Spectrophotometric Characterization of Thin Copper and Gold Films Prepared by Electron Beam Evaporation: Thickness Dependence of the Drude Damping Parameter

Abstract

Copper and gold films with thicknesses between approximately 10 and 60 nm have been prepared by electron beam evaporation and characterized by spectrophotometry from the near infrared up to the near ultraviolet spectral regions. From near normal incidence transmission and reflection spectra, dispersion of optical constants have been determined by means of spectra fits utilizing a merger of the Drude model and the beta-distributed oscillator model. All spectra could be fitted in the full spectral region with a total of seven dispersion parameters. The obtained Drude damping parameters shows a clear trend to increase with decreasing film thickness. This behavior is discussed in the context of additional non-optical characterization results and turned out to be consistent with a simple mean-free path theory.

Theoretical design of multilayered VO2-based switchable terahertz metasurfaces as broadband functional devices

“…Based on the current micro-nano fabrication technology, the unit cell proposed in this paper can be manufactured with several following steps. Firstly, a gold thin layer was obtained by depositing gold vapor on a silicon substrate by electron beam evaporation, and a gold CSRR was fabricated by metallization and twophoton optical lithography [28,29]. Then, a 1 μm thick VO 2 film and MgF 2 insulating spacer layer with the thickness of 35 μm are deposited on the resonant ring in turn.…”

Designing Optical Coatings with Incorporated Thin Metal Films

“…Nevertheless thickness-dependent optical constants in ultrathin metal films may be observed even when the films are closed and smooth (Figure 39b). An example is provided by mean free path effects which occur when the film thickness (here d c ) is smaller than the mean free path a conduction electron in the corresponding bulk material would have [36][37][38]. Representative data for the mean free path of conduction electrons in bulk metals may be found for example in [39], for typical metals it ranges between several nanometers and a few nanometer decades; it is thus in agreement with the thickness range that is in the focus of our study.…”

Spectrophotometric Characterization of Thin Semi-Transparent Aluminum Films Prepared by Electron Beam Evaporation and Magnetron Sputtering

“…Here, we use symbols as introduced in our previous study [21], such that 𝜒 free is the susceptibility characterizing the free electrons, and 𝜒 bound describes the bound electrons. The later sums up from one Lorentzian oscillator (Equation (2) [27,28]:…”

“…In an ex situ spectrophotometric study of Du et al [20], a thickness dependence of the aluminum film optical constants could clearly be confirmed in the thickness range up to approximately 30 nm. In a more recent study [21], we have investigated the thickness dependence of the optical constants of copper and gold ultrathin films in terms of a model that explicitly considers mean free path effects (see later Section 2.2). The changes in the optical constants with thickness are significant, and therefore, thickness-dependent optical constants must be taken into account in any relevant design calculation.…”