Fabrication of Stacked Layers of Fine Particle Assembly Aiming at Wavelength-Selective Reflection

Abstract

This study aims to demonstrate that dielectric particles can be stacked to produce electromagnetic functions. By drawing up a hydrophilic substrate from an aqueous suspension in which fine particles are dispersed, monolayer closed-packed or ordered structures can be obtained by utilizing the meniscus attraction between the particles during the drying process. By repeating this process, particles of different sizes and materials can be stacked layer by layer. By changing the permittivity and/or diameters of the particles through layers, the reflectance of light at a particular wavelength can be increased or decreased. Aiming at selective reflection of the near infrared light, silica (SiO2) particles of φ200 nm and titanium oxide (TiO2) particles of φ33 nm were chosen and two layers were stacked on a silicon wafer. The reflectivity was measured with an original setup. Monochromatic light was focused on the sample at various angles of incidence, and the reflection intensity was measured at specified angles independent of the angle of incidence. By scanning the wavelength of the light, the reflection spectrum at specific incident and reflection angles was obtained. It was confirmed that reflectivity increased by 1.7 μm when the TiO2 oxide layer covered the SiO2 layer, as derived from theory.