Advanced Terahertz Frequency-Domain Ellipsometry Instrumentation for In Situ and Ex Situ Applications

Abstract

Abstract-We present a terahertz (THz) frequency-domain spectroscopic (FDS) ellipsometer design which suppresses formation of standing waves by use of stealth technology approaches. The strategy to suppress standing waves consists of three elements geometry, coating and modulation. The instrument is based on the rotating analyzer ellipsometer principle and can incorporate various sample compartments, such as a superconducting magnet, in-situ gas cells or resonant sample cavities, for example. A backward wave oscillator and three detectors are employed, which permit operation in the spectral range of 0.1-1 THz (3.3-33 cm −1 or 0.4-4 meV). The THz frequency-domain ellipsometer allows for standard and generalized ellipsometry at variable angles of incidence in both reflection and transmission configurations. The methods used to suppress standing waves and strategies for an accurate frequency calibration are presented. Experimental results from dielectric constant determination in anisotropic materials, and free charge carrier determination in optical Hall effect, resonant-cavity enhanced optical Hall effect and in-situ optical Hall effect experiments are discussed. Examples include silicon and sapphire optical constants, free charge carrier properties of two dimensional electron gas in group-III nitride high electron mobility transistor structure, and ambient effects on free electron mobility and density in epitaxial graphene.

On the anomalous optical conductivity dispersion of electrically conducting polymers: ultra-wide spectral range ellipsometry combined with a Drude–Lorentz model

“…THz measurements in the spectral range from 0.41 meV to 4.1 meV (from 100 GHz to 1 THz) were performed employing the THz ellipsometer at the Terahertz Materials Analysis Center at Linköping University. 40 Three angles of incidence F A (401, 501 and 601) were used for THz measurement. All measurements were performed in normal ambient at room temperature.…”

“…[36][37][38][39] We also note that a non-Drude behavior might occur in the far infrared (FIR) or even in the THz range, which until recently was beyond the reach of state-of-the-art ellipsometry instrumentation. 40 Recent progress in frequency-domain THz technology (e.g. backward wave oscillator light sources) now enable SE down to 0.1 THz.…”

“…backward wave oscillator light sources) now enable SE down to 0.1 THz. [40][41][42] THz and FIR ellipsometers, combined with their counterparts in higher energy ranges, make it possible to investigate material properties in an ultra-wide spectral range. 43 To our best knowledge, ECPs have not previously been investigated by SE in a wide spectral range including the THz and FIR regions.…”

“…Here, we investigate the permittivity and optical conductivity of ECPs using ultra-wide spectral range ellipsometry (UV to THz range). The ellipsometric data were acquired using custom-built THz and FIR ellipsometers, 40 combined with their counterparts in the ultraviolet-visible-near infrared (UV-Vis-NIR) and midinfrared (MIR) ranges. As model ECP system, we use thin films of poly [3,4-ethylenedioxythiophene] (PEDOT), which is the most widely used ECP for organic electronic devices, owing to its attractive optical and electrical properties.…”

Terahertz optical properties of polymethacrylates after thermal annealing

“…The thermally annealed polymethacrylate samples were investigated using a custom-built THz spectroscopic ellipsometer system, which is described in detail in Ref. 18. The ellipsometer employs a rotating analyzer configuration (polarizer − sample − rotating analyzer).…”