結構色可透過微奈米結構與光之間的干涉、散射或共振作用產生顏色，不需依賴傳統染料或顏料。本研究以鎵奈米顆粒、稀釋聚二甲基矽氧烷（polydimethylsiloxane， PDMS）薄膜與矽基板組成反射式 Fabry–Pérot cavity，探討 PDMS 膜厚與鎵奈米顆粒尺寸對減色式結構色之影響。實驗透過改變 PDMS 稀釋比例與鎵蒸鍍厚度調整結構參數，並結合反射光譜量測、CIE 1931 色度分析與時域有限差分法模擬，分析其光譜與色彩表現。 結果顯示，PDMS 厚度改變會使反射光譜中的特徵谷值產生位移，進而帶動色度座標移動；鎵奈米顆粒尺寸則會影響反射谷深度、頻寬及色度分布範圍。模擬與實驗結果皆顯示，25 nm 鎵奈米顆粒具有較佳的光譜選擇性與減色式色彩表現。在電場強度分布顯示，光場除分布於 PDMS 腔體內，也集中於鎵奈米顆粒周圍，說明腔體干涉與顆粒的局域光學響應共同參與反射光譜的形成。以 sRGB 色域作為基準計算色彩覆蓋率時，25 nm 樣品之實驗色彩覆蓋率約為 38.87%，高於 10 nm 與 40 nm 樣品，且與模擬結果呈現相同的尺寸變化趨勢。整體而言，鎵奈米顆粒結合可調厚度 PDMS 介電層可形成具有色彩調控能力的反射式 Fabry–Pérot cavity，並提供不同於連續金屬薄膜的結構色設計方式。;Structural colors are generated through interference， scattering， or resonance between light and micro- or nanoscale structures without relying on conventional dyes or pigments. In this study， a reflective Fabry–Pérot cavity composed of gallium nanoparticles， a diluted polydimethylsiloxane (PDMS) film， and a silicon substrate was developed to investigate the effects of PDMS thickness and nanoparticle size on subtractive structural colors. Reflectance spectroscopy， CIE 1931 chromaticity analysis， and finite-difference time-domain (FDTD) simulations were used to evaluate the optical and color characteristics. The results show that PDMS thickness shifts the reflectance dips and corresponding chromaticity coordinates， while nanoparticle size affects the dip depth， bandwidth， and chromaticity distribution. Both simulations and experiments indicate that the 25 nm nanoparticles provide better spectral selectivity and subtractive color performance. Electric-field distributions show optical fields within the PDMS cavity and around the nanoparticles， indicating contributions from both cavity interference and local nanoparticle responses. Relative to the sRGB gamut， the 25 nm sample achieved an experimental color coverage of approximately 38.87%， higher than those of the 10 and 40 nm samples. These results demonstrate a tunable reflective structural-color design that differs from conventional continuous-metal-film cavities.
