Smart and Emerging Materials

Biography

Biography: Arun M Umarji

Abstract

Semiconductor to metal transition (SMT) in metal oxide is the most fascinating field of research in materials science. This transition can be triggered by thermal, electrical, strain, etc. where oxides show a drastic change in resistivity. Large number of oxides are known to show this kind of transition but VO₂ shows this transition near to room temperature (T_SMT ~68 ºC). It undergoes a change in crystal structure from monoclinic phase (M1, P2₁/c) to tetragonal phase (R, P4₂/mnm). Due to this phase transition it has been used for various applications like smart windows, metamaterial, bolometers, etc. Herein, we report the synthesis of device quality VO₂ thin films. Various methods like home-built Ultrasonic Nebulized Spray Pyrolysis of Aqueous Combustion Mixture (UNSPACM), Chemical Vapor Deposition (CVD), Pulsed Laser Deposition (PLD) and DC Reactive sputtering have been employed to synthesize the thin films. The structural characterization of the thins films have been carried out by XRD and Raman measurements which confirms the M1 phase of VO₂ at room temperature followed by high temperature measurements to study the phase change to R phase. A temperature dependent resistance measurement confirms the SMT transition at 68 ºC with a three-four order of magnitude change in resistance. Temperature dependent IR measurements show ~80% change in reflectance across the phase transition where the thin film acts as an IR reflector (T>T_SMT). Effect of substrate, synthesis process, post-annealing on SMT have been studied.

Image

Figure-1: Left figure shows the change in resistance and right shows the change in reflectance as a function of temperature for VO₂ thin films synthesized using UNSPACM.

Recent Publications

1. R Bharathi, A M Umarji, et al. (2017) Thermochromic VO₂ thin films on ITO-coated glass substrates for broadband high absorption at infra-red frequencies. Journal of Applied Physics; 122(16): 163107.

2. Pradhan J K, A M Umarji, et al. (2017) High contrast switchability of VO2 based metamaterial absorbers with ITO ground plane. Optics Express; 25(8): 9116-9121.

References

1. Yang Z, C Ko and S Ramanathan (2011) Oxide Electronics Utilizing Ultrafast Metal Insulator Transitions. Annual Review of Materials Research; 41(1): 337-367.

2. Good enough J B (1971) The two components of the crystallographic transition in VO2. Journal of Solid State Chemistry; 3(4): 490-500.