Measurement of the Optical Constants of Thin Metal Films by THz Differential Time Domain Spectroscopy

Abstract

Three kinds of nanometer-scale metal films (Cr, Ni and Ti) with different thicknesses are fabricated. The complex refractive indices of the three metal films are quantitatively measured by using THz differential time-domain spectroscopy (THz-DTDS). The orders of the complex refractive indices of the thin metal films are equal to those of the reported values. Our results validated that THz-DTDS can be used to study the features of the ultra-thin metal films.

Non-Drude like behaviour of metals in the terahertz spectral range

“…Both transmission and reflection THz TDS measurements have been performed using either a thin metal film deposited on a substrate or thin metal films placed in a multilayer stack [14][15][16][17][18]. In general, the optical constants obtained from these independent measurements appear to match predictions of the Drude model well, as shown in Figure 2 for data obtained from transmission measurements with thin metal films.…”

Terahertz Conductivity of Semiconducting 2H and Metallic 1T Phases of Molybdenum Disulfide

“…The real part of the conductivity is displayed in Figure c. For the 2H phase, the conductivity decreases with temperature, which is to be expected for a semiconducting material due to a decreased thermal electron occupation of the conduction band at lower temperatures. , As shown in Figure b, the imaginary part of n ̂ for 1T-MoS 2 is larger than the real part, which is a hallmark of a metallic-like material. ,, The conductivity (Figure d) for 1T-MoS 2 increases as the temperature decreases, which we attribute to decreased electron–phonon scattering at low temperatures as the phonons are frozen out . The conductivity of the 1T phase is higher than that of the 2H phase, which is to be expected on the basis of the lower overpotential required to drive HER for 1T-MoS 2 .…”

“…41,42 As shown in Figure 2b, the imaginary part of n̂for 1T-MoS 2 is larger than the real part, which is a hallmark of a metallic-like material. 25,43,44 The conductivity (Figure 2d) for 1T-MoS 2 increases as the temperature decreases, which we attribute to decreased electron−phonon scattering at low temperatures as the phonons are frozen out. 41 The conductivity of the 1T phase is higher than that of the 2H phase, which is to be expected on the basis of the lower overpotential required to drive HER for 1T-MoS 2 .…”