Surface of Mid-Infrared Composite Grid Antireflection Micro-Nanostructure

Objective The advancement of micro-nanostructures has gained significant traction owing to their superior broadband antireflective attributes, which span a broad range of incident angles. This progress has expanded their application in photocells and photodetectors. However, these structures often possess subwavelength structural characteristics and high aspect ratio to manage the wavefront distortion of the target light field. The diminutive size and high aspect ratio of these periodic structural units make their surface susceptible to environmental damage, thereby affecting their optical performance. This paper proposes an antireflective micro-nanostructure surface with a composite grid structure. This innovative approach enhances the mechanical stability and longevity of the micro-nanostructure surface without altering its original design and optical properties. Methods We successfully proposed and fabricated an antireflection micro-nanostructure surface with a composite grid. This involved constructing a silicon oxide composite grid on a silicon substrate to protect the internal micro-nanostructural units. The optical and mechanical properties of the composite grid structure were optimized using appropriate material selection, morphological characterization, and size parameters. Moreover, the stress distributions of the three types of grid structure under a fixed load were analyzed using finite element analysis software. Based on the results of this theoretical analysis, the hexagonal composite grid antireflection micro-nanostructure was successfully fabricated by a combination of photolithography and etching technology. Furthermore, its morphology was evaluated using a scanning electron microscope (SEM), while a spectrometer measured its optical reflectivity. Lastly, an adhesive tape test was used to examine the sample surface and discuss the protective capacity of the composite grid for the antireflection micro-nanostructure. Results and Discussions The optical reflectivity test shows an average reflectivity difference of 0.068% between the antireflection micro-nanostructure surface attached to a composite grid and standalone micro-nanostructure [Fig. 17(a)]. This result suggests that the grid structure has negligible impact on the micro-nanostructure's optical performance. The average reflectivity of the composite grid antireflection micro-nanostructure surface in the 3-5 mu m frequency band is less than 4% for incident angles in the range of 8 degrees-40 degrees, demonstrating stable antireflection performance [Fig. 17(b)]. The adhesive tape test on the composite grid antireflection micro-nanostructure confirms the effective maintenance of the micro-nanostructure (Fig. 21) with no substantial change in its antireflection performance [Fig. 23(a)]. In contrast, the surface of the micro-nanostructure without grid is damaged and its reflectivity is increased by 1.5% after the tape test [Fig. 22 (b)]. These results validate the grid structure's protective role without altering the optical properties of the micro-nanostructure. Conclusions This study presents a successful fabrication of antireflection micro-nanostructure surface with composite grid by a combination of photolithography and etching. This design offers robust antireflection performance in the mid-infrared range across a wide incident angle. SEM is used to confirm the morphology of the antireflection micro-nanostructure surface with composite grid, showing structural parameters that closely resemble those of the simulation parameters. The Scotch 3M tape test is used to compare the antireflection micro-nanostructure surface with composite grid and single micro-nanostructure surface. The results indicate that the grid-structured antireflection micro-nanostructure surface maintains its original morphology and antireflection performance even after the tape test. Conversely, the micro-nanostructure surface without grid sustains damages, exhibiting a 1.5% increase in its reflectivity post-test. These findings reveal the grid structure's mechanical protective ability for the micro-nanostructure, improving its optical and mechanical properties. These advancements can propel future research and development of micro-nanostructures for optical and optoelectronic devices.