Synthesis of vanadium oxide films with controlled morphologies: Impact on the metal-insulator transition behaviour

Abstract

Precise control over the growth of VO2 films with different morphologies is achieved by varying the deposition parameters in the DLI‐MOCVD process such as temperature, pressure, concentration of precursor and time of deposition. In this study, thin films of VO2 with wide range of morphologies having Metal to Insulator Transition (MIT) temperature of (τc) ∼ 52 °C were deposited. Adjusting the process parameters has allowed the growth of highly porous nanocrystalline films and dense microcrystalline films with controlled crystallite size up to several hundred nanometres. Vanadium (V) oxy tri‐isopropoxide was used in this study as a single source precursor. Porous films lead to a diffuse change in resistivity across the transition temperature while the crystalline films have sharp and high resistivity drop (Δρ). This enabled a qualitative study of the MIT behaviour with respect to the microstructure of the films and correlates the effect of deposition conditions to the obtained morphologies. Fine control over the morphology without additional doping or post deposition process provides the ability to tailor VO2 thin films for their respective applications. Scanning electron microscopy, Raman spectroscopy and X‐ray diffraction were used to characterize the microstructure of the films while electrical resistivity measurements were carried out to observe the MIT behaviour of the films.

Electrical Switching in Semiconductor-Metal Self-Assembled VO2 Disordered Metamaterial Coatings

“…1a), which contrasts with the crystalline VO 2 films obtained with ethanol at this temperature range23. On the other hand, cyclohexane is thermally more stable than ethanol at 600 °C31.…”

“…Hence, it is crucial to control the growth conditions to a high degree of precision to obtain pure single-phase films. Polycrystalline and epitaxial films have been grown by various deposition techniques including Sol gel17, Pulsed Laser Deposition (PLD)4, Molecular Beam Epitaxy (MBE)18, Atomic Layer Deposition (ALD)19, Sputtering20, and Chemical Vapor Deposition (CVD)212223. Epitaxial films grow on pre-treated and appropriately oriented Al 2 O 3 or TiO 2 substrates or buffer layers242526.…”

“…Ideally, VO 2 films show 3–4 orders of magnitude resistivity change with a narrow hysteresis width of ΔT~ 3–4 K. Bulk single crystal offers slightly higher amplitude of resistivity change but is susceptible to breakdown after few cycles of switching between semiconducting and metallic phases27. Although, polycrystalline thin films withstand frequent cycling, they usually feature broad hysteresis and small amplitudes of resistivity change, due to the presence of high density of grain boundaries and grain-boundary defects232829. Sintering as-grown VO 2 films to decrease the density of grain boundaries is not conceivable for practical applications due to the high melting point of this phase (1970 °C).…”

Vanadium Oxide as a Key Constituent in Reconfigurable Metamaterials

“…The crystalline state of the material has an influence as well; typically, polycrystalline materials have a broader transition than single crystals. The transition temperature also depends on the crystalline state and oxygen stoichiometry [17].…”

Tunable thermochromic properties of V 2 O 5 coatings

“…Thin films of vanadium oxide were deposited on silicon substrates by Direct Liquid Injection (DLI) Metal Organic Chemical Vapor Deposition (MOCVD), the details of which are reported elsewhere [33,34]. Argon was used as the carrier gas at a flow rate of 50 sccm while the chamber pressure was adjusted to 10 mbar.…”