Optical dielectric function of gold

Abstract

In metal optics gold assumes a special status because of its practical importance in opto-electronic and nano-optical devices, and its role as a model system for the study of the elementary electronic excitations that underlie the interaction of electromagnetic fields with metals. However, largely inconsistent values for the frequency dependence of the dielectric function describing the optical response of gold are found in the literature [1][2][3]. We performed precise spectroscopic ellipsometry measurements on evaporated gold, template-stripped gold, and single-crystal gold to determine the optical dielectric function across a broad spectral range of 300 nm -25 µm (0.05 -4.14 eV) with high spectral resolution. We fit the data to the Drude free-electron model, with an electron relaxation time τD = 14 ± 3 fs and plasma energy ωp = 8.48 eV. We find that the variation in dielectric functions for the different types of samples is small compared to the range of values reported in the literature. Our values, however, are comparable to the aggregate mean of the collection of previous measurements from over the past six decades. This suggests that although some variation can be attributed to surface morphology, the past measurements using different approaches seem to have been plagued more by systematic errors than previously assumed.

Gallium Plasmonics: Deep Subwavelength Spectroscopic Imaging of Single and Interacting Gallium Nanoparticles

“…This detailed comparison was performed in the spirit of previous work on plasmonic materials that has noted considerable discrepancies between published dielectric functions. 26 While the full band structure of Ga is complex, the primary features of the solid phase Ga dielectric function can be attributed to Drude-like free electron oscillations in the blue-UV spectral regime, and to interband transitions in the green-red region of the spectrum. 2,4,5 These interband transitions damp plasmonic behavior beyond the visible (λ 0 > 700 nm) based on the well-known SPP resonance condition (ε r < À2) for spherical particles.…”

Optical dielectric function of silver

“…However, similar to the case of gold [16], large variations exist among historical measurements of the dielectric function of silver, especially for the imaginary part near the interband transition in the visible/ultraviolet (Vis/UV) region. [17] Most of these measurements only cover a narrow energy range, making a direct comparison between the different experiments difficult.…”

“…[18][19][20][21][22][23][24][25] Accurate values for the dielectric function of silver are needed in the visible and infrared (IR) spectral ranges, because many important parameters, such as surface plasmon propagation length, plasmon lifetime, non-radiative loss, and even the Casimir force, are sensitively linked to small variations of the dielectric function. [16] In this work, we provide a comprehensive measurement of the optical dielectric function (ω) of evaporated and template-stripped polycrystalline silver using spectroscopic ellipsometry, covering a broad spectral range throughout the mid-IR to Vis/UV of two orders of magnitude, from 0.05 eV to 4.14 eV (25 µm to 300 nm). We analyze the free electron behavior below the interband transition using the Drude model with plasma frequency ω p , dielectric function at infinite frequency ∞ , and relaxation time τ = 1/Γ.…”

Observation of reflectance fluctuations in metals

“…In physics, studying optical properties of materials is perhaps the most powerful tool for investigating their electronic and vibrational properties [1][2][3][4]. As such, in metals, the subject has been studied for some time, and continue to be studied actively to this day [5][6][7]. Properties of reflection are known to depend on the wavelength of light, temperature and the material [1][2][3][4]8], and can further depend on geometric aspects of the material, such as its size and thickness.…”