Objective With the rapid development of modern electronic devices toward higher frequency and greater integration, electromagnetic compatibility (EMC) issues have become increasingly prominent, and the demand for high-performance transparent electromagnetic shielding materials has become more urgent. Gold (Au) films, known for their excellent electrical conductivity and outstanding chemical stability, are an ideal choice for fabricating high-performance transparent electromagnetic shielding devices. However, their high cost significantly restricts large-scale application. This study aims to systematically investigate the regulatory mechanism of gold film thickness (28 nm to 110 nm) on its microstructure and electrical properties, establish a complete research framework of "process parameters - microstructure - macroscopic performance - engineering application," determine the optimal thickness parameter, and based on this, design and fabricate high-performance metal mesh grid electromagnetic shielding windows providing theoretical basis and practical guidance for the development of high-performance transparent electromagnetic shielding materials.

Methods This study employed a high-precision magnetron sputtering system to prepare four characteristic gold film samples with thicknesses of 28 nm, 48 nm, 65 nm, and 110 nm under strictly controlled process parameters (base vacuum better than 5×10⁻⁴ Pa, working pressure 0.5 Pa, sputtering power 220 W). The crystal structure and preferred orientation of the films were systematically analyzed using an X-ray diffractometer (XRD), and the grain size evolution was analyzed using the Scherrer formula. The reflection characteristics of the films in the 300 nm to 2500 nm wavelength range were measured using UV-Vis-NIR spectrophotometry and Fourier transform infrared spectroscopy, and the optical constants were theoretically fitted and analyzed based on the Drude-Lorentz model. The resistivity and mobility of the films were measured using a Hall effect measurement system, and the thickness dependence of electrical properties was deeply analyzed using the Fuch-Sondheimer (F-S) model and Mayadas-Shatzkes (M-S) model. Based on the systematic research results of material properties, combined with microwave transmission line theory and equivalent circuit model, a metal mesh structure with specific geometric parameters (line width 2 μm, period 100 μm) on a quartz glass substrate was optimally designed. The device was fabricated using standard micro-nano fabrication processes (including ultraviolet lithography, magnetron sputtering, and lift-off processes). Finally, the electromagnetic shielding effectiveness of the fabricated metal mesh window in the 8-18 GHz frequency band was measured using a signal generator and signal spectrum analyzer.

Results and Discussions The results show that the microstructure, optical properties, and electrical properties of the gold films exhibit significant thickness dependence. In terms of microstructure, as the film thickness increased from 28 nm to 110 nm, XRD analysis indicated that the (111) plane diffraction peak intensity significantly enhanced, and the grain size calculated using the Scherrer equation systematically increased from 21 nm to 71 nm, an increase of approximately 3.4 times, indicating a significant improvement in the crystallinity quality and continuity of the films (Fig.1). In terms of optical properties, systematic testing showed that as the thickness increased, the reflection characteristics of the gold films in the visible to infrared range significantly improved (Fig.2). Drude-Lorentz model fitting results indicated that the optical constants of thicker gold films are closer to those of ideal bulk gold material, and the extinction coefficient increased with thickness, indicating more light absorption (Fig.4). Skin depth analysis showed that thicker gold films (e.g., 110 nm) have larger skin depths in the short-wavelength region, enabling more effective restriction of electromagnetic wave penetration. In terms of electrical properties, Hall test results showed that the resistivity significantly decreased from 5.9 μΩ·cm to 2.9 μΩ·cm, approaching the resistivity level of bulk gold material. Meanwhile, the carrier mobility increased from 8.8 cm²·V⁻¹·s⁻¹ to 23.2 cm²·V⁻¹·s⁻¹ (Fig.7). F-S and M-S model analysis determined that the electron mean free path of gold is λ₀=38.03 nm, the surface scattering coefficient p=0.22, and the grain boundary reflection coefficient R=0.38. Theoretical analysis showed that as the film thickness increases, the effects of both grain boundary scattering and surface scattering on film resistivity rapidly decrease, with the weight of electron-grain boundary scattering always greater than that of electron-surface scattering. The correlation analysis between grain size and electron mobility confirmed that increasing grain size can effectively reduce grain boundary scattering, thereby improving electron mobility. Results from electromagnetic shielding performance tests show that the metal mesh grid windows fabricated with the optimized thickness (110 nm) exhibit excellent shielding performance across the entire frequency range of 8 GHz to 18 GHz. The measured shielding effectiveness ranges from 21 dB to 30 dB (Fig.11), fully meeting the design requirement of exceeding 20 dB.

Conclusions Through systematic experimental research and theoretical analysis, this study clarified that gold film thickness affects its optoelectronic properties by regulating the microstructure. Optical performance analysis showed that increasing thickness significantly improves reflection characteristics in the visible to infrared range while enhancing the material's skin effect. Electrical performance analysis, based on the F-S and M-S models, deeply revealed the dominant role of grain boundary scattering in the electrical properties of the films. The study identifies 110 nm as the optimal thickness of gold thin films that balances high performance and cost-effectiveness. At this thickness, the gold thin films exhibit excellent optical characteristics, electrical conductivity, and structural stability. The innovation of this study lies in establishing a complete relationship map of gold film thickness-structure-optical properties–electrical properties, deeply revealing the physical mechanisms of optoelectronic property changes using the Drude-Lorentz model and F-S and M-S theoretical models, and organically combining material-level optimization research with device-level engineering design to successfully achieve the preparation and verification of high-performance electromagnetic shielding windows.