Effect of lanthanum doping on modulating thermochromic properties of VO2 thin films = Thermochromic properties of la doped VO2 thin films

• Main Author: Tan, Nigel Chew Shun
• Other Authors: Long Yi
• Format: Final Year Project
• Language: English
• Published: 2016
• Subjects: DRNTU::Engineering; DRNTU::Science
• Online Access: http://hdl.handle.net/10356/67306
• Institution: Nanyang Technological University

Vanadium dioxide (VO2) is a promising candidate for smart windows as it exhibits a reversible metal to insulator (MIT) phase transition. However, the phase transition temperature (τc) of pure VO2 occurs at 68oC which is comparatively higher than room temperature (25oC). Hence, the practical application is limited due to its high τc and low integrated visible transmission (Tlum). Thus, appropriate dopant is required to depress τc to ambient temperature. As a result, Lanthanum, a rare earth element was introduced to modify the optical properties of VO2. Sol-gel technique was utilized to fabricate La doped VO2 thin films. Subsequently, TEM and EDX characterizations were used to verify La doping while UV-Vis-NIR spectroscopy was used to monitor τc. La doping reduces τc of VO2 below the 4 at. % doping level effectively, at a τc reduction rate of -1.1 °C/at.%. Furthermore, the band gap (Eg) decreased progressively along with the addition of La dopants below the 3 at.% doping level. The optimum value for La doped VO2 thin films was found to be 4 at.% doping level with cooling τc of 49.2oC and the combination of integrated visible transmission (Tlum) and solar modulating ability (ΔTsol) were increased to 50% and 10.3% respectively. This result showed superior Tlum and ΔTsol as compared with undoped VO2 thin films.