Nanoscale Structural Insights into Thermochromic VO₂ Thin Films Using Tip-Enhanced Raman Spectroscopy

Area of Science:

• Materials Science
• Nanotechnology
• Spectroscopy

Background:

• Thermochromic vanadium dioxide (VO2) thin films exhibit a metal-insulator transition (MIT) near 68 °C, making them suitable for energy-efficient smart windows.
• Optimizing VO2 structural and interfacial properties is key to enhancing thermochromic performance, but traditional methods lack nanoscale chemical and spatial resolution.

Purpose of the Study:

• To investigate the nanoscale structure and interfacial properties of pristine VO2 and VO2/TiO2 thin films.
• To address the limitations of traditional characterization techniques using hyperspectral tip-enhanced Raman spectroscopy (TERS) imaging.

Main Methods:

• Hyperspectral tip-enhanced Raman spectroscopy (TERS) imaging was employed to analyze VO2 and VO2/TiO2 thin films.
• TERS imaging provided nanoscale spatial resolution and detailed chemical information.

Main Results:

• TERS revealed nanoscale lattice deformations and varied nanocrystallite orientations in VO2 films, indicating grain boundaries that increase the MIT temperature.
• In VO2/TiO2 bilayers, TERS identified coexisting anatase and brookite TiO2 phases with strain, and localized intermixing/strain at the VO2/TiO2 interface.

Conclusions:

• The study highlights the polycrystalline nature of pulsed layer deposited VO2 thin films.
• TERS imaging is demonstrated as a powerful tool for understanding nanoscale structure and interfaces, crucial for designing advanced VO2-based smart coatings and functional materials.