Optical anisotropy of pristine and reduced V₂O₅(010).

Area of Science:

• Materials Science
• Solid State Physics
• Optical Spectroscopy

Background:

• The optical properties of vanadium dioxide (VO2) are highly sensitive to its phase and stoichiometry, making it challenging to study.
• Different V-O phases exhibit distinct electronic and optical characteristics.
• Reflectance anisotropy spectroscopy (RAS) is a powerful non-destructive technique for probing optical anisotropy in real-time.

Purpose of the Study:

• To investigate the optical anisotropy of pristine and reduced single crystalline (010) oriented VO2.
• To identify the spectral features of different VO2 phases formed during reduction and annealing.
• To establish a foundation for using RAS to monitor VO2 thin film growth and modifications.

Main Methods:

• Single crystalline (010) oriented VO2 was subjected to reduction processes.
• Reflectance anisotropy spectroscopy (RAS) was employed for in-situ monitoring.
• Ellipsometry was used to extract axially resolved optical constants.
• Vacuum annealing at various temperatures followed by X-ray Diffraction and RAS analysis.

Main Results:

• Pristine VO2(010) displayed strong optical anisotropy with features beyond its 2.5 eV bandgap.
• Calculated RAS from optical constants showed excellent agreement with experimental data.
• Annealing introduced different VO2 phases ([V2O5], [VO], [V4O7]), each with identifiable spectral features.
• The semiconductor-to-metal phase transition of VO2 at 340 K was observed to influence optical properties.

Conclusions:

• The optical response of ideal single-crystal VO2 was elucidated.
• RAS is effective in identifying different VO2 phases and their spectral characteristics.
• This work provides a framework for real-time monitoring of VO2 thin films using RAS.