Optical Characterization of Few-Layer PtSe₂ Nanosheet Films

Abstract

Thin films of transition-metal dichalcogenides are potential materials for optoelectronic applications. However, the application of these materials in practice requires knowledge of their fundamental optical properties. Many existing methods determine optical constants using predefined models. Here, a different approach was used. We determine the sheet conductance and absorption coefficient of few-layer PtSe 2 in the infrared and UV–vis ranges without recourse to any particular model for the optical constants. PtSe 2 samples with a thickness of about 3–4 layers were prepared by selenization of 0.5 nm thick platinum films on sapphire substrates at different temperatures. Differential reflectance was extracted from transmittance and reflectance measurements from the front and back of the sample. The film thickness, limited to a few atomic layers, allowed a thin-film approximation to calculate the optical conductance and absorption coefficient. The former has a very different energy dependence in the infrared, near-infrared, and visible ranges. The absorption coefficient exhibits a strong power-law dependence on energy with an exponent larger than three in the mid-infrared and near-infrared regions. We have not observed any evidence for a band gap in PtSe 2 thin layers down to an energy of 0.4 eV from our optical measurements.

Synthesis of 2D PtSe2 Nanolayers on Glass Substrates and Their Integration in Near-Infrared Light Shutters

“…The Tauc–Lorentz oscillator model was applied for description of the complex permittivity, ε̂ = ε 1 ̂ + ε 2 , and applied for determination of the optical constants of thin PtSe 2 films from other authors. ,, The model proposed from Jellison and Modine is a combination of the Tauc law, which describes the spectral dependence of the absorption edge in the case of indirect allowed transitions and the Lorentz oscillator model used in the case of the interband transition i.e., electron transition from the valence to conduction band. The model supplies an expression for the imaginary part, ε 2 , of the dielectric function if only a single transition is considered. .25ex2ex ε 2 = A E 0 normalΓ false( E − E g false) 2 false( E 2 − E 0 2 false) 2 + Γ 2 E 2 . 1 E for .25em E > E g ε 2 = 0 for .25em E ≤ E g where E g opt is the optical band gap.…”

Design of Wireless Multiple Gases Complementary Architecture Sensors Based on SnSe2 and PtSe2 Layered Films and Oscillating Circuits

“…As a result, the lattice plane of the PtSe 2 layered film is parallel to the substrate, which is consistent to TEM and FFT results (Figure 2c). [ 18 ] Furthermore, we extracted the line‐cut profiles of 1D diffraction for the out‐of‐plane ( q z ) and in‐plane directions ( q r ), and the corresponding results are shown in Figure 2g,h. In the q z profile (Figure 2g), there is a strong (0001) peak near q z = 1°, which is not evident in the in‐plane direction ( q r , Figure 2h).…”

Lithium-Induced Reorientation of Few-Layer MoS2 Films

“…Figure shows the as-measured transmittance and reflectance spectra of 12 nm and 40 nm thick lithiated MoS 2 layers prepared by a two-step method with 20% (Figure a) and 50% (Figure b) portion of Li on a transparent sapphire substrate. The spectra were measured from the thin film side of the sample (i.e., the light beam hits the thin layer first and then the substrate) . The latter is ∼13.6% if the sapphire refractive index of 1.7 is considered.…”

“…The spectra were measured from the thin film side of the sample (i.e., the light beam hits the thin layer first and then the substrate). 60 The latter is ∼13.6% if the sapphire refractive index of 1.7 is considered. For the thinner samples, the reflectance and transmittance sum up to nearly 100% in the lowest energy part of the spectrum below ∼1.2 eV.…”