Modification of electronic structure in compressively strained vanadium dioxide films

Abstract

Vanadium dioxide (VO 2 ) undergoes a phase transition between an insulating monoclinic (M 1 ) phase and a conducting rutile phase. Like other correlated electron systems, the properties of VO 2 can be extremely sensitive to small changes in external parameters such as strain. In this work, we investigate a compressively strained VO 2 film grown on [001] quartz substrate in which the phase transition temperature (T c ) has been depressed to 325K from the bulk value of 340K. Infrared and optical spectroscopy reveals that the lattice dynamics of this strained film are very similar to unstrained VO 2 . However, some of the electronic inter-band transitions of the strained VO 2 film are significantly shifted in energy from those in unstrained VO 2 . That the lattice dynamics remain largely unchanged, while the T c and some of the electronic inter-band transitions differ substantially from the bulk values highlight the role of electronic correlations in driving this metal-insulator phase transition.

Insulating phases of vanadium dioxide are Mott-Hubbard insulators

“…The energy gap and electronic structure are essentially unchanged across this structural phase transition. Moreover, the optical energy gap of 0.6 ( 0.1 eV in the M 2 and T phases is nearly the same as that measured by numerous previous measurements on the M 1 phase [10,[19][20][21][22][23]; the gap is insensitive to the different vanadium pairing arrangements in the M 1 , M 2 and T phases. It follows that the gap has a common physical origin in the intra-atomic Coulomb correlations in the insulating phases of VO 2 .…”

“…This finding is remarkable given that there are obvious differences in the structural and magnetic properties between the two phases, as discussed above. Interestingly, numerous measurements on single crystals and thin films of the M 1 phase give almost the same magnitude of the energy gap as we measure in the M 2 and T phases [10,[19][20][21][22][23]. The optical energy gap is the spectral region with vanishing conductivity.…”

On the Optical Properties of Thin‐Film Vanadium Dioxide from the Visible to the Far Infrared

“…Knowledge of the complex refractive index of VO 2 across its IMT can enable computational design of various optical and optoelectronic devices incorporating this material. There is a large literature base of experiments that have been used to extract such optical properties; however, many of these investigations focus almost entirely on the visible and near‐infrared ranges, with one recent study extending into the mid infrared …”

“…Knowledge of the complex refractive index of VO2 across its IMT can enable computational design of various optical and optoelectronic devices incorporating this material. There is a large literature base of experiments that have been used to extract such optical properties, most notably using spectroscopic ellipsometry [18]; however, many of these investigations focus almost entirely on the visible and nearinfrared ranges [7] [18] [19] [20] [21], with one recent study extending to the mid infrared [22]. The thickness of the VO2 film may affect its optical properties due to strain relaxation (the strain-relaxation thickness is in the tens of nanometers [24][25]).…”

Revealing the role of oxygen vacancies on the phase transition of VO2 film from the optical-constant measurements

“…In fact, optical conductivity measurements have been demonstrated to be a suitable method in analyzing the electronic structure of material. [24][25][26][27][28][29][30][31][32] For example, Basov group revealed the Mott transition property of VO 2 by using optical conductivity and explained the peaks in optical conductivity curve according to electron transition. 24,25 Lee used optical conductivity method to investigate the electron correlation in W-VO 2 lm.…”