nm. In the wavelength ranges of 250-300 nm and 325-400 nm, the absorptivity exceeds 95%. The ultraviolet ultra -broadband absorber designed in this study exhibits excellent absorption performance, and it is expected to be widely used in the fields of UV detection, UV sensing, and UV protection.