Fig. 1. Characterization of experimental results. (a) Pd nanoparticle colloidal solution and corresponding normalized UV spectra; (b) Schematic diagram for the preparation of self-assembled sample films of Pd nanoparticles; (c) Transmission and reflection microscope photos of sample films; (d) SEM image of the sample film

Fig. 2. Optical characterization and specific surface area of superlattice thin films of Pd nanoparticles. (a) Normalized transmission spectra (solid lines) and numerically calculated transmission spectra (dashed lines) obtained from the testing of superlattice thin films with different numbers of layers; (b) Variation of specific surface area of dense films and Pd nanoparticle films with particle size

Fig. 3. Effect of atomic ratio of H/Pd on transmission spectra of 13-layer Pd nanoparticle films. (a) Calculated transmission spectra of 13-layer Pd nanoparticle film with different atomic ratios of H/Pd, where the particle diameter is 10 nm and the spacing is 2 nm; (b) Change in the transmission spectra under different atomic ratios of H/Pd; (c) Variation values of the transmission intensity of the Pd nanoparticle film at a wavelength of 774 nm under different atomic ratios of H/Pd

Fig. 4. Effect of atomic ratio of H/Pd on transmission spectra of thin films of Pd nanoparticles with different structures. (a) Variation of the transmission intensity of Pd nanoparticle films of different sizes with different atomic ratios of H/Pd, and the films are composed of 13 layers of nanoparticles; (b) Changes in the transmission spectra of Pd nanoparticle films of different layers under different atomic ratios of H/Pd, where the diameter of the nanoparticles is 10 nm; (c) Changes in transmission spectra of Pd nanoparticle films with different spacings under different atomic ratios of H/Pd, and the films are composed of 13 layers of nanoparticles with a diameter of 10 nm