Fig. 3
Color change of Pd-PBVE-Pd etalon with varying H2 concentration. a Schematic illustrations of FP etalon prior to (left) and post to (right) the water bubble formation with resultant optical effect. b, c SEM images of the etalon sample. Top-view- (b) and pseudo-colored side view images (c) after focused ion beam milling (red: epoxy coating layer, blue: PBVE). d Simulated reflection color gradient on the FP etalon with different thicknesses of the PBVE, tPBVE. e Photographs of FP etalon on a 4-inch wafer under 10% H2 showing color reversibility at atmospheric condition. f Measured reflection spectra as a function of H2 concentrations (0–10%) at the red-dashed area of e. g Sampled reflection spectra (each color matches to dashed lines in f). h Alteration of an amplitude of reflectance peak while varying H2 concentration. i Repeatability test of FP etalon undergoing H2 exposure for 28 times over 2.5 h. Scale bar in d, 50 nm. Scale bar in c, 200 nm. Scale bar in e, 2 cm