Resolve the intermediate phases and complete sequence of the VO2 phase transition

Resolve the specific intermediate phases and complete sequence of the M1-to-M2-to-rutile transition in photoexcited VO2 nanoparticles using ultrafast electron microscopy.

Background

Ultrafast electron microscopy has measured particle-dependent structural onset times in photoexcited VO2 nanoparticles. Some particles respond within the approximately 300-fs experimental resolution, whereas others respond after approximately 0.8 or 1.4 ps.

These delays are consistent with a proposed M1-to-M2-to-rutile pathway, but the measurements do not directly identify the intermediate phases or establish the full transition sequence. Directly resolving these stages would clarify the microscopic structural pathway underlying heterogeneous VO2 switching dynamics.

References

Although these delays are consistent with strain-dependent M1-to-M2-to-rutile kinetics, the specific intermediate phases and the complete sequence have not yet been directly resolved (86).

— Ultrafast Electron Microscopy: A Quantitative Platform for Nonequilibrium Materials Research  (2609.30084 - Flannigan et al., 24 Sep 2026) in Section 5.1, “VO2: Real-Space Pathways Through a Correlated Phase Transition”

Indeed, closing this gap is a compelling direction, as no current demonstration has yet established the complete excitation → carrier → phonon → structure → device-function sequence within a single, unified UEM experiment (41, 48).

— Ultrafast Electron Microscopy: A Quantitative Platform for Nonequilibrium Materials Research  (2609.30084 - Flannigan et al., 24 Sep 2026) in Section 8, “Outlook: UEM as a Quantitative Materials Instrument”