Temperature-dependent optical and vibrational properties of PtSe2 thin films

Abstract

PtSe2 has received substantial research attention because of its intriguing physical properties and potential practical applications. In this paper, we investigated the optical properties of bilayer and multilayer PtSe2 thin films through spectroscopic ellipsometry over a spectral range of 0.73–6.42 eV and at temperatures between 4.5 and 500 K. At room temperature, the spectra of refractive index exhibited several anomalous dispersion features below 1000 nm and approached a constant value in the near-infrared frequency range. The thermo-optic coefficients of bilayer and multilayer PtSe2 thin films were (4.31 ± 0.04) × 10−4/K and (–9.20 ± 0.03) × 10−4/K at a wavelength of 1200 nm. Analysis of the optical absorption spectrum at room temperature confirmed that bilayer PtSe2 thin films had an indirect band gap of approximately 0.75 ± 0.01 eV, whereas multilayer PtSe2 thin films exhibited semimetal behavior. The band gap of bilayer PtSe2 thin films increased to 0.83 ± 0.01 eV at 4.5 K because of the suppression of electron–phonon interactions. Furthermore, the frequency shifts of Raman-active Eg and A1g phonon modes of both thin films in the temperature range between 10 and 500 K accorded with the predictions of the anharmonic model. These results provide basic information for the technological development of PtSe2-based optoelectronic and photonic devices at various temperatures.

Thermal Phase Control of Two-Dimensional Pt-Chalcogenide (Se and Te) Ultrathin Epitaxial Films and Nanocrystals

“…Also, STS demonstrates the layer-dependent electronic properties expected for PtSe 2 , with the monolayer exhibiting a semiconducting gap of 1.8 eV and bilayer islands with a gap of 0.6 eV, while multilayers are metallic, as shown in Figure b. Raman of the low-temperature grown sample, as shown in Figure c, is also consistent with that previously reported for PtSe 2 . ,, XPS of PtSe 2 is shown in Figure , with the Pt-4f 5/2 and Pt-4f 7/2 peaks at 76.75/73.4 eV. The Se-3d 1/2 and Se-3d 3/2 are at 55.8/54.9 eV binding energy, respectively.…”

“…Raman of the low-temperature grown sample, as shown in Figure 7c, is also consistent with that previously reported for PtSe 2 . 33,41,42 XPS of PtSe 2 is shown in Figure 8, with the Pt-4f 5/2 and Pt-4f 7/2 peaks at 76.75/73.4 eV. The Se-3d 1/2 and Se-3d 3/2 are at 55.8/54.9 eV binding energy, respectively.…”

Optical Characterization of Few-Layer PtSe2 Nanosheet Films

“…Taking into account the layer thickness of ∼2 × 10 −7 cm, the maximum absorption coefficient is of the order 10 6 cm −1 in the visible region of the spectrum and decreases toward the infrared range according to a power-law dependence. 19,22 The exponents of the α ∼ E m dependence are relatively large, with m between 3 and 4 for the two samples. The absorption coefficient has a more pronounced frequency dependence than previously reported.…”

“…The extinction coefficient is flat in the visible region and decreases in the near-infrared region. 19 − 22 …”

“…The real part of the refractive index increases toward the near-infrared and then remains essentially constant up to 1600 nm. The extinction coefficient is flat in the visible region and decreases in the near-infrared region. − …”