2. Experiment
The Au PPAs were fabricated using NSL method. Firstly, by dropping 10 ml of polystyrene sphere (in size of 1 μm) diluted solution onto a cleaned normal glass substrate, which was inclined about 5° in a chamber at room temperature for 48 h. A homogenous, dense monolayer colloid mask was successfully formed. Secondly, the colloid mask was set into vacuum chamber and sputtered gold target for 30 s. Thirdly, the colloid mask with Au film was immerged into chloroform, and the polystyrene sphere was ultrasonically removed for 10 min. Finally, the uniform and ordered Au PPAs with 50 nm height was obtained.
The Au PPAs and normal glass were put into reactive magnetron sputtering chamber. High purity argon gas (99.9999%) and oxygen gas (99.9999%) were induced into chamber with a partial pressure of ratio of 50:1. The vanadium target (99.99%) was bombarded and reacted with oxygen gas. The precursor of VO2 thin film was deposited on Au PPAs and normal glass, respectively. Then the precursors were annealed for 60 min in the temperature 380 °C under air in Muffle furnace. The Au:VO2 composite thin film and bare VO2 thin film in 200 nm thickness were prepared.
The surface morphology image of Au PPAs was investigated using scanning electron microscopy (SEM) (Hitachi S4800). Atomic force microscopy (AFM) (Nanoscope V) was used to observe the surface of VO2 and Au:VO2 composite thin films. The crystal structure of Au:VO2 was analyzed by X-ray diffraction (D/Mas-RB). X-ray photoelectron spectroscopy data (XPS) were obtained with an ESCALab220i-XL electron spectrometer from VG Scientific using 300 W AlKα radiation. The base pressure was about 3×10−9 mbar. The binding energies were referenced to the C1s line at 284.8 eV from adventitious carbon. The data deal was performed using Avantage 4.15. The electrical property of samples was tested on a four-probe station with a temperature controller. The transmission of the samples was measured using high UV sensitivity thin back-illuminated CCD spectrometer (Avantes).