Optical Characterization of Few-Layer PtSe₂ Nanosheet Films

Area of Science:

• Materials Science
• Condensed Matter Physics
• Optoelectronics

Background:

• Transition-metal dichalcogenides are promising for optoelectronics.
• Understanding their optical properties is crucial for practical applications.
• Existing methods often rely on predefined models for optical constants.

Purpose of the Study:

• To determine the sheet conductance and absorption coefficient of few-layer platinum diselenide (PtSe₂) without using predefined models.
• To investigate the optical properties of PtSe₂ in the infrared and UV-visible ranges.
• To explore the energy dependence of optical properties and search for evidence of a band gap.

Main Methods:

• Preparation of few-layer PtSe₂ (3-4 layers) via selenization of platinum films on sapphire substrates.
• Measurement of transmittance and reflectance from both front and back of the samples.
• Application of thin-film approximation to calculate optical conductance and absorption coefficient from differential reflectance.

Main Results:

• Sheet conductance exhibits distinct energy dependencies across infrared, near-infrared, and visible ranges.
• Absorption coefficient shows a strong power-law dependence (exponent > 3) in mid-infrared and near-infrared regions.
• No evidence of a band gap in PtSe₂ thin layers was observed down to 0.4 eV.

Conclusions:

• A model-independent method successfully characterized the optical properties of few-layer PtSe₂.
• The findings reveal unique optical characteristics of PtSe₂ relevant for optoelectronic device design.
• The absence of a discernible band gap at low energies suggests potential for broadband applications.