Strain Dynamics of Ultrathin VO₂ Film Grown on TiO₂ (001) and the Associated Phase Transition Modulation

Abstract

Tuning the metal insulator transition (MIT) behavior of VO2 film through the interfacial strain is effective for practical applications. However, the mechanism for strain-modulated MIT is still under debate. Here we directly record the strain dynamics of ultrathin VO2 film on TiO2 substrate and reveal the intrinsic modulation process by means of synchrotron radiation and first-principles calculations. It is observed that the MIT process of the obtained VO2 films can be modulated continuously via the interfacial strain. The relationship between the phase transition temperature and the strain evolution is established from the initial film growth. From the interfacial strain dynamics and theoretical calculations, we claim that the electronic orbital occupancy is strongly affected by the interfacial strain, which changes also the electron-electron correlation and controls the phase transition temperature. These findings open the possibility of an active tuning of phase transition for the thin VO2 film through the interfacial lattice engineering.

Nanoscale Phase Separation and Lattice Complexity in VO2: The Metal–Insulator Transition Investigated by XANES via Auger Electron Yield at the Vanadium L23-Edge and Resonant Photoemission

“…Major differences seem to occur during the cooling process. Actually, looking at the hysteresis curves of similar films, this result is not unexpected [8]. The 16 nm thick film (Figure 3a in [6]) exhibits an MIT transition just above 30 • C, and the transition to the metallic state is almost completed at~70 • C. While cooling, the transition starts around~60 • C and is almost completed at~30 • C. experiments performed in transmission, as in [21], where a film of 40 nm of VO2 obtained by oxidizing a thin film of vanadium on a silicon nitride membrane has been measured.…”

“…We report here the investigation of a 16 nm film grown on TiO 2 substrate and, as deeply discussed in [8] for films of similar thickness from 1.6 nm to 74 nm grown on an oriented TiO 2 substrate, the role of the interfacial strain is important. Actually, in ultrathin films, i.e., thinner than 10 nm, a fully strained behavior is observed with an MIT temperature near room temperature, while thicker films, i.e., greater than 24 nm, are characterized by diffraction patterns that point out an almost fully relaxed interface, higher MIT transition temperatures, and lower resistance in the metallic state [6].…”

“…Actually, the scenario can be even more complex if we consider films of VO 2 . As pointed out by Fan et al [8], investigating thin and ultrathin VO 2 films grown on oriented TiO 2 substrates, the strain dynamics also play a role and, in these films, the MIT process is modulated continuously via the interfacial strain [9,12,13]. The presence and role of different phases and the relationship between the phase transition temperature and strain have been investigated during film growth.…”

“…Around 67-68 • C, the vanadium dioxide undergoes the electronic metal-insulator transition upon heating or cooling with hysteretic behavior and a change in the electrical conductivity by several orders of magnitude, coupled to a Structural Phase Transition (SPT) from the monoclinic to the rutile phase. Since the discovery of the MIT transition more than 50 years ago by Morin and Westman [1,2], VO 2 has attracted a lot of interest because of its strong electron correlation; recently the interest has increased because of the wide number of different possible applications in optics, as detectors or sensors, and in novel memory devices based on the occurrence of the reversible MIT transition [5][6][7][8][9][10][11]. However, since its discovery, and even now, the nature of this electronic/structural transition remains an open question.…”

Dynamically tracking the joule heating effect on the voltage induced metal-insulator transition in VO2 crystal film

“…[5][6][7] The normal triggering MIT process of VO 2 material is temperature and much effort has been devoted to decrease the critical temperature of VO 2 for satisfying the practical applications. [8][9][10][11] Recently, several groups [12][13][14][15] have reported the possibility of triggering the MIT phase transition through the route of external dc voltage/current added on two-terminal VO 2 based devices. Those experiments produce much excitement because it seems to open an easily controlled way other than temperature for phase transition modulation as well as inducing new functionalities into VO 2 materials.…”