Study of the structural, thermal, optical, electrical and nanomechanical properties of sputtered vanadium oxide smart thin films

Abstract

Vanadium oxide thin films were grown on both quartz and Si(111) substrates utilizing pulsed RF magnetron sputtering technique at room temperature with RF power at 100 W to 700 W. The corresponding thicknesses of the films were increased from 27.5 nm to 243 nm and 21 nm to 211 nm as RF power increased from 100 W to 700 W for quartz and silicon substrates, respectively. X-ray diffraction and field emission scanning electron microscopy were carried out to investigate the phase and surface morphology of the deposited films. Electronic structure and vanadium oxidation states of the deposited films were investigated thoroughly by X-ray photoelectron spectroscopy. As-grown films show stoichiometric vanadium oxide only where vanadium is in V 5+ and V 4+ states. Phase transition of vanadium oxide films were investigated by differential scanning calorimetric technique. The reversible i.e. smart transition was observed in the region from 337 °C to 343 °C. Average hemispherical emittance of the deposited vanadium oxide films was evaluated by an emissometer in the wavelength range of 3 µm to 30 µm. The sheet resistance of the deposited films was measured by two-probe method and data were in the range of 10 6 to 10 5 Ω/square. Optical properties of the films such as solar transmittance, solar reflectance and solar absorptance as well as optical constants e.g. optical band gap were also evaluated. Finally, mechanical properties such as nanohardness and Young's modulus at microstructural length scale were evaluated employing nanoindentation technique with continuous stiffness mode.

Low reflectance sputtered vanadium oxide thin films on silicon

“…However, in the present study, no other V species was found except V 4+ and V 5+ . The percentage of V 5+ was found as major phase e.g., about 75-80% [9]. The presence of minor VO 2 phase is not detected in XRD analysis possibly due to the dominated amorphous nature of the deposited film.…”

“…oxide states of vanadium (except V 7 O 13 ), shows smart transition behaviour as a function of temperature or voltage. However, smart or reversible phase transition of V 2 O 5 is still debatable issue [10] though the reversible phase transitions of V 2 O 5 thin films/layers are experimentally observed by three groups [9,11,12] including the present authors [9].…”

“…However, the scarcities of the reports are found in particular with the optical properties of V 2 O 5 /Si system [14,15,16] though the systematic and in-depth studies on optical properties of V 2 O 5 are available on transparent glass and quartz substrates [9,12,13,16].…”

“…optical applications e.g., optical switching and optical shutter, in both electrochromic and thermochromic devices [1,2], electronic device applications e.g., cathode material for lithium ion batteries, un-cooled IR imaging [2,3], supercapacitors, [4] Mott transition field effect transistors [5], energy related device applications [6], space applications e.g., IR detectors [7] and variable emittance coating [8,9] Further, V 2+ , V 3+ , V 4+ , V 5+ etc. oxide states of vanadium (except V 7 O 13 ), shows smart transition behaviour as a function of temperature or voltage.…”

Thickness Effect on the Optical Band Gap of V2O5 Thin Films Deposited by Thermal Evaporation

“…Some studies have been described the films characterization with a thickness greater than 160 nm, but do not refer to the material crystalline structure study and its dependence on the thickness (KRISHNA; BHATTACHARYA, 1997).Others studies have been described the crystalline structure and the thickness effects on the optical properties only in films with thickness above 110 nm (RAMANA; SMITH; HUSSAIN, 2003;SINGH;KAUR, 2008;Zhang;Zuo;Lu, 2017) and another the influence of the sputtering power on the optical, electrical and nanomechanical properties for films (Porwal et al, 2015). Thus, no study was found relating the thickness and microstructure of films deposited by thermal evaporation with the optical absorption band.…”