Microstructural evolution and nanograin coherence in VO₂ thin films grown by pulsed laser deposition

Area of Science:

• Materials Science
• Thin Film Physics
• Solid-State Chemistry

Background:

• Vanadium dioxide (VO2) thin films possess a crucial semiconductor-metal transition near room temperature.
• Film performance is significantly influenced by microstructural and interfacial characteristics.
• Understanding these factors is key for advanced VO2 applications.

Purpose of the Study:

• To investigate the microstructural evolution and crystallographic features of VO2 thin films on Z-cut quartz.
• To elucidate the mechanisms behind polygonal grain formation and coherence in these films.
• To explore the role of deposition conditions and interfacial energy on VO2 microstructure.

Main Methods:

• Pulsed laser deposition of VO2 thin films under varied oxygen partial pressures and substrate temperatures.
• Plan-view transmission electron microscopy (TEM) with selected-area electron diffraction (SAD) and nanobeam diffraction (NBD).
• Confocal Raman spectroscopy and mapping for phase uniformity and orientation analysis.

Main Results:

• VO2 films exhibited a dense, polygonal morphology with 50-200 nm faceted grains.
• Polygonal grains formed in the high-temperature R phase and transformed into semi-coherent M1 nanograins upon cooling.
• Surface and interface energy anisotropy across the SiO2 interlayer promoted random in-plane orientation and grain formation.

Conclusions:

• Interface-energy-driven growth mechanisms stabilize ordered microstructures in VO2 thin films on quartz.
• Polygonal grain formation is influenced by phase transitions during deposition and cooling.
• The study provides insights into achieving controlled microstructures in VO2 films for tailored properties.