Nanostructured vanadium dioxide with metal to insulator transition : preparation and thermochromic properties

• Main Author: Wang, Ning
• Other Authors: Long Yi
• Format: Theses and Dissertations
• Language: English
• Published: 2017
• Subjects: DRNTU::Science::Chemistry
• Online Access: http://hdl.handle.net/10356/72069
• Institution: Nanyang Technological University

Vanadium dioxide (VO2) is an interesting phase transition material, and has promising potential applications in smart window/sensors, field-emission transistor and memory devices. However, the application of this material in thermochromic smart windows is facing several critical limitations, namely the low visible transmission (Tlum < 50%) and low solar modulating ability (ΔTsol < 10%) as well as the relatively high phase transition temperature (τc ≈68 °C). To address these few issues, three approaches including, doped thin films, biomimetic nanostructuring and nanobeam structures have been investigated. The rare earth (Eu3+, La3+, Tb3+) doping could enhance both Tlum and ΔTsol, and can reduce the τc to below 50 °C at low doping levels but increase the τc at high doping levels, owing to the competition between the strain and the hole carriers. To further reduce τc, Mg/W-codoping in the VO2 lattice could help to get the τc as low as 35 °C and increase the Tlum as high as 81.3%. The counteraction between the electron and hole carriers results in a slight increase of τc along with the codoping. Moth-eye mimic VO2 surface for the first time have been fabricated via top-down and bottom-up methods. Due to the antireflection effect of such structure with gradient refractive index along the height, it could increase Tlum, and meanwhile the ΔTsol can be simultaneously enhanced due to the higher surface area of VO2 to provide solar modulation. The pristine and doped VO2 nanostructures could be synthesized under normal hydrothermal approaches, and it is of great interests that VO2 nanobeams exhibit the dual surface plasmon resonance (SPR), which was firstly reported and such beam structure is also promising for electronic device.