Effect of W addition on the electrical switching of VO2 thin films

Abstract

Vanadium Oxide has been a frontrunner in the field of oxide electronics because of its metal-insulator transition (MIT). The interplay of different structures of VO2 has played a crucial role in deciding the magnitude of the first order MIT. Substitution doping has been found to introduce different polymorphs of VO2. Hence the role of substitution doping in stabilizing the competing phases of VO2 in the thin film form remains underexplored. Consequently there have been reports both discounting and approving such a stabilization of competing phases in VO2. It is reported in the literature that the bandwidth of the hysteresis and transition temperature of VO2 can be tuned by substitutional doping of VO2 with W. In this work, we have adopted a novel technique called, Ultrasonic Nebulized Spray Pyrolysis of Aqueous Combustion Mixture (UNSPACM) to deposit VO2 and W- doped VO2 as thin films. XRD and Raman spectroscopy were used to investigate the role of tungsten on the structure of VO2 thin films. Morphology of the thin films was found to be consisting of globular and porous nanoparticles of size ∼ 20nm. Transition temperature decreased with the addition of W. We found that for 2.0 at % W doping in VO2, the transition temperature has reduced from 68 o C to 25 o C. It is noted that W-doping in the process of reducing the transition temperature, alters the local structure and also increases room temperature carrier concentration.

Tuning the hysteresis of a metal-insulator transition via lattice compatibility

“…Specifically, the M2 phase has been observed even in nanobeams where interfacial coupling between the nano-sized materials and the underneath substrates is negligible 43 , 44 , suggesting that the intrinsic geometric effects owing to the high surface-to-volume ratios of these quasi-1-dimensional structures facilitate the formation of the intermediate phase through the MIT. Further, according to a number of previous studies 39 , 41 , 45 , 46 , replacing V ions with a small amount (up to few %) of W is expected to reduce the transition temperature of the MIT without introducing the M2 phase through the structural transformation. Therefore, the absence of evidence of the M2 phase in our composition-spread films is consistent with previously V 1− x W x O 2 work on thin films of V 1− x W x O 2 , where unlike in nanobeams, the M2 phase was not observed.…”

Scandium: An efficient dopant to modulate the optical spectrum of vanadium dioxide (VO2)

“…% W doping and 1.8 at. % Mo doping was considered as these are the highest dopant levels for W-and Mo-doping respectively, that leads to reduction in T SMT [24,38].…”

“…There are few limitations to use VO 2 for smart window applications: (a) High T SMT , which has been overcome by adding dopants in vanadium site [17,[24][25][26][27][28][29][30] and the minimum value for T SMT has been observed to be ~ 25…”

New intelligent multifunctional SiO2/VO2 composite films with enhanced infrared light regulation performance, solar modulation capability, and superhydrophobicity

“…VO 2 is the first choice as material for intelligent temperature control due to the abrupt change in its optical properties before and after phase change. However, the main obstacles to the large-scale application of VO 2 films include decreasing phase transition temperature [ 7,8 ], enhancing visible light transmittance [ 9 ], increasing solar conditioning capacity [ 10 ] under strong visible light absorption conditions [ 11 ], and maintaining long-term stability upon exposure to air for a long period [ 12,13 ] or under high temperatures (above 300 °C) [ 14 ].…”