Figure 4. Complex dielectric function and loss function spectra of hp-SNO films with varying thicknesses.

(a) Real part of complex dielectric function, ɛ₁(ω), of hp-SNO (1 × 10⁻⁴ Torr) films with varying thicknesses. (b) Imaginary part of complex dielectric function, ɛ₂(ω), and loss function, −Im [ɛ⁻¹(ω)], of ∼81 nm hp-SNO film. Here, two correlated plasmon peaks are observed at ∼3.2 and ∼4.4 eV. (c) The ɛ₂(ω) and −Im [ɛ⁻¹(ω)] of ∼52 nm hp-SNO film. Here, the only correlated plasmon peak is observed at ∼4.0 eV. (d) The ɛ₂(ω) and −Im [ɛ⁻¹(ω)] of ∼20 nm hp-SNO film. No correlated plasmon peak is observed in this very thin film. For reference, the standard ∼168 nm thick hp-SNO film has three correlated plasmon peaks.