Characteristic Reflection Peak and Its Origin of Nanostructured Material Containing Small Metal Nanoparticles: Two Case Studies

To better understand and utilize the optical reflection behaviors of the nanostructured materials containing small metal nanoparticles (NPs), we once proposed a hypothesis that the recorded characteristic reflection peak should originate from the competition between the localized surface plasmon resonance (LSPR) scattering and absorption of metal NPs. To prove our hypothesis, the Ag- and Au-ion-implanted samples are prepared again by separately introducing 30 keV Ag and Au ions into 0.5-mm-thick SiO₂ wafers to a fluence of 6 × 10¹⁶ ions/cm². Especially, the Au-ion-implanted sample is further annealed in flowing nitrogen at different temperatures. Then, using a transmission electron microscope and a fiber spectrometer, all samples’ cross-sectional observations and spectral measurements are conducted, respectively. Based on the consistency in peak position and the difference in wavelength range of the absorption and reflection light fields measured from the Ag-ion-implanted sample, the LSPR scattering and absorption of Ag NPs are demonstrated to be coexistent, and their competition are testified to be inevitable and achievable via a filtration process. Besides these indirect evidences for our hypothesis, a direct evidence is also found, which is the blueshift shown by the characteristic reflection peak observed from the rear surface of the Au-ion-implanted sample after annealing.