Vanadium dioxide (VO2) films were prepared by the sol–gel method on high-purity silicon substrates, in which cetyltrimethyl ammonium bromide (CTAB) was used as a functional additive to form nano-porous structure in the VO2 films. The morphology, crystalline structure and stoichiometry of the films were investigated by field emission scanning electron microscopy, x-ray diffraction and x-ray photoelectron spectroscopy. Furthermore, the effects of nano-scaled grain size and pores on the THz transmission properties across the phase transition in the VO2 films were studied. The results indicated that the film modified with CTAB can form a nano-porous VO2 structure with a uniform grain size of about 30 nm. The nano-porous VO2 film exhibited significantly broader hysteresis loops and a slight decrease in THz transmission reduction across the phase transition, compared with the common film without a nano-porous structure. A tentative interpretation is given for these phenomena.
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