Metastability Phenomena in VO2 Thin Films

Daniele Gioacchino,Augusto Marcelli,Antonio Bianconi,Lele Fan,Alessandro Puri,Uli Zeitler,Chongwen Zou

doi:10.3390/condmat2010010

Abstract

VO2 is a transition metal oxide in which complex electronic phases appear near the metal-to-insulator transition due to electron correlation and electron–lattice interactions. This system is characterized by a metal-to-insulator transition (MIT) at around 341 K. The metal (high T) phase is tetragonal while the insulator (low T) phase is monoclinic and the resistivity changes at the MIT by about five orders of magnitude. Here, we report investigations of the MIT in a thin VO2 film deposited on a sapphire substrate showing hysteresis. The MIT has been characterized by resistance measurements versus temperature and a DC magnetic field. The thin sample shows different final resistance values in both the insulating and metallic state after different temperature cycles. Moreover, some cycles do not close in the insulating phase. An unexpected magnetic dependence of the temperature cycle in the sample was also observed. The results show that the MIT of VO2 can be controlled by reducing the thickness below 40 nm in micron-sized ribbons since MIT is associated with the emergence of coexisting metastable conformations controlled by the thickness-dependent misfit strain and stress distributions induced by the mismatch between thin ribbon film and the substrate.

Highlights

Vanadium dioxide (VO2) is a transition metal oxide which exhibits unique complex phases where both electronic correlation, local lattice fluctuations, orbital ordering and charge ordering play a key role
The metallic and insulating phases and the transition changes across the metal-to-insulator transition (MIT) in VO2 thin films, are controlled by the electronic orbital occupation tuned by the local strain [3]
VO2 films were realized on Al2O3 (0006) single crystal substrates by a RF-plasma assisted oxide Molecular Beam Epitaxy (MBE) instrument with a base pressure better than 3 × 10−7 Pa

Summary

Introduction

Vanadium dioxide (VO2) is a transition metal oxide which exhibits unique complex phases where both electronic correlation, local lattice fluctuations, orbital ordering and charge ordering play a key role. These competing interactions are at the origin of the complex electronic and structural metal-to-insulator transition (MIT) observed around 341 K [1,2,3]. The metallic and insulating phases and the transition changes across the MIT in VO2 thin films, are controlled by the electronic orbital occupation tuned by the local strain [3]. The hysteresis cycle indicates the emergence of an arrested nanoscale phase separation during the transition, and structural defects

Methods

Results

Discussion

Conclusion